PETROLOGY AND GEOCHEMISTRY OF A MEGACRYSTIC ...

PETROLOGY AND GEOCHEMISTRY OF A MEGACRYSTIC QUARTZ MONZONITE
THE BODOCO PLUTON, NORTHEASTERN BRAZIL
by
JUDE MCMURRY, B.A,, M.A.
A DISSERTATION
IN
GEOSCIENCE
Submitted to the Graduate Faculty
of Texas Tech University in
Partial Fulfillment of
the Requirements for
the Degree of
DOCTOR OF PHILOSOPHY
Approved
May, 1991

H
!•
72
A/D 4^
Copyright 1991, Jude McMurry

ACKNOWLEDGMENTS
I wish first of all to thank Dr. Calvin Barnes for
supervising my research and for many helpful and thoughtprovoking
insights during this study.
Dr. Alcides N. Sial of the Federal University of
Pernambuco provided invaluable logistical support.
I
also thank my field assistant, Cleto de Oliveira
Cavalcanti, and quarry worker Elias Barbosa e Silva.
For their assistance and generous access to laboratory
facilities, I acknowledge Drs. Leon Long, Larry
Mack, and David Awwiller at the University of Texas at
Austin; Dr. David Wenner at the University of Georgia;
and Dr. Dwight Deuring of Southern Methodist University.
Drs. Alan Turnock and George Clark kindly permitted me to
use equipment for petrography and photomicrographs at the
University of Manitoba.
At Texas Tech University, Melanie Barnes provided
TCP analyses of trace elements, and Mike Gower produced
many high-quality thin sections and probe mounts.
Sul
Ross University supplied INAA data for trace elements and
rare-earth elements.
Field work for this study was supported in part by
a grant-in-aid of research from Sigma Xi.
Microprobe
analyses were funded by NSF grant EAR-8720141 to Dr.
Barnes.
11

TABLE OF CONTENTS
ACKNOWLEDGMENTS
ABSTRACT
LIST OF TABLES
LIST OF FIGURES
CHAPTER
• •
ll
v
vii
ix
1. INTRODUCTION 1
Objectives of This Study 3
2. GEOLOGIC SETTING 5
Borborema Structural Province 5
Major Tectonic Events 7
Local Setting of the Bodoco Pluton .... 9
3. LITHOLOGY 12
Overview of Rock Types 13
Rock Names 24
Structural Features 31
4. PETROGRAPHY AND CONDITIONS OF CRYSTALLIZATION 36
Petrographic Descriptions 36
Mineral Compositions 60
Conditions of Crystallization 66
5. MAJOR OXIDES AND TRACE ELEMENTS 75
Major Oxides 78
Trace Elements 81
Summary of Chemical Characteristics .... 89
6. ISOTOPE CHEMISTRY 95
Rb-Sr Geochronology 95
Initial Sr Ratios 105
Oxygen Isotope Chemistry 109
7. EVOLUTION OF THE BODOCO PLUTON 113
Differentiation Processes 114
Source Regions 128
Generation of Porphyritic Granitoids . . . 130
Sequence of Intrusion 132
Summary 138
8. TECTONIC CLASSIFICATION 141
111

9. CONCLUSIONS 144
Suggested Further Research 145
REFERENCES 148
APPENDICES
A. FIGURES 159
B. TABLES 205
C. ANALYTICAL METHODS 251
IV

ABSTRACT
The coarse-grained Bodoco pluton is characterized
by tabular megacrysts of K-feldspar in a matrix of
plagioclase, hornblende, biotite, titanite, and quartz.
The pluton is reversely zoned from a partly granitic and
granodioritic margin to a voluminous quartz monzonitic
(QMZ) core.
Within the pluton, elongated km-wide zones
of deformed, foliated megacrystic QMZ are associated with
synplutonic dikes of dark gray monzonite and monzodiorite.
Limited exposures of a topographically high
region of the pluton have a hybridized texture in which
felsic and mafic compositions are complexly intermingled.
The Bodoco pluton is metaluminous and alkalic.
It
has relatively high values of K2O and P2O5 ^^^ very high
Sr and Ba concentrations.
Si02 values range from 52 to
76 weight percent. Quartz oxygen isotope characteristics
are homogeneous (+9.3 to +9.8 per mil).
Initial Sr
ratios are heterogeneous within narrow limits (0.7057 to
0.7071). Rb-Sr geochronology gives an age for the intrusion
of 555 + 8 Ma (Brasiliano orogeny) and initial Sr of
0.70608.
On the basis of the preserved mineral assemblage,
the Bodoco pluton was intruded as a highly oxidized magma
at pressures of about 2-3 kb.
Isotopic data are compatible
with a source region that is mantle-derived but

that had a crustal component.
A model for the evolution
of the pluton is proposed in which crystal accumulation
processes were enhanced by flow separation to produce the
observed reverse zoning.
Late, shear-related fracturing
in zones of deformed megacrystic QMZ allowed mafic magma
to intrude as synplutonic dikes.
At a structurally high
level in the pluton, the mafic magma mixed and became
hybridized with silicic melt that had segregated from the
megacrystic QMZ.
VI

LIST OF TABLES
1. Textural classification of hand samples .... 206
2. Modal analyses and color index of thin sections 210
3. Mesonorm mineral summary 213
4. K-feldspar compositional analyses 216
5. K-feldspar formula weights 219
6. Plagioclase compositional analyses 222
7. Plagioclase formula weights 226
8. Hornblende compositional analyses 230
9. Hornblende structural formulas for amphibole
classification 231
10. Biotite compositional analyses 233
11. Biotite formula weights 234
12. Clinopyroxene compositional analyses 235
13. Clinopyroxene formula weights 236
14. K(D) values for coexisting biotite and
hornblende 237
15. Major oxides and selected trace elements. . . . 238
16. Trace element and rare-earth analyses
determined by INAA for selected samples ... 241
17. Comparison of analytical results for trace
elements for selected samples 242
18. Rb-Sr isotope analyses (whole-rock) 243
19. Rb-Sr isotope analyses (mineral separates). . . 244
20. Rb-Sr isochron calculations using mineral
separates 245
21. Oxygen isotope analyses for quartz separates
• •
and whole-rocks vii
246

22. Crystal fractionation trials 247
23. Magma mixing trials 248
24. Crystal accumulation trials 249
25. Characteristics of I-type and S-type granitoids,
contrasted with the Bodoc6 pluton 250
Vlll

LIST OF FIGURES
1. Major tectonic provinces of Brazil 160
2. Borboremba tectonic province, northeastern
Brazil 161
3. Geological sketch of the Cachoeirinha Fold
Belt, northeastern Brazil 162
4. Generalized topography and landforms of the
Bodoco pluton 163
5. Generalized geologic map of the Bodoco
pluton and vicinity 164
6. Typical "mixed" texture of an outcrop from
the zone of hybrid rocks 165
7. Typical outcrop texture of megacrystic QMZ. . . 166
8. Sample location map 167
9. lUGS rock classification using modal data . . . 168
10. Chemical Q'/ANOR rock classification based
on mesonorm calculations 169
11. lUGS-type rock classification based on
mesonorm calculations 170
12. lUGS rock classification for samples from
the zone of texturally hybrid rocks 171
13. Orientation of structural features 172
14. Concentric shells in a large K-feldspar crystal 173
15. Histogram of plagioclase compositions 174
16. Classification of calcic amphiboles 175
17. Biotite compositions projected onto
phlogopite-annite-eastonite-siderophyllite
field 176
18. Clinopyroxene compositions in the pyroxene
quadrilateral 177
IX

19. Pressure estimates using amphibole
geobarometry 178
20. Histogram of Si02 values for the Bodoc6 pluton. 179
21. Alkali-Lime Index as applied to the Bodoco
Plutonic suite 180
22. Silica variation diagrams with Al^Oo and
Fe203(tot) ^.-^ 181
23. Silica variation diagrams with MgO and CaO. . . 182
24. Silica variation diagrams with Na20 and K2O . . 183
25. Silica variation diagrams with Ti02 and P205* • 184
26. Si02 and MgO zoning in megacrystic QMZ 185
27. CaO and Sr zoning in megacrystic QMZ 186
28. Silica variation diagrams with Rb and Sr. . . . 187
29. Silica variation diagrams with Ba and Zr. . . . 188
30. Sr and Ba variation in the Bodoco pluton and
adjacent country rock 189
31. Zr and P2O5 variation in the Bodoc6
pluton and adjacent country rock 190
32. Chondrite-normalized plots of rare-earth
elements 191
33. Measured ratios of ^"^Rb/^^Sr vs. ^'^Sr/^^Sr
for the Bodoco plutonic suite 192
34. Whole-rock Rb-Sr isochron for the Bodoco pluton 193
35. Rb-Sr mineral isochrons for two mafic enclaves 194
36. Rb-Sr mineral isochrons for two quartz
monzonites 195
37. Comparison of initial Sr and Si02 content . . . 196
38. Comparison of initial Sr and 1/Sr to detect
possible mixing relationships 197

39. Map of distribution of oxygen isotope values
for quartz separates 198
40. Four-step parent-daughter fractionation model . 199
41. Trace-element test of four-step fractionation
model 200
42. Rb/Zr variation with changes in Rb
concentration 201
43. Two-component mixing curves for Rb/Zr and Rb. . 202
44. Schematic diagram of a porphyritic magma
developing in a chamber that is also
undergoing partial melting 203
45. Major stages in the evolution of the Bodoc6
pluton 204
XI

CHAPTER 1
INTRODUCTION
The mineral assemblages and the textures of most
plutonic rocks have developed during an extended period
of slow cooling and crystallization in which much of the
evidence concerning thier early history is obscured.
In
some plutonic bodies, however, the preserved rocks and
textures are unusual enough that they may serve as clues
to the origin of the intrusion and may provide a framework
for interpretation of chemical and isotopic data.
The Bodoco pluton in northeastern Brazil is an
example of such a texturally distinctive igneous body.
It is characterized by blocky, pink megacrysts of
K-feldspar up to 15 cm in length, many of which are zoned
by concentric rings of oriented mineral inclusions.
These megacrysts occur in a dark, coarse-grained matrix
of hornblende, biotite, plagioclase, and quartz.
Ovoid,
cuspate mafic enclaves with the same mineral assemblage
as their hosts are common.
Broad portions of the pluton
are strongly foliated; in these areas, expanses of megacrystic
quartz monzonite alternate with synplutonic dikes
of dark gray, equigranular monzonite and monzodiorite.
The "dent de cheval" texture of the Bodoc6 pluton
makes it conspicuous, but in Brazil it is by no means
unique.
At least 80 intrusive bodies in northeastern
1

Brazil are characterized by such large, tabular
K-feldspar in a dark matrix (Brito Neves and Pessoa,
1974). Similar bodies are also found elsewhere
throughout Brazil and are roughly the same age as those
in the northeast (Wiedemann and others, 1987; Pimentel
and Fuck [sic], 1987; Schmidt-Thom6 and Weber-Diefenbach,
1987). These intrusions are termed "Itaporanga-type"
granitoids (Almeida, 1971) after a town in the Brazilian
state of Paraiba where excellent exposures are revealed
in a quarry.
They intrude high-grade metamorphic rocks
and commonly are associated with migmatite.
The Bodoc6 pluton was selected for detailed study
because it is one of the largest and most accessible of
the Itaporanga-type bodies.
Also, it is located in the
portion of northeastern Brazil where the greatest number
of igneous rocks have been examined geochemically (Sial,
1987). The pluton manifests the standard characteristics
of Itaporanga-type granitoids as well as some interesting
textural variations.
Itaporanga-type granitoids were emplaced during the
Brasiliano (= Pan-African) orogeny, the last major
tectonothermal event to have affected northeastern Brazil
(Wernick, 1981).
Little is known about the specific
magma-forming processes that operated during the
Brasiliano orogeny, but the widespread and voluminous

occurrence of these Itaporanga-type plutons suggests that
the same processes that generated the Bodoc6 pluton
operated on a regional scale.
Objectives of This Study
A number of researchers have observed the unusual
textures and field relations of Itaporanga-type
granitoids and concluded that there is strong circumstantial
evidence in these bodies for an origin by magma
mixing (Wiedemann and others, 1987; Hackspacher and
others, 1987; Jardim de Sll and others, 1987; Schmidt-
Thome and Weber-Diefenbach, 1987; McMurry and others,
1987). These features include commingled and hybridized
rock types, reverse chemical zoning, abundant microgranitoid
enclaves, and rapakivi overgrowths of plagioclase on
K-feldspar.
On the basis of such characteristics, the Bodoco
pluton appeared to be a good candidate for an examination
of its mineralogy, geochemistry, and isotope characteristics
to assess the validity and the importance of magma
mixing in the evolution of the observed rock types.
To
that end, this study had some objectives that are important
in any detailed analysis of a pluton and other
objectives that specifically evaluated the hypothesis
that the Bodoc6 pluton achieved its present textures by

mixing of phenocryst-laden felsic magma with a quantity
of more nearly liquid mafic magma.
The objectives were;
1. To identify and discriminate the various rock types
of the pluton and to determine their sequence of
intrusion.
2. To characterize the major oxide and trace element
compositions of the principal rock units.
3. To characterize the Rb-Sr and oxygen isotope
systematics of the pluton.
4. To calculate an age for the pluton by the Rb-Sr
method.
5. To estimate depth and temperature of emplacement as
well as fluid phase characteristics of the magma.
6. To characterize, if possible, likely source rocks for
the Bodoc6 magma.
7. To develop a geologically reasonable model for the
evolution of the plutonic rock suite.

CHAPTER 2
GEOLOGIC SETTING
Three types of structural regions dominate the
geology of Brazil in approximately equal proportions
(Fig. 1)^:
1. cratonic areas that have been stable for more than
1700 million years,
2. fold belts that formed in two major episodes between
1700 and 500 million years ago, and
3. undeformed Phanerozoic sedimentary basins and
sedimentary deposits along the continental margin
(Almeida and others, 1981).
Borborema Structural Province
The Bodoc6 pluton is located in the Borborema
structural province, a region characterized by numerous
fold belts.
Almeida and others (1981) provided a
comprehensive summary of the structural features of the
Borborema province, the largest tectonic province in
northeastern Brazil.
In general, it is a complex,
faulted mosaic composed of systems of linear fold belts
of metasedimentary rocks separated by areally less
extensive massifs of older, previously deformed
^All figures pertaining to this dissertation are
contained in Appendix A.

crystalline basement in uplifted fault blocks and cores
of large anticlines.
Major axes of folds, bearings of
lineations, and dominant strike of foliations are
parallel to the regional trends of each fold belt.
The
oriented fold belts extend across the province in a fanshaped
pattern so that each is approximately
perpendicular to the present-day coastal margin.
Major
strike-slip faults repeat the semi-radiating pattern
(Fig. 2).
The fold belts in the central part of the province,
where the study area is located, and in the northeastern
part of the province consist chiefly of at least two
depositional cycles of psconmitic and pelitic metasediments.
The fold belts in the extreme northwest and
southwest of the province abut older cratonic provinces
and consist of strikingly similar sets of thousands of
meters of
metamorphosed interbedded carbonate rocks and
terrigenous clastic rocks.
A complex fault system extends hundreds of km across
the province.
Certain of these faults, including the
Pernambuco Lineament and the Patos Lineament (Fig. 3) are
large-scale strike-slip systems that presumably extended
into what is now western Africa, where they are known as
the Foumbam and Ngaourandere fracture zones of the
Cameroon area (Torquato and Cordani, 1981; Gorini and

Bryan, 1976). Minor en echelon faults parallel the major
strike-slip faults, and tensional (normal) faulting is
locally important. Major offset of fold belts attests
that strike-slip faulting has been active in Phanerozoic
time, probably in relation to the Mesozoic breakup of
Gondawanaland, but the major lineeunents appear to be
reactivations of a much older fault system, of which
transcurrent faulting is only the most recent manifestation.
Total aggregate displacement along the lineaments
is unknown.
Major Tectonic Events
Five major thermotectonic cycles have been identified
in Brazilian geology; these correlate in age with
similar events in western Africa (Dallmeyer and others,
1987; Torquato and Cordani, 1981; Hurley and others,
1967). The oldest Brazilian rocks, located within the
cratonic structural provinces, are attributed to the illdefined
Guriense Cycle about 3 billion years ago. A
better-defined event, the Jequi6 Cycle, produced dates of
2700 ± 100 million years (Ma) of age. The most profound
orogeny to have affected the cratonic rocks was the
Transamazonian Cycle, a tectonothermal episode 2000 ± 200
million years ago.

8
Tectonic provinces (including the Borborema
province) that now constitute areas of fold belts were
affected by the Transamazonian Cycle as well as by two
later orogenies:
(a) the Uruguano/Espinhago Cycle, about
1000 million years ago, and (b) the Brasiliano Cycle,
from about 700 to about 500 million years ago (Wernick,
1981; Brito Neves and others, 1974).
The Brasiliano Cycle, equivalent to the Pan-African
orogeny, is geochronologically the best-documented
orogeny in northeastern Brazil, largely because it
thermally overprinted many of the older rocks.
The major
characteristics of the Borborema structural province were
developed during this time.
Meteunorphic conditions
during the Brasiliano Cycle varied from greenschist to
amphibolite facies.
Migmatization was common, and
Abukuma-type metamorphic conditions (low pressure/high
temperature) predominated.
Geochronologic data for the Brasiliano Cycle
indicate that in northeastern Brazil there were three
peaks of thermal activity related to metamorphism and
igneous intrusions (Almeida and others, 1981; Brito Neves
and others, 1974).
Ages of 700 ± 20 Ma may represent
early thermal metamorphism associated with folding,
accompanied by intrusions of a suite of relatively minor
dioritic and mafic dikes.
The climax of the orogeny,

9
well-documented by K-Ar ages in amphiboles and whole-rock
samples, occurred at around 630 ± 30 Ma.
This was a
period of pervasive deformation during which a transcurrent
shear regime produced upright and inclined folds
accompanied by voluminous intrusions of granitoids
(Jardim de S^ and others, 1987).
The last major thermal
event is bracketed by dates between 580 and 540 million
years ago, during which igneous activity was more important
than regional folding.
A late stage of melting
involved upper crustal and metasedimentary sources to
produce small, isolated bodies of leucogranite.
K-Ar
dates from biotite and amphibole substantiate that
regional cooling occurred about 540 million years ago
(Long and Brito Neves, 1977).
Minor post-tectonic
granites and aligned intrusions of silica-saturated
peralkaline syenite dikes with ages from 540 to 410 Ma
marked the end of Brasiliano activity (Sial, 1987; Sial
and Long, 1978; Sial and others, 1981).
Local Setting of the Bodoc6 Pluton
The Bodoco pluton is part of the central structural
domain of the Borborema structural province.
It is
located along the margin of a major, northeast-trending
metasedimentary fold belt known as the Cachoeirinha-
Salgueiro fold belt (Fig. 3; Sial, 1987).
This fold belt

10
is bounded on the north and south by the Patos and
Pernamibuco Linesiments, respectively.
The Bodoc6 pluton is an elliptically shaped
northeast-trending body in western Pernambuco near the
border with Cear^.
It intrudes fine-grained felsic
gneisses and high-grade schists along a contact between
two metamorphic rock units, the Uau^ Group and the
Salgueiro Group (Dantas, 1974).
Cretaceous redbeds and
evaporites of the Araripe Formation (Fig. 3) form a
regionally extensive topographic plateau, the Chapada do
Araripe (Araripe Plateau), that overlies and conceals the
northwestern margin of the pluton (Fig. 4). An erosional
remnant of this plateau extends over the middle third of
the pluton, dividing the surface exposure of the pluton
into a southwestern lobe and a northeastern lobe.
The
two lobes are connected by a kilometer-wide exposure
along the eastern margin of the pluton (Fig. 4). Were it
not for the sedimentary cover, the areal extent of the
pluton would be at least 600 km*.
Topographic relief in the southwestern lobe of the
pluton is minimal.
Most outcrops are small (tens of
square meters), hummocky features with a maximum of 10
meters of relief.
Despite this, exposures are prominent
on aerial photographs because they are unvegetated and
have a high albedo compared to that of the surrounding

11
brush and cultivated fields.
Both outcrop size and
relief increase near the escarpments of the Araripe
Plateau, where rugged hills rise a hundred meters or more
from the surrounding countryside.
In contrast to the gentle relief of the southwestern
lobe of the pluton, the northeastern lobe consists of
numerous hills and ridges with 50-300 m of relief
(Fig. 4). As a result of its location with respect to
the Araripe Plateau, the northeastern lobe of the pluton
receives large amounts of rainfall.
It is densely
vegetated and in parts is forested.

CHAPTER 3
LITHOLOGY
There are three volumetrically significant felsic
rock types in the Bodoc6 pluton (Fig. 5). All three of
these are quartz monzonitic (QMZ), and they have the same
mineral suite in approximately the same modal proportions.
These rock types, therefore, are more
conveniently characterized by texture rather than by
mineralogy or chemistry (Table 1) . Except for several
minor areas where mafic or hybridized rocks predominate,
these three textural variations of quartz monzonite—
"megacrystic QMZ," "phenocrystic QMZ," and "plumose
QMZ"—comprise most of the exposures of the pluton.
Mafic (sensu lato) rock types in the pluton can be
grouped into three categories by occurrence:
numerous
small mafic enclaves; extensive, vertically oriented
mafic sheets (synplutonic dikes); and scattered minor,
late-stage mafic dikes.
Most samples of all three
categories are gray, fine-grained or medium-grained,
equigranular varieties of monzonite, monzodiorite, quartz
monzodiorite, or diorite.
For clarity and conciseness,
in this study the mafic rock types generally are
characterized by their occurrence as "mafic enclaves" or
^All tables pertaining to this dissertation are contained
in Appendix B.
12

13
"mafic intrusives" (either sheets or dikes) rather than
by their broadly similar textures and compositions.
A small region on the northwestern part of the
northeastern lobe of the pluton is texturally distinct
from the remainder of the intrusion.
Rocks in this area
are best described as hybrid (Fig. 5). Mafic rocks in
this region are blotchy with nebulitic, swirled patches
of felsic rock, and they contain coarse, ellipsoidal
inclusions of K-feldspar, plagioclase, and quartz
(Fig. 6). Correspondingly, felsic rocks in this region
are streaked with schlieren-like bands of mafic material,
and many feldspar crystals are mantled by rapakivi
overgrowths.
The degree of hybridization varies so that
within some outcrops textural types range from
homogeneous to hybridized so that felsic and mafic rock
types are commingled on the scale of a hand sample.
Due
to this variability of textures, semiples from this area
are discussed collectively as "hybrids."
Overview of Rock Types
The megascopic textures of the various rock types of
the Bodoc6 pluton are described in more detail below.
Megacrystic Quartz Monzonite
Approximately 80 percent of the pluton is composed
of coarse-grained, megacrystic Itaporanga-type lithology

14
(Fig. 5). This rock type consists of blocky, tabular
megacrysts of K-feldspar in a dark, coarse-grained matrix
of biotite, hornblende, and plagioclase, plus minor
quartz and titanite (Fig. 7). These conspicuous
megacrysts have seriate distribution but commonly exceed
4 cm in length. The megacrysts are more resistant to
erosion than are minerals in the groundmass, so weathered
surfaces of megacrystic QMZ are characteristically white
and knobby.
Fractured or broken surfaces, in contrast,
split preferentially through biotite-rich portions of the
groundmass so that fresh surfaces of the rock appear
nearly black, highlighted by the pink or pale gray
megacrysts.
In some outcrops the tabular megacrysts are unevenly
distributed in aligned clumps and layers.
Where a
deformational foliation is not superimposed, megacrysts
are either unoriented or else they are subparallel in
curvilinear trains of crystals that appear to parallel a
subtle magmatic flow foliation.
The texture of the megacrystic QMZ is relatively
consistent throughout the pluton although there are some
variations.
The most obvious of these variations is
found in the sheared, northeast-oriented, elongated zones
in the western part of the pluton (Fig. 5). Each zone is
about one km wide and several km long.
In these zones.

15
the megacrystic QMZ has an almost gneissic appearance in
which elongated clusters of mafic minerals alternate with
narrow, linear strings of quartz grains ("ribbon quartz")
and aligned K-feldspar megacrysts. The megacrysts have
rounded or ellipsoid cross-sections.
Other minor textural variations in the megacrystic
QMZ include megacryst size and color.
In the southern
part of the pluton, near the contact with phenocrystic
QMZ (Fig. 5), few megacrysts are larger than 2 cm in
length.
In the northern part of the pluton, the
megacrystic QMZ along the northeastern margin has
K-feldspar megacrysts that are white or buff-colored
rather than pink.
The same samples are also quartz-rich.
In contrast, megacrysts from the western side of the
pluton are a mottled salmon-orange color that is darker
than elsewhere in the intrusion.
Phenocrystic Quartz Monzonite
The "phenocrystic" (as opposed to "megacrystic") QMZ
is porphyritic, with tabular pink K-feldspar in a darkcolored
matrix of biotite, hornblende, plagioclase,
quartz, and titanite.
Texturally, it is a finer-grained
variant of the megacrystic QMZ.
The K-feldspar
phenocrysts rarely exceed 10-12 mm in length, and matrix
minerals are correspondingly finer-grained. The
phenocrystic QMZ crops out in an arcuate band in the

16
southern portion of the pluton (Fig. 5). It is bordered
on the interior by megacrystic QMZ.
Its exterior margin
is a transitional contact, up to 2 km wide, in which
phenocrystic QMZ is intermingled in alternating,
foliated, meters-wide bands with plumose QMZ.
Plumose Quartz Monzonite
The plumose quartz monzonite crops out in the
southernmost part of the pluton (Fig. 5). It is mediumto-coarse-grained,
with a pronounced foliation marked by
alternating one-cm-wide bands of dark and light mineral
aggregates.
These bands are parallel in outcrop for tens
of cm but typically splay into
semi-radiating, sigmoidal
zones.
The resulting megascopic texture is a type of
swirled, plumose pattern commonly ascribed to ductile
shear of an incompletely crystallized magma (Ramsey,
1982; Blumenfeld and Bouchez, 1988).
Unlike the megacrystic QMZ or the phenocrystic QMZ,
the plumose QMZ is a variegated black-and-white color in
outcrop, with subsidiary shades of gray and pink.
The
plumose QMZ is porphyritic, with slender K-feldspar
phenocrysts that average 5 to 8 mm in length.
The
K-feldspar phenocrysts in the plumose QMZ are dark gray,
translucent, and slightly iridescent.
They have anhedral
overgrowths of white K-feldspar.

17
The porphyritic nature of the plumose QMZ is not
easily observed because the groundmass consists of mafic
and felsic mineral aggregates whose overall sizes and
shapes are about the same as the phenocrysts.
Mafic Enclaves
Mafic enclaves (terminology after Didier, 1973, to
avoid the genetic connotations of "xenolith" or
"autolith") in an assortment of sizes, shapes, and
textures occur throughout the pluton in all major rock
types except aplite.
Examples of enclaves include samples that are only
centimeters wide but several meters long; angular,
boulder-sized blocks; and, most commonly, rounded or
discoid masses that range in size from a centimeter to a
meter or more.
The three-dimensional shape of most
enclaves is not smoothly ellipsoidal but instead is
cuspate and/or somewhat boudinaged, and some have bentappearing
boomerang shapes.
Enclaves exposed in vertical
cross section are commonly tadpole-shaped; they have
bulbous tops that narrow gradually, and they terminate in
a trailing fringe of finger-like tatters of enclave
material.
With few exceptions, the mafic enclaves are some
shade of gray.
Some are foliated; others are not; some
are fine-grained; others are medium-grained; most are

18
equigranular. Most mafic enclaves near the pluton margin
are fine-grained, but otherwise an assortment of many
textures and types is found throughout the pluton. Many
enclaves contain coarse glomerocrysts (3-5 mm) of
hornblende that stand out slightly in relief on weathered
surfaces, giving the rock a gray-and-black speckled
texture.
Within the megacrystic QMZ in particular,
ellipsoidal mafic enclaves commonly occur in oriented
swarms of several dozen texturally diverse enclaves.
In
these swarms, few enclaves are in direct contact with
each other.
Instead they are separated by nearly
monomineralic seams of megacrystic K-feldspar and/or
hornblende and, in some exposures, also by minor coarse
plagioclase and biotite.
The megacrysts and hornblende
crystals in these seams are conspicuously coarser than
their counterparts in the surrounding host, and commonly
the K-feldspar is pinker.
Enclaves generally appear to be most abundant in the
elongated zones of sheared megacrystic QMZ in the western
part of the pluton (Fig. 5). Two localities in
particular have impressive three-dimensional exposures of
mafic enclaves. At sample locality 21 (Fig. 8),
voluminous, ellipsoidal enclaves have a pronounced
vertical orientation with a northeast strike that

19
corresponds to the foliation in the megacrystic host.
The elongate, upright enclaves appear to have been
flattened against one another, each separated from its
neighbor by a seam predominantly of coarse K-feldspar.
Many enclaves at this locality enclose rounded K-feldspar
megacrysts with rotated pressure shadows.
Foliated, megacrystic QMZ at sample locality 44
(Fig. 8) contains a smaller enclave-rich zone, several
meters wide, with a diverse assortment of enclave
textures.
Most of these enclaves are smooth-sided and
elongate, about 6 cm in diameter and 30-50 cm in length.
They are elongated horizontally instead of vertically, as
if they had been stacked atop each other, and they
parallel the northeast strike of foliation in their megacrystic
host.
The enclaves at this locality are
separated from each other by narrow selvages of coarse
hornblende and by K-feldspar megacrysts.
Mafic Intrusive Sheets
The mafic intrusive sheets are synplutonic dikes
that occur with strongly foliated megacrystic QMZ in
broad, elongated zones in the western part of the pluton
(Fig. 5). They are the most voluminous mafic rock type
of the pluton; they form extensive exposures several
meters wide and tens of meters long.
These intrusives

20
have a pronounced vertical foliation that is formed
principally by the orientation of biotite and hornblende.
The strike of this foliation corresponds to the foliation
in the megacrystic QMZ.
The synplutonic dikes are gray and equigranular, but
coarse black glomerocrysts of hornblende give many
samples a speckled or spotted texture.
These intrusives
typically are composite.
They consist of two or more
swirled modal or textural variants.
For example, pale
gray speckled rock can be intermingled with a darker,
uniformly gray rock, or a plagioclase/biotite/hornblende
rock can be intermingled with one in which K-feldspar is
also abundant.
Some of the mafic intrusives contain
ptygmatically folded veinlets or stringers of felsic
material that results in a migmatitic appearance.
Some
mafic intrusive sheets are streaked with very finegrained
dark aggregates of hornblende, biotite, and
plagioclase that are texturally distinct from the
surrounding matrix.
These dark aggregates are considered
to be mafic enclaves within the mafic intrusives.
Small Mafic Dikes
Gray, fine-grained monzonitic and monzodioritic
dikes that are clearly late-stage intrusives are the
least abundant mafic lithology.
These dikes are rare and
typically are less than one meter wide.

