Late Jurassic to Middle Cretaceous Evolution of the Southern Sevier Fold-Thrust Belt: Timing of the Wheeler Pass and Keystone Thrust Systems, Southern Nevada and California.
Michael Wells, Department of Geoscience, University of Nevada Las Vegas
Michael Giallorenzo, Department of Geoscience, University of Nevada Las Vegas
Adolph Yonkee, Department of Geosciences, Weber State University
Brian Wernicke, Division of GGeological and Planetary Sciences, California Institute of Technology
Daniel Stockli, Jackson School of Geosciences, University of Texas, Austin
Zircon (U-Th)/He (ZHe) thermochronologic data for 46 samples from the Wheeler Pass (WP) thrust sheet, which carries thick passive margin strata and is discontinuously exposed across the southern part of the Sevier fold-thrust belt, record Late Jurassic cooling related to exhumation during early thrust slip, and local middle Cretaceous cooling related to footwall basement imbrication. Within the frontal part of the WP sheet exposed in the northwest Spring Mountains, ZHe ages decrease from ~160 to 140 Ma over a paleodepth interval of ~6 to 9 km in Devonian to Lower Cambrian strata, interpreted to record exhumation and enhanced cooling above a frontal ramp, followed by slow cooling. A similar pattern of ZHe ages occurs over a more limited paleodepth range exposed within the Resting Spring Range. To the south in the Nopah Range, ZHe ages of ~140 Ma in Lower Cambrian strata record early cooling, followed by slow cooling until ~100 Ma. ZHe ages in underlying Paleoproterozoic basement rocks decrease from ~100 to 85 Ma over a paleodepth interval of ~9 to 12 km, interpreted to record uplift, exhumation and cooling during footwall basement imbrication as slip was transferred eastward onto the Keystone thrust system. New U-Pb detrital zircon geochronology provides maximum depositional ages for synorogenic deposits associated with the Keystone thrust system including the base of the Willow Tank Formation (101.7 +0.4/-0.5 Ma) and the conglomerate of Brownstone basin (3 samples: 102.8 +1.0/-1.2 Ma; 103.3 +1.0/-1.1 Ma; 102.1 +1.7/-0.9 Ma). Late Jurassic slip on the WP thrust overlapped with deformation along the NW-trending East Sierran thrust system, early hinterland crustal thickening, and growth of the Sierra magmatic arc, and may be correlative with early deformation in the Central Nevada thrust belt. Slip on the WP thrust preceded major slip on other thrust sheets that carried thick passive margin strata in more northern parts of the Sevier belt, probably reflecting the influence of different initial widths and tapers of the passive margin sedimentary wedge.