GRAVITY CONSTRAINTS ON THE GEOMETRY AND DISPLACEMENT BUDGET FOR THE CLAYTON VALLEY EXTENSIONAL BASIN, SOUTHWESTERN NEVADA

Clayton Valley is underlain by equant-shaped basin in southwest Nevada and is bounded by an active array of NNE-striking dip-slip and WNW-striking left-oblique slip faults. The structures are part of complex system of active faults that transfer right-oblique displacement between the NNW-striking Furnace Creek – Fish Lake Valley fault of the northern Eastern California Shear Zone and NNW-striking en echelon transcurrent faults in the central Walker Lane. Left-oblique displacement on the WNW-striking Palmetto Mountain fault, which forms the southern boundary of Clayton Valley, is transferred north toward the central Walker Lane via a system of three major NNE-striking normal faults that mark the eastern extent of the basin as a series of topographic steps increasing in elevation to the east. To assess the subsurface geometry and magnitude of extension recorded by these structures, 569 gravity measurements were collected using two Scintrex CG-5 gravimeters at a nominal spacing of 300 m along 7 intersecting transects that crossed the basin. Geospatial control was established by using dual-frequency Leica GNSS receivers and Real Time Kinematic positioning data were post-processed and referenced via the NGS OPUS solution to produce a 2 cm resolution. Gravity data were reduced to a complete Bouguer anomaly using a 2.67 g/cm³ background density. A residual complete Bouguer anomaly was computed using a minimum curvature technique and depth inverted in 3D using GM-SYS 3D. Forward basin-depth models were computed in 2D and 3D providing a depth estimate of 2.2 km for the deepest part of the basin that stretches NNE. Basin depth progressively decreases to the east across three NNE faults with 2.2 km, 0.95 km, and 0.65 km of down-to-the west vertical displacement. Farther north at the northern flank of Clayton Valley, the eastern basin-bounding faults are locally truncated by a NW trending fault, north of which displacement coalesces into two NNE faults. Cumulative vertical displacement for basin-bounding faults, referenced to a common pre-deformational datum of 2550 meters, is 6.1 km. Estimated horizontal displacement across Clayton Valley ranges from 10.5 to 3.5 km, depending upon the dip of the bounding faults which can only be resolved as between 30° to 60°.