Geologic and thermochronologic constraints on the initial orientation of the Raft River detachment and footwall shear zone

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Conference Proceedings: Geologic and thermochronologic constraints on the initial orientation of the Raft River detachment and footwall shear zone

Abstract
The Raft River Mountains of northwestern Utah expose a detachment fault that separates a hanging wall of Paleozoic rocks from Proterozoic and Archean rocks of the footwall. Beneath the detachment lies a 100 to 300m-thick top-to-the-east extensional shear zone. Geologic mapping, strain and kinematic analysis, and 40Ar/39 Ar thermochronology suggest that the shear zone and detachment fault had an initial low-angle regional dip(<20°). Along a 27 km, E-W transect across the south flank of the range, the base of the shear zone everywhere lies 20 to 60 m beneath the Archean/Proterozoic unconformity, despite an eastward-increasing lateral strain gradient. Strain analyses of mylonite coupled with the regional relationship between the unconformity and the shear zone boundary indicates that the unconformity and overlying Proterozoic metasediments were not rotated into parallelism with the shear zone boundary, but were initially subparallel (0--2°). Constraints on the initial orientation and crustal position of the shear zone have been derived from 40Ar/39 thermochronology of mineral suites (hornblende, muscovite, biotite, and k-feldspar) collected within and beneath the shear zone along a 27 km transect parallel to the transport direction. Prior to the middle Eocene, the unconformity was between hornblende and muscovite closure across the E-W extent of the range. The western end of the range was uplifted to temperatures below muscovite and biotite closure at 44--47 Ma. This Eocene uplift is inferred to be related to footwall flexure resulting from tectonic denudation along a top-to-the-west extensional shear system exposed in the western Raft River, northern Grouse Creek, and southern Albion mountains. The unconformity in the central and eastern Raft River Mountain was uplifted to temperatures below muscovite and biotite closure from (approximately)24 to 14 Ma, during top-to-the-east tectonic denudation.

Authors 
Wells, M.L.; Snee and L.W.   








Published 
Geological Society of America, Abstracts with Programs; (United States), 4/1/1993





DOI 
Not Provided
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Citation

Wells, M.L.; Snee, L.W.   . 4/1/1993. Geologic and thermochronologic constraints on the initial orientation of the Raft River detachment and footwall shear zone. Proceedings of (!) ; (!) : Geological Society of America, Abstracts with Programs; (United States).