Reconstruction of Basin and Range extension and westward motion of the Sierra Nevada Block

Abstract

Recent studies, including structural mapping, stratigraphic and sedimentologic studies, geothermochronology, and geodetic measurements, have improved our understanding of the kinematics of Miocene to Recent deformation in the central Basin and Range. Based on reconstructions of rocks in the extensionally dismembered foreland and leading edge of the Sevier thrust belt, offset along the Las Vegas Valley shear zone, and on the provenance of a unique clast assemblage in proximal channel fades deposits at Frenchman Mountain, the southern and northern Lake Mead extensional domains have extended ~94 km and ~46 km, respectively. A compilation of >70 cooling ages from the Gold Butte crystalline block indicates that onset of this extension occurred at ~20 Ma, with rapid, large-magnitude extension beginning at ~15 Ma. In the Death Valley extended domain, studies of the provenance, depositional environment, and age of the Eagle Mountain Formation show that middle Miocene siliciclastic strata occurring in a northwest-trending belt from Chicago Valley to the Cottonwood Mountains were all deposited in an environment proximal to the Hunter Mountain batholith of the Cottonwood Mountains. This requires ~100 km of roughly southeast-northwest extensional and strike-slip displacement since ~11 Ma. Identification of extensionally dismembered Cenozoic structures, correlative with structures in the Cottonwood Mountains, Panamint Range, Bare Mountain, the CP Hills, and the Funeral Mountains, are also consistent with ~100 km of west-northwest extension across the Death Valley region.

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