Paper No. 11
Presentation Time: 11:30 AM


THOMPSON, Ren A., FRIDRICH, Christopher J. and ZELLMAN, Kristine, U.S. Geological Survey, Box 25046, DFC, MS 980, Denver, CO 80225,

The central Death Valley volcanic field records the coincident and related magmatism that occurred during the extreme extension and strike-slip strain that formed the central Death Valley rhombochasm. This rhombochasm is a 65x80-km rhombic pull-apart basin complex that occupies the releasing step-over between the northern Death Valley—Furnace Creek and southern Death Valley faults. In the multi-stage evolution of this tectonic-magmatic feature, changes in volcanic and structural styles, rates, and loci were synchronized, both spatially and temporally. Most of the volcanic terrane was mapped at scales ranging from 1:24k to 1:100k for inclusion in the Death Valley Junction 100k geologic map presented here. The volcanic field covers an area of 3600 km2, and consists of >700 km3 of lava flows, domes, and pyroclastic deposits. Lithostratigraphic map units are the deposits of four major eruptive stages: Stage 1 (11-9 Ma: rhyolite and andesite), Stage 2 (9-7.5 Ma: dacite>basalt>andesite), Stage 3 (7-5 Ma: dacite>basalt), and Stage 4 (4.5-0.7 Ma: basalt). The predominant loci of eruptive centers migrated northwestward during this volcanic evolution, coeval with northwestward migration of tectonically controlled, adjacent depocenters. Stage 1 and 2 volcanism is broadly correlative to the supradetachment stage of rhombochasm development. Related instrusions include exposed upper-plate hypabyssal and lower-plate plutonic bodies. Stage 3 and 4 volcanism occurred during two tectonic stages in which higher-angle faults cut across the detachment fault, forming basins that are nested within the original detachment-floored area of the rhombochasm. Time-transgressive changes from dominantly silicic and intermediate magmas in Stages 1 and 2 to dominantly mafic and lesser intermediate magmas in Stages 3 and 4 coincided with decreases in eruptive volumes and rates, suggesting decreasing recharge to the magma system through time. Because of these changing volcanic rates, early syn-detachment basin fill in the rhombochasm is dominantly volcanic, where post-detachment basin-fill is mainly sedimentary. The spatial and temporal evolution of the central Death Valley volcanic field supports the coupled partitioning of extensional strain between regional faulting and middle to upper crustal magma emplacement.