Hybrids
21
The region of hybrid rocks on the western margin of
the northeastern lobe of the pluton (Fig. 5) contains a
variety of rock textures.
In addition to the intermingled,
nebulitic rocks that are characteristic of the
hybrid zone, there are also exposures of megacrystic,
coarse-grained felsic rocks; other porphyritic felsic
rocks with cm-sized phenocrysts of K-feldspar; equigranular
felsic rocks; and dark gray, equigranular mafic
rocks similar to the mafic intrusive sheets associated
elsewhere with sheared megacrystic QMZ.
The felsic rocks from the hybrid zone are generally
granite and granodiorite; they have more quartz and fewer
mafic minerals than rocks elsewhere in the pluton.
The
presence of so many high-silica rocks in the hybrid
region may be a function of structural position within
the pluton.
Due to the low topographic relief of the
field area, most of the exposures of the Bodoc6 pluton
are at about equal elevations, between 400-550 m in the
south lobe and between 550-600 m in the north lobe.
The
hybrid rocks are only exposed topographically higher, at
elevations of 700-800 m, on the flank of the Araripe
Plateau (Fig. 4). The original three-dimensional shape
and orientation of the pluton are not known.
However, if
the pluton has not been tilted appreciably, which the

22
near-vertical orientation of many enclaves and mafic
intrusive sheets would suggest, it is possible that the
hybrid rocks represent a layer of material near the top
of the intrusion, where felsic magma was more
differentiated than elsewhere.
Small Felsic Dikes
Most of the high-silica equigranular rocks are latestage
intrusives that form narrow dikes and veins of
aplite that crosscut all other lithologies.
Many dikes
are zoned mineralogically, with sides that are somewhat
more mafic than leucocratic interiors, or they are zoned
texturally, with coarse-grained sides and fine-grained
interiors.
Although aplitic rocks are ubiquitous, the
pluton contains almost no pegmatite.
Country Rocks
The Bodoc6 pluton intruded along a northeastoriented
contact between the metamorphic Uaua and
Salgueiro Groups (Fig. 5).
In the region south and west of the pluton, the Uaua
Group consists principally of pale felsic gneisses and
fine-grained, pale schists.
Quartz, plagioclase,
microcline, and muscovite predominate in these rocks,
with minor biotite, scattered epidote, and rare oxides.
The region also contains scattered exposures of

23
amphibolitic gneiss, including one small, chalky outcrop
on the pluton margin.
Near the eastern contact, the metamorphic rocks of
the Salgueiro Group are mostly brown-gray, fine-grained
biotite-sillimanite schist, which is characteristic of
the Salgueiro Group and does not appear to be related to
contact metamorphism.
The sillimanite typically occurs
as fibrolite in spotty white felted patches several mm in
diameter.
The schist contains abundant quartz, minor
plagioclase, and muscovite, but no K-feldspar.
Some
samples also contain garnet, staurolite, and cprdierite.
In addition to metamorphic country rock, an exposure
of clinopyroxene-bearing quartz monzonite borders the
pluton on the southwestern margin (sample locality 37;
Fig. 8). It is coarse-grained and is pink and black in
hand sample.
Igneous country rocks also include two minor
clinopyroxene-bearing syenitic dikes (sample localities
17 and 20, Fig. 8) adjacent to the southwestern margin of
the pluton.
Both dikes are pink, fine-grained, and
equigranular; one of them (Scunple 20-A) has a pronounced
gneissic fabric N40°E that conforms to the regional
metamorphic trend.
Although they are poorly exposed,
both dikes are on strike with a series of aligned,
northeast-trending ridges underlain by peralkaline rocks

24
located about 10 km southwest of the pluton near the town
of Ouricuri (Fig. 3).
The northern part of the pluton is bordered by an
extensive, highly weathered, friable pink granite of
unknown age.
It is medium-grained, equigranular, and
composed of approximately equal proportions of
microcline, chalky white plagioclase, and quartz, with
very minor altered bronze-colored biotite.
Rock Names
Classification of the coarse-grained and variably
porphyritic Itaporanga-type rocks that constitute the
majority of the Bodocd pluton presents difficulties
commonly not encountered with plutonic rocks.
The
standard procedure for assigning rock names using the
lUGS classification for igneous rocks (Streckeisen, 1967;
lUGS, 1973) uses the modal proportions of plagioclase,
K-feldspar, mafic minerals, quartz, and/or feldspathoid
in a sample.
Modal data are commonly obtained by point
counts of petrographic thin sections or of stained,
slabbed surfaces.
Single megacrysts of K-feldspar in the
Bodoc6 rocks are likely to be larger than a standard
petrographic slide, making thin section point counts
unreliable for the megacrystic samples.
Similarly, the
amount of surface area that would need to be gridded for
representative results on a slabbed sample of such

25
coarse-grained rock exceeds the typical size of a hand
sample, regardless of whether megacrysts are unoriented
and evenly distributed.
lUGS Classification
The pluton's various other rock types are better
suited than the megacrystic samples to modal lUGS
classification, so they will be characterized first.
Modal data, based on 500-800 points counted per sample,
indicate that with few exceptions both the plumose and
the "phenocrystic" samples are quartz monzonite (Fig. 9)
The phenocrystic QMZ samples generally contain more
plagioclase than the plumose QMZ, but proportions of
quartz are about the same in both.
The color index,
which is the abundance of mafic minerals in a sample, is
also similar in both textural varieties and ranges from
about 20% to 40% mafic minerals in both (Table 2).
As expected from the assortment of textures, the
modal compositions of mafic enclaves differ widely.
Although they are generally quartz-poor or lack quartz,
enclave compositions range from diorite through
monzodiorite to monzonite and include one quartz
monzonite (Fig. 9).
The mafic intrusive sheets that occur in broad,
foliated zones in the western part of the pluton display

26
considerable variation in quartz content.
They range
from monzonite and monzodiorite to quartz monzodiorite
(Fig. 9). The color index for the mafic intrusives
ranges from 27 to 57 (Table 2). Minor, late-stage mafic
dikes are monzonites and monzodiorites (Table 1).
Aplitic dikes are granite except for one quartz
monzodiorite that plots close to the granite field (Fig.
9). Two samples were slightly coarser-grained than the
other aplitic dikes; both samples are quartz monzonite
although one plots near the granite field (Fig. 9).
Classification of Megacrystic Samples
In order to classify the megacrystic samples, two
methods were tested empirically by the use of norm
calculations.
Results of both methods were cross-checked
by comparing norm and modal data for the other two major
felsic rock types, the phenocrystic QMZ and the plumose
QMZ.
One of the two norm-based classification schemes
tested is based on a rectilinear plot that compares
silica saturation
(q/g+or+ab+an) or feldspathoid
saturation with a ratio of normative anorthite (an) and
orthoclase (or). The method uses a ratio of anorthite
and orthoclase to represent plagioclase and K-feldspar in
an attempt to avoid some of the uncertainties introduced
by the presence of albite component (ab) that can be

27
dissolved in both kinds of feldspar.
Streckeisen and
LeMaitre (1979) devised this "Q'/ANOR" chemical
classification primarily for volcanic rocks and glasses,
where modal data are difficult or impossible to obtain.
They tested its effectiveness with a database of 15,487
analyses of plutonic as well as volcanic rocks.
For
quartz-bearing samples in particular, they found
reasonable agreement between the actual rock type and the
predicted classification.
Because CIPW norm calculations make no provision for
hydrous mafic silicates, the calculated norm for rocks
with large amounts of biotite and hornblende is not
likely to estimate quartz and feldspar proportions
accurately.
Streckeisen and LeMaitre (1979) recommended
that the Barth-Niggli mesonorm (Barth, 1959; Niggli,
1931) be used instead of the CIPW norm for such plutonic
rocks.
The mesonorm is calculated in much the same way
as the CIPW norm except that it uses cation proportions
instead of molecular proportions, and it apportions "Mg"
(» Mg, Fe^"*", Mn) among "biotite" [KAlMg3Si30io(OH)2 ] /
"hornblende" [Ca2Mg4Al2Si7022(OH)2]r and, in low-silica
rocks, "barkevikite" [Na2CaMg4Al2Si2022(OH)2] before
making pyroxene or olivine.
Mesonorm values calculated from chemical analyses of
Bodocd rocks (Table 3) are plotted in Figure 10.
In the

28
Q'/ANOR normative classification, the megacrystic samples
define a roughly linear trend consisting mostly of quartz
syenite, quartz monzonite, and granite.
In comparison
with the modal lUGS classification for the plumose and
phenocrystic samples, however, the Q'/ANOR normative
classification displays a misleading displacement away
from plagioclase-enriched rock types.
The plumose QMZ
samples are termed quartz syenite and even quartz alkali
feldspar syenite, and the phenocrystic QMZ samples are
termed quartz syenite and quartz monzonite (Fig. 10).
The observed discrepancies between the modal and
normative classifications suggest that the Q'/ANOR
classification produces results for the megacrystic
samples that would conform only approximately to a modal
classification.
A more successful correspondence between modal and
chemical data was obtained with a second method of normbased
classification.
This second method also used
mesonorm calculations, but it converted normative an, or,
and ab into "representative" plagioclase and alkali
feldspar, then plotted the norm data as modal proportions
using the lUGS classification.
In the feldspars, the
proportion of alkali feldspar was estimated to contain
about 8% ab component (based on microprobe analyses of
Bodocd samples) in addition to or, and the remaining ab

29
was assigned with an to plagioclase. (The proportion of
unexsolved albite component in alkali feldspar is a
minimum estimate that does not include any additional ab
component in K-feldspar now contained in exsolution
lamellae.)
Results of the second method are displayed in
Figure 11.
The concordance between modal and normative
classification is good for plumose QMZ amd phenocrystic
QMZ; both textural varieties are identified normatively
as quartz monzonite, and the plagioclase-rich nature of
the phenocrystic QMZ is apparent.
Normative classifications
of mafic enclaves and mafic intrusives also
correspond well to their modal counterparts.
The
applicability of this norm-based classification is
enhanced because the true compositions of biotite and
hornblende in the Bodoc6 rocks do not differ much from
the "standard" mineral formulas used in the mesonorm
calculations.
As a result, the correspondence between
modal and normative minerals is generally good.
Given the agreement with modal results, this second
norm-based classification is preferred as the method to
assign rock names to the megacrystic samples.
These
Itaporanga-type rocks define a more-or-less linear array
in the quartz monzonite field that overlaps that of the
plumose QMZ, but the megacrystic samples also include

30
quartz monzodiorite, granodiorite, and granite (Fig. 11).
For the sake of conciseness, however, in this study the
megacrystic samples as a group will be referred to as
quartz monzonite (megacrystic QMZ) except where it is
necessary to be more specific.
Classification of Hybrids
Samples from the "hybrid region" in the northwestern
part of the pluton present another problem in terms of
classification.
Mafic and felsic rock types are mingled
in such a blotchy, diffuse manner in many samples that
neither modal nor chemical data provide descriptive rock
names for them.
For example, modal data from two thin
sections of the same hand sample indicate in one case
that the rock is a quartz syenite and in the other case
that it is a monzonite (Fig. 12). Accordingly, modal
classification (as well as chemical and isotopic
analysis) has been limited to samples from the hybrid
region where either a felsic or a mafic composition is
clearly of a volume that could be analyzed.
The felsic rocks of this region are in general more
silicic than any of the other Bodoc6 granitoids; most are
true granite (Fig. 12). In contrast, modally (as well as
texturally) the mafic hybrid samples closely resemble the

31
mafic intrusive sheets that are associated with sheared
megacrystic QMZ elsewhere (Fig. 12).
Structural Features
In a detailed regional study of Brasiliano-age
structural deformation, Jardim de S^ and others (1987)
found that the Itaporanga-type granitoids in their study
area were synkinematic to late-kinematic.
Emplacement of
many bodies coincided with regional thermal maxima during
the period of greatest folding in a NNE (north-northeast)
transcurrent shear regime that produced upright and
inclined folds.
Itaporanga-type granitoids intruded
during this period have a flow foliation marked by
megacryst alignment.
This foliation was overprinted in
some cases by a regional deformation and in other cases
by ballooning of the plutons due to late magma pulses
(Jardim de S^ and others, 1987).
A detailed strain analysis of the Bodoco pluton was
beyond the scope of this study.
However, routine
structural measurements and field observations support
the hypothesis that the Bodocd pluton was emplaced during
active, shear-related regional deformation.
Also, many
of the observed structural features can be attributed to
post-emplacement ballooning.
Locally, late-stage
deformation overprinted some elongated zones in the
western part of the pluton.

32
Magmas that intrude faults during shear-related
deformation are expected to produce bodies that are
elongate instead of circular in map view (Pitcher, 1979;
Guinberteau and others, 1987).
The overall shape of the
Bodoc6 pluton and its direction of elongation conform to
the regional northeasterly structural trend.
Furthermore,
Itaporanga-type intrusions commonly are associated
with major strike-slip faults (Sial, 1987).
Measurement of small structural features in
megacrystic rocks is difficult (Bateman, 1989).
An
outcrop seldom exposes megacryst surfaces that are
perfectly parallel to foliation, and mica foliations
anastomose complexly in three dimensions around larger
minerals such as feldspars.
Only where megacrysts have
strongly preferred deformation-related orientations or
where they are arranged in apophyses by (apparently)
magmatic flow can structural relations be measured with
confidence (Pitcher, 1979).
On the other hand, many
mafic enclaves are large enough and sufficiently
anisotropic that they provide useful orientation information.
Most of the measured orientations in the Bodoc6
pluton are based on exposures of enclaves.
The orientation of the enclaves generally varies
according to their location within the pluton (Fig. 13).
Most enclaves in rocks near the pluton margins are

33
elongate and tabular parallel to the contact, and they
have near-vertical dips.
The direction of greatest
elongation in these enclaves tends to be vertical.
Towards the interior of the pluton, enclaves are more
randomly oriented and in general seem to be more circular
in plan view than those near the margins.
Foliation in
the nearby metamorphic country rocks generally conforms
to the pluton margins (Fig. 13). All of these features
suggest that the pluton intruded to a certain density
level in the crust then acquired most of its volume by
ballooning outward against the wall rocks (Bateman, 1984,
1985).
Shear deformation appears to have affected some
parts of the pluton more intensely than others, as
indicated by the several wide, elongated bands of mafic
intrusive sheets and foliated megacrystic QMZ that crop
out in the western part of both lobes of the pluton
(Fig. 13). These vertically oriented sheets of mafic
rock conform to the northeast-trending orientation of the
pluton, as if they had risen along fault-related internal
contacts.
The mafic intrusives are everywhere in contact
with strongly foliated megacrystic QMZ.
The petrographic
features of the deformed megacrystic QMZ, described more
fully in Chapter 4, include ribbon texture in quartz,
undulatory extinction in large crystals, and pressure

34
shadows on the terminations of oriented megacrysts.
Hibbard (1987) attributed such features to the
deformation of a rigid (more than 70% crystals) but not
yet solidified crystal mush.
Within the westernmost band of very foliated
granitoid and mafic intrusives, the orientation of many
enclaves and megacrysts trends almost due north,
transverse to the northeasterly orientation of the
elongated outcrops in which they occur (Fig. 13).
Guinberteau and others (1987) found similarly juxtaposed
orientations during a study of fault-controlled granite
emplacement in France.
The granite was emplaced in a
pull-apart structure that was created along a shear zone.
In the pluton that they studied, most magmatic flow and
granite foliation patterns were parallel to the overall
elongation of the pluton.
In several places, however,
foliation planes were progressively rotated into
orientations that were transverse and nearly
perpendicular to the dominant structural trend.
These
zones were interpreted to represent magmatic flow
responses to dextral and sinistral transcurrent forces
that were subsidiary to the major shear forces.
Blumenfeld and Bouchez (1988) observed a similar pattern
produced in a massif that underwent shear during magmatic
conditions.

35
The other portion of the Bodoc6 pluton where shearrelated
deformation appears to have been important is in
the plumose QMZ in the southernmost part of the pluton
and in the adjacent transition zone where the plumose and
phenocrystic QMZ are intermingled (Fig. 13). As noted
above, the sigmoidal, swirled patterns in the foliated
plumose rocks probably developed by shearing, as did the
pronounced foliation in the phenocrystic QMZ in the
exposures where the two rock types are interlayered.
Shearing in the southern part of the pluton predated
ballooning, however, because the preserved foliation
conforms to the pluton margins (Fig. 13).
Few of the Bodoco rocks display any evidence of
cataclastic deformation.
The only mylonitized rock
encountered was a seam several cm wide in one of the
elongate zones of shear-deformed megacrystic granitoid.
This suggests that very little deformation post-dated
solidification of the intrusion.

CHAPTER 4
PETROGRAPHY AND CONDITIONS
OF CRYSTALLIZATION
With few exceptions, the various rock types of the
Bodoco pluton are characterized by a mineral assemblage
of K-feldspar, plagioclase, hornblende, biotite, quartz,
and titanite, with accessory apatite, Fe-Ti oxides,
zircon, allanite, and some clinopyroxene.
This chapter
examines in detail the textural characteristics and
compositions of these rock-forming minerals and discusses
the variables that may have affected the crystallization
of the pluton.
Petrographic Descriptions
Megacrystic QMZ
Samples of megacrystic QMZ are coarse-grained and
porphyritic, featuring blocky megacrysts of K-feldspar up
to 5 cm in length in a matrix of anhedral or subhedral
plagioclase, hornblende, biotite, quartz, and titanite.
Plagioclase crystals are the most abundant matrix
mineral. They range in size from 3 to 10 mm. Hornblende,
biotite, and titanite are generally finer-grained
than plagioclase, but they occur in glomerocrysts that
approximate the grain size of plagioclase and so
contribute to the coarse-grained texture of the matrix.
36

37
No consistent orientation of minerals is commonly
discernible on the scale of a thin section.
Biotite
forms anastomosing three-dimensional stringers that rim
the mafic glomerocrysts and extend in a net-like fashion
around individual grains of feldspar and quartz.
These
minerals, as well as accessory and secondary minerals,
are described more fully below.
Megacrysts of K-feldspar are perthitic with some
grid twinning.
The interiors of many megacrysts are
zoned by concentric rings that resemble a nested series
of euhedral growth faces (Fig. 14a). These rings are
similar to the megascopically discernible "shells" of
zonally arranged inclusions that are found worldwide in
megacrystic granitoids (Vernon, 1986).
The zoned pattern
in the Bodoc6 megacrysts is seen to result primarily from
concentric crystallographically controlled bands of
exsolved albite (Fig. 14b). Some (but not all) of these
"exsolution shells" do contain rows of mineral
inclusions, most of which are small, elongate, slightly
rounded crystals of sericitized plagioclase.
Minor
inclusions in some of the oriented rows are biotite,
hornblende, clinopyroxene, and Fe-Ti oxides.
Of these
inclusions, biotite and clinopyroxene typically are
euhedral; hornblende commonly is pseudomorphous after
equant, prismatic grains of pyroxene.
Rows of inclusions

38
of all kinds of minerals are more common in the outer
two-thirds of the megacrysts than they are in the
megacryst centers.
Although the megascopic appearance of the K-feldspar
megacrysts is euhedral, microscopically the crystal faces
are anhedral.
The megacrysts have rounded corners and
irregular edges that are rimmed by an intergrowth of very
fine-grained plagioclase, microcline, quartz, biotite,
hornblende, and lobate myrmekite.
Rarely, megacrysts
have plagioclase overgrowths.
In many samples the ends
(but not the longer sides) of the megacrysts have
pressure shadows of non-perthitic microcline.
There is little K-feldspar in the groundmass of most
of the megacrystic QMZ, most of it being contained in the
megacrysts.
Where it does occur, matrix K-feldspar is
fine-grained, anhedral equant microcline.
Plagioclase is more abundant than K-feldspar in the
megacrystic QMZ, but it is less conspicuous because it is
not megacrystic.
The maximum size of the plagioclase
crystals rarely exceeds 1 cm and is generally less than
5 mm. Plagioclase forms anhedral equant to slightly
tabular subhedral crystals that are slightly sericitized
and otherwise are unaltered.
Untwinned grains are
common.
Mottled, possibly strained extinction is more
common than is a smooth, concentric zoning pattern.

39
Inclusions of other minerals in plagioclase crystals are
not common.
Some plagioclase has inclusion-rich rings.
Lozenge-shaped cores of some plagioclase crystals are
fretted with small biotite inclusions.
These fretted
cores are commonly outlined by a narrow band of sericite
and are surrounded by inclusion-free plagioclase that is
optically continuous with the plagioclase in the core.
In addition to biotite, rare plagioclase cores contain
small glomerocrysts of K-feldspar, clinopyroxene,
hornblende, oxides, abundant slender apatite prisms,
and/or euhedral epidote.
Hornblende and biotite are the two most abundant
mafic mineral phases of the megacrystic QMZ.
They
typically occur as glomerocrystic stringers of anhedral
or subhedral grains.
Hornblende crystals are the most common glomerocryst
phase.
The glomerocrysts range up to 5 mm in width and
several cm in length, but individual grains within them
are much finer.
A typical glomerocryst contains a mosaic
of one or two "coarse" anhedral, equant hornblende
crystals that are 1-2 mm in diameter, and numerous
smaller anhedral hornblende crystals that are less than
0.5 mm in diameter. Individual grains of hornblende that
are not in glomerocrysts tend to be coarse (3-10 mm in
maximum dimension) and are slightly prismatic.

40
Hornblende throughout is strongly pleochroic pale (olive)
green to blue-green to dark (forest) green.
Many
hornblende crystals, particularly the larger ones, have
mottled pleochroism; many are also vermicular.
Some
grains have centers of fibrous, pale green amphibole;
these centers generally are ringed by very fine-grained
or dusty Fe-Ti oxides.
Rarely, some hornblende crystals
retain patchy cores of clinopyroxene.
Euhedral and subhedral prisms of coarse-grained
hornblende (up to 10 mm in length) are more common than
glomerocrystic hornblende in a few exposures of
megacrystic QMZ, particularly in the quartz-rich rocks
along the northeastern margin (localities 5, 6, 56, 76,
and 77; Fig. 8), and near the contact between the
megacrystic QMZ and the phenocrystic QMZ (locality 69;
Fig. 8).
Biotite in the megacrystic QMZ occurs in glomerocrysts
with hornblende as small anhedral to subhedral,
equant to tabular flakes.
In many glomerocrysts, the
hornblende grains make up the central part of the
glomerocryst and the biotite flakes rim the outside; in
others, the biotite flakes are dispersed throughout the
glomerocryst.
Most glomerocrysts have an elongate or
ellipsoid shape terminating in pinched "tails" of ragged,
fine-grained biotite.
In many cases, fine-grained

41
biotite and equally fine-grained plagioclase anastomose
in net-like stringers around coarser minerals in the
matrix and blend into the "tails" of neighboring glomerocrysts.
Biotite is consistently pleochroic pale yellow to
brown-green to very dark green.
It commonly has numerous
small inclusions of euhedral apatite and minor inclusions
of very fine-grained zircon.
In all but the most
siliceous samples, alteration of biotite to chlorite is
rare except where flakes are enclosed by K-feldspar or
where they are very fine-grained and tattered in
appearance.
The proportion of hornblende to biotite varies from
locality to locality in the megacrystic QMZ, but both
minerals are abundant in most samples (Table 2).
Exceptions include sample 69-A, with much coarse-grained
euhedral to subhedral hornblende and virtually no
biotite, and sample 68-B, from a foliated and somewhat
hybridized locality in the northern part of the pluton
(Fig. 8), that has about 15% biotite and no hornblende
(Table 2). Sample 68-B is also unusual in that it is
plagioclase-rich and has only sparse, relatively small
K-feldspar megacrysts.
Quartz occurs in the matrix of the coarse-grained
megacrystic rocks as irregularly shaped equant to

42
slightly elongated pools, 1-4 mm in length, of several
composite grains.
Inclusions in quartz are very rare.
Titanite is a ubiquitous accessory mineral in the
megacrystic QMZ, where it occurs in glomerocrysts as
euhedral or subhedral, slightly pleochroic pink to tan
grains 1 mm in length.
It is commonly adjacent to or
surrounded by grains of hornblende.
In most samples, a
less conspicuous but equally abundant second variety of
titanite occurs as very fine-grained, anhedral, beige,
bead-like grains along the boundaries of two or more
abutting biotite flakes.
Such titanite blebs are
considered to be secondary and to have been formed by
exsolution of Ti02 from biotite (see, among others,
Nironen and others, 1989; Noyes and others, 1983; Barnes,
1983; Speer, 1987).
Apatite is also a ubiquitous accessory mineral in
the megacrystic QMZ.
It occurs almost exclusively in the
mafic glomerocrysts where it forms slender euhedral
inclusions in biotite and hornblende or forms discrete,
stubby prisms adjacent to separate grains of hornblende,
biotite, and/or titanite.
Very little apatite is
associated with feldspars or quartz.
Few other accessory minerals are present in more
than trace amounts.
Oxide minerals such as magnetite and
ilmenite are conspicuously sparse; most occur either as

43
fine-grained granular inclusions within hornblende,
either sprinkled through the grain or in dusty rings, or
else as discrete grains adjacent to other mafic minerals.
Most zircon crystals are very fine-grained inclusions in
biotite; they are rare as discrete, larger grains.
Minor
allanite occurs in most samples, commonly as yelloworange
metamict prisms several mm in length, some of
which have epitaxial rims of secondary epidote.
Epidote
also occurs as a fine-grained alteration product of
plagioclase and biotite.
Samples of megcrystic QMZ from the broad, elongated
zones of foliated rock in the western part of the pluton
are texturally distinct from the megacrystic QMZ
described above.
Megascopically, these samples have an
almost gneissic texture (Chapter 3). In thin section,
evidence for deformation is less obvious.
It is most
typically expressed by pronounced pressure shadows on the
ends of megacrysts, giving the crystals an augen-like
appearance, and as narrow zones between megacrysts that
display a mortar texture of very fine-grained feldspar,
quartz, biotite, and chlorite.
Few of the larger mineral
grains—either megacrysts or matrix minerals—appear
broken, but strained and undulatory extinction is common.

Phenocrystic OMZ
44
In petrographic terms as in hand sample, the
phenocrystic QMZ is a scaled-down textural variant of the
megacrystic QMZ.
The phenocrystic QMZ has the same major
and accessory mineral assemblage in roughly the same
proportions, but the size of most grains is one-fourth to
one-third that of the megacrystic QMZ.
Phenocrysts of
K-feldspar have the same overall shape as the megacrysts
but rarely exceed about one cm in length.
Plagioclase,
quartz, and mafic glomerocrysts in the groundmass are
proportionately smaller as well, so that most grains are
in the 1-2 mm size range.
Phenocrysts of K-feldspar are characterized, like
K-feldspar megacrysts, by concentric exsolution rings
(Fig. 14). In the phenocrystic QMZ, these albitic rings
are dusty-looking in thin section, possibly due to
sericitization or to submicroscopic inclusions.
Unlike
in the megacrystic QMZ, the exsolution rings extend from
near the center completely to the edges of many
K-feldspar phenocrysts, so that the outermost ring abuts
the groundmass on (010) faces.
However, the rings do not
extend into the microcline overgrowths at the tips of the
phenocrysts.
The exsolution rings contain the same set
of mineral inclusions as do those in the megacrystic QMZ.

45
With few exceptions, the groundmass minerals
correspond texturally to those in the megacrystic QMZ.
Slight differences in the phenocrystic QMZ include the
presence of traces of secondary calcite crystals.
Acicular apatite forms inclusions in cores of some
plagioclase crystals. Preserved cores of clinopyroxene
in hornblende are slightly more common than in
megacrystic QMZ. Biotite is rare within glomerocrysts
but is common rimming them.
Atypical samples of phenocrystic QMZ include those
from exposures in the southern portion of the pluton
where the phenocrystic QMZ is strongly foliated and is
intermingled in bands with plumose QMZ (Fig. 5).
Numerous K-feldspar phenocrysts and coarse-grained
plagioclase crystals in the phenocrystic QMZ from this
region are broken, fractured, bent, elliptical, or
almond-shaped.
Phenocrysts of K-feldspar with concentric
exsolution rings have been broken across the albitic
exsolution rings, then subsequently overgrown with
K-feldspar that has no rings.
Minor bands of mortar
texture (very fine-grained plagioclase and biotite)
suggest granulation due to shearing.
The intensity of
deformation and foliation in these exposures, however,
varies on outcrop scale as well as in thin section.

Plumose OMZ
46
As described in Chapter 3, the porphyritic texture
of the plumose QMZ is masked by the groundmass minerals,
which occur in elongate felsic and mafic stringers that
have approximately the same dimensions as the phenocrysts
of K-feldspar.
Plumose QMZ samples are medium-grained,
with a seriate distribution of grain sizes in the
groundmass up to about 3 mm.
Phenocrysts of K-feldspar
rarely exceed 8 mm in length.
The pronounced foliation of these samples that gives
them a "plumose" texture megascopically is less visible
in thin section, but it is suggested by alternating
glomerocrystic stringers of mafic and felsic minerals in
the groundmass.
Although the stringers define a
foliation, individual grains within them are generally
unoriented.
The groundmass mineral assemblage consists
of plagioclase, hornblende, biotite, quartz, and
titanite, with minor interstitial K-feldspar, and an
accessory assemblage of apatite, Fe-Ti oxides, zircon,
and allanite.
Secondary titanite and epidote are also
present.
K-feldspar phenocrysts are the most obvious
petrographic difference between the plumose QMZ and
either the megacrystic QMZ or the phenocrystic QMZ.
The
K-feldspar phenocrysts in the plumose QMZ are

47
proportionately more slender and are more euhedral than
in the other two rock types, and they have thick,
optically continuous overgrowths of a second generation
of K-feldspar that completely rim the phenocrysts.
The
phenocrysts themselves are dusty-looking and perthitic,
but the overgrowths are limpid and either display grid
twinning or are more finely exsolved than the phenocrysts.
The phenocrysts contain concentric exsolution
rings with rows of oriented mineral inclusions, as do the
K-feldspar megacrysts and phenocrysts in the other two
rock types, but the euhedral rings do not extend beyond
the phenocryst proper into the overgrowth K-feldspar.
In
samples with pronounced foliation, the overgrowth
material is thicker at the terminations than on the long
faces of the phenocrysts, and it pinches out and merges
into interstitial K-feldspar in the matrix.
Plagioclase crystals are anhedral, tabular or
equant, and 1 to 3 mm in length.
In general, plagioclase
in the plumose QMZ appears more altered than in the other
two types of QMZ.
Cores, cleavage planes, and some
entire crystals are turbid and/or are extensively
sericitized. Some grains are sausseritized. Plagioclase
crystals included in K-feldspar or adjacent to it are the
most altered.
Twinning and zoning are indistinct in most

48
grains, although mottled extinction is common.
Myrmekite
is present in both polygonal and lobate forms.
Hornblende in the plumose granitoid is anhedral and
crystals range in size from about 0.2 mm to about 2 mm.
Near the pluton margin hornblende is coarser-grained than
near the interior boundary where the plumose and phenocrystic
QMZ are in contact.
It occurs almost exclusively
in mafic glomerocrysts that range from 2 to 6 mm in
diameter. In the two-dimensional perspective of a thin
section, some glomerocrysts are a mosaic of more than 30
small, equant hornblende grains; others consist instead
of only three or four coarse grains.
Pleochroism is pale
(olive) green to blue-green to dark (forest) green, and
much hornblende is vermicular, uralitized, or has patchy
cores of clinopyroxene.
Inclusions of fine-grained apatite
and zircon are common.
Vermicular or uralitized
grains commonly are peppered with inclusions of granular
Fe-Ti oxides, some of which occur in rings of inclusions
around hornblende cores.
In general, the plumose QMZ samples have less biotite
than hornblende (Table 2). Most of the biotite
occurs as very fine-grained, anhedral, splinter-like
flakes in narrow, oriented stringers that connect
hornblende-rich glomerocrysts.
Biotite partly rims some
glomerocrysts and occurs as inclusions in hornblende.

