TRANSITIONS BETWEEN THE SIERRA NEVADA, BASIN AND RANGE, AND WALKER LANE IN THE NORTHERN PINE NUT MOUNTAINS, NEVADA: INSIGHTS FROM GEOLOGIC MAPPING AND AR/AR GEOCHRONOLOGY

The northern Pine Nut Mountains, western Nevada, are located in the Carson Domain of the Walker Lane and are also the westernmost structural and topographic expression of the Basin and Range province adjacent to the rigid Sierra Nevada block. The unique study location straddles these deformation provinces and is comprised of datable middle Miocene and younger pre-, syn-, and post-kinematic volcanic rocks, which allows for a nearly complete record of faulting history within this complex area. In this study, detailed geologic mapping and systematic Ar/Ar dating were completed to elucidate the faulting history through cross-cutting relationships between normal- and strike-slip-faulting. Geochemistry and petrographic analyses were performed on the volcanic stratigraphy for characterization and likely magmatic origin. North- and northeast-striking faults are preserved in cut Quaternary fan deposits and basaltic andesite to andesite volcanic rocks (56-63% SiO₂). North-striking faults cutting andesite flows record the local initiation of Basin and Range extension that propagated westward through the Pine Nut Mountains during the late Miocene. Northeast-striking left-slip faults observed on eastern flank of the range are probably Quaternary in age and are parallel to other Walker Lane left-slip faults in the Carson Domain (i.e., the Olinghouse, Wabuska, and Carson faults). Other dip-slip north-striking faults on the western flank of the range cut Quaternary fan deposits and probably represent present-day Basin and Range east-west extension. Our preliminary results show that Basin and Range extension initiated across the Pine Nut Mountains in the late Miocene and clockwise rotation of the fault-bounded blocks in the Carson Domain produced the northeast-striking left-slip faults that initiated after ca. 6 Ma. These results provide new insights to the kinematics of the Carson Domain of the Walker Lane and the initiation of Basin and Range extension as it encroached westward toward the rigid Sierra Nevada.