Abstract

New field and geophysical evidence from Jurassic mafic and ultramafic rocks in western Nevada indicate the presence of two major ophiolite complexes tectonically overlying the rocks of the North American continental margin. Coupled with the existence of Jurassic and older island arc-marginal basin complexes and overthrust relations in the adjacent Sierran-Klamath region, these ophiolitic thrust nappes in Nevada support collision models for the middle Jurassic deformation. The geometry of the observed structures and their relative age relationships suggest that this deformation might have resulted from the collision of the North American continent with a west-dipping subduction zone which resulted in ophiolite emplacement and continental underthrusting. Continued westward motion of North America beneath the allochthonous oceanic terranes during the late Mesozoic developed extensive thrust and possible strike-slip faulting in the western US Cordillera and caused migration of deformation towards the east. This eastward propagation of deformation is interpreted to have resulted in the development of the Sevier foreland thrust belt of latest Jurassic to latest Cretaceous age. These collisional processes and the geometry of the proposed collision orogen are reminiscent of the alpine-type collision belts.

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