STRUCTURES IN THE TIMPAHUTE AND PAHRANAGAT RANGES, SOUTH-CENTRAL NEVADA, AS A PART OF REGIONAL LATE PALEOZOIC DEFORMATIONS

Pennsylvanian and Permian structures are exposed in north-central Nevada and Death Valley/southern Nevada. Our new data from the intervening region in the Timpahute and Pahranagat ranges, south-central Nevada, suggest late Paleozoic deformation is more widely distributed. New map data detailing cross-cutting relationships, U/Pb dating and retrodeformable cross sections aided in recognizing these late Paleozoic structures.

In the Timpahute Range, all contraction is constrained between Pennsylvanian and intrusion of the 102.9 ± 3.2 Ma Lincoln stock. The Range contains a W-vergent, N-trending fold, the Chocolate Drop anticline (CDA). One CDA limb is cut by the ~N-striking, steeply dipping, W-vergent Schofield Pass fault zone (SPFZ) and is refolded by mesoscale folds parallel to the SPFZ. The SPFZ juxtaposes Cambrian and Pennsylvanian units. Deeper water facies occur on the W, in the footwall, than on the E. Retrodeformed cross sections suggest uplift of the CDA and SPFZ along a ramp where a duplex formed during later, Mesozoic Central Nevada Thrust Belt (CNTB) shortening.

In the Pahranagat Range, the ~N-striking, Badger Mountain fault (BMF) locally places Cambrian units on the E against Mississippian clastic units on the W. The BMF was excised or reactivated because Oligocene-Miocene tuffs also are offset, but much less than Paleozoic units. Deeper water facies occur on the W than on the E. Cenozoic normal faults obscure the BMF dip direction, but map patterns suggest a steep E dip, making the BMF originally W-vergent. Retrodeformed cross sections show uplift of the BMF along a ramp in a CNTB thrust.

The CDA, SPFZ, and BMF likely formed at the same time as other ~N-trending, W-vergent structures in the Nevada National Security (Test) Site and Death Valley area. Near Death Valley, the age is better constrained to before ~230 Ma, but probably Permian (Snow et al., 1991, Geology). During late Pennsylvanian-Permian, these structures lay inboard of two different tectonic regimes: the oblique subduction/transpressional closing of the Slide Mountain Ocean to the NW and the Oauchita-Marathon orogeny far to the SE. The orientation, structural style and spatial location are consistent with formation as a result of transpression to the NW followed by (1) uplift by Mesozoic CNTB structures and (2) Cenozoic extensional overprint.