49
The other minerals of the groundmass, including
quartz, titanite, interstitial K-feldspar, Fe-Ti oxides,
apatite, zircon, and allanite, closely resemble those of
the megacrystic QMZ.
Where plagioclase is strongly
altered, minor epidote has formed as a secondary mineral.
Two atypical outcrop localities of plumose QMZ are
noteworthy.
The only plumose sample that is not quartz
monzonitic is quartz monzodiorite from locality 29
(Fig. 8). Rocks from this locality are more foliated
than elsewhere and have an almost gneissic texture.
The
K-feldspar phenocrysts are more pink than dark gray, and
they are rimmed by plagioclase overgrowths rather than by
K-feldspar overgrowths.
These plagioclase overgrowths,
as well as discrete plagioclase in the matrix, have
conspicuous inclusions of acicular apatite.
In contrast
to other examples of plumose QMZ, hornblende is rare, but
biotite is abundant; it occurs in glomerocrysts with and
without hornblende and in net-like stringers between
glomerocrysts.
The biotite-dominated glomerocrysts are
rimmed in part by anhedral epidote.
The other atypical example of plumose QMZ is cataclastically
deformed rock from locality 23 on the eastern
margin of the pluton (Fig. 8). Strongly foliated biotite
from this locality is so fine-grained that it imparts a
pearly gray luster to hand samples.
In thin section, the

pleochroism of the biotite is more brown than green, and
50
it forms fine-grained, shredded flakes that anastomose
around other minerals.
K-feldspar crystals are lensshaped
and have tails of fine-grained felsic minerals.
Isolated, foliated felsic stringers dominated either by
plagioclase or K-feldspar have rounded, broken grains
1-2 mm in diameter with tails of a much finer-grained
mosaic of quartz, plagioclase, K-feldspar, biotite, and
hornblende.
In the most deformed samples from this
locality, hornblende is a turbid olive color in thin
section and has fibrous, uralitized cores.
Mafic Enclaves
Most of the mafic enclaves are an equigranular
intergrowth of fine-grained or medium-grained plagioclase,
hornblende, biotite, and K-feldspar, with
accessory titanite and (in some samples) quartz.
Numerous enclaves also contain clinopyroxene as ragged
cores in hornblende.
In portions of individual enclaves, mineral distribution
is heterogeneous.
Many enclaves are "speckled"
with 1-4 mm glomerocrysts of equant hornblende, biotite,
and titanite.
Furthermore, the presence or absence of
K-feldspar in portions of mafic enclaves can be
correlated with the distribution of various mafic
minerals.
Where K-feldspar is absent or rare.

51
plagioclase and biotite are common but hornblende is
absent or rare.
Regardless of the abundance of
K-feldspar or hornblende elsewhere in the enclave, many
samples have a thin rind of very fine-grained plagioclase
and biotite.
Some small enclaves that are fine-grained
throughout contain biotite but no hornblende or titanite.
In contrast, other enclaves have banded zones in which
K-feldspar is the most abundant phase and in which the
associated hornblende crystals are generally coarser,
more abundant, and more euhedral than elsewhere in the
enclave.
or absent.
Biotite in these zones is correspondingly rare
The extreme example of this relationship is
enclave 12-A, in which hornblende is present only in the
K-feldspar-enriched parts of the enclave.
There is a
comparable paragenetic relationship between clinopyroxene
and K-feldspar in some enclaves.
For example, the
K-feldspar-enriched portion of one enclave (sample 2-A)
has euhedral, discrete 0.25 mm crystals of clinopyroxene
without hornblende rims.
Similarly, in enclave 13-B a
clinopyroxene crystal is preserved where it is enclosed
by K-feldspar but has been replaced by hornblende where
the original clinopyroxene crystal protruded into the
groundmass.
The mafic enclaves are not porphyritic, strictly
speaking, but many have a bimodal texture because they

52
contain inclusions of coarse-grained felsic minerals.
The most common of these are large crystals of perthitic
K-feldspar that are the same size as or slightly smaller
than the megacrysts or phenocrysts of K-feldspar in the
host.
Some of the K-feldspar crystals are rounded or
ellipsoidal; others are tabular like the equivalent
crystals in the host.
Rounded megacrysts commonly have
optically continuous outer shells that contain abundant
biotite inclusions.
These megacrysts typically have
pressure shadow overgrowths of inclusion-free microcline
that extend beyond the rounded terminations of the
megacrysts into the matrix.
In some megacrystic QMZ,
K-feldspar megacrysts appear to have been pushed from the
host rock against the enclave, where they indent the
surface of the enclave and cause the biotite and
hornblende foliation to deflect around the megacrysts.
In other enclaves, megacrysts from the host granitoid
appear to have penetrated through a rind-like enclave
"skin" into the enclave's interior.
In such cases, the
portion of the megacryst that is surrounded by enclave
material typically has a rounded shape and may have an
optically continuous overgrowth enriched in very finegrained
biotite and hornblende inclusions; the portion of
the megacryst that remained within the host granitoid is
rectangular and pristine.

53
Many enclaves also contain rounded, coarse-grained
plagioclase crystals that have checkered or biotitefretted
cores or that have rings of biotite-rich
inclusions.
Some enclaves also have glomerocrysts of
several coarse-grained plagioclase crystals.
These
glomerocrysts have biotite-rich plagioclase overgrowths
that surround the glomerocryst as a whole.
Several enclaves, particularly those that are quartz
monzonite or quartz monzodiorite, have anhedral 0.5-2.0
mm pods of quartz that are rimmed by hornblende,
K-feldspar, or very fine-grained plagioclase and biotite.
The quartz in some of these pods is rutilated.
In most enclaves, K-feldspar occurs as equant,
anhedral interstitial fine-grained crystals of nonperthitic
microcline.
Only one enclave, sample 56-C, had
almost no K-feldspar (Table 2).
In general, K-feldspar
is heterogeneously distributed in diffuse patches or
layers with other felsic minerals.
The K-feldspar in a
few enclaves contains inclusions of acicular apatite.
In
such enclaves with a bimodal size distribution of
K-feldspar (1-5 mm vs. 0.1-0.5 mm), only the coarser
fraction has apatite inclusions.
Plagioclase forms equant anhedral and slightly
tabular subhedral crystals in which acicular apatite
inclusions are common.
It is untwinned or faintly

54
twinned, and large grains have concentric zoning and
sericitized cores.
Except for some atypical hornblende noted below that
is a turbid green in thin section, most hornblende in the
mafic enclaves resembles that in the megacrystic QMZ.
Hornblende in most enclaves occurs in glomerocrysts and
in disaggregated stringers.
ranges from 0.25 to 0.50 mm.
The average grain size
Many hornblende crystals
have cores of uralitic amphibole or ragged clinopyroxene.
Biotite forms wide, subhedral flakes, 0.25-1.0 mm,
with minor apatite and zircon inclusions.
Pleochroism in
some samples is browner than in other rock types, but
most biotite has the same yellow to brown-green to very
dark green pleochroism observed throughout the pluton.
Accessory minerals include titanite, very finegrained
Fe-Ti oxides (rare), apatite, zircon, allanite,
and epidote.
Acicular apatite is common in plagioclase
but rare to absent in K-feldspar.
Slightly coarser
apatite is common as inclusions in biotite and hornblende.
Most allanite has epitaxial rims of secondary
epidote.
Because in general most of the mafic enclaves are
petrographically similar to each other, several atypical
enclaves merit some additional comment.

55
Sample 27-B is a small, very cuspate enclave several
cm long. The center part of the enclave is a dense
mosaic of 0.2 mm idiomorphic granular crystals of pale
green clinopyroxene, and the outer part is a rind of
coarser (0.6 to 1.0 mm) vermicular pale green to bluegreen
to dark green hornblende. At the contact between
the enclave's core and the rind, the outer halves of some
clinopyroxene grains appear to have been pseudomorphed by
hornblende.
Sample 9-C is an angular mafic enclave that consists
of a mosaic of anhedral, glomerocrystic, equant, turbid
green hornblende cut by veins of fine-grained microcline.
Plagioclase is rare. The K-feldspar and minor biotite in
this enclave contain abundant acicular apatite inclusions
whereas the amphibole lacks such inclusions.
Mafic enclave 77-B is a medium-grained enclave with
many inclusions of coarse-grained felsic minerals.
It
has pale green, turbid hornblende and reddish-brown
biotite that contains wire-like rods of exsolved oxides.
Although biotite in the metamorphic country rocks is
consistently pleochroic reddish-brown, sample 77-B has
the only such reddish-brown biotite observed within the
pluton.
The most conspicuous feature of this enclave is
the abundance of acicular apatite inclusions in
plagioclase and K-feldspar and the scarcity of such

56
inclusions in hornblende and biotite.
This is the
reverse of what is commonly observed in the other rock
types of the pluton.
The largest plagioclase and
K-feldspar crystals in this enclave lack apatite, but
they have apatite-rich K-feldspar overgrowths.
Mafic Intrusives
The synplutonic dikes characterized in this study as
mafic intrusive sheets contain fine-grained plagioclase,
K-feldspar, hornblende, biotite, minor clinopyroxene (in
cores of hornblende), and minor titanite.
Quartz is
minor or absent.
Clinopyroxene in hornblende is particularly
evident where K-feldspar encloses hornblende.
Feldspars occur in anhedral equant or slightly
tabular grains that are commonly arranged in diffuse,
elongate felsic stringers that, with comparable mafic
stringers, impart a slight foliation to samples.
K-feldspar (microcline) is present as distinct 1 mm
grains that are commonly in felsic stringers with
plagioclase; as nebulitic, interstitial patches, and as
monomineralic, crosscutting veinlets.
Plagioclase is
mostly untwinned and typically contains numerous
inclusions of acicular apatite.
Fe-Ti oxides are rare; most are very fine-grained
granular inclusions in hornblende.
Allanite is common as

57
a minor accessory mineral; most allanite prisms have
secondary epidote rims.
The minor late-stage mafic dikes resemble the mafic
intrusive sheets petrographically.
They contain very
fine-grained (less than 0.5 mm) equigranular plagioclase,
K-feldspar, hornblende, biotite, and very little quartz.
Aplites and Other Felsic Dikes
The felsic dike rocks have approximately equal
proportions of fine-grained K-feldspar, plagioclase, and
quartz.
One sample (9-A) is granophyric.
Most K-feldspar in the aplitic samples is
microcline.
It is interstitial and anhedral, imparting
(with quartz) an interlocking, granitoid texture to the
rocks.
Plagioclase is equigranular or else has seriate
distribution up to (rarely) 3 mm; it is commonly very
sericitized and contains minor muscovite.
Partly chloritized, small, ragged flakes of brown or
green biotite are present in all samples, but only two
samples (13-C and 14-B) contain minor hornblende.
Titanite is nearly ubiquitous.
Other accessory minerals
include scattered coarse-grained Fe-Ti oxides, some of
which are rimmed by titanite, and stubby prisms of
allanite (rimmed by epidote in samples 13-C and 14-B).
Secondary minerals include minor chlorite and muscovite.

Hybrid Rocks
58
The swirled, megascopically blotchy appearance of
many rocks in the hybrid region is not as apparent on the
scale of a thin section, but these rocks nevertheless
have unusual petrographic characteristics in comparison
with the remainder of the pluton.
For example, granitic
and granodioritic rocks from the hybrid region have
conspicuous overgrowths of plagioclase on K-feldspar and
plagioclase on plagioclase.
Megacrystic K-feldspar is
consistently coarser-grained than anywhere else in the
pluton, commonly up to 6 cm in length.
The cores of many
plagioclase crystals are lozenge-shaped and fretted with
biotite. Biotite in these rocks is vermicular on (001)
and occurs in hornblende-free glomerocrysts with
secondary epidote.
The accessory mineral assemblage
includes minor allanite, titanite, and stubby apatite
prisms.
Secondary minerals include calcite, muscovite,
chlorite, and epidote.
One sample of granite (61-E) has
optically zoned zircon crystals.
Mafic hybrid rocks also have plagioclase crystals
with lozenge-shaped, biotite-fretted cores, and they have
large plagioclase and K-feldspar crystals with plagioclase
overgrowths.
They have rutilated quartz grains in
small, round clusters that are rimmed either by hornblende
or by fine-grained felsic minerals.
Interstitial

59
K-feldspar (microcline) in the hybridized mafic rocks is
heterogeneously distributed in diffuse patches and
layers.
Where such K-feldspar is present, associated
hornblende crystals are coarser, more abundant, and more
euhedral than elsewhere in the rock.
Acicular apatite is
present as inclusions in some plagioclase and rarely in
fine-grained interstitial K-feldspar, but not in coarsegrained
K-feldspar.
Allanite and titanite are minor but
common accessory minerals, and traces of calcite and
epidote are present as secondary minerals.
Country Rocks
The three exposures of clinopyroxene-bearing igneous
rocks west of the pluton are petrographically distinct
from the Bodoc6 samples.
The clinopyroxene-bearing
quartz monzonite, sample 37-A (Fig. 8), has coarsegrained,
markedly perthitic K-feldspar, plagioclase with
distinct albite twinning, fine-grained quartz, pleochroic
brown biotite, and very minor hornblende.
Clinopyroxene
forms one-mm grains that have equant, roughly prismatic
cross-sections.
It is faintly pleochroic green and
occurs with biotite in glomerocrysts.
Both of the syenitic dikes (samples 17-B and 20-A;
Fig. 8) contain microcline and fractured, fine-grained
equant clinopyroxene that has pale green pleochroism.
Titanite and stubby crystals of apatite are important

60
accessory phases in sample 20-A.
Sample 17-B has about
3% coarse-grained, anhedral calcite, making it the third
most abundant mineral in the sample after K-feldspar
(90%) and clinopyroxene (5%) (Table 2).
Mineral Compositions
On the basis of petrographic study, representative
and unusual samples were selected for further analysis
with an electron microprobe to obtain mineral
compositions.
Appendix C.
Analytical techniques are described in
K-feldspar
Microprobe analytical results for K-feldspar are
summarized in Tables 4 and 5.
The analyses indicate that
the proportion of albite component in solid solution with
K-feldspar is generally about 8-9 percent.
The
variability in K and Na content of the analyses is in
part due to the difficulty of avoiding exsolved albitic
lamellae with the probe beam despite the small beam
diameter used.
Of the trace elements commonly present in
K-feldspar, only Ba is present in the Bodoc6 samples in
relatively large amounts, between 0.6 and 1.7 weight
percent (Table 4). At elevated temperatures, the large

61
Ba^"*" cation (d=1.35 A) substitutes with Al for K"^
(d=1.33 A) and Si.
The coupled substitution retards Ba
migration during subsolidus exsolution (Michael, 1984),
so zoned Ba concentration in K-feldspar megacrysts has
been used qualitatively to justify a magmatic origin for
megacrysts in felsic rocks (Mehnert and Busch, 1981;
Vernon, 1986).
Abrupt Ba zoning has been detected in
megacrysts of other Itaporanga-type granitoids in northeastern
Brazil (McMurry and others, 1987).
The
K-feldspar megacrysts in the Bodoc6 megacrystic QMZ do
not demonstrate appreciable Ba zoning but are relatively
homogeneous, with non-systematic variations between 1.0
and 1.3 wt% BaO in a traverse of a typical megacryst
(Table 4). On the other hand, K-feldspar phenocrysts are
slightly zoned in both the phenocrystic and plumose QMZ.
Core values of BaO are about 0.6 wt% higher than rim
values in both rock types (Table 4).
K-feldspar crystals in some mafic enclaves and in
some aplitic dikes have BaO values as low as 0.3 wt.%
(Table 4). K-feldspar values of BaO in gneissic country
rock are also low (0.1 to 0.4 wt%).
The K-feldspar in
the clinopyroxene-bearing quartz monzonite (37-A, Fig. 8)
adjacent to the southwestern margin of the pluton has BaO
values of about 0.5-0.6 wt%, lower than that of most
Bodocd rocks.

Plagioclase
62
Plagioclase from megacrystic QMZ, plumose QMZ, most
mafic enclaves, mafic intrusives, textural hybrids, and
felsic dikes is oligoclase with the narrow compositional
range An^^y to kn2i
(Fig. 15). Plagioclase in these rocks
is either unzoned or else weakly normal or reverse zoned
(Tables 6 and 7).
In contrast to most of the other rock types in the
pluton, the phenocrystic QMZ samples contain plagioclase
with consistently higher An content and pronounced normal
zoning.
Plagioclase crystals in these samples have cores
in the compositional range An3y to An25
(Table 6), zoned
to oligoclase rims that are comparable in An content
(An28-An22) "to plagioclase elsewhere in the pluton.
Plagioclase grains that form inclusions within K-feldspar
phenocrysts have compositions of An2]^ to An25 that are
bracketed by the rim and core compositions of plagioclase
in the groundmass of the same samples (Table 6).
The total range of plagioclase compositions in the
mafic enclaves is An^y^s to An22 (Fig. 15). The one
exception is a mafic enclave (24-A) with a plagioclase
composition of An27.
The anorthite content of
plagioclase in individual samples is restricted; it
varies only 1-2% An per sample.

63
The gneiss and schist of country rocks also contain
oligoclase (AnjQ for schist, An22_23 ^°^ gneiss;
Table 6). In contrast, the clinopyroxene-bearing quartz
monzonite (37-A, Fig. 8) adjacent to the southwest margin
of the pluton has Na-rich plagioclase (Ang to An^^^)
(Fig. 15). The albitic composition of the plagioclase in
sample 37-A is one of the most pronounced differences
between sample 37-A and any of the Bodoco QMZ.
Hornblende
Amphibole compositions in the pluton are varied
(Table 8). On the basis of the analytical data, cation
proportions (based on 23 oxygens) were assigned to
specific crystallographic sites (Hammarstrom, 1984).
For
some microprobe analyses, two reasonable solutions were
possible for cation assignment (Table 9): one with all Fe
apportioned as Fe^"*" (as is routinely reported from
"3 J.
microprobe analyses) and another with some Fe"^
as well
as Fe^"*". Because the amount of Fe^"*" apportioned to the
M1-M33 sites is small compared to the amount of Fe^"*" in
each case, both solutions produce similar results.
All Bodoc6 amphiboles are members of the calcic
amphibole group (terminology and classification after
Leake, 1978), in which (Ca + Na)3 > 1.34 and Nag < 0.67
(standard formula: Ao_iB2C^^^T^^g022(OH, F, Cl)2.
Within
the calcic amphibole group, the analyzed amphiboles are

64
further characterized, depending on (Na + K)^, Si, and
Mg/(Mg + Fe^"*"), as edenite or hornblende (Fig. 16).
Bodoco amphiboles probably contain more oxidized Fe
than is indicated by apportionment estimates in Table 9.
Quantitative proportions of Fe^"*" and Fe^"*" in amphiboles
of two samples were determined by titration for mineral
separates of a megacrystic QMZ (63-A) and a mafic enclave
(56-C).
In both cases, measured Fe^''' was slightly
greater than estimated Fe^"*" (Table 9). This difference
affects some of the amphibole classifications because an
increase in Fe^"*" in the M2^-M33 crystallographic sites
increases the amount of Na apportioned to the M^
crystallographic site and decreases the Na in the A site.
As a result, several of the BodocO amphiboles (in
particular, 56-A, 63-B, 48-B, and rims of 75-A) that
appear to have (Na + K)^ only slightly greater than 0.50
are probably magnesio-hornblende, not edenite.
Megacrystic QMZ and plumose QMZ samples contain
magnesio-hornblende and/or edenite.
A sample of phenocrystic
QMZ (33-D) from the zone of intermingled plumose
and phenocrystic QMZ in the southern part of the pluton
contains actinolite, which is the most silicic amphibole
analyzed (Fig. 16). Where plumose and phenocrystic QMZ
are intermingled, the amphibole core compositions differ
between the two rock types.
However, the rim composition

65
of amphibole in phenocrystic QMZ sample 75-B matches that
of the core composition of amphibole in the intermingled
plumose sample 75-A (Fig. 16).
Several mafic enclaves and mafic intrusives have
low-Si amphiboles, with compositions clustering near the
edenitic hornblende and ferro-edenitic hornblende
boundary (Fig. 16). One mafic enclave, 56-C, contains
actinolitic hornblende.
Biotite
Biotite compositions proved to be relatively
homogeneous in a variety of rock types (Tables 10
and 11). Most biotite has an Fe/(Fe + Mg) ratio of 0.3
to 0.4, and the tetrahedral Al content of Bodoco biotite
is higher than in pure annite and phlogopite end members
(Fig. 17). In general, Ti02 content is highest in the
cores of coarse-grained flakes of biotite, in biotite in
the "biotite-fretted" inclusions of large plagioclase
grains, and in biotite in most mafic enclaves (Table 10).
The concentration of BaO in biotite in enclaves is
slightly greater than that in biotite from other rock
types.
Atypical compositions include the biotite in enclave
24-A, which is more aluminous and Fe-rich than is typical
in the other samples.
The biotite in a small enclave in

66
sample 33-D is distinct from that in the host
phenocrystic QMZ.
Biotite from sillimanite schist adjacent to the
pluton is more aluminous and slightly more Fe-rich than
the plutonic biotite (Fig. 17).
Clinopyroxene
Tables 12 and 13 summarize the results of microprobe
analyses of clinopyroxene.
All clinopyroxene analyzed is
salite (Fig. 18). Proportions of minor constituents (Na,
Al, Ti, and Mn) do not vary appreciably among the various
samples except that the clinopyroxene in mafic intrusive
21-B has less Na and slightly more Ti than the other
samples.
The FeO content of a mineral separate of
clinopyroxene from quartz monzonitic sample 37-A was
analyzed by titration.
Results indicate that approximately
one-fourth of the Fe in the clinopyroxene is Fe^"*"
(Table 13). The clinopyroxene in the syenitic dikes
(17-B and 20-A) in the nearby country rock is less
magnesian than that of the other samples.
Conditions of Crystallization
The distribution of chemical components among
mineral phases and hence the variation in composition of
specific minerals is a function of temperature, pressure,
and activities or fugacities of components.
The

67
compositions of phase assemblages in a rock therefore can
provide at least a partial record of the intensive
variables that have affected the system.
Like most
plutonic rocks, the Bodoc6 pluton cooled slowly and many
of its textures and mineral compositions evolved as a
result of supersolidus reactions, subsolidus exsolution,
and probably some open system behavior.
These processes
thwart most attempts to estimate magmatic conditions.
Nevertheless, the preserved mineral assemblage allows a
few conclusions about magmatic temperature, pressure, and
fugacity in the Bodoc6 pluton.
Intensive Variables
Due to post-crystallization exsolution, mineralbased
geothermometry in plutonic rocks commonly yields
subsolidus closure temperatures instead of magmatic
temperatures.
This proved to be the case with Bodoc6
samples. Two-feldspar geothermometry (Stormer, 1975;
Whitney and Stormer, 1976, 1977) and minimum temperature
estimates from clinopyroxene compositions (Lindsley,
1983) gave temperatures of less than 500°C in all cases.
Certain mineral equilibria are sensitive to one
particular intensive variable but remain relatively
unaffected by changes in others.
Hammarstrom and Zen
(1986) contended that in calc-alkalic plutons the total
Al content of amphiboles that crystallize at near-solidus

68
temperatures varies linearly with pressure.
In rocks of
appropriate bulk composition, they found that the Al^ of
amphiboles in equilibrium with an assemblage of quartz,
K-feldspar, plagioclase, biotite, titanite, and an Fe-Ti
oxide could be used as a geobarometer that was reliable
to within ± 3 kb.
Hollister and others (1987) refined
the calibration of this geobarometer over a range of
2-8 kb and reduced the error estimate to ± 1 kb. The
compositions of hornblende rims are plotted for BodocO
samples in Figure 19.
Because the pluton has variable
amphibole compositions, the hornblende geobarometer
produces a range of pressure estimates.
However, most of
the granitoid values range between 2-3 kb.
Mafic
enclaves and mafic intrusives for which hornblende
analyses were available were essentially quartz-free and
so were not suitable for pressure estimates.
In metamorphic country rock, the paragenesis of
staurolite plus biotite, sillimanite, and altered garnet
(now pseudomorphed by quartz and muscovite intergrowths)
suggests a minimum pressure in excess of 4 kb (Miyashiro,
1973).
As noted above, Fe-Ti oxides are rare in the Bodoc6
rocks.
Most occur as minute inclusions in hornblende,
where it appears that they may have formed by a supersolidus
reaction of clinopyroxene to amphibole.
At least

69
some discrete grains of magnetite in the mafic glomerocrysts
appear to be primary, however.
The assemblage of
magnetite, quartz, ferromagnesian silicates, and euhedral
titanite constitute a mineral assemblage that is characteristic
of a relatively high oxygen fugacity (Wones,
1989). However, the ratio of Mg/(Mg + Fe) in Bodoc6
hornblende is between 0.30 and 0.50 (Table 8). Under
conditions of oxygen fugacities implied by equilibrium
among quartz, magnetite, and titanite, higher values of
Mg/(Mg + Fe) are expected (Wones, 1989).
During most of its crystallization history, the
BodocO magma was probably undersaturated in H2O.
Petrographic evidence for undersaturation is provided by
the supersolidus reaction of clinopyroxene and melt to
form hornblende, an equilibrium that requires about
3-3.5 weight percent H2O at upper to middle crustal
levels (Eggler, 1972).
Growth of K-Feldspar Megacrysts
Under most circumstances, K-feldspar is one of the
last phases to nucleate in a crystallizing magma.
At
pressures between 2 kb and 5 kb, K-feldspar saturation in
a felsic melt generally occurs only 15-25°C above the
solidus (Wall and others, 1987).
The presence of
K-feldspar megacrysts at first seems contradictory, and

70
the phenocrystic vs. porphyroblastic origin of megacrystic
K-feldspar was debated for decades (Vernon,
1986). However, K-feldspar has a low nucleation rate but
a rapid growth rate at small degrees of undercooling.
This results in scattered, large crystals compared to
other minerals (Swanson, 1977; Fenn, 1977).
Most other
igneous minerals begin to nucleate at higher temperatures
than K-feldspar, but they grow more slowly.
On the basis
of experimental data, Winkler and Schultes (1982) estimated
that even at as little as 6-ll°C above the solidus,
granitic melts may still be 65 to 70 percent liquid.
In the BodocO pluton, several lines of evidence
indicate that the megacrystic K-feldspar grew in a
crystal-poor medium.
Within the megacrysts, the
concentric rings outlined by plagioclase inclusions are
euhedral.
This suggests that megacrystic growth was not
impeded by crowding from other minerals in the liquid
except during growth of their outer shells, which are
anhedral.
Mineral inclusions in the megacrysts are
smaller than their groundmass equivalents, and they are
more likely to be euhedral.
In general, the cores of the
megacrysts contain fewer mineral inclusions than the
outer shells, and the variety of minerals is greater in
the outer rows of inclusions.
Vernon (1986) theorized
that there are fewer inclusions of any type in megacryst

71
cores because the most rapid K-feldspar growth takes
place in just-nucleated crystals at low undercooling
(when crystals of all kinds are sparse in the melt).
Supersolidus Mineral Growth
The presence of patchy cores of clinopyroxene in
hornblende and of uralitic amphibole rimmed by hornblende,
both of which are common in the BodocO samples,
indicates that high-temperature mineral phases like
clinopyroxene reacted (incompletely) with cooling melt to
form other mineral phases such as hornblende and Fe-Ti
oxides that were more stable at lower magmatic
temperatures.
It is possible that most of the biotite in the
Bodoc6 samples did not crystallize directly from a melt
but formed as a supersolidus reaction between hornblende
and residual liquid.
In most igneous rocks, hornblende
is more magnesian than coexisting magmatic biotite
(Speer, 1987).
In the Peruvian Coastal Batholith, Mason
(1985) found that the Kp value [ (X^^^j^g/X^^^Pg) /
(X^^^j^g/X^^^Pg) ] could be used to discriminate between
biotite that formed by replacement of hornblende and
biotite that crystallized directly from a melt.
Rocks
with "igneous" biotite had Kj^ values of about 0.63, but
rocks in which biotite had replaced hornblende had Kj^ of
about 1.0, similar to that in meteunorphic rocks.
Speer

72
(1987) found that biotite that replaced hornblende in the
Liberty Hill pluton of South Carolina also had Kj^ values
of about 1.0.
In the BodocO pluton, hornblende-biotite pairs from
coarse-grained megacrystic quartz monzonite have average
Kj) values of about 1.03 (Table 14). Hornblende-biotite
pairs in mafic enclaves have Kp values that range from
0.86 to 1.08. These data suggest that much of the
biotite is the product of a supersolidus reaction between
hornblende and the remaining liquid.
Where hornblende
and biotite occur together in glomerocrysts, biotite is
most common in the outer portion, where hornblende and
melt presumably could have reacted with each other the
most efficiently.
On the other hand, a "supersolidus"
origin for all of the Bodoc6 biotite does not necessarily
explain the presence of presumably early biotite
inclusions fretting plagioclase cores or of euhedral
biotite inclusions in K-feldspar megacrysts.
Also,
biotite-hornblende pairs in a cm-phenocrystic granitoid
(33-D) have Kj^ values of 0.66-0.69 that correspond to
values cited by Mason (1985) for magmatic biotite.
These
discrepancies suggest that biotite was a primary phase
but that some biotite formed by reaction with hornblende.

