Abstract

The Rawhide fault in western Arizona is a major Miocene detachment surface that separates an autochthonous Mesozoic–early Tertiary(?) metamorphic complex from an allochthon of chaotically imbricated Precambrian(?) igneous and metamorphic, Paleozoic metasedimentary, Mesozoic(?) igneous and metamorphic, and Tertiary sedimentary and volcanic rocks. Lower-plate metamorphic rocks consist largely of mylonitic quartzofeldspathic gneisses with a strong mineral lineation trending 20° S, 48° W. These gneisses yield early Tertiary K-Ar ages. The allochthon is composed of two major sheets that are broken, independently, by a myriad of Miocene high- and low-angle normal faults.

The Rawhide fault formed by the coalescing of listric normal faults along a favorable structural horizon, presumably near the top of the metamorphic complex. Tectonic denudation of the metamorphic complex along the Rawhide fault occurred between 16.2 and 9.6 m.y. ago. Structural analyses indicate movement of the allochthon toward the northeast. The nature, geometry, and style of deformation suggest that the highly disrupted upper-plate terrane was most likely produced by the detachment, probably by gravity, of the Precambrian(?) to Miocene cover rocks from the underlying Mesozoic–early Tertiary(?) metamorphic complex.

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