PENNSYLVANIAN - CRETACEOUS SHORTENING IN NEVADA: EVIDENCE FROM THE TIMPAHUTE RANGE

Between the Devonian-Mississippian Antler and the Permian-Triassic Sonoma orogenies, south-central Nevada was thought to be tectonically quiet. However deformations of this age are exposed in north-central Nevada and Death Valley/southern Nevada. Both areas also expose Jurassic-Cretaceous (Sevier) age deformation. If the orogenic belts in these two regions are continuous, then they should be present in south-central Nevada. We investigated the Timaphaute Range in this intermediate area to determine whether deformations of these ages track through the area. Identifying geometries, spatial relationships, and relative timing of strctures in this area, is essential to completing the understanding of western U.S. tectonism. New geologic maps documenting cross-cutting relationships of structures, U/Pb ion microprobe dating and cross sections result in recognizing new structural relationships.

All contraction in the Range is constrained between Mississippian to Pennsylvanian units of the Antler foreland basin/overlap assemblage and newly dated 102.9 ±3.2Ma zircons of the Lincoln stock. The western Timpahute Range contains the W-vergent, N-trending Chocolate Drop anticline (CDA) that represents the earliest shortening. The eastern limb of the CDA is cut by the W-vergent Schofield Pass fault zone (SPFZ). This E-dipping limb of the CDA is refolded by mesoscale folds that parallel the SPFZ. The last contraction formed the NE-vergent Lincoln duplex of the central Nevada thrust belt (CNTB). New mapping allows correlation of the Lincoln duplex through the range. Retrodeformable cross sections show uplift of the CDA and SPFZ along the ramp where the Lincoln duplex formed.

Given the timing and geometries of these structures, correlation through the region is possible. Pre-Sevier/CNTB structures (CDA, SPFZ) likely correlate N and S to zones of N-trending, W-vergent structures. The Lincoln duplex correlates N to the Frieberg-Rimrock thrusts, and thus, farther N into the CNTB. The structures join S into the Spotted Range thrust in the Nevada Test Site. These correlations suggest (1) a zone of pre-Sevier contraction that continues from Death Valley/southern Nevada into north-central Nevada that locally is overprinted by Sonoma or Sevier/CNTB age structures and (2) spatially non-sequential tectonic development.