Paragenesis of K-feldspar
and Mafic Silicates
73
Within mafic BodocO samples (including enclaves,
intrusives, and hybrids), hornblende or clinopyroxene is
coarser, more abundant, and/or present only where
K-feldspar is present.
Similarly, Chappell (1978) noted
that the amount of hornblende in mafic enclaves in
Australian granitoids is proportional to the amount of
K-feldspar that they contain.
If hornblende is a
supersolidus reaction product between clinopyroxene and
melt, and biotite is a supersolidus reaction product
between hornblende and a more evolved melt, then the
mineral paragenesis of K-feldspar and clinopyroxene or of
K-feldspar and hornblende suggests that K-feldspar
prevented such supersolidus mineral growth.
K-feldspar
may have retarded biotite growth by removing K from the
melt, or it may have nucleated around the mafic silicates
and blanketed them from further reaction with the melt.
There is no analogous correlation in abundance
between K-feldspar and hornblende or clinopyroxene in the
various types of QMZ because there is very little
interstitial K-feldspar present.
Typically, however,
equant grains of clinopyroxene and pseudomorphs of
hornblende after clinopyroxene are preserved only as
inclusions in K-feldspar megacrysts and phenocrysts in
the QMZ.

74
Where mafic enclaves are present in oriented swarms
in the megacrystic QMZ, they are typically separated from
one another by seams of K-feldspar megacrysts that are
coarser-grained and pinker than equivalent megacrysts in
the host.
Many workers have noted such associations of
megacrysts and enclave swarms in granitoids, and most
have attributed the texture to segregation by magmatic
flow (Vernon, 1986).
However, this does not explain why
the megacrysts are commonly coarser and pinker than those
in the host matrix, nor does it account for the association
between enclaves and megacrysts in rocks that are
otherwise non-megacrystic (Chappell, 1978).
If the mafic
enclaves represent thermally quenched blobs of a mafic
magma that mixed with the granitoid magma, then the H2O
that they lose during relatively rapid crystallization
(Eichelberger, 1980) may dissolve in the host magma and
cause both oxidation of Fe and enhanced growth of the
megacrysts.
Kawachi and Sato (1978) observed that orthoclase
megacrysts found in clusters with mafic xenoliths
had late-stage overgrowths.
They concluded that flow
segregation had trapped the megacrysts with the xenoliths
but that the orthoclase overgrowths resulted from postentrapment
crystallization.

CHAPTER 5
MAJOR OXIDES AND TRACE ELEMENTS
Major elements combine with oxygen and H2O to make
the most abundant rock-forming minerals.
Magmatic
differentiation—whether by fractional crystallization,
partial melting, magma mixing, or assimilation—produces
non-random variation of chemical components in a rock
suite.
Major oxide patterns may not be distinctive for a
given process, however, and can be obscured if the magma
evolves by more than one process.
In plutonic rocks,
crystal accumulation processes further obscure chemical
evidence for true liquid lines of descent (Cox and
others, 1979).
Nevertheless, major oxide analyses are
the basic data for chemical classification of rock suites
and norm characterization of specific rocks.
Atypical
compositions and distinct compositional trends may reveal
samples that are not genetically related to others in the
suite, or they may highlight chemical features that
warrant further study.
Major oxides also may indicate
important lateral/spatial chemical variation within a
pluton.
In addition to these general considerations for any
igneous suite, chemical analyses provide information
about some specific questions concerning the Bodocd
pluton:
75

76
The pluton has three textural types of QMZ—a
megacrystic variety, a porphyritic ("phenocrystic")
variety, and a plumose variety. Can these three rock
types be discriminated chemically as well as
texturally?
Most of the pluton is composed of coarse-grained,
megacrystic QMZ. Does this extensive textural
homogeneity mask spatial chemical variation? Is the
pluton zoned chemically? Can more than one episode
of emplacement of megacrystic QMZ be detected
chemically?
The other two textural varieties of QMZ, phenocrystic
and plumose, crop out as distinct units and are
physically intermingled in a transition zone.
Do
samples from the transition zone display chemical
evidence for mixing of the rock types?
"Mafic" intrusives are present as vertically oriented
sheets (synplutonic dikes) and as small, late-stage
dikes.
How does the composition of these intrusives
vary, if at all?
Can the late-stage dikes be
discriminated chemically from the intrusive sheets?
Does either type of mafic intrusive have anomalous
chemical characteristics compared to the remainder of
the pluton?
Do chemical data suggest that the
intrusive sheets are representative of a mafic magma

77
that elsewhere in the pluton mixed completely with a
more felsic magma to create the observed quartz
monzonitic rocks?
5. Do some or all of the mafic enclaves represent
xenoliths of country rock incorporated by the magma
during ascent?
Alternatively, are they disrupted
synplutonic dikes or chilled blobs of a mafic magma?
Do they resemble the mafic intrusives chemically?
6. Exposures of clinopyroxene-bearing igneous rocks,
including two syenitic dikes (17-B and 20-A) and a
quartz monzonite (37-A), crop out next to the
southwestern margin of the pluton.
Are any or all of
these rocks genetically related to the BodocO pluton?
These questions were addressed by major oxide and
trace element chemical analysis of a total of 85 wholerock
samples that represent a range of rock types and
sample localities.
Samples collected for geochemical
analysis were at least an order of magnitude greater in
volume than the largest crystals they contained.
Large
sample size was especially important for the megacrystic
QMZ samples in order to obtain chemically representative
data.
Sample localities are indicated on Figure 8, and
unusual features of particular seunples are noted in
Table 1. Analytical methods are detailed in Appendix C.

78
Major Oxides
Major oxide analytical results are reported in
Table 15.
General features are summarized below.
SiOo Content
The total suite of samples for the BodocO pluton
spans an intermediate range of silica content (Williams
and others, 1954) from around 52 weight percent Si02 for
some mafic intrusives to about 72 weight percent for a
few aplite dikes (Fig. 20). The plumose QMZ and the
majority of the megacrystic QMZ samples share a limited
range of Si02/ from about 60 to 64 weight percent.
The
phenocrystic QMZ has slightly lower Si02, from 58 to 60
weight percent. A few megacrystic QMZ samples from the
eastern margin of the intrusion and the highly evolved
felsic hybrids from the western margin have Si02 as high
as 70 weight percent.
Mafic enclaves and most mafic intrusives have Si02
content between 52 and 56 weight percent, although a few
mafic intrusives are more silicic than this.
The mafic
intrusives (sensu lato) with the highest Si02 content,
samples 19-A and 41-A, are as silicic as many of the QMZ
samples.
Several small mafic dikes as well as mafic
rocks from the hybrid area have Si02 contents that are
intermediate between those of other mafic samples and the
various textural types of QMZ (Fig. 20).

79
Chemical Classification of the Suite
The molecular proportions of AI2O3, CaO, and
(Na20 + K2O) are such that almost all samples analyzed
represent metaluminous rocks in the sense of Shand
(1951). The exceptions include about half of the aplites
analyzed; enclaves 12-A and 22-B; and felsic hybrid 61-F,
all of which are slightly peraluminous.
The alkali-lime
index of the Bodoco plutonic suite is about 50 (Fig. 21),
characterizing the pluton as alkalic (Peacock, 1931).
Other Major Oxides
With the exception of MnO, which was at or below
detection limits in nearly all samples, the distributions
and ranges of the major oxides are summarized graphically
with respect to Si02 in Figures 22 through 25. The
following general observations can be made about the
variation diagrams.
All major oxides decrease with increasing Si02
(Fig. 22, 23, and 25) except Na20 and K2O, both of which
are scattered and uncorrelated with variation of SiOj
(Fig. 24a and 24b).
Mafic intrusives and enclaves have
more scattered Na20 contents than do the various types of
QMZ.
Relative to the felsic samples, the mafic enclaves
and intrusives display considerable variation of AI2O3
(Fig. 22a). Also, the distribution of AI2O3 is such that

80
the felsic hybrids define a different compositional trend
compared to other high-Si samples such as aplites.
Chemical differences between the megacrystic QMZ and
the plumose QMZ are generally indistinguishable except
for K2O and Na20.
Plumose QMZ samples as a group have
higher K2O values and slightly lower Na20 contents
(Fig. 24) than do megacrystic QMZ samples.
Several mafic enclaves are distinctly anomalous.
These include samples 9-C (very high MgO and very low
AI2O3 relative to other enclaves), 12-A (high Na20, high
AI2O3, low MgO), and 22-B (low CaO, high K2O, low P205)'
Several other enclaves display anomalous behavior with
respect to one or two oxides, including samples 63-B
(high TiOj and P2O5) and 24-A (high AI2O3) (Figs. 22
through 25) .
Of the three clinopyroxene-bearing igneous rocks
near the western margin of the pluton, the two syenitic
dikes (17-B and 20-A) are distinct in many respects
compared not only to samples from the pluton but also to
each other.
Sample 17-B has low MgO, FeO^^^, Na20, Ti02,
and P2O5/ ^"d very high K2O.
Sample 20-A has low AI2O3,
MgO, and Na20, and high CaO and K2O (Fig. 22 through 25).
Quartz monzonite sample 37-A, on the other hand, cannot
be distinguished from plumose QMZ on the basis of major
oxides.

Zoning
81
Spatial variation of several major oxides indicates
that the BodocO pluton is reversely zoned from a more
felsic margin to a less felsic core (Fig. 26 and 27).
The distributions of Si02 and MgO most clearly indicate
the zoned pattern (Fig. 26a and 26b) although it is also
indicated by CaO and Sr (Fig. 27a and 27b). Systematic
zonation is confined to the megacrystic QMZ.
Zoning
patterns end abruptly at the contact between megacrystic
QMZ and phenocrystic QMZ and against the contacts with
metamorphic wall rocks.
It appears that neither the
phenocrystic QMZ nor plumose QMZ are zoned.
Trace Elements
Analytical techniques to acquire trace element data
are described in Appendix C.
Trace elements Rb, Sr, Ba,
Y, and Zr were determined for all chemically analyzed
samples (Table 15). In addition, trace element data for
Sc, Cr, Co, Cs, Hf, U, Th, Ta, and the rare-earth
elements (and additional analyses of Rb, Sr, Ba, and Zr)
were obtained for 15 samples (Table 16). Concentrations
of Rb and Sr were measured by three separate processes in
some samples, providing an opportunity to confirm that
the data obtained by the various analytical methods
generally agreed well with each other (Table 17).

Rubidium
82
Concentrations of Rb range between 95 and 175 ppm
for most samples (Fig. 28a). Within this range, plumose
QMZ samples have slightly higher Rb (140-190 ppm) than do
either the megacrystic QMZ or phenocrystic QMZ
(105-160 ppm). Most mafic intrusives have Rb less than
120 ppm, but mafic enclaves have higher and more varied
Rb, from 110 to 175 ppm. One mafic enclave, sample 22-B,
has 261 ppm Rb (Fig. 28a).
One of the syenitic dikes west of the pluton, sample
17-B, has a high Rb concentration, 342 ppm (Fig. 28a);
this is consistent with its high K2O content.
Concentrations of Rb in the various gneisses and schists
range between 10 and 160 ppm; most samples have lower Rb
than the pluton.
Strontium
Strontium concentrations are high and varied
(Fig. 28b); they range from 269 ppm in aplite to 2431 ppm
in a plumose QMZ.
Samples of megacrystic QMZ have a high
though more limited range of Sr content, between about
1000 and 1500 ppm. The megacrystic QMZ is zoned with
respect to Sr, with lower Sr at the margins of the pluton
(Fig.
28b). Strontium content increases toward the
center, but a low-Sr zone is present in the central part
of the pluton.
Strontium in the plumose QMZ overlaps the

83
range observed in the megacrystic QMZ and, with the
exception of the anomalously high value of 2431 ppm
(sample 29-A) mentioned above, has approximately the same
concentration range, from about 1250 to 1650 ppm Sr.
In
the phenocrystic QMZ, Sr content ranges between 1400 and
1800 ppm.
Mafic rocks in the pluton range widely in Sr
concentration, from 1050 to 2150 ppm in mafic intrusives
and from 750 to 2150 in mafic enclaves. Strontium and
Si02 are negatively correlated among QMZ and felsic
hybrids, are less so for aplites, and are random among
mafic rocks.
Of the igneous country rocks, sample 37-A has
anomalously high Sr (2040 ppm) compared to most of the
felsic samples from the plutonic suite.
Barium
As with Sr, Ba concentrations are high throughout
the pluton.
In most cases, Ba ranges between 2000 and
4000 ppm. Among the megacrystic QMZ samples, those from
the central region of the pluton (67-A, 68-B, and 71-A)
have lower Ba values than in the remaining megacrystic
QMZ samples with comparable Si02 content (Fig. 29a).
Samples that plot away from the overall trend include

mafic enclave sample 56-C (614 ppm Ba), and enclave 22-B
(1940 ppm Ba) (Fig. 29a).
84
Although Ba values are high throughout the pluton,
extreme enrichment is concentrated in the southwestern
part of the pluton.
Aplites from this area (samples
74-B, 18-B, and 24-B) are Ba-enriched by nearly 2000 ppm
compared to the other aplite samples (Fig. 29a).
Latestage
mafic dike 12-B, also from the southwestern part of
the pluton, is also Ba-rich (5134 ppm).
The three samples of igneous country rock adjacent
to the southwestern portion of the pluton are also
distinctly Ba-rich.
For example, the clinopyroxenebearing
quartz monzonite sample, 37-A, has 4097 ppm Ba,
much higher than the plumose QMZ with which it is
otherwise chemically similar.
Of the two syenitic dikes
located west of the pluton, sample 17-B has 6727 ppm Ba,
and sample 20-A has 14456 ppm Ba.
However, Ba values in
the host-rock gneisses of this area are low (between 500
and 600 ppm).
Zirconium
Of all trace elements analyzed, Zr proved to be the
most effective chemical discriminator of the various rock
types in the pluton (Fig. 29b). Plumose QMZ samples, for
example, are characterized by high Zr (330 to 480 ppm for
all samples except 29-A, which contains 285 ppm).

85
Phenocrystic QMZ samples generally contain less than 200
ppm Zr, and in this respect they resemble a subgroup of
megacrystic QMZ samples from the central part of the
pluton.
The remainder of the megacrystic QMZ samples
have relatively restricted values of Zr between 250 and
350 ppm (Fig. 29b). Mafic intrusives either contain less
than 100 ppm Zr or contain 250-300 ppm Zr.
Concentrations
of Zr are more variable for mafic enclaves than for
any other rock type-
Only two samples have elevated Zr contents. Mafic
enclave sample 12-A has 707 ppm Zr, and felsic dike 43-B
has 489 ppm Zr. Zircon is not a conspicuous accessory
mineral in either sample.
Sr versus Ba
Strontium and Ba vary in a systematic way with
regard to one another (Fig. 30). The megacrystic QMZ
scimples that have the lowest Sr and Ba are either the
most evolved in terms of Si02 (from the eastern margin of
the pluton), or the least evolved (from the core of the
pluton).
This suggests that Ba and Sr variation is not a
function of simple fractionation.
Except for relatively
Sr- and Ba-rich aplite samples in the western part of the
pluton, high-silica rocks such as aplite, felsic hybrids,
and metamorphic country rocks all have relatively low Ba

86
and Sr compared to the other rock types.
The majority of
mafic enclaves are enriched in Sr relative to the pluton
as a whole; enclaves 56-C and 9-C are Sr-poor exceptions.
Zr versus P205
The various rock types can be discriminated even
more clearly by contrasting Zr with P2O5 content.
The
enrichment or depletion of a melt in P2O5 is controlled
by the fractionation of apatite (or monazite), which may
crystallize early or late depending on a number of
intensive variables controlling crystallization.
Zirconium is generally enriched in melts until it is
depleted by the removal of zircon.
The relationship between Zr and P2O5 in the Bodoco
pluton forms two trends in Figure 31. Megacrystic QMZ
samples from the core of the pluton and phenocrystic QMZ
samples contain lower Zr and higher P2O5 than the
majority of megacrystic QMZ samples.
Plumose QMZ scimples
are substantially more Zr-rich than the other rocks but
contain slightly less P205*
The most mafic samples have
low P2O5 contents but are Zr-enriched.
The four most
silicic mafic intrusives have slightly lower P2O5 but
distinctly higher Zr contents than the other mafic
intrusives.
The remaining scimples from the plutonic suite form a
second trend (Fig. 31) that consists of evolved rocks.

87
This group is composed of aplites and felsic hybrids and
includes one mafic enclave, sample 22-B.
The compositions
of gneissic and schistose country rocks plot within
this second trend, as well.
Yttrium
Concentrations of Y are between about 10 and 25 ppm
for the various QMZ and for most mafic intrusives,
between 20 and 35 ppm for the mafic enclaves and
remaining mafic intrusives, and less than 15 ppm for
aplites and felsic hybrids.
The Y content of country
rocks is slightly higher, between 30 and 50 ppm
(Table 15).
Other Trace Elements
The various rock types of the BodocO pluton have
similar concentration ranges of Sc, Cr, Co, Cs, Hf, U,
Th, Ta, and rare-earth elements (Table 16). However, the
Cr content of mafic intrusives ranges from 194 to
603 ppm, whereas the Cr content of the various felsic
rocks is consistently less than 130 ppm.
The Th content
of most samples is less than 25 ppm, but the
clinopyroxene-bearing quartz monzonite (37-A) west of the
pluton has a Th concentration of more than 200 ppm.

Rare-earth Elements
88
Concentrations of rare-earth elements, normalized to
chondritic abundances, are presented in Figure 32.
The
compositions of the megacrystic QMZ, phenocrystic QMZ,
and plumose QMZ samples, as well as of one mafic enclave
and one mafic intrusive, plot parallel to each other
within a narrow field (Fig. 32). All of these samples
are strongly enriched in LREE relative to chondritic
abundances.
None displays a Eu anomaly, suggesting that
fQ2 was high enough that Eu"*"^ was sparse, or that
residual hornblende was important in the source rocks, or
that plagioclase fractionation was accompanied by
hornblende fractionation (Hanson, 1978).
Samples with slightly different REE patterns include
mafic intrusive sample 21-B (elevated HREE) and aplitic
sample 8-A (lower REE overall and a small positive Eu
anomaly).
Sample 61-F, a felsic hybrid, has low REE
abundances compared to the QMZ samples, and it has a
small negative Eu anomaly.
The contrast between the
pattern of REE abundances for most of the plutonic
samples and that of metamorphic country rocks is distinct
(Fig. 32).
The pattern and abundances of REE among BodocO QMZ
are similar to those observed for a number of Itaporangatype
plutons in northeastern Brazil (Sial, 1987).

89
Summary of Chemical Characteristics
The geochemical data indicate that the BodocO pluton
is a metaluminous, mildly alkalic intrusion of
intermediate silica content.
The three textural types of QMZ differ slightly from
each other in that the phenocrystic QMZ has slightly
lower Si02 contents than the other two types, and the
plumose QMZ has slightly higher abundances of K2O, Rb,
and Zr and lower Na20 than the megacrystic QMZ.
The
megacrystic QMZ is reversely zoned from more felsic
margins to a more mafic core.
No comparable zoning was
observed in the other two types of QMZ.
There is no chemical evidence for mixing of
phenocrystic QMZ and plumose QMZ in the area where the
two rock types are physically intermingled on an outcrop
scale.
Where systematic variation might be expected due
to mixing, the variation displayed by both rock types is
non-linear and contradicts a mixing model.
For example,
the phenocrystic QMZ samples and the plumose QMZ samples
in the intermingled zone both have lower Ba values than
they do elsewhere, whereas mixing should produce a range
of values intermediate between the two end members.
Similar contradictory behavior is observed in these
rock types for Sr and Rb, even where there is some
textural basis for mixing.
For example, plumose QMZ

90
sample 29-A differs from the other plumose samples
because it has plagioclase overgrowths on its slender
K-feldspar phenocrysts.
These rapakivi overgrowths
contain acicular apatite inclusions.
Both features can
be attributed to magma mixing (Hibbard, 1981; Vernon,
1983). Chemically and modally, the sample has some of
the same characteristics as the phenocrystic QMZ with
which it is intermingled.
However, its Sr concentration
(more than 2400 ppm) far exceeds that of any other rock
type in the pluton.
Although there does appear to be a
subtle geochemical difference between rocks from the
intermingled area and their textural counterparts elsewhere,
that difference cannot be attributed to mixing
plumose and phenocrystic QMZ magma with each other.
The chemical variation of the mafic intrusives is in
general more scattered than that of the QMZ samples, but
there is little to indicate whether the mafic intrusives
are a genetic component of the pluton as a whole.
The
range of silica content among the mafic intrusives
indicates that many are chemically evolved.
The latestage
mafic dikes and the earlier synplutonic dikes are
indistinguishable on a chemical basis, and both types
span the range of compositions that characterize all of
the mafic intrusives.

91
The relationship of the mafic enclaves to their host
rocks is even more problematic than that of the mafic
intrusives.
Most small microgranitoid mafic enclaves,
including those of the Bodoc6 pluton, probably do not
preserve an original parent magma composition.
Instead
they may be disaggregated portions of larger enclaves
complexly affected by a variety of physical and diffusive
processes involving the host granitoid and the mafic
parent.
Many workers have noted that microgranitoid
enclaves from a single plutonic suite display a range of
chemical composition.
If the enclaves resulted from
magma mixing (Vernon, 1983), then this variation commonly
can be'attributed to several possibilities:
(1) differentiation of the basaltic end member (Reid and
others, 1983); (2) successive mixing episodes with
different proportions of end members (Dorais and others,
1990; Cantagrel and others, 1984); and (3) multiple
sources of enclave magma (Eberz and Nicholls, 1990).
In
addition to these factors, it is likely that most
microgranitoid enclaves lose many of their original
magmatic characteristics upon crystallization.
Bacon
(1986) noted that chemical diffusion between the residual
liquids of enclave and host magmas may have a significant
effect on enclave compositions.
Bacon also found that
large enclaves (greater than 12 cm) had undergone in situ

92
differentiation so that liquid from the enclave magma had
moved into the host magma.
This produced enclave
interiors that were more mafic than the starting
composition.
Eberz and Nicholls (1990) observed an
opposite result:
in situ differentiation in large
(greater than 1 m) mafic enclaves left the enclaves
internally zoned from fine-grained, mafic rinds enriched
in Mg, Na, K, Rb, and Ba to coarser-grained, differentiated
(more felsic) centers.
Although most mafic enclaves in the Bodoc6 pluton
have chemical characteristics that are broadly similar to
those of the mafic intrusives, several mafic enclaves are
chemically distinct from the other enclaves.
The unusual
samples may consist of xenoliths of amphibolitic or
schistose wall rocks.
These enclaves include sample 9-C,
which is petrographically anomalous as well (Chapter 4,
and Table 1), and samples 12-A and 22-B, both of which
are peraluminous and are very fine-grained compared to
most of the other enclaves.
Other enclaves that have
some but not many anomalous chemical characteristics
include samples 24-A, 41-B, 56-C, and 63-B.
Except for
sample 63-B, all of the unusual enclaves are located near
the pluton margin (Fig. 8), increasing the likelihood
that they may be xenolithic.

93
The chemical characteristics of the clinopyroxenebearing
igneous rocks exposed west of the pluton indicate
that the two syenitic dikes are not related to the Bodoc6
pluton.
Sample 17-B is anomalous with respect to most of
the major oxides and numerous trace elements; sample 20-A
also has distinct major oxide compositions and has
extremely high, anomalous Ba.
Furthermore, the chemical
variations of the two aplites suggest that the two are
not related to each other.
The quartz monzonite (sample 37-A) that crops out
west of the pluton is similar chemically to the plumose
QMZ (with which it is on strike) except for its lower MgO
and higher Sr and Ba contents.
It may be noteworthy that
a sample of plumose QMZ (29-A) also has high Sr and Ba
contents (Table 15). However, plagioclase in sample 37-A
is much more albitic than plagioclase in any of the
plumose granitoids (Table 6). Thus, the relationship of
this rock to the BodocO pluton remains uncertain.
Compared to most intermediate rock suites, the
BodocO pluton is characterized by high K2O and P2O5 as
well as very high Sr and Ba (Le Maitre, 1976).
Elevated
values of Sr (and Ba, where reported) are characteristic
of other Itaporanga-type plutons, not only in northeastern
Brazil (Sial, Mariano, and others, 1989) but also
in central and southern Brazil (Pimentel and Fuck, 1987;

94
Wiedemann and others, 1987).
In northeastern Brazil
igneous intrusions of many types and ages have high to
extremely high Sr, Ba, K2O, and P2O5 contents.
These
include numerous Brasiliano-age intrusives (Sial, 1987;
Ferreira and Sial, 1987) as well as a Transamazonian-age
dike, Mesozoic volcanic rocks, and Tertiary alkali basalt
(Sial, Ferreira, and others, 1989).

CHAPTER 6
ISOTOPE CHEMISTRY
Two objectives of this study were to characterize
the Rb-Sr and b^^O isotope systematics of the Bodoco
pluton.
Accordingly, powders of 35 whole-rock samples
were selected for isotopic analysis.
Of these samples,
thirty were from the pluton, four were of metamorphic
country rock, and one was the clinopyroxene-bearing
quartz monzonite (37-A) from the pluton's southwestern
margin (Fig. 8). Analytical methods are described in
Appendix C.
Rb-Sr Geochronology
Most attempts to date the intrusive rocks of
northeastern Brazil have employed the Rb-Sr, the
^^Ar/^^K, or the ^^Ar/'^^Ar methods (Brito Neves and
others, 1974; Dallmeyer and others, 1987).
None of these
methods consistently has yielded satisfactory results.
Rb-Sr ages typically have large relative errors.
For
example, three Itaporanga-type plutons yielded ages of
630 + 24 Ma, 625 + 24 Ma, and 512 + 36 Ma (McMurry and
others, 1987).
The error in these estimates is as much
as 7 percent of the total age whereas "well-behaved"
isochrons generally have ranges of error within 1-2
percent of the total age (L.E. Long, personal
95

96
communication).
Many ^^Ar/^^K and ^^Ar/^^Ar ages appear
to have been reset by a thermal event late in the
Brasiliano orogeny (Dallmeyer and others, 1987).
For practical reasons, most studies of the Rb-Sr
geochronology of rocks in northeastern Brazil have used
small sample groups.
However, there is enough scatter in
the isotope data from these plutons that the isochron
obtained in many cases depends on the number and type of
samples analyzed.
One focus of this study was to examine
the Rb and Sr isotopes of numerous scunples from a variety
of rock types in an Itaporanga-type pluton in order to
characterize more fully the behavior of data for specific
rock types for geochronological calculations.
Whole-rock Geochronology
Table 18 summarizes the results of Rb-Sr analyses of
the 35 whole-rock samples.
Corrections for Sr mass
fractionation were applied assuming ^^Sr/^^Sr = 0.1194
(Faure and Powell, 1972).
The decay constant used in
isochron calculations was 1.42 xlO"^^ y"^.
Ratios of
^^Rb/^^Sr and ^^Sr/^^Sr are displayed in Figure 33.
Clinopyroxene-bearing quartz monzonite 37-A has Rb
and Sr isotopic ratios similar to those of the plumose
QMZ.
The metamorphic country rocks analyzed are
characterized by high and divergent ratios of ^^Sr/^^Sr
(Table IB). These high ratios are not due to large

97
amounts of Rb but rather result from the relatively small
amounts of common Sr (hence small values of ^^Sr) in the
metamorphic rocks as compared to the Bodoco plutonic
samples.
Data points for most of the plutonic samples form a
dense but linear cluster in the lower left portion of
Figure 33.
Two aplites (samples 8-A and 13-C) and an
equigranular granite (61-F) from the area of hybrid rocks
are distinct from the remaining data points.
An isochron calculated on the best fit of a line to
all 30 samples from the pluton yields an age of about
640 ± 50 Ma. However, not all of the samples should be
included in geochronological calculations.
For example,
geochemical evidence presented in Chapter 5 indicates
that at least two of the mafic enclaves shown in
Figure 33, samples 9-C (very high MgO, very low AI2O3)
and 12-A (high Na20, AI2O3, low MgO, low CaO, and low
P2O5), are probably xenoliths.
Some geochemical evidence
suggests that mafic enclaves 56-C (low Sr, Ba) and 63-B
(high P2O5/ ^^igh Ti02) may be xenoliths as well.
The
fact that the sample 63-B datum plots off the trend
defined by the other data suggests that it can be omitted
from the isochron.
Similarly, the data point for
megacrystic QMZ sample 48-A departs conspicuously from
the trend indicated by the other samples (Fig. 33).

98
Although this sample was not chemically anomalous in
other respects (Chapter 5), it may represent a poor
analysis and has been excluded from isochron
calculations.
A Rb-Sr isochron is most precise when samples span a
large range of ^"^Rb/^^Sr.
In the Bodoco pluton, if none
of the high-^'^Rb/^^Sr samples (13-C, 8-A, 61-F, 62-E) is
used in isochron calculations, the resulting "age" is
poorly defined (590 ± 34 Ma). The 6% relative error of
this estimate is similar to the results commonly obtained
for other Itaporanga-type plutons.
Because late-stage
differentiates of a magma tend to be enriched in Rb, they
have an important influence on age calculations because
their data plot at the upper end of an isochron.
However, establishing whether or not late-stage dikes are
oogenetic with the main plutonic facies can be very
difficult.
Such rocks tend to be simple granites sensu
stricto with few distinctive chemical or mineralogical
characteristics.
Because they are late magmatic
features, field relations cannot always establish if a
specific aplite was closely related in time or origin to
the pluton that it intrudes.
Furthermore, because
aplites are small bodies volumetrically, they are
relatively easily modified by assimilation of wall rocks
or by mixing with anatectic melts.

99
By similar reasoning, mafic intrusive 12-B has not
been included in isochron calculations.
This sample
represents a small, very late-stage dike.
It has high Sr
compared to other mafic intrusives suggesting that it may
have come from a different source than the others.
One of the two aplites analyzed from the Bodoco
pluton, sample 13-C, departs from the trend suggested by
the other Rb-Sr data.
As noted in a following section,
it also has a different oxygen isotope value than the
rest of the pluton.
For these reasons, sample 13-C is
excluded from isochron calculations.
An isochron calculated from the remaining 22 samples
gives t = 579 ± 14 Ma.
This result is heavily biased by
another aplitic sample (8-A).
If sample 8-A is omitted,
the only remaining high-^^Rb/^^Sr sample is 61-F, which
is from a large exposure of equigranular granite from the
area of hybrid rocks on the pluton's northwestern side.
The resulting 21-point isochron gives t = 555 ± 8 Ma
and an initial ^'^Sr/^^sr = 0.70608 ± 4 (Fig. 34). The
mean standard weighted deviation of this calculation is
3.20, approximately the same as the standard deviation
caused by analytical uncertainty alone.

