Abstract

Late Cretaceous deformation in southern Nevada and the adjacent part of California is part of the Sevier orogenic belt discussed by Armstrong (1968). Regional observations and detailed study in the northern Spring Mountains reveal a penetrative deformation, involving thrust faulting and folding that produced as much as 40 mi of crustal shortening. The tectonic style suggests a genetic relationship between folds and thrust faults, as translation occurred along the overturned limbs and axial surfaces of strongly asymmetric folds. The lack of stratigraphic control of thrust surfaces, the pervasive nature of the deformation, and the continuation of thrusts into Precambrian crystalline rocks are considered inconsistent with décollement or gravity-slide origins. The presence of a deep-seated Abscherungszone, as proposed by Armstrong (1963, 1968) and Armstrong and Hansen (1966) is consistent with observations. Thrust faulting was confined to a period between approximately 75 and 90 m.y. ago, although folding probably began somewhat earlier.

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