The Mahogany Peaks fault, a late Cretaceous-Paleocene(?) normal fault in the hinterland of the Sevier orogen

Wells, Michael L. and Hoisch, Thomas D. and Peters, Mark T. and Miller, David M. and Wolff, Evan D. and Hanson, Lori M. (1998) The Mahogany Peaks fault, a late Cretaceous-Paleocene(?) normal fault in the hinterland of the Sevier orogen. Journal of Geology, 106. pp. 623-634. ISSN 1537-5269

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Abstract

The contact separating Ordovician rocks from the underlying lower part of the Raft River Mountains sequence, northwestern Utah, is reinterpreted as a large-displacement low-angle normal fault, the Mahogany Peaks fault, that excised 4-5 km of structural section. High delta(13)C values identified in marble in the lower part of the Raft River Mountains sequence suggest a Proterozoic, rather than Cambrian age. Metamorphic conditions of hanging wall Ordovician and footwall Proterozoic strata are upper greenschist and middle amphibolite facies, respectively, and quantitative geothermometry indicates a temperature discontinuity of about 100 degrees C. A discordance in muscovite Ar-40/Ar-39 cooling ages between hanging wall and footwall strata in eastern exposures, and the lack of a corresponding cooling age discordance in western exposures, suggest a component of west dip for the fault. The juxtaposition of younger over older and colder over hotter rocks, the muscovite cooling age discordance with older over younger, and top-to-the-west shearing down-structure are consistent with an extensional origin. The age of faulting is bracketed between 90 and 47 Ma, and may be synchronous with footwall cooling at about 60-70 Ma. Recognition of the Mahogany Peaks fault, its extensional origin, and its probable latest Cretaceous to Paleocene age provides further evidence that episodes of extension at mid-crustal levels in the hinterland of the Sevier orogenic belt were synchronous with protracted shortening in the foreland fold and thrust belt, and that the Sevier orogen acted as a dynamic orogenic wedge.

Item Type:	Article
Publisher’s Statement:	© 1998 by The University of Chicago. Published in the Journal of Geology.
ID number or DOI:	10.1086/516046
Keywords:	Stratigraphic geology -- Ordovicianxtension; metamorphic core complex; muscovite; northwestern canada; precambrian carbonates; Rocks; southern Idaho; thrust belt; Utah
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Faculty/Staff
Department/Unit:	College of Engineering, Forestry, and Natural Science > School of Earth Sciences and Environmental Sustainability
Date Deposited:	11 Dec 2015 16:47
URI:	http://openknowledge.nau.edu/id/eprint/894

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