Mineral Isochrons
100
Although the data used to plot the whole-rock
isochron in Fig. 34 are relatively linear, the amount of
scatter about the isochron is typical for Itaporanga-type
granitoids.
In addition to the possibility of isotopic
inhomogeneity that may be introduced into any magma by
incomplete assimilation of or mixing with a second
source, two intrinsic qualities of the megacrystic QMZ
account for much of the observed scatter of isochron
data.
First, in order to achieve a representative,
homogenized whole-rock powder of these coarse-grained and
megacrystic rocks, it is necessary to crush and process a
large volume of sample.
In such cases, it is nearly
impossible to identify and remove all the small and
commonly deformed mafic enclaves that these rocks
contain.
If the enclaves are not oogenetic, then
inevitably they contaminate the whole-rock isotope
analysis.
Second, the abundant common Sr in the Bodoco
rocks tends to mask the relatively small amount of
radiogenic °'Sr.
In an attempt to avoid some of these problems, Rb-Sr
isochrons were obtained for individual rock samples by
the use of mineral separates.
Mineral isochrons
generally are not calculated in an igneous rock suite
unless a metamorphic overprint is suspected.
If Sr

101
isotopes in the minerals, like their bulk rocks, have
never been re-equilibrated, then the mineral isochron is
superimposed on the whole-rock isochron and no additional
information is obtained.
On the other hand, sets of
mineral isochrons that yield different initial ^"^Sr/^^Sr
have been used as evidence that a given magma was heterogeneous
when it was intruded (Hill and others, 1984).
Sample Selection.
Mineral separates were prepared
as described in Appendix C for four samples:
two mafic
enclaves (samples 56-C and 12-A), a megacrystic QMZ
(sample 63-A), and the clinopyroxene-bearing quartz
monzonitic rock (scunple 37-A) from the western margin of
the pluton.
Mafic enclave sample 56-C was selected on the basis
of petrographic evidence that it may have crystallized
from an undercooled, non-porphyritic melt.
It is a finegrained
equigranular diorite in which plagioclase and
biotite have numerous inclusions of acicular apatite,
suggestive of rapid crystallization.
Unlike most of the
pluton's enclaves, Scimple 56-C is not cut by nebulitic
veinlets of K-feldspar that, if they are related to a
late-stage phase of crystallization of the host QMZ, may
have affected the Rb-Sr isotope systematics of enclaves.
Although the Bodoco magma may have been isotopically
heterogeneous on a pluton-wide scale, in theory a small

102
volume of melt should be locally homogeneous.
If the
enclave melt contained few early crystals that had
nucleated in some other part of the magma (where isotopic
characteristics may have been different), then the
preserved, rapidly crystallized mineral assemblage should
have been isotopically homogeneous.
Furthermore, enclave
56-C was collected from the eastern margin of the pluton,
where it was incorporated in the granodioritic variant of
megacrystic QMZ.
If enclave 56-C represents a small
volume of dioritic magma that was quenched in cooler
felsic magma, both its location (near cooler wallrocks)
and its host (compositionally and thermally distinct from
a dioritic magma) may have contributed to its crystallization
in an environment that locally was isotopically
homogeneous.
Mafic enclave 12-A was selected for a mineral
isochron because much petrographic and chemical evidence
suggests that it was incorporated in the magma as a small
metasedimentary xenolith.
A mafic enclave need not
necessarily have been magmatic to produce a useful
mineral isochron because the heat of the enclosing magma
can be expected to re-equilibrate the Sr isotopes of the
xenolith's constituent minerals.
The minerals of the
xenolith then record the time of its incorporation and

103
cooling as a metamorphic event that corresponds to the
age of the pluton.
Megacrystic QMZ sample 63-A was selected as a
representative main rock type.
Presumably the minerals
in this sample were subjected to the large-scale
processes that affected most of the pluton, including
crystal accumulation, slow cooling, supersolidus and
subsolidus reactions, and, perhaps, magma mixing.
It was
therefore expected to exhibit the same variable Rb-Sr
behavior that the megacrystic QMZ samples exhibit as a
group.
Mineral separates of sample 37-A, the clinopyroxenebearing
quartz monzonitic country rock adjacent to the
pluton, were analyzed isotopically for several reasons.
Because its chemical relationship to the Bodoco pluton is
ambiguous, an isotopic comparison would be useful.
For
example, a large difference in age might be revealed by
data from the mineral separates.
On the other hand, if
the quartz monzonite is comagmatic with the Bodoco
pluton, its texture and its location at the pluton margin
suggest that it was a relatively quickly cooled,
undeformed, early phase of the intrusion.
As such, its
constituent minerals might preserve the isotopic
characteristics of the magma better than would slowly
cooled rocks from the interior of the pluton.

104
Results.
The results of Rb-Sr isotope analyses and
isochron calculations based on the mineral separates are
summarized in Tables 19 and 20.
In all cases, high Rb
content made biotite the controlling data point for each
isochron.
All isochrons using biotite yielded dates in
the 530-540 Ma range.
This appears to represent a postcrystallization
cooling age for the biotite.
If biotite is not included in the data sets, the
mineral isochrons change significantly (Figs. 35 and 36).
The isochron with the lowest relative error is that for
mafic enclave 56-C.
It yielded an age of 561 ± 9 Ma and
an initial ^"^Sr/^^Sr of 0.70618 ± 0.00006. This age and
initial ratio are within the uncertainty of the values of
t = 555 Ma and initial ^"^Sr/^^Sr = 0.70608 obtained by
the 21-point whole-rock isochron (Fig. 35a).
The isochron for the mafic enclave sample 12-A gave
an age of 593 ± 21 Ma (Fig. 35b). Relative error is
high, perhaps because apatite was omitted from the data
set because it never completely dissolved during
preparation for analysis.
Megacrystic QMZ sample 63-A produced a scatterchron,
with an "age" of 402 ± 78 Ma (Fig. 36a). Quartz
monzonite sample 37-A was also poorly behaved.
It gave a
value of t = 524 + 48 Ma (Fig. 36b).

Initial Sr Ratios
105
Initial ^"^Sr/^^Sr was calculated for each whole-rock
sample by assuming a crystallization age of 555 Ma.
Ratios of initial ^"^Sr/^^Sr are relatively consistent for
the plutonic suite, with a range in general from 0.7057
to 0.7062 (Table 18). The plumose QMZ and phenocrystic
QMZ display small variations of initial ^^Sr/^^Sr;
however, the megacrystic QMZ has a somewhat wider range.
Except for one slightly high value of 0.7071 (Table 18),
mafic enclave samples have initial ^^Sr/^^Sr values
within the same range as those of their QMZ hosts; for
example, mafic enclave sample 56-C has an initial
87gj./86gj. Qf 0.70621 in a megacrystic QMZ host (56-A)
with initial ^"^Sr/^^Sr of 0.70619 (Table 18).
The variation in initial °'Sr/°^Sr is not related to
whole-rock Si02 content (Fig. 37).
The back-calculated initial °'Sr/°^Sr values compare
favorably with the measured (present-day) °'Sr/°^Sr in
the analyzed apatite separates:
Apatite Sample
87SJ./86SJ.
37-A 0.70612
56-C 0.70610
63-A 0.70600

106
Apatite contains negligible Rb, but Sr substitutes
easily for Ca in the apatite structure, as the measured
abundances of Rb and Sr in apatite indicate (Table 19).
As a result, present-day measurements of ^^Sr/^^Sr
closely approximate ^'^Sr/^^Sr at the time of
crystallization, regardless of the time elapsed since
then.
Significance of Sr Ratios
Most of the Bodoco samples except aplite have
initial ^"^Sr/^^Sr in the range 0.7057 to 0.7066.
These
values are higher than would be expected for completely
mantle-derived rocks, but they are low compared to the
ratios to be expected in rocks derived completely from
partial melting of ensialic crust.
Instead, these ratios
most likely represent a mantle-derived magma that was
contaminated by crustal material from assimilation at
depth or during ascent, or else the ratios result from a
mixture of a mantle-derived magma and a lower crustal
partial melt.
The similarity of initial ^'Sr/°°Sr between mafic
enclaves and their host rocks is not necessarily
important.
Because of their relatively small size, most
mafic enclaves are isotopically equilibrated with their
hosts (Vidal, 1987), and so mafic enclaves do not provide
reliable isotopic data about their source regions.

107
Chemical diffusion of K2O and Rb across a granite/basalt
melt interface has been documented experimentally (Watson
and Jurewicz, 1984) and in microgranitoid mafic enclaves
(Eberz and Nicholls, 1990).
At magmatic temperatures,
the self-diffusivity of Sr isotopes may be great enough
to cause complete isotopic re-equilibration in small
mafic enclaves even where bulk chemical diffusion is not
important (Baker, 1989).
Given the likelihood of
isotopic re-equilibration with host granitoid, probably
only very large mafic enclaves constitute isotopically
closed subsystems.
Few if any of the Bodoc6 mafic
enclaves satisfy this constraint.
The mafic intrusive sheets have isotopic
characteristics that closely resemble most of the other
rock types of the pluton, suggesting that all are
oogenetic.
However, the significance of initial
87g^/86g^ in the mafic intrusive samples is equivocal.
The synplutonic dikes are larger and more extensive than
mafic enclaves and so perhaps were less likely to have
experienced isotopic re-equilibration with host rocks.
On the other hand, the three-dimensional geometry of the
mafic intrusive sheets presents a large surface-to-volume
ratio that could have facilitated isotopic exchange.
The
isotopic characteristics of the mafic intrusive sheets,
therefore, probably are not indicative of their source.

108
The clinopyroxene-bearing quartz monzonitic country
rock, sample 37-A, has initial ^'^Sr/^^Sr of 0.70593,
which is within the range of Sr ratios of the Bodoco
pluton.
The similarity of isotopic values suggests
either that sample 37-A is oogenetic with the Bodoco
pluton or that it had similar source rocks.
Initial Sr and Mixing Relationships
The similarity of initial Sr ratios between the QMZ
samples and the mafic intrusive samples precludes an
isotopic test for mixing.
In a system where two endmembers
are combined that have disparate initial
87gj./86g^ and common Sr concentrations, the mixing relationship
can be approximated by a hyperbolic relationship
in terms of Sr concentration and initial ^"^Sr/^^Sr.
This
hyperbola is transformed into a straight line by plotting
1/Sr instead of Sr, and the quality of the fit of data to
the line may be used as a test for the validity of a
mixing hypothesis (Faure, 1986).
The relationship
between 1/Sr and initial ^"^Sr/^^Sr is non-systematic in
the samples because initial ^'^Sr/^^Sr is approximately
the same for all the major rock types (Fig. 38a). On the
Other hand. Figure 38b compares the initial Sr/ Sr and
1/Sr of the plutonic suite with the data for country
rocks with initial 87gr/86sj. back-calculated at

109
t = 555 Ma.
The data suggest that minor isotopic change
due to assimilation of country rock is plausible and
could account for some of the observed scatter in isotope
ratios.
In particular, the two samples of gneiss have
such high ^^Sr/^^Sr that assimilation of one or two percent
of gneiss relative to the pluton's mass could
produce much of the observed scatter in the granitoid
data.
Arakawa (1990) contrasted the Sr isotope compositions
of granites emplaced in shear zones with granites
emplaced in unsheared host rocks in the Hida belt of
Japan.
He found that intrusions in ductile shear zones
had a large crustal component.
He attributed this to
assimilation of country rocks in the compressional stress
regimes.
Structural evidence that the Bodoc6 pluton is
shear-related indicates that similar contamination could
have accompanied its emplacement.
Oxygen Isotope Chemistry
Oxygen isotope analyses were performed on twenty of
the samples analyzed for Rb-Sr isotopes.
Where possible,
oxygen isotope values were determined from quartz
separates because quartz is the common mineral that is
the most resistant to post-crystallization isotopic
exchange or alteration.
Whole-rock powders were analyzed
for samples that were quartz-free or that were suspected

110
of containing xenocrystic quartz.
For comparison, wholerock
powders were also analyzed for each of the three
textural types of QMZ.
Results are reported using a
standard 6 notation in per mil, relative to standard mean
ocean water (SMOW).
within 0.1 per mil.
Results are considered accurate to
Analytical procedures are described
in more detail in Appendix C.
Analytical Results
Table 21 summarizes the results of the oxygen
isotope analyses.
Regardless of rock type, whole-rock
d
0 values have an observed spread of only 0.4 per mil,
from +6.8 to +7.2 per mil.
Quartz in the samples has a comparably small spread
of d^^O values (0.5 per mil) regardless of rock type or
location within the pluton (Fig. 39). Values range from
+9.3 to +9.8 per mil. The one exception is quartz from
aplitic sample 13-C, which also has anomalous ^'Rb/^^Sr
and Q*7sr/^^Sr (Table 18); it has a fi^^O value of +13.0
per mil.
Quartz from the clinopyroxene-bearing quartz
monzonite (37-A) at the pluton's southwestern margin has
a 6^^0 value of +9.5 per mil.
Oxygen isotope ratios in
quartz from metamorphic country rocks are +11.0 per mil
in a felsic gneiss from the Uau^ Group west of the pluton

and +16.0 per mil in a pelitic schist from the Salgueiro
Group southeast of the pluton.
Ill
Discussion
Oxygen isotopes are sensitive to the effects of wall
rock interaction, hydrothermal interaction, and
differences in source rocks.
Major oxides in a magma may
not be changed significantly by assimilation (or
comparably, by a small amount of mixing), but oxygen
isotopic effects can be drastic (Taylor, 1980).
Massdependent
fractionation increases as temperature
decreases, so magmas are particularly sensitive to
isotopic exchange due to near-surface processes such as
hydrothermal alteration by meteoric groundwater.
The near-uniformity of Bodoc6 6^°0 values for wholerock
samples and for quartz separates suggests that the
observed values have been inherited from the source and
that they are in isotopic equilibrium with each other.
If wall-rock interaction had been important locally,
isotopic zoning or variability in the plutonic rocks
should have been pronounced because the b^°0 values of
gneiss and (especially) schist in the country rocks are
18
higher than the plutonic values.
Similarly, hydrothermal
alteration would have been likely to result in more
variability between whole-rock and quartz 5^^0 pairs than
is observed.

112
Whole-rock fi^^O values of about +7 per mil are
typical of many intermediate igneous felsic rocks (Faure,
1986). Because rocks that have been through a weathering
cycle at the earth's surface become enriched in ^°0,
whole-rock fi^^O values less than about +10 per mil are
thought to represent magmas from a mantle-derived igneous
protolith or from a cont2uninated mantle melt (Faure,
1986; O'Neil and Chappell, 1977; O'Neil and others,
1977).

CHAPTER 7
EVOLUTION OF THE BODOCO PLUTON
The evolution of the Bodoc6 intrusion, like that of
many other plutonic bodies, is complicated by an extended
history that includes dynamic crystallization, multiple
magma compositions, and supersolidus and subsolidus
reactions.
A magma can evolve by several processes,
including fractional crystallization, assimilation of
wall rocks, flow separation, magma mixing, and restite
unmixing.
More than one of these processes probably
affected most felsic plutons, making it difficult to
assess the contribution of each processs (Reid and
Hamilton, 1987).
Furthermore, different processes can
produce similar results.
In the Bodoco pluton,
megacrystic QMZ is reversely zoned from a granodioritic
margin to a quartz monzonitic center.
This is the
opposite of the mafic-to-felsic sequence expected from in
situ crystal fractionation (Bateman and Chappell, 1977;
Ragland and Butler, 1972) and has been cited as evidence
for magma mixing (e.g., Wiedemann and others, 1987).
However, reverse zoning has also been attributed to flow
separation (Speer and others, 1989) and to autointrusion
of a single fractionated magma that was layered, with the
deeper and more mafic layers intruded last (Nironen and
Bateman, 1989; Nabelek and others, 1986).
113

114
Any model proposed for the evolution of the Bodoco
pluton must apply as much of the textural, chemical,
mineralogical, and isotopic data as possible to explain
the temporal and genetic relationship of the various rock
types, to explain how the megacrystic QMZ became
reversely zoned, and to identify the likely source rocks
for the intrusion.
Differentiation Processes
On the basis of chemical and textural data, the
igneous processes most likely to have affected the
evolution of the Bodoco pluton are fractional
crystallization, magma mixing, and crystal accumulation.
There is little isotopic evidence for contamination of
magma by assimilation of wall rocks at upper crustal
levels, nor is there evidence for restite unmixing as an
important differentiation process.
Models of Fractional Crystallization
The evolution of the plutonic suite by fractional
crystallization was modeled from mafic to felsic end
members by subtracting proportions of mineral
compositions in a sequence of intermediate parentdaughter
steps and evaluating the quality of the linear
regression in each case.
The compositions of mineral
phases removed were based on microprobe analyses of

115
Bodoc6 samples. A fractionation step was considered
unacceptable if the sum of the squares of the residuals
(rf) was greater than 1.00; a value of r£ less than 0.10
was considered definitive.
Representative fractionation calculations are
described in Table 22.
The mafic intrusive sheets were
considered to be the best approximation to the parent
because overall they demonstrate more systematic chemical
behavior than the mafic enclave samples. Table 22
indicates that by using mafic intrusive sample 19-B as a
starting composition it is possible to model the
evolution of the suite through the range of megacrystic
QMZ and terminate the sequence either with steps (Nos. 5
and 6, Table 22) that produce aplite, or an alternative
step (No. 4, Table 22) that produces a late-stage
equigranular granite (sample 61-F) from the hybrid
region.
The fractionation sequence can be modeled in as few
as four steps (Fig. 40; Steps 1-4 of Table 22) with
values of r^ that range from 0.19 to 0.67.
The kinds
and proportions of minerals removed agree reasonably well
with modal data.
Other solutions involving more, smaller
fractionation steps are also possible, but including the
extra steps does not improve the quality of the linear
regression for each step.
This is not a surprising

116
result, given petrographic evidence that most of the
Bodoc6 samples did not crystallize from true liquid
compositions but more realistically represent accumulated
phenocrysts plus liquid.
Table 22 also records successful fractionation steps
that produce phenocrystic QMZ and plumose QMZ compositions
using mafic intrusive 19-B as a parent.
Some samples could not be modeled successfully by
fractional crystallization.
It is noteworthy, for
example, that by using only samples from the hybrid
region (localities 60, 61, and 62), it was not possible
to fractionate the "most felsic" mafic sample (60-A) to
produce the "least felsic" felsic saumple (61-E).
The
best result obtained had rf of more than 2.0 (Table 22).
By assuming that mafic intrusive 19-B represents the
composition of the parent melt, it is possible to calculate
the fraction of liquid remaining, F, after each step
in the fractionation process.
For each step, it is then
possible to relate the fraction of liquid remaining to
the concentration of trace elements in the parent and
daughter "liquids."
Crystal fractionation produces
characteristic differentiation trends that depend on the
bulk distribution coefficient for a given trace element.
The Bodoc6 trace element data for Sr, Ba, and Y
applied to the fractionation model have gently curving

117
concave-downward trends that approximate those expected
by Rayleigh fractional crystallization (Fig. 41).
Rubidium is correspondingly enriched with an upwardcurving
trend that approximates that produced by a bulk
partition coefficient of about 0.6.
In contrast, Zr is
enriched through most of the process beyond values that
can be produced by Rayleigh fractionation even if the
bulk partition coefficient equaled zero.
This indicates
that the trace element data do not fit a fractional
crystallization model that uses the mafic intrusive
sample 19-B as a parent.
However, a different parent
magma with a similar major element composition but lower
trace element concentrations could satisfy the model.
Magma Mixing Models
To evaluate the viability of a model of magma mixing
in the evolution of the plutonic suite, mixing possibilities
were tested by major oxide mass balance calculations
in which various proportions of selected end members were
combined to form intermediate daughter compositions.
In
most cases, mafic intrusive sample 19-B was used as the
mafic end member composition (Table 23). Megacrystic QMZ
compositions as well as plumose and phenocrystic QMZ
compositions can be achieved by such linear mixing
without fractional crystallization.
The sums of the
squares of the residuals for the various mixing steps are

118
of the same order of magnitude as those for crystal
fractionation.
Notable exceptions involve the rocks from
the hybrid zone, for which the results of mixing models
are superior to fractional crystallization.
Trial
mixtures of a granitic sample (61-F) from the hybrid zone
with various mafic samples consistently produced mafic
hybrid compositions with values of r^ near or less than
0.10, as illustrated by two examples in Table 23. The
quality of this fit is particularly impressive given the
wide range of Si02 content between the respective end
members and the "mixed" daughter.
It is also significant
that equivalent steps using these same samples could not
be modeled successfully using crystal fractionation
(Table 22).
Another test for magmatic differentiation processes
examines the trace element behavior of Rb and Zr for the
entire suite.
Because Rb and Zr are excluded from most
crystals growing in a melt, their bulk distribution
coefficients are less than 1.0.
In a Rayleigh fractionation
process where this condition is satisfied, the
overall concentration of Rb and Zr in the melt should
increase as crystals are removed, but the ratio of the Rb
and Zr concentrations should remain approximately uniform
until the magma is nearly crystallized.
Consequently,
crystal fractionation should be indicated by a nearly

119
horizontal trend in a plot of Rb/Zr and Rb (Treuil,
1973).
Figure 42 contrasts Rb/Zr and Rb for the Bodoco
samples.
Regardless of Rb concentration, most of the
megacrystic QMZ samples and all of the plumose QMZ
samples have Rb/Zr of about 0.5, suggesting that they may
be related by fractional crystallization.
Also, granite
sample 61-F from the hybrid zone had been modeled above
(Step 4, Table 22) to represent the end product of
fractionation of megacrystic QMZ, and its Rb/Zr value is
located very nearly along the sub-horizontal linear trend
established by most of the other megacrystic QMZ samples
(Fig. 42).
On the other hand, many of the data shown in
Figure 42 do not plot in arrays typical of fractional
crystallization.
The megacrystic QMZ samples from the
center of the pluton and the phenocrystic QMZ samples
have higher but scattered Rb/Zr compared to most of the
other megacrystic QMZ.
Data trends for samples from the
hybrid zone and for the mafic intrusives also do not
indicate fractional crystallization.
It is possible to account for much of the observed
scatter in Rb/Zr in Figure 42 by magma mixing.
A mixing
relationship where the end members have very different
proportions of Rb and Zr will produce a hyperbolic trend.

120
Mixing hyperbolas generated by several magma mixing
calculations, based on end members tested in Table 23,
are superimposed on the data in Figure 43.
As required
by a mixing hypothesis in a reversely zoned pluton, the
data for samples from the center of the pluton are the
ones on the mixing hyperbolas that have a greater
proportion of mafic end member.
Many of the hybrid rocks plot on or near a mixing
hyperbola for which mafic and felsic hybrid samples were
used as end members (Fig. 43).
Crystal Accumulation Models
Crystals may become segregated from melt by gravitational
settling, by flotation of less dense phases
towards the magma chamber roof, or by flow differentiation
in narrow conduits.
In coarse-grained felsic rocks
in particular it may be difficult to distinguish cumulus
phases from minerals that crystallized in situ.
In a mass balance procedure analogous to tests of
fractional crystallization, mathematical modeling of
crystal accumulation for the Bodoc6 pluton produced
linear regressions of excellent quality, with values of
r^ typically less than 0.100 (Table 24). Using
high-silica QMZ or felsic hybrid samples as starting
compositions, it was possible to add reasonable

121
proportions of K-feldspar, plagioclase, and hornblende
(plus minor titanite, apatite, and magnetite) to produce
a variety of lower-silica QMZ end members. Biotite was
not a significant required phase for the crystal
accumulation models.
As expected from their relatively fine-grained and
phenocryst-free textures, mafic hybrid and mafic
intrusive samples were statistically unsatisfactory end
members for crystal accumulation models. In contrast, a
model in which crystals were added to an equigranular
hybrid-zone granite (sample 61-F) to produce a megacrystic
granite (sample 77-A) resulted in an excellent
linear regression with an r£ of only 0.004 (Table 24,
Trial 17).
Inasmuch as Ba is partitioned strongly into
K-feldspar, it was used as a trace element to test the
crystal accumulation procedures modeled in Table 24.
The
concentration of Ba in K-feldspar was estimated from
microprobe analyses and was used to calculate the amount
of K-feldspar necessary to produce the observed wholerock
concentration of Ba in samples.
The calculated
percentage of K-feldspar was then compared with the
proportions of K-feldspar required by the crystal
accumulation models in Table 24.
The amount of
K-feldspar predicted by Ba concentrations and the amount

122
of K-feldspar required by accumulation models agreed to
within 0.5% in all cases.
Evaluation of Differentiation Models
The mass-balance models of differentiation
processes described above suggest that crystal accumulation
was more important in the Bodoc6 pluton than was
fractional crystallization or magma mixing.
Given that
evidence is not apparent either for crystal settling or
for flotation, the method of crystal accumulation that
affected the Bodoco pluton was probably flow separation.
During the ascent of a phenocrystic magma in a conduit,
crystals are segregated by grain dispersive pressure
(Komar, 1976) towards the center of the pipe.
Differentiation
occurs because the magma adjacent to the sides of
the conduit contains fewer and smaller crystals and
proportionately more of the evolved intercrystalline melt
than does the crystal-laden magma in the center of the
conduit.
Presumably there are fewer accumulated crystals
in the upper portion of a conduit than in the lower
portion because the mobility of crystals is mutually
restricted during ascent.
Although flow differentiation
is best documented in small igneous bodies, in theory it
should be possible to change the bulk composition of a
large mass of magma if the magma ascended through a
network of conduits that acted as a flow differentiation

123
"filter" (Barker, 1983).
No single sample would be
likely to preserve the starting composition of the
original, pre-emplacement magma.
In the Bodoc6 pluton the spatial association of
K-feldspar megacryst clusters with swarms of small mafic
enclaves has been noted as textural evidence for flow
differentiation (Chapter 4). Although K-feldspar is
commonly a late-stage, interstitial mineral in felsic
rocks, the tabular and megascopically zoned megacrysts in
the Bodoc6 samples appear to have had a prolonged history
of growth in and reaction with the magma.
From petrographic
observations, it is reasonable to assume that
K-feldspar megacrysts, plagioclase crystals, and glomerocrysts
of hornblende (± clinopyroxene, titanite, apatite,
and perhaps biotite) were the major crystalline phases in
the Bodoco quartz monzonitic magma at depth.
Biotite,
though abundant in most samples, may have formed late in
the paragenetic sequence by supersolidus reaction of
hornblende.
If so, biotite would not necessarily have
been an important phase during crystal accumulation.
Quartz, the only other relatively common mineral, appears
to be generally late-stage and interstitial.
Crystal
accumulation models in Table 24 attest to the importance
of K-feldspar, plagioclase, and hornblende as required
solid phases in the magma.
In agreement with

124
petrographic observations, crystal accumulation of
neither biotite nor quartz is required by the models.
Magmatic suites derived by fractional crystallization
generally become more enriched in quartz and
K-feldspar as they evolve.
Samples from the Bodoco
plutonic suite display a contrary trend, in which rocks
contain less K-feldspar as they become more quartz-rich
(Fig. 9 and Fig. 11). This quartz-monzonite-togranodiorite
trend for the Bodoc6 samples is reversed
toward granitic compositions only for aplites and for the
felsic samples from the hybrid zone (Fig. 12).
As the crystal accumulation trials in Table 24
suggest, the Bodoco plutonic suite may have obtained its
range of rock types from a starting magma of relatively
felsic composition compared to that of most of the
preserved suite.
During flow separation, a minor portion
of magma along the conduit walls became more silicic by
losing crystals whereas most of the magma acquired a
range of less silicic compositions by accumulating
different proportions of K-feldspar megacrysts,
plagioclase crystals, and hornblende glomerocrysts.
The importance of crystal accumulation is also
suggested texturally by the granitic and granodioritic
samples of megacrystic QMZ from the eastern margin of the
pluton.
If this border facies represents the first pulse

125
of magma to be emplaced after flow separation somewhere
at depth, it should have been more silicic than elsewhere
in the megacrystic QMZ, having relatively few accumulated
crystals and correspondingly more melt.
Such differences
in the magma seem to be preserved petrographically in the
samples of megacrystic QMZ from the eastern margin of the
pluton.
Such samples are more quartz-rich than elsewhere
and contain the only euhedral hornblende in the pluton,
implying that they crystallized from a magma that was
silicic and relatively fluid.
Plagioclase compositions in the megacrystic QMZ also
attest to possible flow separation.
Crystals are mostly
unzoned and have a restricted range of composition (An^^y
to An22/ Table 6) despite a corresponding whole-rock
variation of Si02 from 60 to 70 weight percent.
If
differentiation occurred by flow separation, the
composition of a magma in which plagioclase was
crystallizing might not have evolved significantly until
after most plagioclase had formed.
Consequently,
plagioclase crystals would record little compositional
variation from rim to core.
Much more compositional
variation might be expected through a process of
fractional crystallization.
Plumose QMZ and phenocrystic QMZ may also be
related to each other by flow separation.
They are

126
intermingled in the field, and they have similar mineral
assemblages and grain sizes.
Both have K-feldspar
phenocrysts that are zoned with "exsolution shells."
If
the plumose QMZ and phenocrystic QMZ represent complementary
phases of flow separation, then the earlier-emplaced
plumose QMZ magma should have contained fewer and smaller
accumulated crystals and relatively more evolved melt
than the phenocrystic QMZ magma.
Crystals of K-feldspar
in the plumose QMZ are in fact smaller and more slender
than those in the phenocrystic QMZ, and they are mantled
by continuous K-feldspar overgrowths.
Presumably a
significant amount of felsic melt was available in the
plumose QMZ magma to form such overgrowths in response to
changing P-T conditions.
Evidence for flow separation in the plumose and
phenocrystic QMZ is contradicted, however, by the fact
that both types of QMZ have approximately the same modal
proportions of quartz.
The model predicts that plumose
QMZ should contain more quartz than phenocrystic QMZ.
Furthermore, plagioclase in phenocrystic QMZ has a wide
compositional range, from An^^g to An3g (Table 6). In
contrast, plagioclase compositions in plumose QMZ are
restricted from An^y to An2i (Table 6). It is unlikely
that flow separation could remove only calcic plagioclase
from plumose QMZ magma.

