Geometry and magnitude of extension in the Basin and Range Province (39°N), Utah, Nevada, and California, USA: Constraints from a province-scale cross section

Abstract

The Basin and Range Province is a clas sic locality of continental extension, and it is ideal for analyzing factors that control the collapse of thickened orogenic crust. How ever, the magnitude and distribution of exten sion, which are critical parameters for this analysis, remain poorly constrained in many areas. To address this problem, a cross section spanning the province at ~39°N is presented. Retro deformation yields 230 ± 42 km of cumu lative extension (46% ± 8%), and an aver age preextensional thickness of 54 ± 6 km. When viewed at the scale of multiple ranges, two highmagnitude (~60%-66%) and two low magnitude (~11%) domains of extension are apparent, and each can be related spatially to portions of the Cordilleran orogen that have high and low predicted crustal thickness, re spectively. The eastern highmagnitude do main restores to a 60 ± 11 km thickness and corresponds to the western portion of the Sevier thrust belt and the estimated spatial extent of thick, underthrusted North Ameri can crust. The western highmagnitude do main restores to a 66 ± 5 km thickness and corresponds to the eastern part of the Sierran magmatic arc. Thickness variations inherited from Cordilleran orogenesis are interpreted as the primary control on extensional strain distribution. The eastern domain underwent a protracted, Late Cretaceous-Miocene tran sition to an extensional regime, while wide spread extension in the western domain did not start until the Miocene, which is attrib uted to uppercrustal rheological differences between the granitic arc and the sedimentary section in the retroarc. Most extension can be temporally related to geodynamic driving events, including delamination, slab rollback, and plateboundary reorganization, which caused gravitational collapse to proceed in distinct episodes.

Syncontractional deposition of the Cretaceous Newark Canyon Formation, Diamond Mountains, Nevada: Implications for strain partitioning within the U.S. Cordillera

“…During the Late Cretaceous and Paleogene, eastern Nevada is interpreted to have been a high (up to ~3 km elevation) orogenic plateau (e.g., Coney and Harms, 1984;DeCelles, 2004;Best et al, 2009;Cassel et al, 2014;Snell et al, 2014), termed the "Nevadaplano" (e.g., DeCelles, 2004). Crustal thicknesses up to 50-60 km are estimated to have been attained in eastern Nevada by the time shortening terminated in the Sevier thrust belt during the Paleocene (Coney and Harms, 1984;DeCelles, 2004;Long, 2019). Despite its high elevation, however, the Nevadaplano experienced minimal synorogenic erosion (up to ~2-3 km) (Long, 2012).…”

“…During the Late Eocene and Oligocene, a northeast to southwest migration of magmatism known as the Great Basin ignimbrite flare-up swept across Nevada and is interpreted to be related to post-Laramide rollback of the Farallon slab (e.g., Humphreys, 1995;Best et al, 2009;Smith et al, 2014). During the ignimbrite flare-up, several areas in eastern Nevada experienced localized extension (e.g., Gans and Miller, 1983;Druschke et al, 2011;Lee et al, 2017;Long et al, 2019;Long, 2019). However, paleoaltimetry data indicate that elevations were still high (~2.5-3.5 km) during, and possibly in response to, the ignimbrite flare-up, and therefore the Nevadaplano still existed during the mid-Cenozoic .…”

“…Most of the widespread extension that constructed the Basin and Range Province, which is the tectonic setting that presently defines this region, took place from the middle Miocene to present (e.g., Dickinson, 2002;Colgan and Henry, 2009;Long, 2019). Basin and Range extension has been attributed to the reorganization of the Pacific-North American plate boundary from an Andean-style subduction system to a continental transform system (e.g., Atwater, 1970;Dickinson, 2002Dickinson, , 2006.…”

“…145 Ma estimate for the timing of initial slip on the Canyon Range thrust could also be a maximum (e.g., Yonkee and Weil, 2015). Initiation of motion on the Canyon Range thrust represented an ~300 km eastward jump in the Cordilleran thrust front, as estimated from the restored distance between the Luning-Fencemaker thrust belt in western Nevada and the trace of the Canyon Range thrust in west-central Utah on the restored cross section of Long (2019). This defines an accretion event that incorporated the upper crust of much of Nevada and western Utah.…”

“…Therefore, the CNTB preserves a record of partitioning of shortening between frontal and interior positions of the Cordilleran orogenic wedge. Because the CNTB was situated far to the west of the frontal, active portion of the Sevier thrust belt (~180 km, based on the distance between the NCF basin and the Pavant duplex on the restored cross section of Long, 2019), it is difficult to interpret this hinterland deformation in the context of critical taper dynamics. Instead, below we summarize several transitions that were taking place in the Cordilleran orogenic wedge during this time interval, in order to speculate on how the CNTB fits into this larger framework.…”