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epizonb'l granitic Miss, mixed with intermediatetemperature
intermediate- to high-prme faciesseries
roaks. The ages of the protoliths are not known,
but a L40-m.y. age (Smith end others, 1979) has been
determined for some orthogneiss masses. Most of the
metamorphic rocks consist of migmatite, biotite
schist, gneissose schlst, biotite gneiss, marble, and
lqe orthogneiss units. The protoliths of the
migmatite, schist, and paragneiss cannot be
unequfvocfdly determined, but they probably were
dominantly clastic sedimentary rocks and Limestone
containing only minor amounts of volcanic material,
their age is not known. The most important intrusive
unit is the conspicuous tonalite sill that runs almost
the whole length of southeastern ALaska (Brew and
others, 1976; Brew and Ford, 1981). This sill and some
nearby less continuous dominantly granodiorite sills
make up the Coast plutonic-metamorphic complex sill
belt (Brew and Morrell, 1980a). Some evidence
suggests that these sills are probably 55 to 60 m.y. old
(J. G. Smith, oral commun., 1979; Smith and others,
1979).
The central granitic zone consists of generally
crosscutting mostly unfoliated grartodiorite and quartz
monzodiorite plutons, with subordinate screens and
pendants of metamorphic rocks like those in the
central metamorphic zone to the southw~t. Most of
these plutons, which arc about 50 m.y. old wherever
they have been dated (Brew and others, 1977; Wilson
and others, 2979; Forbes and Engels, 19701, are
mesozonal to epizonal. They define the Coast
plutonic-metamorphic complex belt 1 (Brew and
Morrell, 1980a). Mapping in progress near the Stikine
River suggests that these bodies may in part be closely
related to some of the granodiorite sills within the
Coast plutonjc-metamorphic complex sill belt in the
central metamorphic zone (S. M. I(&, unpub. data,
1981). The Sloko Volcanics (fig. 79) of British
Columbia, which is approximately coeval, is
interpreted to be the extrusive equivalent (Souther,
1971).
Several 20- to 30-rn.y.ald granite and
grandiorite plutons occur in the Behm Canal belt
(8cew and Morrell, 1980a1, which overlaps both the
central panitlc and the central metamorphic zones.
These epizonal bodies, which are notable for their
sparseness and their association with molybdenite
deposits (Hudson and others, 1979), somewhat resemble
those noted above in the Kuiu-Etblin belt within the
western metamorphic zone.
The eastern metamorphic zone consists of lowto
high-temperature generalIy low pressure faciesseries
metamorphic rocks and scattered to abundant
epizonal granitic bodies. This zone is separated from
the central granitic zone because (1) it is dominantly
metamorphic and (2) the metamorphism differs; the
boundary between the two zones is both arbitrary and
gradational. The gr~nitic rocks in the astern zone
resemble those in the central granitic zone, whereas
the metamorphic rocks are dominantly hornfek
derived from pmtoliths of intermediate to mafic
volcmic, semlpelltic, and carbonate composition. The
age of the protoUths are not known everywhere,
although Carboniferous, Permian, and Triassic rocks
are present at some localities.
Not far northeast of the Coast glutan1~-
metamorphic complex (fig. 79) are the extensive late
Miocene to PIeistocene volcanic fields of Level
Mountain and Mount Rdziza (Souther and others,
197'9). They apparently have no c~unterparts within
the Coast plutonic-metamorphic complex except,
possibly, for some dikes, although they are probably
related to the general evolution of the complex.
A few Holocene basalt flows occur within the
bounderies of the Coast plutonic-metamorphic
complex but show m clear relation to the complex.
They are as young as 360 years B.P. (EUiott and others,
19811, and more flows can probably be expected ta be
erupted In the future.
The three most significant strueturd features in
the northern Coast plutonic-metamorphic Complex are
(1) the Chatham Strait fault (fig. 79), (2) the Coast
Range megalineament (CRML), and (3) n narrow linear
area straddIing the boundary between the wester11 and
central metamorphic zones in which the deformation
and metamorphism were apparently most intense. The
Chatham Strait fault to the north (Ovenshine and
Brew, 19721 Sonnevll, 1981) truncates the southwest
margin of the Coast plutonic-metamorphic complex.
The CRML ls a profound structural element (Brew and
Pod, 1978) that probably has a long and cornplex
hlstory. Because of map scale, the CRML is Iocaily
shown on five 79 as the boundary between the
western and central metamorphic zone; in those
places, the CRML actually lies within the western
metamorphic zone but close to the boundery with the
central zone. Although the narrow linear area of
intense deformation and metamorphism is probably
related to the CRML, this area may simply mark the
locus of greater uplift of the Coast plutonic
metemorphlc complex. Other structural boundaries
stated to be present in the Coast plutonic?
metamorphic complex, such 8s tectonostratigraphic-
terrane contacts (Berg and others, 19781, either
coincide with the CRML, are not verifiable in the
field, or are related to sedimentary, Intrusive, or
metamorphic processes that are only indirectly linked
to the accretion of the exotic Chlrgach terrane to the
west (fig. 79).
The Coast plutonicmetamorphic c6mplex Is
lnterpre tad to have resulted primarily horn the effects
of n major Cretaceous and early Tertiary accretionel
event that occurred about 100 km to b e southwest, at
which time the Chugach terrane kame attached to
the Alexander and Wrargellia terranes (Plafier and
others, 1977). The effects of that distant event were
superposed on both upper Paleozoic and lower
Mesozoic Alexander-terrene rocks and on an upper
Mesozoic overlap assemblage (the Grevina belt) that
probably accumulated in a rifted backarc
envlmnment. These effects are Interpreted to include
two ages of penetrative deformation, two ages of
progressive metamorphism, four main Lntruslve events,
and sporadic volcanism. The main part of the
Alexander terrane, which intervenes 'between the
Coast plutonlcrnetamorphic complex and the accreted
Chugach terrane to the southwest, apparently was lea