127
Despite much evidence that the Bodoco pluton
acquired many chemical and textural characteristics by
crystal accumulation derived from flow separation, there
is also widespread evidence for at least limited magma
mixing.
Mafic and felsic rocks in the topographically
high western area of the pluton are hybridized, with
nebulitic swirls of one rock type in another.
Felsic
xenocrysts are common in the mafic portions of these
hybrid rocks, and many phenocrysts and megacrysts of
Hibbard (1981) proposed that this unusual texture
could be caused by magma mixing, in which plagioclase
components from a mafic magma grow epitaxially on any
available feldspar during the pronounced thermal or
chemical disequilibrium that may accompany mixing.
As
discussed, many of the hybrid rock compositions can be
modeled by magma mixing using felsic and mafic end
members from the hybrid zone (Table 23 and Fig. 43).
In the megacrystic QMZ, crystal accumulation
processes may have overprinted much evidence for either
magma mixing or fractional crystallization.
K-feldspar are mantled by rapakivi overgrowths of plagioclase.
Nevertheless,
trace element tests for magma mixing based on
concentrations of Rb and Zr (Fig. 43) suggest that at
least some megacrystic QMZ samples, including those from

the core of the pluton, had mixed with a chemically
distinct magma.
128
Other textural evidence for magma mingling, if not
mixing, includes the exposures of plumose QMZ and
phenocrystic QMZ that are intermingled on an outcrop
scale.
Microgranitoid enclaves throughout the pluton are
finer-grained and more mafic than their host rock, and
they are ellipsoid and plastically deformed (stretched,
boudinaged, cuspate, bent around megacrysts).
These
features suggest that the mafic enclaves had been
incorporated in the magmatic state (Vernon, 1983).
Source Regions
Igneous bodies of many ages in northeastern Brazil
are characterized by high concentrations of K2O, P2O5,
Sr, and Ba (Sial, 1987; Ferreira and Sial, 1987).
This
suggests that the underlying mantle or the crust is
enriched in these elements.
Throughout Brazil, high
concentrations of these same elements characterize
Itaporanga-type granitoids, suggesting either that an
enriched protolith underlies an extensive part of the
South American continent or that the igneous process that
produced these coarse-grained megacrystic bodies also
operated to concentrate alkali and alkaline earth
elements.
Low concentrations of Rb relative to K2O and
to Sr suggest that the source rocks may have experienced

129
a previous episode of melting that involved preferential
loss of Rb from a K-rich phase (phlogopite? biotite?) but
that retained K-feldspar and plagioclase.
On the basis of relatively low initial ^"^Sr/^^Sr
values and low 5^^0, it is reasonable to conclude that
the Bodoco magma was not derived from ancient upper
crustal continental rocks or from a metasedimentary
source.
Partial melting of any upper crustal source, in
fact, would not be likely to produce quartz monzonitic
magma (Wyllie, 1977).
At the other extreme, the Bodoc6 rocks cannot be
entirely mantle-derived because their initial ^^Sr/^^Sr
and 5^^0 values are too high.
Instead, an origin in
depleted lower or middle crust or some combination of
mantle and crustal components is required.
In any case, the heat for magma generation was
likely supplied to the crust by a mantle-derived magma
(Clemens and Wall, 1981).
Basaltic dike swarms elevate
the temperature of the crustal country rocks that they
intrude, making partial melting of crustal rocks feasible
(Hildreth, 1981).
In northeastern Brazil, the earliest
Brasiliano igneous activity was pre-folding.
It consisted
of a regionally dispersed, differentiated suite of
relatively mafic diorite (Almeida and others, 1981;
Jardim de S^ and others, 1987).
Voluminous Itaporanga-

130
type magmatism widely accompanied the Abukuma-type
metamorphism associated with Brasiliano-age fold belts,
suggesting that the geological circumstances that
generated the megacrystic granitoids prevailed throughout
northeastern Brazil.
In fact, megacrystic granitoids
composed of quartz monzonite, plagioclase-rich granite,
and granodiorite are common in erogenic belts worldwide
where they are typically emplaced in the cores of fold
belts under metamorphic conditions of high temperature
and (relatively) low pressure (Vernon, 1986; Kawachi and
Sato, 1978).
Generation of Porphyritic Granitoids
Given the textural characteristics of the Bodoco
pluton and its erogenic setting, a model for granitoid
genesis proposed by Huppert and Sparks (1988) merits
consideration.
Voluminous, highly porphyritic felsic
magma is generated by the emplacement of basaltic sills
in crustal rocks that have been pre-heated by basaltic
dike swarms.
As regional temperature increases, crustal
rocks become ductile, and basaltic dikes can no longer
propagate vertically through them.
The rising basaltic
magma is forced to pond as sill-like bodies, perhaps near
the base of the crust.
In theory, a convecting basaltic
sill of sufficient thickness would lose enough heat by

131
conduction into the overlying crustal roof to produce
significant partial melting.
Ultimately, the entire
melted volume may begin to convect independently of the
underlying basaltic sill (Wickham, 1987).
A highly porphyritic magma can form in the
convecting granitoid magma as it simultaneously melts and
crystallizes in different parts of the magma chamber.
As
the magma partly melts and destabilizes its roof, it
entrains the resulting liquid plus refractory matrix
minerals (Fig. 44). At the same time, new minerals
crystallize in the interior of the chcunber where
convected cooler magma from above has decreased the
temperature at depth.
New crystals may nucleate directly
as phenocrysts, or on small clots or grains of refractory
minerals (Chappell and others, 1987).
Having developed
at depth, the granitoid intrusions that result are
potentially coarse-grained as well as megacrystic.
At
the same time, the heated crustal country rocks become
susceptible to ductile deformation and may form fold
belts.
The thermodynamic and fluid dynamic calculations
presented in the Huppert and Sparks model (1988) could
apply to partial melting of granodiorite in the middle or
upper crust, or to regions of the lower crust that were
formed by underplating during earlier magmatism.
The

132
latter lithology would be largely mantle-derived, and it
could have assimilated and become homogenized with enough
crustal material to have acquired oxygen and Rb-Sr
isotope characteristics comparable to those seen in the
Bodoc6 rocks. Rocks that had been formed by differentiation
during underplating would have relatively low fusion
temperatures compared to their mantle-derived predecessors
and thus would be amenable to partial melting by the
intrusion of basaltic sills.
Sequence of Intrusion
The Bodoco magma intruded a region of the upper
crust (2-3 kb?) that was undergoing northeast-trending
shear deformation.
With the possible exception of
aplites and of rocks in the hybrid zone, the Bodoco
pluton was formed from magma far beneath the region of
final emplacement.
Castro (1987) proposed that
extensional fractures generated in shear zones are one of
the most effective means of transport of magma from the
mantle or lower crust.
In the case of the Bodoco pluton,
extension during shear deformation could have allowed
crystal-rich granodioritic or quartz monzonitic magma to
propagate upwards along relatively narrow fractures,
thereby promoting flow separation.
The following
discussion proposes a possible scenario of development.

Mafic Enclaves
133
Small amounts of an underlying sill of mafic magma
may have become stirred into highly porphyritic QMZ magma
to become an assortment of quenched microgranitoid mafic
enclaves.
A variety of physical and diffusive processes
caused the enclaves to lose many of their original
magmatic characteristics.
Megacrystic, Phenocrystic, and
Plumose Quartz Monzonite
Despite minor differences, all three textural types
of QMZ have generally similar oxide, trace element, and
isotope compositions.
Petrographically, they share the
same mineral assemblage and have the same pattern of
"exsolution shells" in K-feldspar phenocrysts.
Plumose
and phenocrystic QMZ may have been derived from one
episode of intrusion and the megacrystic QMZ from a later
episode, or all three may represent successive pulses
from a source that was modified slightly between
intrusive episodes.
Clinopyroxene-bearing quartz
monzonitic country rock (sample 37-A) may be a fourth
variety of this QMZ source.
During Brasiliano regional shear deformation, deep
extensional fractures presumably developed in the crust
and promoted the ascent of QMZ magma.
The first pulse to
intrude was enriched in Rb, Zr, and K2O relative to those

134
that followed it. The K-feldspar phenocrysts in this
pulse developed in at least two stages.
The first stage
consisted of slender phenocrysts (now perthitic).
In the
second stage, these phenocrysts were mantled by (nonperthitic)
K-feldspar overgrowths that may have
crystallized as residual melt cooled against country
rocks.
Before the first pulse of QMZ magma solidified
completely, a pronounced sigmoidal ("plumose") foliation
was impressed upon it by ductile shear.
Intrusion of the plumose QMZ magma was accompanied
or closely followed by a pulse of a second, more
plagioclase-rich quartz monzonitic magma that formed the
phenocrystic QMZ. Both varieties of QMZ appear to have
been nearly solidified (less than 30 percent melt) when
intruded, for they developed petrographic textures
typical of dynamic crystallization (Hibbard, 1987).
They
responded plastically to deformation and were intermingled
(but not mixed chemically) in wide, foliated
bands over a transition zone several km long and one km
wide.
Toward the center of the pluton (away from the
contact with plumose QMZ), the phenocrystic QMZ was less
deformed.
The final, most voluminous pulse consisted of
megacrystic QMZ magma.
The coarser grain size of
K-feldspar and of other minerals suggests a relatively

135
prolonged stage of pre-emplacement growth. The preserved
range of megacrystic rock types, from quartz monzonite
with relatively little quartz or plagioclase to granodiorite
and plagioclase-rich granite, suggests that
crystal accumulation processes were the most important
method of differentiation.
The more silicic and (relatively) crystal-poor
portion of the megacrystic QMZ magma was emplaced first
and was preserved as granite and granodiorite along the
eastern and northeastern margins of the pluton.
At a few
such localities, the magma was undercooled adjacent to
wall rocks so that acicular apatite was formed and
trapped in feldspar overgrowths.
Continued intrusion brought up more crystal-laden
and consequently less silicic magma, resulting in a
reversely zoned pluton from a granitic and granodioritic
margin to a quartz monzonitic core.
The most mafic
samples of megacrystic QMZ are from the central region of
the pluton. Limited trace element data (Rb/Zr, Fig. 43)
suggest that these variants became more mafic by mixing
with small amounts of mafic magma (monzodioritic to
monzonitic), perhaps similar to the mafic intrusive
sheets.
When the QMZ magma reached a level of neutral
density or when overlying conduits were closed by

136
deformation, continued intrusion of magma caused the
pluton to balloon, creating marginal foliations that are
subparallel to the contact of the pluton.
Mafic Intrusive Sheets and
Deformed Quartz Monzonite
The megacrystic QMZ continued to crystallize after
emplacement.
After 70-80% solidification, the crystals
could no longer move about freely.
The viscosity of the
QMZ magma increased to the point that it began to behave
more as a rigid body (Arzi, 1978; Van der Molen and
Paterson, 1979).
Continued localized shear caused the
megacrystic QMZ to develop elongated deformed zones with
dynamically crystallized textures.
Increased strain or further solidification in these
shear zones caused the body to fracture rather than to
deform plastically.
Mafic monzodioritic or monzonitic
magma was then able to ascend via these elongated,
vertically oriented fractures.
The northeast-trending
shear zones are preserved as strongly foliated
megacrystic QMZ and synplutonic mafic dikes.
Hybrid Rocks
The zone of hybrid rocks on the western margin of
the pluton is located in the portion of the pluton
characterized by the elongate zones of mafic intrusive
sheets and foliated megacrystic QMZ (Fig. 5). It also

137
appears to consist of a structurally high level of the
pluton that is not preserved elsewhere.
Felsic rocks in
the hybrid zone are more silicic and more equigranular
than elsewhere, but the mafic hybrids are chemically and
texturally similar to the mafic intrusive sheets with
which they are more-or-less on strike.
The granites and granodiorites of the hybrid zone
may have been derived from in situ fractionation of
megacrystic QMZ magma.
During localized shearing of
incompletely solidified megacrystic QMZ, some evolved,
hydrous intercrystalline melt could have separated and
migrated slightly upwards along fractures to become the
felsic magma of the hybrid zone.
As magma of the mafic intrusive sheets ascended, it
encountered previously separated felsic melt.
Active
shearing, a mechanical process, effectively combined the
mafic and felsic melts (Whalen and Currie, 1984).
The
large thermal and compositional contrasts caused the two
magmas to commingle rather than to mix thoroughly (Frost
and Mahood, 1987; Hyndman and Foster, 1988), producing
texturally diverse rocks of the hybrid zone.
Minor Dikes
The final stage of pluton development was
characterized by fracturing and intrusion of small

138
aplitic and mafic dikes. Some of these are possibly
related to the major rock types by late-stage in situ
differentiation.
Summary
Important stages in the evolution of the Bodoco
pluton are summarized schematically in Figure 45.
In the
first stage, a porphyritic felsic magma was generated at
depth (Fig. 45a). To satisfy isotopic constraints, the
source for this magma must have included a mantle-derived
component and a crustal component, but the process by
which the magma formed is not known.
One possible
scenario, as depicted in Figure 45a, involves the partial
melting of crustal rocks due to heat conducted by an
underlying mafic sill.
In such a case, the resulting
magma may have achieved its isotopic characteristics by
mixing, or alternatively the protolith that was melted
may itself have been a mantle-derived differentiate of an
earlier episode of crustal underplating.
A second important stage in the development of the
Bodoc6 pluton apparently involved differentiation of the
magma by flow separation during ascent through a network
of conduits (Fig. 45b). Large crystals migrated toward
the centers of conduits during flow, producing an evolved
and crystal-poor melt along the walls.
The magma in the

139
central part of the conduits was correspondingly crystalenriched
and less silicic.
In addition, the magma in the
upper part of the conduits may have contained fewer
accumulated crystals and relatively more evolved,
intercrystalline melt than the lower portions of crystalladen
magma that followed it.
Flow separation of
megacrystic QMZ magma produced a reversely zoned pluton
in which crystal accumulation processes dominated.
Regional deformation and structures within the
pluton suggest that the Bodoc6 magma was emplaced in
response to shear stresses at a level in the crust
corresponding to about 2 or 3 kb.
After emplacement and
much in situ crystallization, localized shear deformation
produced elongated zones of foliated megacrystic QMZ in
the western portion of the pluton (Fig. 45c). The
megacrystic QMZ crystallizing in these zones developed
ellipsoidal K-feldspar, ribbon quartz, pressure shadows,
and other textures indicative of dynamic crystallization.
In response to extensional forces generated by shearing
in these zones, some residual felsic melt from the
megacrystic QMZ may have migrated upwards in the magma
chamber.
With continued localized shearing, the foliated
megacrystic QMZ responded rigidly instead of plastically
and developed extensional fractures (Fig. 45d). Mafic

140
magma, either from depth where the QMZ magma had been
generated or from some other source, rose along these
fractures to become synplutonic dikes ("mafic intrusive
sheets").
Mafic magma propagating along fractures to
higher levels of the chamber encountered the still-fluid
felsic melt that had separated from the megacrystic QMZ.
The mafic and felsic melts were mixed by shear to form
texturally hybridized rocks.

CHAPTER 8
TECTONIC CLASSIFICATION
Pitcher (1982) examined the occurrences of granitic
rocks in Phanerozoic tectonic belts worldwide and
proposed that granites with predictable chemical compositions
are produced in specific tectonic settings.
His
classification system was a modification of the S- and
I-type granite classification developed by Chappell and
White and their coworkers (Chappell and White, 1974;
White and Chappell, 1977; Hine and others, 1978; White,
1979). The original classification of I-type and S-type
granites works well for some circum-Pacific intrusions,
but many other granites have characteristics that are
more-or-less intermediate between the two types.
Pitcher
expanded the S- and I-type classification to recognize
two subcategories of I-type granites, I-(Cordilleran)
type and I-(Caledonian) type.
I-(Cordilleran) type granitoids represent the
voluminous subduction-related biotite-hornblende tonalite
magmatism typical of convergent ocean-continental plate
margins.
These intrusions are characterized by a broad
range of rock types, form linear batholiths, have initial
Q'^Sr/^^Sr less than 0.706, and host porphyry Cu and Mo
mineralization.
In contrast, I-(Caledonian) type
granitoids have a more restricted range of rock types,
141

142
form dispersed and isolated plutons, and rarely have
economic mineralization.
These latter granitoids
apparently are not directly related to subduction but are
believed to be produced by post-collision uplift.
Table 25 contrasts the pertinent characteristics of
the Bodoc6 pluton with Pitcher's (1982) descriptors of
S-type, I-(Cordilleran) type, and I-(Caledonian) type
granitoids.
The Bodoc6 pluton (as well as Itaporangatype
granitoids in general) is best described by the
I-(Caledonian) type classification.
The Bodoc6 pluton
has a limited range of felsic compositions (quartz
monzonite to granodiorite) that are associated with but
not compositionally continuous with a group of more mafic
compositions (monzonite to monzodiorite). Chemical
characteristics or features of the Bodoc6 rocks such as
the alumina index and initial Sr ratio correspond to
those of the I-(Caledonian) type granites, as do the
enclave population, intrusion style, and absence of
economic mineralization.
The Bodoc6 pluton differs from the typical
I-(Caledonian) type granitoid in several respects.
First, its mafic mineral assemblage of hornblende,
biotite, titanite, and magnetite is more like that of
I-(Cordilleran) type rocks than of any other category.
Second/ Pitcher considered megacrystic K-feldspar to be

143
characteristic of S-type plutons. On the other hand,
interstitial K-feldspar (such as that in the Bodoco
hybrid samples is typical of I-(Caledonian) type
granitoids.
The likely source regions for the Bodoco pluton that
are indicated by isotopic data are also in general
agreement with the tectonic origin of I-(Caledonian) type
granitoids.
According to Pitcher's model, the parental
melts of I-(Caledonian) type granitoids had a mixed
source, derived from mantle/lower crust and mixed with
partial melts of different crustal rocks at higher
levels.
The higher-level partial melts may have resulted
from relatively rapid adiabatic decompression due to
uplift and erosion after plate collision and wrenching
had largely ceased.
Hot magma from the mantle rose along
faults to come into contact with the crustal rocks that
were then partly melted.

CHAPTER 9
CONCLUSIONS
The Bodoc6 pluton is typical of numerous Brasilianoage
"Itaporanga-type" granitoids that are characterized
by tabular megacrysts of K-feldspar in a coarse, dark
matrix of plagioclase, glomerocrystic hornblende, and
biotite (Almeida, 1971).
Most of the features of the
Itaporanga-type intrusions identify them as I-
(Caledonian) type granitoids in the tectonic granite
classification developed by Pitcher (1982).
The Bodoco plutonic suite consists principally of
three textural varieties of porphyritic quartz monzonite
with intermediate Si02 content (58-70 wt%).
The suite
also contains minor amounts of mafic dikes and mafic
enclaves (principally monzonite and monzodiorite) with
Si02 from 52 to 61 wt% and texturally hybridized rocks
with Si02 from 57 to 70 wt%.
The plutonic suite is
further characterized by high concentrations of Sr (up to
2400 ppm) and Ba (up to 5100 ppm).
The oxygen isotope characteristics of the pluton are
homogeneous (6^^0 from +6.8 to +7.2 for a range of wholerock
compositions), and its initial Sr ratios are
somewhat heterogeneous within limits of about 0.7057 to
0.7071. The various textural types of QMZ and the mafic
intrusive units share similar ranges of Rb-Sr and oxygen
144

145
isotope values.
The isotopic values are compatible with
a source region that included a mantle-derived component
modified by a crustal component.
Relatively low concentrations
of Rb in comparison to Sr and Ba suggest that
the protolith may have experienced a prior episode of
melting that nevertheless retained plagioclase and
K-feldspar.
Petrographic and chemical data indicate that crystal
accumulation processes associated with flow separation
during magma ascent can best account for many of the
observed textures and differentiated rock types in the
Bodoco pluton.
Limited magma mixing may have been
responsible for low-silica samples of megacrystic QMZ
from the central part of the reversely zoned pluton, and
magma mixing appears to have been important in the origin
of texturally hybridized rocks in the upper portion of
the pluton.
Suggested Further Research
A major conclusion of this study has been the
importance of shearing in the evolution of the Bodoco
pluton.
Deep, shear-related extensional fractures
associated with regional deformation were probably
critical for magma ascent and provided conduits that
promoted flow separation of porphyritic magma.
Within
the pluton, foliations are preserved that are compatible

146
with emplacement in a shear-related pull-apart.
The
relationship between the mafic intrusives and the
foliated megacrystic QMZ indicates that shearing and
dynamic crystallization locally were important in
generating the textures and rock types preserved in the
pluton.
Shearing may also have played an important role
in mixing felsic and mafic melts to produce the rocks in
the structurally high hybrid region.
A detailed study of
structural features in the pluton and in adjacent country
rocks would be useful to develop a more complete picture
of the stress regime in which the pluton was intruded and
to determine whether this style of intrusion is generally
characteristic of the Itaporanga-type plutons.
In this study, detailed Rb-Sr isochrons based on 22
whole-rock samples and on mineral separates provided an
estimated age of emplacement of 555 ± 8 Ma for the Bodoco
pluton.
The relative error associated with this age is
small compared to the results of Rb-Sr geochronology for
a number of other Itaporanga-type granitoids, and it
implies that Rb-Sr geochronology is likely to produce
misleading results for these granitoids if isochrons are
based on limited sample sets.
In spite of this
difficulty, most published ages of plutons in northeastern
Brazil are based on such limited Rb-Sr data.
A
critical next step for geochronologic studies in

147
northeastern Brazil would be to assess the reliability of
published Rb-Sr and K-Ar ages by using Sm-Nd dating or
U-Th-Pb dating of zircon separates to obtain an independent
age for the Bodoc6 pluton or for another previously
dated Itaporanga-type body.
The homogeneity of oxygen isotope values and the
relatively small variation in initial Sr ratios suggest
that the three textural types of QMZ were oogenetic, with
a source that included mantle and crustal contributions.
Despite comparable ranges of isotopic values for mafic
enclave and mafic intrusive samples, however, fewer
conclusions can be permitted about the origin of the
mafic rocks.
The small size of mafic enclaves and the
three-dimensional geometry of the mafic dikes suggest
that most mafic samples have undergone isotopic reequilibration
with their hosts.
This is unfortunate
because it lessens the reliability of mafic samples used
as hypothetical endmembers for models of fractional
crystallization or magma mixing.
Other types of isotopic
data less susceptible to re-equilibration, including
^^•^Nd/^^^Nd
studies, might characterize the source
region(s) for the mafic samples more explicitly.

REFERENCES
Almeida, F.F.M., 1971. Review on granitic rocks of
northeast South America. lUGS, Committee for the
Study of Geologic Documentation, 41 p.
Almeida, F.F.M., Hasui, Y., Brito Neves, B.B., and Fuck,
R.A., 1981. Brazilian structural provinces: an
introduction. Earth-Science Reviews, r7: 1-29.
Arakawa, Y., 1990. Relationship between shear zones and
Sr isotope compositions of granitic rocks in the
Hida belt, Japan. Jour. Geology, 98:81-90.
Arth, J.G-, 1976. Behavior of trace elements during
magmatic processes—a summary of theoretical models
and their applications. U.S. Geological Survey
Jour. Research, 4.:41-47.
Arzi, A.A., 1976. Critical phenomena in the rheology of
partially melted rocks. Tectonophysics, 44;173-184.
Bacon, C.R., 1986. Magmatic inclusions in silicic and
intermediate volcanic rocks. Jour. Geophysical
Research, 91:6091-6112.
Baker, D.R., 1989. Tracer versus trace element
diffusion: diffusional decoupling of Sr
concentration from Sr isotope composition.
Geochimica et Cosmochimica Acta, S3:3015-3023.
Barker, D.S., 1983. Igneous rocks. Englewood Cliffs,
NJ: Prentice-Hall.
Barnes, C.G., 1983. Petrology and upward zonation of the
Wooley Creek batholith, Klamath Mountains,
California. Jour. Petrology, 24:495-537.
Barth, T.F.W., 1959. Principles of classification and
norm calculations of metamorphic rocks. Jour.
Geology, 67:135-152.
Bateman, P.C., and Chappell, B.W., 1977.
Crystallization, fractionation, and solidification
of the Tuolemne Intrusive Series, Yosemite National
Park, Calif. Geological Society of America
Bulletin, 20:465-482.
148

Bateman, R., 1984. On the role of diapirism in the
segregation, ascent and final emplacement of
granitoid magmas. Tectonophysics, 110:211-231.
Bateman, R., 1985. Aureole deformation by flattening
around a diapir during in situ ballooning: the
Cannibal Creek granite. Jour. Geology, 93:293-310.
Bateman, R., 1989. Cannibal Creek granite: posttectonic
"ballooning" pluton or pre-tectonic
piercement diapir?: a discussion. Jour. Geology,
27:766-768.
149
Bence, A.E., and Albee, A.L., 1968. Empirical correction
factors for the electron microanalysis of silicates
and oxides. Jour. Geology, 76:382-403.
Blumenfeld, P., and Bouchez, J., 1988. Shear criteria in
granite and migmatite deformed in the magmatic and
solid states. Jour. Structural Geology, 10:361-372.
Brito Neves, B.B., Vandoros, P., Pessoa, D.A.R., and
Cordani, U.G-, 1974. Revaliacao dos dados
geocronologicos do Precambriano do nordeste
brasileiro. Anais, 28 Congresso, ^:261-271.
Brito Neves, B.B., and Pessoa, J.R., 1974. Consideracoes
sobre as rochas graniticas do nordeste oriental:
Anais, 28 Congresso, j4:261-271.
Cantagrel, J.M., Didier, J., and Gourgaud, A., 1984.
Magma mixing: origin of intermediate rocks and
"enclaves" from volcanism to plutonism. Physics of
Earth and Planetary Interiors, 35:63-76.
Castro, A., 1987. On granitoid emplacement and related
structures: A review. Geologische Rundschau,
26:101-124.
Chappell, B.W., 1978. Granitoids from the Moonbi
District, New England Batholith, eastern Australia.
Jour. Geological Society of Australia, 25:267-283.
Chappell, B.W., and White, A.J.R., 1974. Two contrasting
granite types. Pacific Geology, 2:173-174.
Chappell, B.W., White, A.J.R., and Wyborn, D., 1987. The
importance of residual source material (restite) in
granite petrogenesis. Jour. Petrology, 28:1111-
1138.

Clemens, J.D., and Wall, V.J., 1981. Origin and
crystallization of some peraluminous (S-type)
granitic magmas. Canadian Mineralogist, 19:111-131.
Cox, K.G., Bell, J.D., and Pankhurst, R.J., 1979. The
interpretation of igneous rocks. London: Allen &
Unwin.
Dallmeyer, R.D., Sial, A.N., Long, L.E., and McMurry, J.,
1987. New evidence for polyphase tectonothermal
evolution of the Brasiliano orogen, northeastern
Brazil. Geological Society of America Abstracts
with Programs, 19(7) :634.
Dantas, J.R.A., 1974. Carta geol6gica do Brasil ao
milion^simo, Jaguaribe Sheet (SB-24). Minist^rio
das Minas e Energia, Depto. Nacional de Produgao
Mineral do Brasil.
Didier, J., 1973. Granites and their enclaves: the
bearing of enclaves on the origin of granites, J.T.
Renouf, trans. New York: Elsevier.
Dorais, M.J., Whitney, J.A., and Roden, M.F., 1990,
Origin of mafic enclaves in the Dinkey Creek pluton,
central Sierra Nevada batholith, California. Jour.
Petrology, 31:853-881.
Eberz, G.W., and Nicholls, I.A., 1990. Chemical
modification of enclave magma by post-emplacement
crystal fractionation, diffusion, and metasomatism.
Contrib. Mineral. Petrol., 104:47-55.
Eichelberger, J.C., 1980. Vesiculation of mafic magma
during replenishment of silicic magma reservoirs.
Nature, 288:446-450.
Eggler, D.H., 1972. Water-saturated and undersaturated
melting relations in a Paricutin andesite and an
estimate of water content in the natural magma.
Contrib. Mineral. Petrol., 34:261-171.
Faure, G., 1986. Principles of isotope geology (2nd
ed.). New York: Wiley & Sons.
Faure, G., and Powell, J.L., 1972. Strontium isotope
geology. New York: Springer-Verlag.
150

Fenn, P.M., 1977. The nucleation and growth of alkali
feldspars from hydrous melts. Canadian
Mineralogist, 15:135-161.
151
Ferreira, V.P., and Sial, A.N., 1987. Ultra-potassic
peralkaline province of the Precambrian Cachoeira-
Salgueiro fold-belt, northeast Brazil.
International Symposium on Granites and Associated
Mineralizations (Salvador, Brazil), Extended
Abstracts:199-204.
Frost, T.P., and Mahood, G.A., 1987. Field, chemical,
and physical constraints on mafic-felsic magma
interaction in the Lamarck granodiorite. Sierra
Nevada, California. Geological Society of America
Bulletin, 22^272-291.
Gorini, M.A., and Bryan, G.M., 1976. The tectonic fabric
of the equatorial Atlantic and adjoining continental
margins: Gulf of Guinea to northeastern Brazil.
Annais Acad. Bras. Cien., 48:101-119.
Guineberteau, B., Bouchez, J., and Vigneresse, J., 1987.
The Mortagne granite pluton (France) emplaced by
pullapart along a shear zone: structural and
gravimetric arguments and regional implication.
Geological Society of America Bulletin, 99:763-770.
Hackspacher, P.C., Macambira, M., McReath, I, and
Scheller, T., 1987. Tectono-magmatic evolution of
the Taipu-Cardoso polydiapiric granitoid bodies, Rio
Grande do Norte, Brazil. International Symposium on
Granites and Associated Mineralizations (Salvador,
Brazil), Extended Abstracts:91-95.
Hammarstrom, J., 1984. Microprobe analyses of
hornblendes from 5 calc-alkalic intrusive complexes,
with data tables for other calcic amphiboles and
BASIC computer programs for data manipulation. U.S.
Geological Survey Open-File Report 84-652.
Hammarstrom, J.M., and Zen, E., 1986. Aluminum in
hornblende: An empirical igneous geobarometer.
American Mineralogist, 71:1297-1313.
Hanson, G.N., 1978. The application of trace elements to
the petrogenesis of igneous rocks of granitic
composition. Earth and Planetary Science Letters,
38:26-43.

Haskin, L.A., 1979.
igneous rocks.
11:175-189.
On rare-earth element behavior in
Physics and Chemistry of the Earth,
152
Hibbard, M.J., 1981. The magma mixing origin of mantled
feldspars. Contrib. Mineral. Petrol., 76:158-170.
Hibbard, M.J., 1987. Deformation of incompletely
crystallized magma systems: granitic gneisses and
their tectonic implications. Jour. Geology, 95:543-
561. —
Hildreth, W., 1981. Gradients in silicic magma chambers;
implications for lithospheric magmatism. Jour.
Geophysical Research, 86:10153-10192.
Hill, M., O'Neil, J., and Frey, F., 1984. Sr and 0
isotopic heterogeneity in the zoned Eagle Peak
pluton. Sierra Nevada, California. Geological
Society of America Abstracts with Programs, 16:289.
Hine, R., Williams, I.S., Chappell, B.W., and White,
A.J.R., 1978. Contrasts between I- and S-type
granitoids of the Kosciusko batholith. Jour.
Geological Society of Australia, 25:219-234.
Hollister, L.S., Grissom, G.C., Peters, E.K., Stowell,
H.H., and Sisson, V.B., 1987. Confirmation of the
empirical correlation of Al in hornblende with
pressure of solidification of calc-alkaline plutons.
American Mineralogist, 72:231-239.
Huppert, H.E., and Sparks, R.S.J., 1988. The generation
of granitic magmas by intrusion of basalt into
continental crust. Jour. Petrology, 29:599-624.
Hurley, P.M., Almeida, F.F.M., Melcher, G.C., Cordani,
U.G., Rand, J.R., Kawashita, K., Vandoros, P.,
Pinson, W.H., Jr., and Fairbairn, H.W., 1967. Test
of continental drift by comparison of radiometric
ages. Science, 157:495-500.
Hyndman, D.W., and Foster, D.A., 1988. The role of
tonalites and mafic dikes in the generation of the
Idaho batholith. Jour. Geology, 96:31-46.
lUGS (International Union of Geological Sciences)
Subcommission on the Systematics of Igneous Rocks,
1973. Plutonic rocks, classification and
nomenclature. Geotimes, 18:26-30.

