Abstract
Miocene basalt lavas in eastern California provide a useful tool for deciphering the recent structural evolution of the White Mountains (WM). The Tres Plumas (TP) and Deep Springs Valley (DSV) basalt lavas are two separated (~22 km apart) exposures that have been loosely correlated in other studies. Trace element geochemistry suggests the lavas are correlated. Geologic mapping has revealed an accumulation of scoria, indicating a vent proximal deposit, at Chocolate Mountain in DSV. Exposures of lava in DSV extend to the west and thin distally relative to Chocolate Mountain, indicating a westward flow direction. An alluvial sedimentary deposit beneath the basalt in DSV and at Iron Mountain, a locality between DSV and TP, suggests the lavas flowed within one or multiple paleo-channels. A tephrochronology analysis on the tuff of TP yields glass compositions similar to tuffs sourced from the Southern Nevada Volcanic Field, 100 km to the southeast of TP. This indicates the ash-flow tuff of TP flowed in a northwest direction toward emplacement prior to the tilting of the White Mountain fault block. The tuff of Cottonwood is a ~40 meter thick ash-flow, welded rhyolitic tuff unit. The tuff is exposed underlying lava, has equal mineral assemblage to the tuff of TP, is tilted 21° to the east. The tuff of Cottonwood likely has a similar emplacement history as the tuff of TP. The overlying lava is interpreted to be close in age to the tuff of Cottonwood and TP, meaning it is possible the lava flowed in the same northwest direction as the tuff of Cottonwood. Due to the current elevation differences of scattered basalt outcrops in the WM, a northwest interpreted flow for the lavas would indicate that their eruption and emplacement predates tectonic tilting of the WM fault block. The whole rock radiometric 40Ar/39Ar age of 11.75 Ma for the basalt at TP could serve as a timing constraint for the initiation of southeast WM tilting. The structural and temporal constraint for WM tilting proposed is in close agreement with the models of previous workers. The tilting deciphered here happened concurrently, and potentially in association with, the uplift of the WM fault block.