PALEOMAGNETIC DATA BEARING ON VERTICAL AXIS ROTATION IN THE SOUTHERN WALKER LANE DISPLACEMENT TRANSFER SYSTEM

Paleomagnetic data have been acquired to evaluate the presence and magnitude of vertical axis rotation of crustal elements involved in the development of the displacement transfer system that connects the north Furnace Creek and southern Fish Lake Valley faults to structures in the central Walker Lane, western Great Basin. Rotation is a likely component of deformation during displacement transfer, in particular in rocks that constitute the upper plate of a system of regional scale northwest-dipping detachment faults extending from around Beatty to north of Silver Peak, NV. Paleomagnetic sampling has concentrated on regionally extensive Miocene ignimbrites including Stonewall Flat Tuff (7.62 ± 0.01 Ma) sourced from the Stonewall Mountain caldera, Timber Mountain Tuff (11.55 ± 0.012 Ma) sourced from the nested calderas of the Timber Mountain eruptive complex, and at least one older ignimbrite, the tuff of Mount Dunfee (16.31 ± 0.009 Ma). Sampling localities (277 sites with 8 to 20 samples per site) include areas around Goldfield, Gold Point, Bullfrog Hills, and northeast Death Valley. Paleomagnetic data provide evidence of variable magnitudes of vertical axis rotation across the study area. The area south of Gold Mountain is characterized by large (50-70° or more) magnitudes of clockwise rotation (GP51 Ds=88.8 Is=22.5 α95=2.1; GP56 Ds=229.9 Is=-41.3 α95=3.6; GP58 Ds=245.5 Is=-60.1 α95=0.8; GP119 Ds=229.3 Is=-58 α95=8; GP126 Ds=234.2 Is=-55.2 α95=4; GP283 Ds=294.6 Is=69.8 α95=2.8). Paleomagnetic data from the Stonewall Flat tuff suggest minimal rotation (GP16 Ds=352.8 Is=63.2 α95=3; GP48 Ds=328 Is=64.2 α95=4.5; GP211 Ds=350.2 Is=61.1 α95=3.3; GP284 Ds=328.8 Is=54 α95=8.5) and thus allow us to refine the timing of rotation to prior to about 7.6 Ma. The dominant sense of rotation in the study area is clockwise, but counterclockwise rotation is also present. Response to progressive alternating field (AF) and/or thermal demagnetization, where necessary because of high coercivity remanence, provides well-defined trajectories and shows that magnetite and/or maghemite are principal remanence carriers, as supported by rock magnetic data, including first order reversal curve (FORC) data.