Abstract

Geologic mapping of active to recently active geologic structures in Panamint Valley (western United States) and in the Haiyuan region and northern Tibetan plateau (China) suggests detachment in the middle and lower crust on a scale of tens of kilometres to at least several hundred kilometres. Detachment occurs similarly in predominantly extensional (Panamint Valley) and in predominantly compressional (China) environments. It involves structures with displacements of more than 10 km and displacement rates of more than 3 mm/yr, perhaps more than 10 mm/yr. The steeply dipping strike-slip faults present in all three areas (Hunter Mountain fault, Haiyuan fault, and Altyn Tagh fault zone) terminate in zones of extension or compression, and geometric relations indicate that all structures (including strike-slip faults) are thin-skinned and restricted to the upper crust. In Panamint Valley and in the Haiyuan region deformation within these systems can be reconstructed in three dimensions. Displacement on the strike-slip faults is absorbed by extension or compression occurring at the termination of the faults, so strike-slip displacement is roughly equal to and in the same direction as shortening or extension. We propose that left slip on the Altyn Tagh fault zone in northern Tibet is similarly absorbed by shortening southeast of the fault zone within the Qaidam basin and the Nan Shan.

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