Geologic Studies in Alaska by the U.S. Geological Survey, 1992

152 GEOLOGIC STUDIES IN ALASKA BY THE U.S. GEOLOGICAL SURVEY, 1992
crystallization, the release of magmatic fluids affected the
wall rocks around the pluton.
The felsite dikes in the study area are subvertical and
generally strike northwest-southeast, but the strikes range
from east-west to north-south (fig. 11). The dikes near
Unakwik Inlet with K-feldspar and quartz phenocrysts
strike east-west (fig. 1 I). Pegmatite and autobrecciated
granitic dikes associated with the Granite Cove pluton
strike northwest-southeast (fig. 11). As mentioned earlier,
a dike in domain F is slightly boudinaged with subvertical
boudin axes. This is the only indication of ductile defor-
mation of any of the dikes.
FAULTS
Steeply dipping brittle faults with quartz veins, brecci-
ated wall rock, and clayey gouge less than several centi-
meters thick are found throughout the study area. The
orientation of these faults is roughly the same in all do-
mains, and thus we consider them together. A plot of all
known fault orientations and their sense of offset (fig. 12),
where it was determined, demonstrates that (1) the most
common fault orientation is north-south- or NNW-SSE-
striking and subvertically dipping, and (2) most of these
faults (18 of 24 with known offset) are strike-slip faults.
North-south-striking sinistral-slip faults cut the Cedar Bay
pluton, and north-south-striking dextral- and sinistral-slip
faults cut the Granite Cove pluton. It is puzzling that both
dextral and sinistral faults have approximately the same
orientation but the opposite sense of slip.
Abundant geomorphic lineaments cross the study area,
and many of these have a north-south or NNW-SSE trend.
Lineaments with the same orientation cut the Miners Bay,
Cedar Bay, and Terentiev Lake plutons. The Cedar Bay
pluton, in particular, has a strong NNW-SSE-striking set.
The fractures are subvertical, as indicated by their linear
trace across topography. The strikes of fractures in the
southern half of the study area were measured from
Condon and Cass" (1958) compilation of linear geologic
features in western Prince William Sound (fig. 13). The
lineaments strike north-south to NNW-SSE, similar to the
Figure 7. Eight localities within study area show quasi-fold
geometry, which at 1:63,360-map scale show apparent fanning
of bedding planes, although facing direction remains the same.
This figure shows in cross-sectional view our use of the term
"quasi-fold" and the two types of geometry observed in the
field. Arrows show upward-facing direction of rocks.
most common orientation of faults, and thus we interpret
the lineaments as fractures that are probably strike-slip
faults with minor offset.
The amount of offset on these north-south to NNW-
SSE-striking brittle faults probably is not significant be-
cause no pluton contact or stratigraphic horizon is offset
along them. However, there may be approximately 11 km
of dextral map separation along a (ENE-WSW-striking)
splay of the Contact fault (Winkler, 1992) that runs be-
tween Miners Bay and Kadin Lake (fig. 2). Conglomerate
south of Miners Lake (fig. 2) strikes into the Miners Bay-
Kadin Lake splay, and the closest conglomerate on the
north side of the splay is located near the Columbia Red
Metals prospect (CRM, fig. 2) between Kadin Lake and
the Columbia Glacier. This fault also truncates the -35-Ma
Miners Bay pluton. Traverses across the Miners Bay-
Kadin Lake splay of the Contact fault did not reveal areas
of high ductile strain. In conglomerate adjacent to the
fault, clasts were not noticeably flattened. No brittle faults
were observed in the vicinity of the fault at either the east
or west end of Kadin Lake, but numerous subvertical lin-
eaments along the splay indicate that there has been some
Figure 8. Quasi-folds may be explained by tilting of
hanging-wall and footwall cutoffs of fault-bend folds.
Arrows show upward-facing direction of sedimentary
section.