153
Jardim de S^, E.F., Macedo, M.H.F., Legrand, J.M.,
McReath, I., Galindo, A.C., and S^, J.M., 1987.
Proterozoic granitoids in a polycyclic setting: the
Serido region, NE Brazil. International Symposium
on Granites and Associated Mineralizations
(Salvador, Brazil), Extended Abstracts:103-110.
Kawachi, Y., and Sato, 1978. Orthoclase megacrysts in
the Yakushima granite, southern Kyushu, Japan. N.
Jb. Miner. Abh. 132:136-152.
Komar, P.D., 1976. Phenocryst interactions and the
velocity profile of magma flowing through dikes or
sills. Geological Society of America Bulletin,
22:1336-1342.
Leake, B.E., 1978. Nomenclature of amphiboles. Canadian
Mineralogist, 16:501-520.
LeMaitre, R.W., 1976. The chemical variability of some
common igneous rocks. Jour. Petrology, 17:589-637.
Lindsley, D.H., 1983. Pyroxene thermometry. American
Mineralogist, 18:477-493.
Long, L.E., and Brito Neves, B.B., 1977. Geochronology
of Preccunbrian basement, northeastern Brazil. Geol.
Society of America, Abstracts with Programs, 2*1074.
Mahood, G., and Hildreth, W., 1983. Large partition
coefficients for trace elements in high-silica
rhyolites. Geochimica et Cosmochimica Acta, 47:11-
30.
Mason, G.H., 1985. The mineralogy and textures of the
Coastal batholith, Peru. In W.S. Pitcher and
others, Eds., Magmatism at a plage edge, the
Peruvian Andes. New York: Wiley, pp. 156-166.
McMurry, J., Long, L.E., and Sial, A.N., 1987. Petrology
and isotope systematics of magma/crystal mushes:
some porphyritic granitoids of northeastern Brazil.
Revista Brasileira de Geociencias, 17:473-480.
Mehnert, K.R., and Busch, W., 1981. The Ba content of K-
feldspar megacrysts in granites: a criterion for
their formation. Neues Jahrbuch fur Mineralogie
Abhandlungen, 140:221-252.

Michael, P.J., 1984. Chemical differentiation of the
Cordillera Paine granite (southern Chile) by in situ
fractional crystallization. Contrib. Mineral":
Petrol., 27:179-195.
Miyashiro, A., 1973. Metamorphism and metamorphic belts.
London: Allen & U n w i n . "
Nabelek, P.I., Papike, J.J., and Laul, J.C, 1986. The
Notch Peak granitic stock, Utah: origin of reverse
zoning and petrogenesis. Jour. Petrology, 27:1035-
Niggli, P., 1931. Die quantitative mineralogische
klassifikation der eruptivgesteine. Schweiz. Miner.
Petrogrpah. Mitt., 11:296-364.
Nironen, M., and Bateman, R., 1989. Petrogenesis and
syntectonic emplacement in the early Proterozoic of
south-central Finland: a reversely zoned dioritegranodiorite
and a granite. Geologische Rundschau,
28:617-631.
Noyes, H.J., Wones, D.R., and Frey, F.A., 1983. A tale
of two plutons: petrographic and mineralogie
constraints on the petrogenesis of the Red Lake and
Eagle Peak plutons, central Sierra Nevada,
California. Jour. Geology, 91:353-379.
O'Neil, J.R., and Chappell, B.W., 1977. Oxygen and
hydrogen isotope relations in the Berridale
batholith, southeastern Australia. Jour. Geological
Society of London, 133:554-571.
O'Neil, J.R., Shaw, S.E., and Flood, R.H., 1977. Oxygen
and hydrogen isotope compositions as indicators of
granite genesis in the New England batholith,
Australia. Contrib. Mineral. Petrol., 62:313-328.
Peacock, M.A., 1931. Classification of igneous rock
series. Jour. Geology, 39:54-67.
Pimentel, M.M., and Fuck, R.A., 1987. Late Proterozoic
granitic magmatism in southwestern Goi^s, Brazil.
International Symposium on Granites and Associated
Mineralizations (Salvador, Brazil), Extended
Abstracts:97-102.
154

Pitcher, W.S., 1979. The nature, ascent and emplacement
of granitic magmas. Jour. Geological Society of
London, 136:627-662.
155
Pitcher, W.S., 1982. Granite type and tectonic
environment, in Hsu, K.J., ed.. Mountain Building
Processes. New York:Academic Press, p. 19-40.
Ragland, P.C, and Butler, J.R., 1972. Crystallization
of the West Farrington pluton. North Carolina,
U.S.A. Jour. Petrol., 13:381-404.
Ramsey, J.G., 1982. Rock ductility and its influence on
the development of tectonic structures in mountain
belts. In Hsu, K.J., ed.. Mountain Building
Processes. New York:Academic Press, p. 111-127.
Reid, J.B.,Jr., and Hamilton, M.A., 1987. Origin of
Sierra Nevadan granite: evidence from small scale
composite dikes. Contrib. Mineral. Petrol. 96:441-
454.
Reid, J.B.,Jr., Evans, O.C., and Fates, D.G., 1983.
Magma mixing in grantic rocks of the central Sierra
Nevada, California. Earth and Planetary Science
Letters, 66:243-261.
Schmidt-Thom6, S., and Weber-Diefenbach, K., 1987.
Evidence for "frozen" magma mixing in Brasiliano
calc-alkaline intrusions: the Santa Angelica
pluton, southern Espirito Santo, Brazil.
International Symposium on Granites and Associated
Mineralizations (Salvador, Brazil), Extended
Abstracts:193-198.
Shand, S.J., 1951. The study of rocks. London: Thomas
Murby & Co.
Sial, A.N., 1987. Granitic rocks of northeast Brazil.
International Symposium on Granites and Associated
Mineralizations (Salvador, Brazil), Extended
Abstracts:61-69.
Sial, A.N., and Long, L.E., 1978. Rb-Sr and oxygen
isotope study of the Meruoca and Moccunbo granites,
northeastern Brazil. Short papers. Fourth Int.
Conf. Geochr. Cosmochr., Isotope Geol., U.S.
Geological Survey Open-File Report 78-701:398-400.

Sial, A.N., Ferreira, V.P., and Mariano, G., 1987.
Proterozoic granitoids, western Pernambuco and
Paraiba states, northeast Brazil. International
Symposium on Granites and Associated Mineralizations
(Salvador, Brazil), Excursion Guides: 9-29.
Sial, A.N., Figueiredo, M.C.H., and Long, L.E., 1981.
Rare-earth elements geochemistry of the Meruoca and
Mocambo plutons, Ceara, northeast Brazil. Chemical
Geology, 11:271-283.
Sial, A.N., Mariano, G., McMurry, J., and Long, L.E.,
1989. Isotopic variation among Late Proterozoic-
Cambrian, potassic calcalkaline, coarsely
porphyritic granitoids of northeast Brazil. 28th
International Geological Congress (Washington,
D.C), Abstracts, 2:105-106.
Sial, A.N., Ferreira, V.P., Whitney, J.A., Wenner, D.B.,
Sasaki, A., and Long, L.E., 1989. LILE 180- and
34S-enriched mantle beneath northeast Brazil:
evidences from shoshonitic to ultrapotassic plutonic
rocks. 28th International Geological Congress
(Washington, D-C), Abstracts, 2*106-107.
Speer, J.A., 1987. Evolution of magmatic AFM mineral
assemblages in granitoid rocks: The hornblende +
melt = biotite reaction in the Liberty Hill pluton,
South Carolina. American Mineralogist, 72:863-878.
Speer, J.A., Naeem, A., and Almohandis, A.A., 1989.
Small-scale variations and subtle zoning in
granitoid plutons: the Liberty Hill pluton. South
Carolina, U.S.A. Chemical Geology, 75:153-181.
Streckeisen, A.L., 1967. Classification and nomenclature
of igneous rocks (final report of an enquiry).
Neues Jahrbuch fur Mineralogie Abhandlungen,
107:144-240.
Streckeisen, A., and LeMaitre, R.W., 1979. A chemical
approximation to the modal QAPF classification of
the igneous rocks. Neues Jahrbuch fur Mineralogie
Abhandlungen, 136:169-206.
Stormer, J.C,Jr., 1975. A practical two-feldspar
geothermometer. American Mineralogist, 62^667-674.
156

Swanson, S.E., 1977. Relation of nucleation and crystalgrowth
rate to the development of granitic textures.
American Mineralogist, 62:966-978.
Taylor, H.P.,Jr., 1980. The effects of assimilation of
country rocks by magmas on 180/160 and 87Sr/86Sr
systematics in igneous rocks. Earth and Planetary
Science Letters, 47:243-254.
Treuil, M., 1973. Criteres petrologiques, geochimiques
et structuraux de la genese et de la differenciation
des magmas basaltiques: examples de I'Afar. Ph.D.
thesis, Orleans.
Torquato, J.R., and Cordani, U.G., 1981. Brazil-Africa
geological links. Earth-Science Reviews, 17:155-
176.
Van der Molen, I., and Paterson, M.S., 1979.
Experimental deformation of partially-melted
granite. Contrib. Mineral. Petrol., 70:299-318.
Vernon, R.H., 1983. Restite, xenoliths, and
microgranitoid enclaves in granites. Jour, of the
Proceedings of the Royal Society of New South Wales,
116:77-103.
Vernon, R.H., 1986. K-felspar megacrysts in granites —
phenocrysts, not porphyroblasts. Earth-Science
Reviews, 23;1-63.
Vidal, P., 1987. Use and misuse of radiogenic isotopes
in granite petrology. International Symposium on
Granites and Associated Mineralizations (Salvador,
Brazil), Extended Abstracts:149-151.
Wall, V.J., Clemens, J.D., and Clarke, D.B., 1987.
Models for granitoid evolution and source
compositions. Jour. Geology, 95:731-749.
Watson, E.B., and Jurewicz, S.R., 1984. Behavior of
alkalies during diffusive interaction of granitic
xenoliths with basaltic magma. Jour. Geology,
92:121-131.
Wernick, E., 1981. The Archaean of Brazil. Earth-
Science Reviews, 17:31-48.
157

Whalen, J.B., and Currie, K.L., 1984. The Topsails
igneous terrane. Western Newfoundland: evidence for
magma mixing. Contrib. Mineral. Petrol., 87:319-
327. —
White, A.J.R., 1979. Source rocks of granitic magmas.
Geological Society of America Abstracts with
Programs, 11:539.
White, A.J.R., and Chappell, B.W., 1977.
Ultrametamorphism and granitoid genesis.
Tectonophysics, 43:7-22.
Whitney, J.A., and Stormer, J.C,Jr., 1976.
Geothermometry and geobarometry in epizonal granitic
intrusions: a comparison of iron-titanium oxides
and coexisting feldspars. American Mineralogist,
21:751-761.
Whitney, J.A., and Stormer, J.C,Jr., 1977. The
distribution of NaAlSi308 between coexisting
microcline and plagioclase and its effect on
geothermometric calculations. American
Mineralogist, 62:687-691.
Wickham, S.M., 1987. The segregation and emplacement of
granitic magmas. Jour. Geological Society of
London, 144:281-297.
Wiedemann, CM., Weber-Diefenbach, K., and Lammerer, B.,
1987. Zoned diapirs within the Late Precambrian
Ribeira belt. International Symposium on Granites
and Associated Mineralizations, Extended Abstracts,
p. 47-50.
Williams, H., Turner, F.J., and Gilbert, CM., 1954.
Petrography: An Introduction to the Study of Rocks
in Thin Sections. San Francisco: W.H.Freeman.
Winkler, H.G.F., and Schultes, H., 1982. On the problem
of alkali feldspar phenocrysts in granitic rocks.
Neues Jahrbuch fur Mineralogie, Montash., 12:558-
564.
Wones, D.R., 1989. Significance of the assemblage
titanite + magnetite + quartz in granitic rocks.
American Mineralogist, 74:744-749.
Wyllie, P.J./ 1977. Crustal anatexis: an experimental
review. Tectonophysics, 43:41-71.
158

APPENDIX A:
FIGURES
159

160
Borborema
structural
province
Wk =
'JZ&
rr"
• =
cratonic regions which stabilized more than
1700 million years ago
fold belts produced between I700 and 500
million years ago
undeformed Phanerozoic sedimentary basins
and continental margins
study area
Figure 1. Major tectonic provinces of Brazil (after
Almeida and others, 1981). The location of study area
within the Borborema tectonic province is indicated by
a star on the map.

161
2QQ
« ' KM
EXPLANATION
rn = massifs of older basement, reworked during
the Proterozoic.
= Brasiliano metasedimentary fold belts
= sedimentary cover
:*.] = adjacent tectonic provinces
* = study area
= major strike-slip faults
Figure 2. Borborema tectonic province, northeastern
Brazil (after Almeida and others, 1981).

162
Geology of Central NE Brazil
37^W
Symbols
-k
Cretaceous sedimentary cover
Peralkalic intrusions
Itaporanga-type intrusions
Other Brasiliano-age intrusions
Proterozoic metamorphic rocks
Basement rocks
Bodoc5
\^ Faults and/or major lineaments
Towns mentioned in text
Figure 3. Geological sketch of the Cachoeirinha-
^salgueiro fold belt, northeastern Brazil (after Sial
and others, 1987). The fold belt is bounded on the
north by the Patos Lineament and on the south by the
pernambuco Lineament. The shaded rectangle in the
inset map represents the location of the map area.

163
Topography and Landforms
Contour Interval: 200 m
y Intermittent Stream
• Town
Paved Road
Figure 4. Generalized topography and landforms of the
Bodoc6 pluton. Although the 600-m and 800-m contour
intervals are shown, most of the pluton is at
elevations less than 600 m but more than 400 m.

164
Geologic Map
N
Bodoco Pluton:
Informal Rock Units
|'*'j,'*|*inegacrystic' qtz. monzonite (QMZ)
^yy^
f^^
'pbenocrystic" QMZ
"plumose" QMZ
,^-jl5 defonned megacrystic QMZ and
"mafic intrusive sheets"
Titi intermingled phenocrv-stic QMZ
and plumose QMZ
bybnd" textures
« & X
X (
Country Flocks:
Cretaceous sedimentary rocks
(Aranpe Group)
[•"^rCJ Proterozoic gneiss
(Uaua Group)
[ I Proterozoic schist
ry^'A
(Salgueiro Group)
weathered pink granite
(unknown age)
Figure 5. Generalized geologic map of the Bodoc6 pluton
and vicinity. The informal rock units within the
Bodoc6 pluton are based principally on textures (see
text for further description).

165
Figure 6. Typical "mixed" texture of an outcrop from the
zone of hybrid rocks. Note the swirled mafic and
felsic portions of the rock and the sparse but large
K-feldspar megacrysts. Field of view: appx. 75 cm.

166
Figure 7. Typical outcrop texture of megacrystic QMZ.
Megacrysts of K-feldspar stand out in relief on
weathered surfaces. Concentric zoning is visible in
some of the megacrysts, accented by uneven weathering
of albitic exsolution rings and oriented shells of
plagioclase inclusions. Field of view: appx. 22 cm.

Sample Location Map
167
Bodoco Pluton:
"megacrystic* qtz. monzonite (QMZ)
"phenocrystic" QMZ
'plumose" QMZ
I Def I deformed megacrystic QMZ and
'mafic intrusive sheets"
I p-?i intermingled phenocrv-stic QMZ
and plumose QMZ
Hvb ! "bvbnd" textures
Country Rocks:
Cretaceous sedimentary rocks
(Aranpe Group)
pC Proterozoic gneiss
(Uaua Group)
pCjJ Proterozoic schist
(Salgueiro Group)
}r I "*eathcred pmk granite
H-
(unknown age)
Figure 8. Sample location map. Numbers on map correspond
to sample numbers in text (e.g., "28-A").

168
Modal Classification of Samples
GD
APQS
QS
Qieo
QD
AfS
»
ICO
Abbreviations
Granodiorite
Alkali Feldspar Qtz. Syenite
Qtz, Syenite
Qtz, Monzonite
Qtz. Monzodiorite
Qtz. Diorite
Alkali Feldspar Syenite
Monzonite
Monzodiorite
Symbols
• Phenocrystic QUE
A Plumose QIC
• Mafic Enclave
A Mafic Intrusive
O Aplite
Figure 9. lUGS rock classification using modal data.
Samples of "igneous country rock" refer to small
exposures adjacent to the pluton margin.

169
o
Chemical Approximation to Modal Classen
50T-
Abbreviations
Alkali Fspar Granite
Alkali Fspar Qtz Syenite
Alkali Fspar Syenite
Quartz Syenite
Syenite
Quartz Monzonite
Monzonite
Quartz Monzodiorite
Monzodiorite
20 30 40 50 60 80 90 100
ANOR
Symbols
megacrystic QMZ
phenocrystic QMZ
plumose QMZ
mafic enclave
•
X
O
0
mafic intrusive
hybnd
aplite
ign. country rock
Fiqure 10. Chemical Q'/ANOR rock classification
(Streckeisen and LeMaitre, 1979) based on mesonorm
calculations. Abbreviations:
Q' = normative g/(3+or+ab+an+);
ANOR = an/(an + or).

170
Chemical (Mesonorm) Classification of Samples
* ^•K.f
GD
APQS
QS
Qte
QMD
QD
AFS
IC
ICD
Abbreviations
Granodiorite
Alkali Feldspar Qtz Syenite
Quartz Syenite
Quartz Monzonite
Quartz Monzodiorite
Quartz Diorite
Alkali Feldspar Syenite
Monzonite
Monzodiorite
SyTBt)Ol8
a Megacrystic QIC
• Phenocrystic QIC
A Plumose QIC
• Mafic enclave
* Mafic Intrusive
O Aplite
"Q" = mesonormative q/(q + or + ab + an)
"A" = mesonormative or/(q + or + ab + an)
"P" = mesonormative (an + ab)y(q + or + ab + an)
^proportion of ab in "P" adjusted
slightly to compensate for ab^in
K-feldspar; see text for details
Figure U. lUGS-type rock classification based on
mesonorm calculations.

171
Classification of Samples from Hybnd Region
GD
AFQS
QS
QMZ
QMD
QD
APS
MZ
ICD
Abbreviations
Granodiorite
Alkali Feldspar Qtz.Syenite
Quartz Syenite
Quartz Monzonite
Quartz Monzodiorite
Quartz Diorite
Alkali Feldspar Syenite
Monzonite
Monzodiorite
TEXTURAL TYPES OF HYBRID
a megacrystic felsic
• porphyritic ("phenocrystic
V equigranular felsic
O aplitic
A equigranular mafic
•^f hybridized on scale of cms.
Fiaure 12. lUGS rock classifications for samples from
^the like of texturally hybrid rocks. Dotted line
outlines field of most of the other felsic samples in
?he pluton Dashed line outlines field of most of the
^fiI intrusive (sheets and dikes samples. The two
^nfiyses of hybrid sample 61-A indicated in the figure
represent different portions of the same hand sample.

172
Informal Rock Umt3
Boioco Plutoa:
*xnegacry»6c" qtt. monzonite (QMZ)
\ft\»\ "pbenocrystic"QMZ
[piu[ "plumote"QMZ
[ptf I defonaed OMpciyvtic QMZ aod
"aufic iatru*ive >beet«*
|p-p| intenningied pbenocryibcQMZ
tod pluffiote QMZ
iKyb I 'hybrid* texture*
Country Rocks:
paTj Cretaceouf sedimentary rock»
(Araripe Group)
u»| Proterozoic gtieiM
(Uauj Group)
ic{ Proterozoic tcfaict
(Salgueiro Group)
I Or I *eathcred pink grinjte
(unknown «ge)
Figure 13. Orientation of structural features. Most
measurements within the pluton are from mafic enclaves
and in country rock are from schistose foliation.

173
Figure 14. Concentric shells in a large K-feldspar
crystal, a) zonally arranged "exsolution rings" in a
K-feldspar from sample 25-A. Field of view: 5 mm;
cross-polarized light, b) Enlarged view of same
crystal, showing that the "rings" are formed by small
inclusions and by stubby blebs of perthitic lamellae
that are oriented parallel to the perthite in the rest
of the phenocryst. Field of view: 2 mm; planepolarized
light.

174
Plagioclase Compositions
Bodoco Pluton
Megacrystic QMZ
^
G
: Phenocrystic QMZ
P Mafic Intrusive
L

1.00
Calcic Amphiboles:
Case A: (Na+K)A < 0.50; Ti < 0.50
175
+
00
0.00+
6.50
Case B: (Na+K)A >= 0.50; Ti < 0.50; Fe3+ > Al-vi
I.OOi
+
DM
00
00
2
0.004
aso
a MegaxticQMZ + Phenoxtic QMZ * Plumose QMZ
• M.Enclave A M. intnjsive ^ igp. Wall Fix
Figure 16. Classification of calcic amphiboles (after
Leake, 1978). Calcic amphiboles have (Ca + Na)g >
1.34 and Na^ < 0.67. Samples represented by stars in
the figure nave Fe recalculated on the basis of
analyzed FeO and Fe203.

176
eastonite
Mg^Ali^Si^02o(OH)i^
3
siderophyilite
Fe3Ali^Si302o(OH)^
Megaxt QMZ
Phenoxt QMZ
M. Enclave
X
Hybrid
Aplite
Schist
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
phlogopite -» -• X annite
K2Mg6Al2Si602o(OH)i* Fe/(Fe + Mg) ^2^^ S^h^^^ZO^^^K
Fiaure 17. Biotite compositions projected onto
phlogopite-annite-eastonite-siderophyllite field.
Refer to text for discussion of labeled samples.

177
Pyroxene Analyses
CaSiO
Diopside
Hedenbergite
MgSiOj
FeSiO,
Samples Analyzed
• 17-B (alk.fsp.syenite dike)
A 20-A (syenite dike)
• 21-B (mafic intrusive sheet)
• 37-A (QMZ country rock)
O 37-A w/ Fe-^ measured chemically
Figure 18. Clinopyroxene compositions in the pyroxene
quadrilateral.

178
Amphibole Geobarometry
P = -4.76 + 5.64* (Al-total)
1
I
r
4-
I !
Megaxt QMZ
Phenoxt QMZ
a.
m
Plumose QMZ
M.Enclave
] M.Intrusive
Al-total
Figure 19. Pressure estimates using amphibole
geobarometry (based on algorithm of Hollister and
others, 1987). Estimates for mafic enclaves and mafic
intrusives should not be considered reliable because
the hornblende crystals that they contain probably
were not in equilibrium with quartz.

179
Ranee of Si02 Values
Megacrystic QMZ
s
o
o
J
^
Phenocrystic QMZ
Plumose QMZ
Mafic Intrusive
Mafic Enclave
L Hybrid
Aplite
50 55 60 65 70 75 80
Si02 (wt.%)
Figure 20.
pluton.
Histogram of Si02 values for the Bodoc6

180
Peacock's Alkali-Lime Index
o
Si02
Fiaure 21. Alkali-Lime Index (Peacock, 1931) as applied
to the Bodoc6 plutonic suite. The extrapolated trend
for CaO intersects the trend for (Na^O + K2O) at ^
approximately 50 wt.% SiOj, classifying the Bodoco
pluton as an alkalic suite.

181
o
10
Si02 (wt.%)
8
- ^ =
• «c
+ A + A. °
I
O
2-
•o «°^«° % .
)«(
O
-1—I—I—I—I—I—I—I—I—I—I I r
'50 55 60 65
op
o
o o o
T 1—1 1 1 1 1 1 1 1 1 1—I 1 r
Si02 (wt.%)
o
70 75 80
Symbols
• megacrystic OMZ • mafic intrusive
•¥ phenocrystic QMZ X hybnd
M plumose OMZ O aplite
• mafic enclave O ign- country rock
Figure 22. Silica variation diagrams with AI2O3 and
FeoOo (tot): a) AI2O3 vs. Si02;
b) FIOO. (tot) vs. Si62. Fe203 (tot) = Fe203 plus FeO
reported as Fe203.

182
a.
not shown:
enclave 9-C (14 1 % MgO)
o
2
40^
3.0
2.0
1.0-i
50-A
A^
a.Ch
7.0-
6.0
5.0
%^-
# D
0.0 -T 1 1 1 1 r-
50 55 60 65
o
H2-A
n
O
D
CD
•
X 61-e
0-17-B °< o o o o
Si02 (wt.%)
a
- I — I — T — I — t — 1 — I — r — 1 — I — J "
70 75 80
^
U
Si02 (wt.%)
Symbols 1
D megacrystic OMZ
+ phenocrystic QMZ
m plumose QMZ
• mafic enclave
• mafic intrusive
X hybnd
O aplite
O Ign. country rock
Figure 23. Silica variation diagrams with MgO and CaO:
a) MgO vs. Si02; b) CaO vs. Si02.

183
a.
9.0
^
o
12-A
t:" :>^^
CO B
.21-B
O20-A
O O O
a o w o
9-C
017-B
^-^
^
wt.
^—^
o
00
50
"T I I I 1 ! 1 1 1 r 1 1—1 r 1 \ 1 1 1 \ 1 1 T T 1 1-
55 60 65 70 75 80
8.0-
7.0-
6.0-
5.0-
4.0
3.0-
2.0
1.0-
Si02 (wt.%)
^ to 1 7-B
(13.0wt%K2O)
9.0
8.0-
7.0-
-
6.0-
5.0-
•
4.0-
3.0-
20-
1.0-
0.0
50
Si02 (wt.%)
I Symbols
a megacrystic QMZ
••• phenocrystic QMZ
M plumose QMZ
• mafic enclave
• mafic intrusive
X hybnd
O aplite
O ign. country rock
Figure 24. Silica variation diagrams with Na20 and K2O:
a) Na20 vs. Si02; b) KjO vs. SiOj.

184
Si02 (wt.%)
b. '-'^
3.5
3.0;
^
2.5:
-
20=
O 1.5
,68-A
,^63-a
^ 1.0:
0.5:
H \ .-y
QD
10
• a
22-B • """O OcdS^ ^
0.0
50
^ ^^^*o O o O O i
1 ,—I 1—I 1—I r—1 1—I r — I — 1 — I — 1 1—I 1—' 1 — r ' ^ 1 r"-i ; 1 I
55 60 65 70 75 80
Si02 (wt.%)
Symbols
a megacrystic QMZ
••• phenocrystic QMZ
m plumose QMZ
• mafic enclave
• mafic intrusive
X hybnd
O aplite
O Ign. country rock
Figure 25. Silica variation diagrams with Ti02 and P2O5:
a) TiOj vs. Si02; b) P2O5 vs. Si02.

185
MgO Zoning
(Contour Interval,
3.5 wt.,«)
Figure 26. Si02 and MgO zoning in megacrystic QMZ.
Dotted lines indicate regions of deformed (sheared)
megacrystic QMZ. Dashed lines indicate internal
contacts of other plutonic map units. Solid lines
(within the pluton boundaries) indicate contour
intervals.

186
Sr Zoning
(Contour Interval;
ICOO ppm)
Figure 27. CaO and Sr zoning in megacrystic QMZ. Dotted
lines indicate regions of deformed (sheared)
megacrystic QMZ. Dashed lines indicate internal
contacts of other plutonic map units. Solid lines
(within the pluton boundaries) indicate contour
intervals.

187
350T
T^ 7-B
30a
250^
• 22-B
0^
20a
15a
loo­
^ %
o «
J?
o
o
se
50
"T ' ' I 1 I T 1 r r 1 1 1 1 1 1 1 1 ( 1 1 1 1 1 1 1 1 '
55 60 65 70 75 80
Si02 (wt.%)
b. 2500
* 29-A
2000
24-A
A 12-B
O 37-A
S 1500
a-
a-
C/3
1000-
500-
9-C
^
A
56-C
n
en
• O^
O
o
o
X
O
O
- 1 — I 1—1 1—I 1—I 1—I 1 — r — T 1 1—1 ' I I I I 1—I 1 1 — r -
50 55 60 65 70 75
Si02 (wt.%)
80
Symbols
a megacrystic QMZ
-»• phenocrystic QMZ
M plumose QMZ
• mafic enclave
• mafic intrusive
X hybnd
O aplite
O Ign. country rock
Figure 28. Silica variation diagrams with Rb and Sr:
a) Rb vs. Si02; b) Sr vs. SiOj.

188
7000
6000
^
I
to 20-A O
(14456 ppm Ba)
o 17-B
e
5000-
4000
3000
, m O
12-B
0 37-A
O 74-B
18-B
J;^
from W
margin
2000H
1000
22-B
'56-C
67-A - ° a a ''-^
a • a n
71 -A \, , co_a 68-B Q^
X
from pluton core *-*
O
O
O
O
0
50
"T—I—I—I—r-
55 60
-T 1 1 1 1 1 1 r 1
65 70
Si02 (wt.%)
— I r 1 1 r-
75 80
. 800T
D.
12-A
700:
600:
^ 50o:
a.
a, 4oo^
200
100H
43-BO X 24-C
24-A - ^^ ^ ^ a 4.
22-B-i
:•
- I — I — I — 1 — I — I — I — 1 — 1 — r
'50 55 60
* 71 -A o.
&• -e^-*
a
O^
)P o o
7 T f r T 1 1 1 1
65 70 75
Si02 (wt.%)
1 . I
80
I Symbols n
a megacrystic QMZ
• phenocrystic QMZ
m plumose QMZ
• mafic enclave
• mafic intrusive
X hybrid
O aplite
O Ign. country rock
Figure 29. Silica variation diagrams with Ba and Zr
a) Ba vs. Si02; b) Zr vs. Si02.

189
G
3000
2500
2000
^ 1500
1000-
500-
not shown:
ICR 20-A
(14456 ppm Ba) * 29-A
o
56-Co ^
x^
c7 o o
V
Oi ' r
T
1 o
^€°"
•
a a O
.12-8
4 .
o
0«9-C
1 r 1 r
0 1000 2000 3000 4000 5000 6000 7000
Ba (ppm)
^ym bo Is
megacrystic QMZ
phenocrystic QMZ
plumose QMZ
mafic enclave
mafic intrusive
X
0
0
7
T
hybnd
aplite
ign. country rock
gneiss
schist
Figure 30. Sr and Ba variation in the Bodoc6 pluton and
adjacent country rock.

