Pliocene Kinematic Reorganization, Fault Geometry, Basin Evolution, and Displacement Budget Along the Furnace Creek – Fish Lake Valley Fault Zone, Eastern California and Western Nevada
Mueller, Nicholas James
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The active northwest-striking Furnace Creek – Fish Lake Valley fault system of eastern California and western Nevada records a protracted history of displacement that has accumulated 45-50 km of right-lateral offset since inception of motion in the middle Miocene. Geologic mapping and 40Ar/39Ar geochronologic data document that ~22 km of right-lateral offset occurred from ~11.6 – 4 Ma, at a long-term average rate of 2.9 mm/yr. A kinematic transition from wrench-dominated deformation to right-oblique transtensional deformation is recorded along the Furnace Creek – Fish Lake Valley fault zone beginning in the middle Pliocene, and has resulted in the remaining right-lateral displacement at a long-term average slip rate of 5.75 – 7 mm/yr. Both the total magnitude of right-lateral displacement and late Pleistocene slip rates are demonstrated to decrease from south to north along the Fish Lake Valley part of the fault zone and are related to displacement transfer onto kinematically linked fault systems. New geologic mapping, structural and stratigraphic analysis, and modeling of gravity data are used to determine the subsurface architecture of Fish Lake Valley and place constraints on the displacement budget for the region. Three-dimensional depth inversion of gravity data indicates that Fish Lake Valley is internally dissected by a system of faults that segments the subsurface into multiple sub-basins with depths of ~1.8 to 3.0 km, filled with lower Miocene to Quaternary volcanic and sedimentary deposits. A grid of 2-dimensional forward gravity models, based on geologic mapping and subsurface data in northern Fish Lake Valley, reveals the internal distribution of basin filling deposits and allows for the estimation of Pliocene and younger displacement on basin bounding faults. Offsets markers mapped in the highlands and inferred in the subsurface indicate that 4 to 5.5 kilometers of vertical offset has accumulated on faults bounding and within southern and central Fish Lake Valley, and around 3.6 km of vertical offset has accrued along the Emigrant Peak fault zone and structures bounding northeastern Fish Lake Valley since the middle Pliocene. Around 2 to 3 km of right-lateral displacement has been transferred from the Fish Lake Valley fault zone to structures bounding northeastern Fish Lake Valley in the last 4 Ma. These results, combined with prior work in the area, indicate that of the 23-28 km of right-lateral displacement accumulated on the Fish Lake Valley fault zone since the mid-Pliocene, only ~10 km of displacement is transferred away to kinematically linked structures to the east of the Fish Lake Valley fault zone. The remaining displacement is likely transferred to the north and west via a horse-tail array of structures underlying northwestern Fish Lake Valley.