KINEMATICS OF DEFORMATION IN WEST-CENTRAL WALKER LANE; PALEOMAGNETIC TESTING OF FAULT-BLOCK ROTATION AND DOMING MODELS, EASTERN CALIFORNIA AND WESTERN NEVADA

Walker Lane (WL) is a broad (~100-200 km) zone of dextral shear lying between the Sierra Nevada Microplate and the Basin and Range Province. Bodie Hills is considered a part of WL as it has experienced clockwise, vertical-axis rotation of crustal blocks due to dextral shear accommodation. This strain is variable, resulting in rotations ranging from 10° to nearly 60°, depending on specific location. The Eureka Valley Tuff (EVT) of the Stanislaus Group (10.4-9.4 Ma) and the Tuff of Jack Springs (TJS) are ideal strain markers, as they are geologically instantaneous and laterally extensive units. We use paleomagnetic analysis of these ignimbrites to improve the resolution of strain domain boundaries as well as test for doming in Bodie Hills.

EVT site mean directions were compared to reference directions of Tollhouse Flat and By Day Members collected from the stable Sierra Nevada to determine vertical-axis rotations. EVT collected from Clark Canyon exhibits 40.5°±7.1° of clockwise rotation, improving the definition of a high-strain domain centered on Bridgeport Valley. More data are needed to assess whether strain boundaries are gradual or sharp. Near Mormon Meadow, EVT has undergone about 90° of tilting since emplacement, whereas some localities may demonstrate original dips, complicating interpretations of some sites. New and previously collected paleomagnetic data from the EVT will be used to perform a fold test to assess the presence of doming centered on Potato Peak. Rejection of doming would require that the ignimbrites flowed about 2000 ft upslope over Potato Peak or that vertical crustal displacements have occurred without doming. The duration of tectonic rotation in Bodie Hills is unknown. Paleomagnetic investigation of the TJS (12 Ma), a sanidine and biotite phyric rhyolitic ignimbrite, will be used to extend the spatial coverage of rotation measurement and better constrain duration of rotation. Since it has thus far not been found on a stable crustal block, we tentatively establish a reference direction for TJS in a location with known minimal rotation measured using EVT. Testing these hypotheses will provide vital constraints on the kinematics of deformation in the region. This study enhances the general understanding of the kinematics of crustal deformation and sheds light on the tectonic history of Bodie Hills.