Abstract

Spokane dome, located in the southern Priest River complex, is defined by a zone of gently dipping mylonitic rocks about 4 km thick. In contrast to more "typical" core complexes, the mylonitic deformation gradually fades both above and below the zone without an intervening, nearly concordant zone of chloritic brecciation. Thin, younger, mylonitic rocks within the synformal Newport Fault Zone overlie Spokane dome to the north, and a younger, low-angle(?) fault cuts the mylonites in the Purcell Trench to the east.The mylonitic rocks within Spokane dome contain C and S surfaces and other mesoscopic structures indicating, in all cases, top to the east movement. In contrast, the mylonitic rocks within the Newport Fault Zone formed during normal movement on both the eastern and western limbs of the fault. The mylonites of Spokane dome probably formed during large-scale, Mesozoic, top to the east intracontinental shear, whereas the Newport Fault records Eocene extension and crustal "megaboudinage."

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