190
1.4
^
o
1.2-
1.0-
08-
06
0A-\
02
O04
o
68-B
63-B
^50-A
1^ +%
n
• ° a
C?"nPo
a
a
CO *
mtf.
^ 24-C
O 43-B
-I I r—I ^ T T I r 1 I 1 1 1 r—T—T 1 1 \—-r—i 1 1 1—p
100 200 300 400 500
Zr (ppm)
1 Symbols
a megacrystic QMZ
••• phenocrystic QMZ
m plumose QMZ
• mafic enclave
• mafic intrusive
X
0
0
V
T
hybnd
aplite
ign. country rock
gneiss
schist
Figure 31. Zr and P9O5 variation in the Bodoc6 pluton
and adjacent country rock.

191
1000 7
REE Profiles, Bodoco Pluton
CO
c
100:
X
0)
c
o
lOd
o
G
0.1
Analyses within shaded field:
• 5 < ^ — ;>« 1
48-A, 56-A, 63-A, 71-A, 76-A (MEG),
75-A (PLU), 75-B (PHE), 63-B (ENC),
16-B. 48-B (INT). 37-A (ICR)
^
La Ce Pr Nd (Pm) Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
• 8A(APL) -^ 21B (INT) ^ 17A (GNq
• 65C (SCH) X 61F(HYB)
Figure 32. Chondrite-normalized (Haskin, 1979) plots of
rare-earth elements. Most Bodoc6 samples plot in the
shaded field, in contrast to analyzed samples of
country rock (17-A and 65-C) and one aplite (8-A).

192
07260
O7240
07220
0.7200
07180
0-13-C
0-8-A
X-61-F
oo
Ui
GO
48-A I-9-C
63 B /
1-56-C
07160
07140H
07120
07100-
O7080-
O7060
12-B
12-A
07040
1 1 1 1 1 1 1 1 1 1 1 1 1 1 I I I I r -
0 05 1.0 1.5 20
87Rb/86Sr
Symbols
a megacrystic QMZ
• phenocrystic QMZ
M plumose QMZ
• mafic enclave
• mafic intrusive
X hybnd
O aplite
Fiaure 33. Measured ratios of
87Rb/86sr vs. 87sr/«6sr 86
Tot ll. pl^tonlrsulte!" R^fer* "to text for discussion
of labelled data points.

193
07200
07180
07160
Bodoco Pluton (n=21)
t = 555 +/- 8 Ma
Initial Sr = 0.70608
61F-X
00
00
07140
07120
071 OO
O7080
O7060
O 7040H—\—I—'—I—I—^—I—I—'—'—'—'—'—'—^—'—^^—'
OO 05 1.0 1.5 ZO
87Rb/86Sr
^
Symbols \
n megacrystic QMZ • mafic intrusive
.f phenocrystic QMZ X hybnd
m plumose QMZ
Figure 34. Whole-rock Rb-Sr isochron for the Bodoc6
pluton (based on 21 data points).

194
a.
Mineral Isochron: Mafic Enclave $6-C
'86Sr
87Sr/
0.707j^
0.706^
t = 561 -I-/- 9 Ma
Initial Sr = 0.70618 -I-/-6
MSWD = 2,83
0.715-
0.714-
0.713-
0.712-
0.711-
-
0.710-
0.709-
-
0.708^
0.705-
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
87Rb/86Sr
Symbols
•
Apatite
Plagioclase
Hornblende
•
Whole-rock
b.
Mineral Isochron: Mafic Enclave 12-A
0.715-
0.714-
0.7131
t = 593 -»-/- 21 Ma
Initial Sr = 0.70615 +/-8
MSWD = 0.73
y^ \
Symbols
m
OO
CD
00
0.712
0.711
0.710-
0.709-
0.708-
Feldspar
'ilk
, t Hornblende
•
Whole-rock
0.707-
0.706
0.705
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
87Rb/86Sr
Figure 35. Rb-Sr mineral isochrons for two mafic
enclaves: a) sample 56-C, b) sample 12-A.

195
Mineral Isochron: QMZ (Megaxtic) 63-A
0.715^1 t = 402 +/- 78 Ma
0.714^ Initial Sr = 0.70600 +/- 33
MSWD = 16.97
0.713
! I Symbols
^86Sr
87Sr/
0.712^
0.711^
i 0.710H
0.709-
0.708-
0.707-
I
i
Apatite
K-feldspar
! Hornblende
Whole-rock J
0.705 0.0 0.1 0.2 0.3 0.4 0.5 0.8 0.7 0,8 0.9 1,0
87Rb/86Sr
Mineral Isochron: QMZ (Country Rx) 37-A
in
OO
in
00
0,715-;! t = 524 -I-/- 48 Ma |
0.714^ Initial Sr = 0.70596 -I-/-9 1
^1 MSWD = 1.18
0.713-^
0.705 0!0 0,1 0.2 0.3 0,4 0.5 0.6 0.7 0.8 0,9 1.0
87Rb/86Sr
Figure 36. Rb-Sr mineral isochrons for two quartz
monzonites: a) sample 63-A (megacrystic QMZ);
b) sample 37-A (igneous country rock).

196
in
00
Ui
07140-
07130-
07120
07110
07100
0-13-C
00
O7090
O7080
O7070
I-63-B
n-48A
8A-0
O7060
O7050
• -^ A. •
n
a n
XX
O7040
45 50 55 60 65 70 75
Si02
Symbols
a megacrystic QMZ
+ phenocrystic QMZ
M plumose QMZ
• mafic enclave
A
X
O
mafic intrusive
hybnd
aplite
Figure 37. Comparison of initial Sr (t=555 Ma) and SiO^
content. Regardless of rock type or Si02 value, most
samples have initial Sr values between 0.7055 and
0.7065.

a.
0.712
Symbols
j
197
u
in
o
00
0711
0710-
0709-
0
a
•
•
X
0
megacrystic QMZ
phenocrystic OMZ
plumose QMZ
Tiafic enclave
mafic intrusive
hybrid
aplite
00
O708
0707
0706-
a
•
•
^ -x
X
o
b.
in
0726
0.724
0.722
0.718
0.716
0.705- !
I r T 1
I 1
OOOO O001 O002 0003 0.004 0,005
1/Sr
0720-
0.714-
0712-
0710
0708-1
0706
O704
0.702-1
»
^
V- 34 A
V-17 A
o T —4A
most samples
Symbols
0.700
0.000 O0O5 0.010 O015 0.020 0.025
l/Sr
a
•f
m
m
•
X
o
0
V
T
megacrystic QMZ
phenocrystic QMZ
plumose QMZ
mafic enclave
r^.dfK intrusive
hvbnd
aplite
Ign. country rock
gneiss
schist
Figure 38. Comparison of initial Sr and 1/Sr to^detegt
possible mixing relationships, a). Initial Sr/ Sr
vs. 1/Sr for plutonic samples only. b). Sr/ Sr vs.
1/Sr for plutonic samples and for metamorphic country
rocks at t = 555 Ma. Note scale changes between the
two diagrauns.

198
Oxygen Isotope Distribution
•
*
o
4^
iJr
megacrystic QMZ
phenocrystic QMZ
plumose QMZ
mafic enclave
hybrid
O
•
•
•
aplite
Igneous country rx
gneiss
schist
Fiaure 39. Map of distribution of oxygen isotope values
^4:^r- for r.y^^^^y quartz «pnarates separates an (in per Der mil relative to SMOW).

199
O
fl n^
o.u
7.0-
6.0-
5.0-
4.0-
3.0-
20-
1.0-
Four-step Fractionation Model
^
^
1 r 1 1 1 I
• *
1
" ^ ^
2
J
3
-So
^--
• T • •f' T • I r 1 I I 1 1 1 1 1 I T r
50 55 60 65 70
Si02
4
° Megaxtic QMZ •»• Phenoxtic QMZ ^ Plumose QMZ
A Mafic Intrusive ^ Hybrid
Figure 40. Four-step parent-daughter fractionation
model. The fractionation path for each step is
illustrated for CaO vs. SiO^. Numbered boxes refer to
the equivalently numbered steps in Table 22.

200

201
4.5
Test for Fractional Crystallization
4.0
3.5
3.0-
N
25-
20-
1.5
1.0
QMZ from
pluton core
V. ,y
aV
D :
05^
D
cP aq,*^* ^
^
OO
80 100 120
n r
-| r~-—•—1 r
140 160 180 200
Rb (ppm)
Symbols
C3 megacrystic QMZ • mafic intrusive
.f phenocrystic OMZ X hybnd
M plumose OMZ
Figure 42. Rb/Zr variation with changes in Rb
concentration. The Rb/Zr ratio for most megacrystic
QMZ and for plumose QMZ is fairly uniform at
approximately Rb/Zr =0.5. Such a pattern could be
produced if both elements had been strongly
incompatible with crystallizing phases during
fractional crystallization.

202
4.5j-
4.0
Mixing Curves for QMZ
^19b
3.5
N
3.0-1
25
20
1.5
1.0
05-I
OO
80
100 120 140
Rb (ppm)
200
Symbols ;
a megacrystic OMZ • mafic intrusive
.,. phenocrystic QMZ X hybnd
3K plumose QMZ
Fiaure 43. Two-component mixing curves for Rb/Zr and Rb.
Bodoca QMZ samples with relatively high values of
Rb/Zr Dlot along or near curves generated by two-
Lln^ mixina models between mafic intrusive sample
lITanS varioSI ?ellic end members. (based on mixing
irials evaluated in Table 23). Mafic and felsic
u i '^ =,milps define another mixing curve dashed
'^^''ft line) that .h^^inlludes inciuaes It at least one intermediate ^ ^^^ rock mixing
type from the hybrid ^°^*- ^ion of thi total
=?^t:re°?eprllented°b5'thl mific end merrier at that
point on the curve.

203
RES0R8TI0N IN COLO
THERMAL BOUNDARY
;iV'LAYER
Figure 44. Schematic diagram of a porphyritic magma
developing in a chamber that is also undergoing
partial melting (from Huppert and Sparks, 1988, p.
617). Partial melting of crustal rock occurs in a
roof-zone (A). The thermal boundary (B) is a region
of heating in which matrix crystals (restite) are
resorbed. Portions of this boundary region randomly
detach to form plumes that move downwards and mix into
the hotter interior. This convecting interior (C) is
a region of small temperature variations where
crystallization occurs due to mixing in of cold magma
from above. Some phenocrysts may nucleate on
incompletely resorbed restite minerals. The overall
effect is to form a highly porphyritic magma at depth.

204
Evolution of the Bodoco Pluton
X '^ crustal rocks
X X X X X X
accuaulatad
crystals and
proportionat.iy
aore B«lt
"^ ^-j, J. porphyritic
naficaiii
nuaaroua accunulat.d
crystals
a. Genesis of highly
porphyritic magma
at depth
b. Flow separation
during emplacement
active
shearin*^
shearing
stresses
hybridiied
magma
re laic
liquid
c. Localized deformation
(dynamic xln) of QMZ
d. Magma mbdng
(hybridization)
near top of pluton
fructurea filled
>y synplutonlo
Mfic dikes
Figure 45. Major stages in the evolution of the Bodoco
pluton. (Note that the diagrams are not drawn to
scale relative to each other.) a). A porphyritic
magma is generated in the mid-to-lower crust.
b). Crystal accumulation operates during ascent to
produce a differentiated guartz monzonitic magma that
will be reversely zoned upon emplacement. c). Zones
of foliated megacrystic QMZ develop in response to
post-emplacement shearing stresses. d). Mafic magma
rises along fractures in deformed megacrystic QMZ to
form synplutonic dikes and, at a higher level in the
pluton, to hybridize with felsic magma that had
fractionated from megacrystic QMZ.

APPENDIX B:
TABLES
205

206
Table 1:
Textural classification of hand samples.
Textural Sample
Category No.
lUGS
Rock Type
Unusual Features
MEG
MEG
MEG
MEG
MEG
5-A
6-A
11-A
11-C
13-A
granodiorite
quartz monzonite
quartz monzonite
quartz monzonite
quartz monzonite
MEG
MEG
MEG
MEG
MEG
14-D
16-A
18-A
28-A
40-A
quartz
quartz
quartz
quartz
quartz
monzonite
monzonite
monzonite
monzonite
monzonite
on internal fault contact
pronounced foliation
pronounced foliation
MEG
MEG
MEG
MEG
MEG
45-B
48-A
48-C
51-A
54-A
quartz
quartz
quartz
quartz
quartz
monzonite
monzonite
monzonite
monzonite
monzonite
rapakivi overgrowths
pronounced foliation
MEG
MEG
MEG
MEG
MEG
55-A
56-A
57-A
5 9-A
63-A
quartz monzonite
granite
quartz monzonite
quartz monzodiorite
quartz monzonite
MEG
MEG
MEG
MEG
MEG
64-A
67-A
68-B
69-A
70-A
quartz
quartz
granodiorite
quartz
quartz
monzonite
monzodiorite
monzonite
monzonite
strongly foliated
MEG
MEG
MEG
MEG
MEG
71-A
72-A
73-A
76-A
77-A
quartz
quartz
quartz
granite
granite
monzodiorite
monzonite
monzonite
PHE
PHE
PHE
PHE
PHE
9-B
22-A
22-C
24-D
25-A
quartz
quartz
queurtz
quartz
—
monzonite
monzonite
monzonite
monzonite
sheared
PHE
PHE
PHE
PHE
27-A
33-D
74-A
75-B
quartz
quartz
quartz
quartz
monzonite
monzonite
monzonite
monzonite

207
Table 1:
continued
Textural
Category
Sample
No.
lUGS
Rock Type
Unusual Features
PLU
PLU
PLU
PLU
PLU
1-B
2-A
22-D
23-A
23-B
quartz monzonite
—
quartz monzonite
quartz monzonite
monzonite
cataclastically defonned
PLU
PLU
PLU
PLU
PLU
24-C
29-A
38-A
52-A
75-A
quartz monzonite
quartz monzodiorite
quartz monzonite
quartz monzonite
quartz monzonite
plagioclase overgrowths
ENC
ENC
ENC
ENC
ENC
2-A
7-A
9-C
10-A
11-B
—
—
(alk.fsp.q.syenite)
diorite
——
pale, turbid hbl; invasive Ksp
ENC
ENC
ENC
ENC
12-A
13-B
21-C
22-B
monzonite
-—
monzodiorite
monzodiorite
biot but no hbl or tit
ENC
ENC
ENC
ENC
ENC
24-A
2 6-A
27-B
33-A
33-B
monzodiorite
monzonite
——
diorite
——
mostly cpx and minor hbl
biot but no hbl or tit
ENC
ENC
ENC
ENC
ENC
ENC
ENC
ENC
INT
INT
INT
INT
INT
39-A
41-B
44-C
56-C
63-B
68-A
70-B
77-B
2-B
12-B
16-B
16-C
16-D
quartz monzonite
monzonite
composite
diorite
monzodiorite
monzodiorite
monzodiorite
monzonite
monzodiorite
monzonite
monzodiorite
monzodiorite
quartz monzodiorite
very little Kfsp
rapakivi overgrowths
pale, turbid hbl
small, late-stage dike
small, late-stage dike
migmatitic
intermingled with 16-D
intermingled with 16-C

208
Table li
continued
Textural^ Sample
Category No.
lUGS
Rock Type
Unusual Features
INT
INT
INT
INT
INT
19-A
19-B
21-A
21-B
41-A
quartz monzodiorite
quartz monzodiorite
monzonite
monzonite
quartz monzodiorite
has folded aplite veinlet
INT
INT
INT
INT
43-A
48-B
50-A
58-A
monzodiorite
monzodiorite
monzodiorite
monzonite
late-stage dike, ptygmatic fsp
late-stage dike, cpx-bearing
HYB
HYB
HYB
HYB
HYB
60-A
61-A
61-B
61-C
61-D
monzonite
—
quartz monzodiorite
—
quartz monzodiorite
mafic/felsic hybridized
small miarolitic cavities
mafic/felsic hybridized
mafic/felsic hybridized
much xenolithic qtz
HYB
HYB
HYB
HYB
HYB
61-E
61-F
62-A
62-B
62-C
granite
granite
granite
granodiorite
granite
one-cm phenos Kfsp; zoned zir
equigranular, med-gr.
equigranular, med-gr.
one-cm phenos Kfsp, rapakivi
equigranular
HYB
HYB
62-D
62-E
granite
—
hybridized, rapakivi texture
megacrysts of Kfsp (like MEG)
APL
APL
APL
APL
APL
6-B
8-A
9-A
13-C
14-B
granite
granite
granite
granite
granite
granophyric
porphyritic—buff Kfsp phenos
APL
APL
APL
APL
APL
14-C
18-B
24-B
33-C
43-B
quartz monzonite
granite
granite
granite
queurtz monzonite
med-gr. felsic dike
buff (not pink) rocl
small zoned dike
med-gr. felsic dike
APL
APL
APL
APL
44-A
4 5-A
4 9-A
74-B
granite
granite
—
——
small zoned dike
ICR
ICR
ICR
17-B
20-A
37-A
alk.fsp.syenite
syenite
quartz monzonite
cpx-bearing dike
cpx-bearing dike
cpx-bearing

Table 1:
continued
209
Textural
Category
Sample
No.
lUGS
Rock Type
Unusual Features
GNE
GNE
GNE
GNE
GNE
3-A
15-B
17-A
34-A
35-A
hbl-biot gneiss
qtz-fsp gneiss
qtz-fsp gneiss
qtz-fsp gneiss
amphibolite
GNE
GNE
GNE
GNE
GNE
35-B
36-A
46-C
53-A
53-B
amphibolite
qtz-fsp gneiss
felsic gneiss
qtz-fsp-musc gneiss
quartzite
cataclastically deformed
GNE
GNE
53-C
53-D
amphibolite
amphibolite
cpx-bearing
hbl w/uralitized cores
SCH
SCH
SCH
SCH
SCH
4-A
15-A
30-A
31-A
32-B
biot schist
biot-hbl schist
biot-sill schist
biot schist
staur-sill schist
SCH
SCH
SCH
SCH
SCH
32-C
32-D
32-E
46-B
56-B
garnet schist
garnet schist
garnet schist
biot schist?
biot-sill schist
acic. amphibole
acic. amphibole
acic. amphibole
acic. apa in plag
SCH
SCH
SCH
SCH
SCH
65-B
65-C
65-D
66-A
77-D
biot-gar-sill schist
biot-sill schist
biot-muse schist
biot-sill schist
biot-musc schist
"Textural Category" abbreviations are as follows:
MEG « megacrystic, coeurse-grained
PHE = similar to MEG but with one-cm phenocrysts (not megacrysts
PLU = foliated black/white queurtz monzonite with plumose texture
ENC = mafic enclave
INT « equigranular mafic intrusive
HYB » from zone of texturally hybridized (mafic/felsic) rocks
APL - aplite and other equigranular felsic dikes
ICR » equigranular felsic igneous country rock
GNE = gneiss (country rock)
SCH » schist (country rock)

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Table 17:
Comparison of analytical results for trace
elements for selected samples (all values ppm)
a
Textural
Category
Seuonple
No.
AA
.-Rb-
ID INAA
ICP
lalytical Me thodfl^
-Sr
ID INAA
Zr—
ICP INAA
Ba
ICP INAA
MEG
MEG
MEG
MEG
MEG
bod-48a
bod-56a
bod-63a
bod-71a
bod-76a
120
150
128
107
132
116
148
126
111
133
121
138
131
106
132
1454
1097
1266
1259
1100
1325
1092
1250
1247
1078
1063
1168
1277
920
1102
292 309
263 276
150 315
161 414
281 299
3124 2984
2467 2394
2675 2445
1906 1962
1961 1845
PHE
bod-75b
153
153
154
1405
1393
1395
210
297
3143 2962
PLU
bod-75a
174
169
166
1273
1257
1246
360
404
2691 2485
ENC
bod-63b
165
134
133
1825
1745
1823
69
321
3402 3256
INT
INT
INT
HYB
APL
ICR
GNE
SCH
bod-16b
bod-21b
bo

243
Table 18; Rb-Sr isotope analyses (whole-rock).
Textural^ Sample
Category
No.
MEG
MEG
MEG
MEG
MEG
MEG
MEG
MEG
MEG
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PHE
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PLU
PLU
PLU
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bod63a
bod67a
bod68b
bod70a
bod71a
bod76a
bod74a
bod75b
bodSSa
bod52a
bod75a
bod9c
bodl2a
bod56c
bodSSb
bod2b
bodl2b
bodl6b
bodl9a
bod21b
bod48b
bod61b
bod61f
bod62e
bodSa
bodl3c
bod37a
bodlTa
bod34a
bod4a
bod65c
Rb87/Sr86
0.23170
0.28784
0.25238
0.39282
0.29123
0.22294
0.34983
0.28283
0.25551
0.35482
0.22950
0.31558
0.41436
0.25732
0.38707
0.53762
0.19147
0.68142
0.22057
0.26913
0.14320
0.25973
0.26595
0.42313
0.25292
0.19004
1.49038
0.45191
1.45676
1.24090
0.23870
0.79161
0.44515
1.37470
7.17938
Sr87/Sr86
0.70793
0.70846
0.70927
0.70930
0.70823
0.70773
0.70881
0.70805
0.70771
0.70862
0.70799
0.70860
0.70937
0.70815
0.70911
0.71083
0.70772
0.71160
0.70884
0.70828
0.70685
0.70806
0.70840
0.70907
0.70800
0.70737
0.71785
0.70967
0.71899
0.72102
0.70782
0.72327
0.72738
0.71807
0.75853
Initial^
Sr
0.70610
0.70618
0.70727
0.70619
0.70592
0.70597
0.70604
0.70581
0.70569
0.70581
0.70617
0.70610
0.70609
0.70611
0.70605
0.70657
0.70620
0.70621
0.70709
0.70615
0.70572
0.70600
0.70630
0.70572
0.70600
0.70587
0.70605
0.70609
0.70746
0.71120
0.70593
0.71700
0.72386
0.70719
0.70171
Rb
(ppm
108
122
116
148
126
103
129
118
111
133
123
153
179
138
169
155
101
184
134
163
100
no
94
190
132
107
186
111
131
149
163
142
56
77
103
Sr
(ppm)
1338
1222
1325
1092
1250
1326
1060
1201
1247
1078
1549
1393
1245
1541
1257
832
1524
781
1745
1737
2008
1216
1019
1295
1509
1617
361
708
260
348
1961
518
366
162
42
Refer to Table 1 for explanation of abbreviations,
'initial 87Sr/86Sr back-calculated using t - 5.552E*8 Ma.

Table 19:
Rb-Sr isotope analyses (mineral separates).
244
Textural Sample ^ Sr
Category No. Mineral Rb87/Sr86 Sr87/Sr8 (ppm (ppm)
MEG
MEG
MEG
MEG
MEG
63-A
63-A
63-A
63-A
63-A
apatite
hornblende
K-feldspar
whole rock
biotite
0.00960
0.33997
0.27787
0.29123
48.85354
0.70600
0-70786
0.70802
0.70823
1.07643
4
10
183
126
551
1108
86
1892
1250
34
ENC
ENC
ENC
ENC
ENC
56-C
56-C
56-C
56-C
56-C
apatite
plagioclase
hornblende
whole-rock
biotite
0.00250
0.02493
0.45098
0.68142
32.99697
0.70610
0.70643
0.70980
0.71160
0.95526
0.7
14
13
184
717
859
1592
84
781
64
ENC
ENC
ENC
ENC
ENC
12-A
12-A
12-A
12-A
12-A
apatite
feldspar
whole rock
hornblende
biotite
no data
0.13217
0.19147
0.32591
38.25275
no data
0.70729
0.70772
0.70891
0.99791
n.d.
82
101
16
508
n.d.
1776
1524
141
40
ICR
ICR
ICR
ICR
ICR
37-A
37-A
37-A
37-A
37-A
apatite
clinopyroxene
K-feldspar
whole-rock
biotite
0.01925
0.05324
0.13029
0.23870
45.84530
0.70612
0.70646
0.70685
0.70782
1.06013
16
2
121
163
683
2448
109
2658
1961
45
^ Refer to Taible 1 for explemation of cJ3breviations.

245
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246
Table 21:
Oxygen isotope analyses for quartz
separates and whole-rocks.
Textural^
Category
MEG
MEG
MEG
MEG
Sample
No.
bod-13a
bod-18a
bod-56a
bod-63a
del
Quartz
+9.5
+9.4
+9.4
+9.4
0 18—-
Whole-rock
—
OOO
bod-67a
bod-70a
bod-71a
+9.6
+9.3
+9.6
+7.2
PHE
PHE
bod-74a
bod-75b
+9.8
+9.6
+7.2
PLU
PLU
bod-52a
bod-75a
+9.5
+9.5
+7.0
ENC
bod-63b
+9.3
+7.2
INT
bod-12b
-
+7.1
HYB
HYB
bod-61f
bod-62e
+9.7
+9.6
-
APL
APL
bod-8a
bod-13c
+9.4
+13.0
-
ICR
bod-37a
+9.5
-
GNE
bod-34a
+11.0
-
SCH
bod-4a
+16.0
-
^ Refer to Table 1 for explanation of abbreviations
.
b All values in per mil, relative to Standard
Mean Ocean Water (SMOW).

247
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APPENDIX C:
ANALYTICAL METHODS
251

252
Microprobe Analyses
Microprobe analyses of the major mineral phases were
performed at Southern Methodist University using a JEOL
JXA-733 electron probe. All compositions were determined
by wavelength dispersive analysis using natural and
synthetic standards. Secondary standards were checked
routinely for accuracy and precision during analytical
sessions.
An accelerating voltage of 15 kV and a beam current
of 20 nA were maintained for all analyses. An electron
beam spot diameter of 20 microns was used for most
analyses. Count rates were corrected automatically for
beam current drift and detector deadtime losses. Data
were reduced by computer using the procedure of Bence and
Albee (1968).
Major Oxide and Trace Element Chemistry
To prepare large samples for analysis, samples were
crushed and divided with a Jones splitter at the sample
preparation laboratories of SUDENE in Recife, Brazil.
Remaining samples received comparable treatment at Texas
Tech University, where all samples were split further and
were powdered in a tungsten carbide shatterbox mill.
Whole-rock powders were prepared for atomic absorption
spectrometry (AA) and inductively coupled plasma-atomic
emission spectrometry (ICP) by fusing 0.2000 ± 0.0005 gm

253
of powdered sample with 1.2000 ± 0.0005 gm of lithium
metaborate flux and dissolving the resulting bead in a
solution of deionized H2O and 4% HNO3. Standards of
known composition and a blank solution were used to
develop calibration curves and to check for precision and
accuracy.
Major oxides and the trace elements Rb, Sr, Ba, Y,
and Zr were analyzed at Texas Tech University.
All major
elements were determined by AA except Na and K, which
were determined by flame photometry, and P, determined by
ICP. FeO was measured by titration. Trace elements Sr,
Ba, Y, and Zr were determined for all geochemical samples
by ICP, and Rb was determined by AA.
Trace element data for 15 samples were obtained by
neutron activation analysis (INAA) at Sul Ross University
for Rb, Sr, Ba, Zr, Sc, Cr, Co, Cs, Hf, U, Th, Ta, and
the rare-earth elements La, Ce, Nd, Sm, Eu, Tb, Yb, and
Lu.
Rb-Sr Isotope Chemistry
Rb-Sr isotopic analysis was performed at the
Department of Geological Sciences of the University of
Texas at Austin.
To prepare samples for isotopic
analysis, approximately 15-20 milligrams of whole-rock
powder were decomposed in concentrated, hot hydrofluoric

254
acid.
This step was followed by leaching in hydrochloric
acid and repeated attack with HF until all of the sample
was dissolved.
Samples were then spiked by known amounts
of ^"^Rb and ^"^Sr isotopic tracers.
Rubidium and
strontium were separated from each other and from all
other major and minor elements on a cation exchange
column, and the eluted samples were taken to dryness.
Prior to analysis, the dried residue was treated with
HNO3 to destroy any traces of resin that may have escaped
from the column.
Rubidium isotope ratios were measured on a 30-cm
radius, 60-degree sector field, solid-source mass
spectrometer using a 3.5 kV ion beam acceleration.
The
Rb sample, dissolved in a drop of ultrapure tripledistilled
H2O (D3), was loaded onto the side filament of
a rhenium double-filament assembly.
The other filament
was heated to ionize the Rb.
Peaks of ^^Rb and ^^Rb were
measured sequentially and compared periodically to
baseline values.
Forty-five to seventy-five sets of peak
measurements were recorded for each analysis.
Strontium isotope ratios were measured on an
automated Finnegan-MAT 261 seven-collector, solid-source
mass spectrometer.
Samples were dissolved in ultrapure
triple-distilled HjO, then loaded onto a tantalum singlefilament
assembly, on a spot where a small drop of H3PO4

255
had previously been placed and evaporated nearly to
dryness.
Peaks of ^^Sr, ^"^Sr, ^^Sr, and ^^Sr were
measured simultaneously; between 40 and 60 sets of peak
measurements were recorded for each analysis.
Uncertainties in the calibration of spike
concentration for both ^^Sr and ^^Rb were assigned a
value of ±0.5%; blanks of 0.00006 micromoles (5
nanograms) of Sr and 0.00001 micromoles (less than 1
nanogram) of Rb were assigned; these are trivial compared
to quantities of Rb or Sr in the samples.
Isotope ratios in a mass spectrometer run that
diverged more than 2.0 or 2.5 standard deviations from
the mean value were not included in the mean.
Mineral separates for Rb-Sr isotopic analysis were
prepared from crushed whole-rock samples by processing
the samples in a roller mill, after which the minerals
were separated by using a combination of heavy liquids,
magnetic separation, and hand-picking.
Analytical
procedures for mineral separates differed from wholerocks
only in that mineral separates were crushed in a
ceramic mortar rather than in a shatterbox mill.
They
then were dissolved by the same methods as whole-rock
samples.

Oxygen Isotope Chemistry
256
Oxygen isotope analyses were performed at the
Department of Geological Sciences at the University of
Georgia.
Quartz was separated from rock samples for
isotopic analysis by crushing samples in a roller mill,
sieving, and hand-picking.
Prior to analysis, the quartz
was washed in ultrasonic baths of water, alcohol, and
acetone.
Separates then were etched with pure HF until
all traces of feldspar were removed.
Whole-rock powders
were prepared as described for major oxide analyses.
Sample masses ranged from 11 to 14 milligrams.
Oxygen was liberated in an extraction line using
ultrapure fluorine gas generated from a salt, K3NiF-7, at
high temperature.
The oxygen then was reacted with a
carbon rod to form CO2 for mass spectrometer analysis.
Samples were analyzed on a Finnegan MAT isotope
ratio mass spectrometer.
A rose quartz standard was
analyzed repeatedly and used to normalize analyses for
comparison with standard mean ocean water (SMOW).