ENIGMATIC WALKER LANE DEXTRAL-SHEAR ACCOMMODATION: PALEOMAGNETICALLY-DETERMINED VERTICAL-AXIS ROTATION OF CRUSTAL BLOCKS BETWEEN THE CENTRAL WALKER LANE AND SIERRA NEVADA FRONTAL FAULT SYSTEM

Located west of dextral fault systems of the central Walker Lane and east of the Sierra Nevada frontal-fault system is a region of north-striking normal faults and asymmetric basins, where geodetic studies define ~5 mm/yr of northwest-directed dextral strain. As this region is devoid of major strike-slip fault systems, how this strain is accommodated is poorly understood. To elucidate the long-term tectonic development of this region, paleomagnetic data from late Oligocene ash-flow tuffs are used to determine magnitudes of vertical-axis rotation of crustal blocks, as a potential mechanism for accommodation of dextral shear.

Paleomagnetic directions collected from multiple locations across the region define domains of vertical-axis rotation of varying magnitudes. Preliminary paleomagnetic data have identified low/no rotations within translating blocks of the central Walker Lane (Walker Lake domain), statistically-significant magnitudes of ~20-30° clockwise vertical-axis rotation west of central Walker Lane dextral faults, and ~30-60° of clockwise rotation to the northwest in the northern Walker Lane (Carson domain). Boundaries between these domains, although potentially gradational, are relatively discrete and support a distinction of domains by style of faulting. Future work will focus on collecting additional paleomagnetic data within domains, better defining domain boundaries, and address the timing and rates of vertical-axis rotation through the sampling of Miocene-Pliocene volcanics. This paleomagnetic data set will be compared with ongoing and complementary studies of subsurface basin geometry and recent fault-slip motions to ultimately understand the tectonic development of this enigmatic part of the Walker Lane.