Paleogeographic isolation of the Cretaceous to Eocene Sevier hinterland, east-central Nevada: Insights from U-Pb and (U-Th)/He detrital zircon ages of hinterland strata

Abstract

The Late Cretaceous to Paleogene Sevier hinterland of east-central Nevada is widely regarded as an orogenic plateau that has since undergone topographic collapse. New U-Pb detrital zircon age data consisting of 1296 analyses from the Lower Cretaceous Newark Canyon Formation and the Upper Cretaceous to Eocene Sheep Pass Formation indicate that Precambrian detrital zircon populations recycled from local Paleozoic strata are dominant. Subordinate Mesozoic zircon populations are derived mainly from local backarc volcanic centers of Late Jurassic and Early Cretaceous age, while ca. 38-36 Ma detrital zircon age peaks record the local onset of Eocene volcanism. Sevier hinter land deposits of east-central Nevada lack signifi cant Triassic, Early Jurassic, and Late Cretaceous populations common in terranes of western Nevada and the Sierra Nevada magmatic arc. These data suggest that long-term evolution of the Sevier Plateau involved geographic isolation through a combination of high relief and rugged topography related to Early Cretaceous shortening, and continued isolation through development of latest Cretaceous to Eocene internally drained, extensional basins. The (U-Th)/He zircon ages obtained from the Sheep Pass Formation record late Paleozoic, Early Cretaceous, and Late Cretaceous cooling through 180 °C. Preservation of late Paleozoic (ca. 265 Ma) cooling ages indicates that much of the Upper Paleozoic section within east-central Nevada that contributed detritus to the Sheep Pass basin was un affected by deep thrust burial, or by burial beneath thick Mesozoic sedimentary cover. Early Cretaceous (ca. 135 Ma) cooling ages are potentially coeval with shortening along the central Nevada fold-and-thrust belt, although ca. 80 Ma cooling ages within the Sheep Pass Formation are coeval with hinter land midcrustal extension. Together, these new data provide support for previous interpretations that the Sevier hinterland represents an ancient high-elevation orogenic plateau, and that the latest Cretaceous locally marks a transition from contraction to extension.

Profile of a paleo-orogen: High topography across the present-day Basin and Range from 40 to 23 Ma

“…Researchers have also associated extensional episodes with the end of normal slab-angle subduction (ca. 80 Ma; Wells and Hoisch, 2008;Druschke et al, 2011) and with plate motion changes during the transition to a transform margin (ca. 16 Ma;McQuarrie and Wernicke, 2005;Colgan and Henry, 2009).…”

“…1), including the Piñon Range (Horton et al, 2004), Copper Basin (Wolfe et al, 1998), and the Snake Range (Gébelin et al, 2012), but regionally extensive records before the middle Miocene are lacking (Chamberlain et al, 2012, their figures 2C-2F). Pre-extensional crustal thicknesses, estimated at up to 50-60 km (e.g., Coney and Harms, 1984), may have supported high topography in the region, but it is unclear how proposed large-magnitude Cretaceous to Eocene extension and core-complex formation (e.g., Wells and Hoisch, 2008;Druschke et al, 2011) or rollback of the shallow Farallon slab (e.g., Hodges and Walker, 1992;Chamberlain et al, 2012) would have affected topography. Arguments for major surface lowering driven by 16-10 Ma extension (e.g., McQuarrie and Wernicke, 2005;Colgan and Henry, 2009) and evidence of Oligocene drainage network connectivity (Cassel et al, 2012;Henry et al, 2012), however, suggest minimal pre-Miocene extension or surface lowering.…”

The Confusion Range, west-central Utah: Fold-thrust deformation and a western Utah thrust belt in the Sevier hinterland

“…Paleogene conglomerates, lacustrine limestones, and interbedded volcanics were deposited in local basins and paleochannels, possibly related to early extensional collapse within the plateau (Vandervoort and Schmitt, 1990;Constenius, 1996;Greene and Herring, 1998;Hintze and Davis, 2003;Druschke et al, 2011;Lechler et al, 2013). Widespread pyroclastic volcanism, the "ignimbrite fl areup" (Coney, 1978;Best et al, 2009Best et al, , 2013, began in the late Eocene and continued through the early Miocene.…”

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“…1). Intramontane CretaceousPaleogene deposits within the Sevier orogen between the Sierra Nevada and the Sevier thrust belt contain few arc-derived detrital zircon grains (Druschke et al, 2011). Minor detrital zircon grains of Jurassic and Cretaceous age may have reached the foredeep from backarc igneous centers (du Bray, 2007) located east of the main arc trend along the Sierra Nevada.…”