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

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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 deformation 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 between 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 lineaments 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.
STRUCTURAL EVOLUTION OF THE CHUGACH-PRINCE WILLIAM TERRANE 153 motion along steeply dipping faults. At the east end of faults. Along the trace of the "true" Contact fault in the Kadin Lake, a silicic dike with disseminated sulfides may northwestern part of the study area (Winkler, 1992), the have been dextrally offset about 1 km along one of these Miners Bay pluton has apparent sinistral offset of about A 0 0.5 MILLIMETERS B 0 0.5 MILLIMETER Figure 9. A, Staurolite porphyroblast in matrix of biotite and quartz in metasedimentary rocks near margin of Terentiev Lake pluton. There is no indication that there was ductile deformation during or after emplacement of plutons. Plane-polarized light. B, Typical primary igneous hypidiomorphic- granular texture of granite of Terentiev Lake pluton. There is only minor evidence of later deformation. All plutons are similarly undeformed in thin section.
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Geologic Studies in Alaska by the U
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CONTENTS Introduction Cynthia Dusel
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CONTENTS CONTRIBUTORS TO THIS BULLE
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GEOLOGIC STUDIES IN ALASKA BY THE U
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LATE HOLOCENE LONGITUDINAL AND PARA
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DEEP-WATER LITHOFACIES AND CONODONT
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Table 1. Locality register for key
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Table 1. Locality register for key
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LITHOFACIES AND CONODONTS OF CARBON
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LITHOFACES AND CONODONTS OF CARBONI
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Table 1. Conodont faunules and lith
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DEPOSITIONAL SEQUENCES IN ATIGUN SY
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U-Pb AGES OF ZIRCON, MONAZITE, AND
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APPEAL FOR NONPROLIFERATION OF ESCA
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FAVORABLE AREAS FOR METALLIC MINERA
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GOLD AND CINNABAR IN HEAVY-MINERAL
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Page 107 and 108: EARLY CENOZOIC DEPOSITIONAL SYSTEMS
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Table 3. Summary of geochemical sig
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GEOCHEMICAL CHARACTER OF UPPER PALE
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RECONNAISSANCE GEOCHEMISTRY OF BASA
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OSTRACODE ASSEMBLAGES FROM MODERN B
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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RUBIDIUM-STRONTIUM ISOTOPIC SYSTEMA
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US. GEOLOGICAL SURVEY REPORTS ON AL
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U.S. GEOLOGICAL SURVEY REPORTS ON A
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U.S. GEOLOGICAL SURVEY REPOR TS ON
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REPORTS ABOUT ALASKA IN NON-USGS PU
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REPORTS ABOUT ALASKA IN NON-USGS PU
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Geologic Studies in Alaska by the U.S. Geological Survey, 1992

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