CONSTRAINTS ON POST-MIDDLE-PLEISTOCENE OFFSETS AND NEW PERSPECTIVES ON PLIO-PLEISTOCENE TECTONISM ALONG THE SOUTHERN DEATH VALLEY FAULT ZONE

New mapping and tephrochronology along the Southern Death Valley fault zone (SDVFZ) provide constraints on Pleistocene offsets and insights into post~3.3 Ma tectonism in Southern Death Valley (SDV). In the Confidence Hills (CH), initial movement along the right-lateral SDVFZ was preceded by intensive northeast-vergent, fault-propagation folding of the Confidence Hills Formation (CHF). This earlier folding resulted in ~0.6 km of shortening between 1.2-0.9 Ma. The intensive (~2 mm/yr), short-lived episode of shortening reflects northeast motion of the Owlshead Mountains (OM) block that was likely accommodated by coeval left-lateral slip on the Wingate Wash fault. Right-lateral offset of previously-folded CHF (~2.6-1.2 Ma) and unconformable capping gravel (≤0.9 Ma) are identical (~600 m), showing movement on the SDVFZ began after 0.9 Ma in the CH and yielding a well-constrained, average slip rate of ~0.7 mm/yr. Previous flower-structure models for the CH are problematic because: 1) earlier northeast-vergent folds require blind thrusts that are rooted southwest of the SDVFZ; and 2) slip along the SDVFZ trace began after earlier folding. Constraints on net offset (~420 m) along the SDVFZ northeast of the Noble Hills (NH) are based on shortening of Pliocene strata across a persistent restraining step over. Elsewhere in the area, the most prominent traces of the fault are expressed as small pressure ridges involving ≤0.64 Ma deposits. Field relations show that at least one previously mapped SDVFZ strand in the central NH is actually a subvertical depositional contact that lies in the steep-to-overturned forelimb of a large, northeast-vergent, fault-propagation fold involving ~500 m of conformable ≥3.3 Ma strata. Hence, intensive northeast-vergent contraction that extends the length of the NH likely began after 3.3 Ma. The conformable Pliocene strata contain clasts from both the OM to the north and the Avawatz Mountains to south, which brings into question previous interpretations of large-magnitude, right-lateral offset of these deposits. We view northeast-vergent contraction throughout SDV as being driven by clockwise rotation of the northeast Mojave block and resultant northeast-directed block movements north of the Garlock fault, not as secondary shortening along strands of the SDVFZ.