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Figwe 86.-Ketchiknn area, showing locations of samples utilized for oxygen-isotope analyses and
approdmate distribution of plutonic and metamorphic rocks of the Coast plutontc complex.
intermontane belt and wes fueled by the emplacement
of Eocene plutons and dikes (Magarit2 and Taylor,
1376). Figure 89 compares the isotopic variations
within and east of the Coast plutonic complex near
Prince Rupert (~ageitz end Taylor, 1976), with those
measured in this sfgdy. The approximately Unear
relation between A O , and the distance of the
sample locality from tsy;est edge of the batholith
may be fortuitous, or this relation may be the isotopic
signature of hydrothermal activlty that ckaubted
prmessively lighter waters toward the east. A
somewhat similar gradient in hydrothermal-fluid
~omposltion was recognized along a traverse ecross
aneouver Islend end the southern part of the Coast
lutonlc complexl~ylor and Magarite, 1878). Both of
-8ese inferred 6 OH 0 gradients are similar to the
present-day varietion2ln surface-water composItlon
across southeastern Alaska and western British
Columbia (~aylor, L974, fig. 6).
On the basis of the geolaglc and isotopic
reletions described above, we infer that the oxygenisotopic
variations in the Ketchikan area may record
InteractIan with huge hydrothermal systems which
were driven by thermal events in the Coast plutonic
complex. These isotopic relations also suggest that on
the west side of the study area, fairly heavy fluids
were involved--possibly marine or metamorphic in
origin. Toward the east, the circulating fluids became
Ughter and were at least in part of meteoric origin on
the east side 04 the Coast plutonic complex (Taylor
and Magarite, 1078). Investigations are currently in
progress on the composition and age of the
hydrothermal systems within and west of the
batholithic belt, and on the relation between this
hydrothermal activity and the mineralization history
of southeastern Alaska.
Acknowledgments.-We thank Jan B. Saleeby
and fiervy C. Berg tor the samples analyeed in this
study. Financial support for this research was
provlded by National Science Poundaff on Grant EAR-
7816874, awarded to K. P. Taylor, Jr. This is
contribution No. 3722 of the Division of Geological and
Planetary Sciences, CaliPornf a Iwtitute of Technology,
Pasadena, CA 91125.
REFERENCES CITED
Criss, R. B., md Taylor, H, P., 1983, An 180/180
and
DIH study of Tertiary hydrothermal systems in
the southern half of the Idaho Betholith: