GEOMETRY KINEMATICS AND AGE OF THE NORTHERN HALF OF THE WHITE MOUNTAIN SHEAR ZONE: EXTENDING THE RANGE AND DURATION OF LATE CRETACEOUS DEXTRAL TRANSPRESSION ALONG THE WESTERN MARGIN OF NORTH AMERICA

The White Mountain shear zone (WMSZ) is a zone of intense penetrative crystal plastic deformation that lies along the western front of the northern White-Inyo Range in eastern-most California and western-most Nevada. The northern half of the WMSZ is characterized by a NNE to NNW-striking steeply dipping foliation and associated shallowly plunging stretching lineations. S-C fabrics observed in outcrop, microstructural shear sense indicators and kilometer-scale foliation geometry all indicate dextral movement on the zone. Microstructural data from localized discrete domains of steeply plunging stretching lineations indicates a high component of pure shear and hence a transpressional history for the WMSZ. Geometric relationships between quartz c-axis fabric and shape fabric orientation data indicate that the domains of steeply plunging lineations developed in response to a separate kinematic framework that is coeval with strike-slip motion, but differs in architecture from the large-scale strike-slip kinematic framework. A strong solid state penetrative fabric within the ca. 92 Ma Pellisier Flats pluton indicates that deformation occurred after pluton crystallization. The ca. 72 Ma Boundary Peak pluton contains only a weak localized deformation fabric. However, a lack of annealing recrystallization in deformed quartz and the presence of high temperature crystallographic fabrics near the margins of the Boundary Peak pluton indicate significant strain accumulation within the WMSZ after pluton emplacement. These observations extend the known duration of Late Cretaceous dextral transpression in eastern California to at least as recent as 72 Ma. The WMSZ appears to be geometrically and temporally related to both the Sierra Crest shear system located along the axis of the Sierran magmatic arc to the west and the Santa Rita shear system (SRSS) located along the western front of the White-Inyo Range to the south. Correlation between the WMSZ and the SRSS indicates that a zone of Late Cretaceous dextral transpression may extend up to 120 km along the western front of the White-Inyo Range. Foliation geometry within the WMSZ and SRSS appears to have directly controlled the geometry of Cenozoic brittle normal faulting along the western front of the White-Inyo range.