MIOCENE MAGMATISM OF THE CENTRAL DEATH VALLEY RHOMBOCHASM, USA

The Central Death Valley Rhombochasm (CDVR) is a transtensional sequence of basins and volcanic highlands superposed on a supracrustal detachment, the Amargosa Fault. The CDVR formed in the releasing step-over between the Furnace Creek and southern Death Valley faults; both NW-trending, right-lateral, strike-slip faults. Bounding structures include the eastern and western frontal faults of the Resting Spring and Panamint ranges, respectively. Oblique-slip faults internal to the CDVR also accommodate NW migration of depocenters. The Navadu assemblage of syn-basin-range fill (Fridrich and Thompson, 2011) of the CDVR includes volcanic deposits (ca. 11.5-7.8 Ma) and intrusions (ca. 10.2-8.6 Ma) of the Central Death Valley volcanic field and associated basin deposits emplaced during periods of high magmatic flux, extension, uplift, and erosion of the area underlain by the Black Mountains and Greenwater Range. Detailed- and regional-scale geologic mapping, correlation of volcanic units, and new geochronology, including ⁴⁰Ar/³⁹Ar ages of volcanic rocks and U-Pb LA-ICP-MS zircon crystallization ages for plutons and ignimbrites, are used to establish constraints on fault slip orientation, timing, and offset for the time-transgressive propagation of CDVR bounding and intrabasin faults.

The Rhodes Tuff (ca. 10.8 Ma) and tuff of Resting Spring Pass (ca. 10.0 Ma) are inferred to be sourced from a buried caldera central to the CVDR in the Greenwater range. In the south-central CDVR, from Salsberry Pass to Sheephead Pass, outflow Rhodes Tuff thickens north of, but is absent south of the intrabasin, right-lateral Sheephead fault. The fault is intruded by ca. 10.9 Ma dacite porphyry dikes, suggesting concurrent oblique-slip motion. Outflow tuff of Resting Spring Pass caps and ponds against the western Resting Spring range front, suggesting range tilting occurred prior to ~10Ma. The tuff of Resting Springs Pass occurs as debris flow deposits in the Artist Drive Fm, and as distal deposits along the eastern rangefront of the Panamint Mountains. Exposed Navadu-stage silicic intrusions, unconformably overlain by ca. 8.7 to 8.0 Ma Shoshone rhyolite lava flows, constrain significant uplift and post-detachment denudation of the Black Mountains and Greenwater Range to between approximately 10-8 Ma.