Structural and stratigraphic evolution of the Weepah Hills Area, NV : transition from basin-and-range extension to Miocene core complex formation
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The Weepah Hills Area (Nevada) exposes exhumed metamorphic and plutonic rocks and upper-plate (supradetachment) volcano-sedimentary rocks that have experienced a complex, multi-stage deformational and depositional history. The Weepah Hills metamorphic core complex (WHMCC) is located in a region of the western Cordillera that was affected by both Miocene Basin-and-Range style E-W extension and Mio-Pliocene Walker Lane transcurrent shearing. Mio-Pliocene transcurrent deformation is transferred across a ~175 km releasing bend, known as the Mina Deflection, that kinematically links dextral strike-slip faults of the Death Valley-Fish Lake Valley with the central Walker Lane Belt. Progressive Mio-Pliocene transtension is characterized by core complex detachment faulting and younger high-angle normal faults. Timing of detachment faulting is constrained by both (U-Th)/He thermochronometry of footwall rocks and detailed chronostratigraphy of upper-plate strata to between 9-6 Ma. This age is supported by deformation recorded in the upper-plate strata that is attributed to progressive folding of the detachment associated with corrugation development. Earlier Miocene Basin-and-Range style extension is characterized by N-S trending high-angle normal faults and half-grabens that are strongly overprinted by Mio-Pliocene structures. (U-Th)/He zircon cooling ages from the detachment footwall range from ~12-20 Ma and are attributed to exhumation and unroofing related to E-W Basin-and-Range extension. New detailed sedimentological and geochronologic data show that, in contrast to previous research, the WHMCC upper-plate strata do not form a single supradetachment package, but rather three temporally distinct Miocene stratigraphic packages bounded by angular unconformities. The stratigraphic, structural, and exhumational record preserved in the WHMCC elucidates the timing of deformation and sedimentary basin evolution related to both Basin-and-Range E-W extension and Walker Lane related NW-directed transtension.