Structural, stratigraphic, and geochronologic evidence for extension predating Palaeogene volcanism in the Sevier hinterland, east-central Nevada

Eocene-Early Miocene paleotopography of the Sierra Nevada-Great Basin-Nevadaplano based on widespread ash-flow tuffs and paleovalleys

“…1; Henry, 2008;Cassel et al, 2009aCassel et al, , 2009bHenry and Faulds, 2010). The absolute elevation and structural-topographic evolution of this highland in the mid-Cenozoic remain highly controversial, however, particularly the paleoelevation of what is now the Sierra Nevada (Wakabayashi and Sawyer, 2001;Mulch et al, 2006Mulch et al, , 2008Cassel et al, 2009aCassel et al, , 2009bMolnar, 2010) and the timing of extension in northeastern Nevada, especially around the Ruby Mountains-East Humboldt Range metamorphic core complex (McGrew and Snee, 1994;Snoke et al, 1997;McGrew et al, 2000;Howard, 2003;Colgan and Henry, 2009;Druschke et al, 2009;Colgan et al, 2010;Henry et al, 2011;Mix et al, 2011).…”

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“…In support of this assumption, many have argued that much of the Sevier hinterland was a tectonically quiescent, low-relief, externally drained landscape that persisted until initiation of regional extension in the Middle Miocene (e.g., Henry et al, 2004Henry et al, , 2011Henry et al, , 2012Faulds et al, 2005;Henry, 2008;Best et al, 2009;Colgan and Henry, 2009;Colgan et al, 2010). However, in contrast, several authors have argued for locally rugged topography in the Sevier hinterland as a result of localized extensional faulting possibly as old as latest Cretaceous, which continued through the middle Cenozoic (e.g., Vandervoort and Schmitt, 1990;Fouch et al, 1991;Potter et al, 1995;Camilleri, 1996;Dubiel et al, 1996;Druschke et al, 2009aDruschke et al, , 2009bDruschke et al, , 2011. This indicates that additional work is needed to justify the assumption of low relief, and for this reason only regional-scale subcrop patterns suggesting folding are labeled with fold axes in Plate 2.…”

“…Across the majority of the study area, the oldest preserved post-Triassic rocks are Late Eocene and Oligocene intermediate to silicic lavas and tuffs of the ignimbrite fl areup (e.g., Hose and Blake, 1976;Coney, 1978Coney, , 1980Armstrong and Ward, 1991;Best and Christiansen, 1991;Henry, 2008;Best et al, 2009). However, in several places in western Utah and eastern Nevada, scattered exposures of alluvial and lacustrine rocks between latest Cretaceous (Maastrichtian) and Middle Eocene age, including the Sheep Pass Formation and correlative strata (e.g., Vandervoort and Schmitt, 1990;Fouch et al, 1991;Potter et al, 1995;Camilleri, 1996;Dubiel et al, 1996;Druschke et al, 2009aDruschke et al, , 2009bDruschke et al, , 2011, are the oldest preserved post-Triassic rocks. The subcrop data compiled in Plate 1 do not distinguish between localities where Eocene-Oligocene or latest Cretaceous-Eocene rock units overlie the unconformity.…”

“…To generate a detailed paleogeologic map, multiple exposures of a regionally extensive unconformity are required to allow compilation of data on the spatial distribution and ages of rocks exposed beneath it. In the Sevier hinterland region in eastern Nevada and western Utah, a regional unconformity exists beneath Eocene to Oligocene volcanic rocks (e.g., Coney, 1978Coney, , 1980Stewart and Carlson, 1978;Armstrong and Ward, 1991;Best and Christiansen, 1991), and locally beneath latest Cretaceous to Eocene sedimentary rocks (e.g., Fouch et al, 1979Fouch et al, , 1991Vandervoort and Schmitt, 1990;Druschke et al, 2009b). In this study, these unconformities are utilized to generate a Paleogene paleogeologic (or subcrop) map of the Sevier hinterland, in order to illustrate the preextensional structural relief of this region.…”

“…Thus, this map illustrates magnitudes and spatial patterns of synorogenic erosional exhumation in the Sevier hinterland. Several important regional implications of these subcrop and exhumation data sets are examined, including evidence in favor of structural correlations between the central Nevada and Sevier thrust belts originally suggested by Taylor et al (2000), constraints on the map pattern of the Windermere thrust of Camilleri and Chamberlain (1997), and a valuable contribution to the vigorously debated controversy over the timing, magnitude, and spatial distribution of pre-Middle Miocene extensional deformation in the Sevier hinterland (e.g., Gans and Miller, 1983;Vandervoort and Schmitt, 1990;Best and Christiansen, 1991;Hodges and Walker, 1992;Camilleri and Chamberlain, 1997;Snoke et al, 1997;McGrew et al, 2000;Henry, 2008;Wallace et al, 2008;Colgan and Henry, 2009;Colgan et al, 2010;Druschke et al, 2009aDruschke et al, , 2009bDruschke et al, , 2011Henry et al, 2011Henry et al, , 2012. In addition, a comparison of exhumation patterns between the Sevier and central Andean orogenic plateaus is included, as well as a discussion of the fi rstorder controls on exhumation patterns in orogenic plateaus.…”