Geometry and structural history of the Mesozoic thrust belt in the Goodsprings district, southern Spring Mountains, Nevada

Abstract

The geometry of Mesozoic thrust faults in the Goodsprings district is typical of the Mesozoic frontal thrust belt between Nevada and Canada in that the thrust plates have a decollement geometry. Each thrust fault carries a sequence of shallow-water marine carbonate rocks ranging from Middle Cambrian through Permian in age eastward over coeval rocks of a more cratonal facies. Unlike the general pattern in much of the thrust belt to the north, younger thrusts did not develop progressively eastward of older thrusts in the Goodsprings area. Spatial and temporal relations of thrust faults in the Goodsprings area are more like those in the nearby Mesozoic thrust belt of southeastern California, where younger thrust faults are superposed on, or reactivate, older ones. The three major west-dipping Mesozoic thrust faults in the Goodsprings district are, from west to east, the Green Monster, Keystone, and Contact thrusts. The trace of the Keystone thrust, which traverses the entire length of the Spring Mountains, has a westward recess in the Goodsprings area, within which remnants of the older Contact thrust plate are exposed structurally beneath the Keystone thrust fault. A complex system of east-trending structures, transverse to the regional strike of the thrust belt, occurs adjacent to the south side of the recess in the Keystone thrust trace and is genetically related to the emplacement of the Keystone thrust plate. This system of transverse structures was fundamentally controlled by a set of frontal and transverse ramps on which the Keystone plate was thrust over the Contact plate and the autochthon. The Green Monster thrust plate, which is also older than the Keystone plate, apparently was carried passively within the Keystone plate during movement on the Keystone thrust fault. Parts of the Contact and Keystone thrust plates appear to have moved over erosional surfaces.