CONSTRAINTS ON TIMING AND RATES OF DEFORMATION, VOLCANISM AND ASSOCIATED BASIN FORMATION IN THE CENTRAL DEATH VALLEY REGION, CALIFORNIA AND NEVADA

Volcanism (12.5-0.4 Ma) in the central Death Valley region of California and Nevada was spatially and temporally coincident with large-scale regional extension accommodated in part by regional detachment faulting, extensive footwall uplift, and significant strike-slip displacement along northwest-trending faults. In excess of 700 km³ of lava flows, domes, and pyroclastic deposits were emplaced from numerous centers mainly in the upper plate of a northwestward propagating detachment system. Four stages of volcanism (12-8.5 Ma; 8.5-7.5 Ma; 7.0-5.5 Ma; 5.0 -0.4 Ma) are defined for central Death Valley based on identification of both local and regional unconformities within the volcanic field and on regional correlation of preserved, but variably distended volcanic sections. These correlations are supported by ⁴⁰Ar/³⁹Ar geochronology, in addition to 1:24,000 scale geologic mapping, petrographic, and geochemical characterization of the stratigraphic section comprising the central Death Valley volcanic field. The degree of extensional deformation or attenuation associated with any given eruptive cycle is used to constrain rates of extension and the reconstruction of aerial distribution of volcanic deposits provides estimates of eruptive volumes. Uplift associated with extension is temporally constrained by field observations, petrologic correlation and geochronology relating extrusive rocks to their exposed subvolcanic plutons in the lower plates of regional detachment systems and by regional correlation with associated sedimentary deposits. Sedimentary sequences within the central Death Valley region have been correlated with regional-scale basal unconformities that have approximate initiation ages of 16, 12.5, 6 and 3 Ma. These unconformities are time-transgressive, and in part record northwestward migrations of causative tectonic pulses over intervals of 2-5 million years. These basal unconformities currently occupy positions within locally preserved sedimentary sequences that range from regionally distended, structurally disparate occurrences for sections older than 6 m.y. to largely intact younger stratigraphic sections deposited in small, closed basins adjacent to active volcanic centers.