EVIDENCE FOR MULTIPLE STRANDS OF THE LATE PALEOZOIC TRUNCATIONAL FAULT OF NORTH AMERICA WITHIN EXPOSURES OF THE KENNEDY MEADOWS PENDANT: SIERRA NEVADA, CA

In the southeast Sierra Nevada, the Kennedy Meadows pendant (KMP), composed of eugeoclinal Paleozoic strata that are apparently located >300 km south of their origin, is bounded along its southwest margin by the prominent, ductile, Kern Plateau Shear zone (KPSZ). The KPSZ has yielded evidence of multiple movement episodes of diverse slip senses during Mesozoic and, speculatively, Paleozoic time, and some workers have proposed that the zone represents a rare, surviving strand of a major, predominantly sinistral fault zone that truncated the southwest margin of North America in late Paleozoic time. However, if the KMP itself is anomalously located, then another strand of the truncating fault must lie northeast of the KMP.

Our field and petrologic study of small, scattered outliers of metasedimentary rock and enclosing granitoids located a few km northeast of the main KMP suggests that these rocks are caught up in another ductile shear zone, informally, the northeast shear zone (NESZ), that may represent the additional strand of the KPSZ needed to explain the anomalous location of the KMP. The overall deformational fabric in the NESZ is NW-striking, steeply NE-dipping and parallels the orientation of the KPSZ. Metasedimentary rocks caught up in the NESZ are incongruent with rocks in the main part of the KMP in terms of protolith, metamorphic grade, and style of deformation. At least three distinct, lens-like suites of metasedimentary rock have been recognized, including highly migmatized amphibolites (quartz+oligoclase+diopside+hornblende), lower granulite-facies schists (quartz+hypersthene) and albite-epidote hornfels (clinozoisite+quartz). These suites are broadly separated and internally intruded by ~0.25- to 0.75-km-wide, bands of thoroughly mylonitized granitoids. Both mylonitic granitoids and metasedimentary rocks are intruded by distinctly less deformed granitoids of the Sacatar Intrusive Suite (~177 Ma) and by undeformed intrusives of an undated mafic complex. These relationships suggest a multi-episode slip history for the NESZ.