Zircon and apatite (U-Th)/He evidence for Paleogene and Neogene extension in the Southern Snake Range, Nevada, USA

Abstract

Despite decades of study, the timing, rates, and magnitude of extension in the Basin and Range are poorly quantified in some areas. This study integrates new zircon and apatite (U-Th)/He analyses (ZrnHe and ApHe) with published thermochronologic data to quantify these extensional parameters in the Southern Snake Range (SSR) of east-central Nevada. The new ZrnHe dates range from 40.7 ± 4.9 Ma in the western SSR to 21.0 ± 3.3 Ma near the present-day trace of the Southern Snake Range Décollement (SSRD), and the ApHe dates range from 15.1 ± 2.4 Ma in the central SSR to 13.6 ± 0.7 Ma closest to the SSRD trace. These new and previously published low-temperature thermochronologic cooling ages were inverted for the extensional history of the SSR using a Bayesian Monte Carlo method incorporating Pecube. The posterior extensional histories indicate three significant pulses of extension occurred during the Paleogene and Neogene: (1)~50-45 to~38 Ma (Eocene), (2)~33-30 to~23 Ma (Oligocene), and (3)~23-20 to~10-8 Ma (Miocene). Modeled rates of extension were low at ≤ 0.5 mm a À1 ; however, more rapid rates possibly occurred during the Eocene and the Miocene based on posterior histories. Net cumulative extension from posterior histories is 19.8 to 34.9 km, with a mean of 29.7 km. About 10-18 km of extension occurred during the Eocene and Oligocene. Model results indicate no relationship between extension and magmatism in the SSR. Our new model results and interpretations also indicate extensional collapse of the Nevadaplano initiated prior to~17 Ma.

Timing of mid-crustal ductile extension in the northern Snake Range metamorphic core complex, Nevada: Evidence from U/Pb zircon ages

“…23-21 to ca. 11-8 Ma, in part possibly overlapping with cessation of ductile extension in the lower plate of the northern Snake Range Metcalf, 2006;Evans et al, 2015). Combining our new U/Pb zircon data with these data, along with published moderate-to low-temperature thermochronologic data (Lee and Sutter, 1991;Lee, 1995;Gébelin et al, 2011), and timing of normal faulting and sedimentary basin formation in and around the northern Snake Range (Drewes, 1967;Grier, 1984;Gans et al, 1989;Martinez et al, 1998;Miller et al, 1999a;Ruksznis, 2015), indicates that our zircon age brackets for ductile extension in the lower plate overlap temporally with a minor phase of middle to late Eocene upper crustal extension in the vicin ity of the northern Snake Range and the onset of the major episode of brittle extension during the early to middle Miocene (Fig.…”

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

“…Volcanic rocks of the ignimbrite flare-up overlie Paleozoic-Mesozoic rocks across a regionally distributed Paleogene unconformity, which represents a postorogenic erosion surface that predates extension in most places (e.g., Armstrong, 1972;Gans and Miller, 1983;Long, 2012Long, , 2015. In eastern Nevada and western Utah, some areas experienced Eocene-Oligocene extension (e.g., Gans et al, 1989Gans et al, , 2001Potter et al, 1995;Constenius, 1996;Evans et al, 2015;Long and Walker, 2015;Lee et al, 2017). However, extension was localized, and paleoaltimetry data indicate that surface elevations were still high during this time (Wolfe et al, 1997;Horton et al, 2004;Cassel et al, 2014).…”

Rapid Oligocene to Early Miocene Extension Along the Grant Range Detachment System, Nevada, USA: Insights From Multipart Cooling Histories of Footwall Rocks

“…During and after the terminal stages of Sevier shortening, eastward migration of crustal shortening and magmatism during Paleocene‐early Eocene (~65–45 Ma) construction of the Laramide province is interpreted as a consequence of shallowing of the subducting Farallon slab (e.g., Dickinson & Snyder, ; Dickinson, ; Saleeby, ; Yonkee & Weil, ). On the area of Figure (and in proximal areas to the north), extension of this age is documented in only four places, including normal faulting in the Egan Range in eastern Nevada (Druschke, Hanson, & Wells, ) and the Deep Creek Range in western Utah (Potter et al, ), normal faulting and continued exhumation in the Ruby‐East Humboldt core complex (Camilleri & Chamberlain, ; McGrew et al, ), and initial exhumation in the Snake Range (Evans et al, ; Gébelin et al, ; Lee, ).…”

“…Spatially isolated Late Cretaceous to Paleocene (~80-60 Ma) extension, which was contemporaneous with the final stages of shortening in the Sevier thrust belt, has been documented (e.g., Camilleri & Chamberlain, 1997;Druschke, Hanson, Wells, Rasbury, et al, 2009;Hodges & Walker, 1992;, and has been interpreted to have been initiated by lithospheric delamination (Wells & Hoisch, 2008). Eocene-Oligocene extension has also been documented (e.g., Gans et al, 1989Gans et al, , 2001Evans et al, 2015;Lee et al, 2017;Long & Walker, 2015), and was often associated spatially and temporally with the Great Basin ignimbrite flare-up, a NE to SW sweep of silicic volcanism interpreted to have accompanied post-Laramide slab rollback (Figure 1a; e.g., Dickinson, 2002;Humphreys, 1995). The initiation of widespread extension that formed the Basin and Range Province, which is attributed to establishment of the San Andreas transform system (e.g., Atwater, 1970), was not until the middle Miocene (e.g., Cassel et al, 2014;Colgan & Henry, 2009;Dickinson, 2002).…”

“…The Grant Range detachment system, along with the Snake Range core complex and Stampede detachment system, represent three regional-scale fault systems on the area of Figure 11 that accommodated much or all of their overall motion during the late Eocene-Oligocene. In the Snake Range, denudation-related cooling of footwall rocks and dated field relations with volcanic, intrusive and sedimentary rocks defines a protracted history of extension that spans from the early Eocene to the middle Miocene (Evans et al, 2015;Gans et al, 1989;Gébelin et al, 2014;Lee & Sutter, 1991;Lee, 1995;Lee et al, 2017;Miller et al, 1999). The Stampede detachment system was active during deposition of~34-31 Ma sedimentary rocks and prior to~29-31 Ma volcanism (Axen et al, , 1993Bartley et al, 1988;Taylor, 1990;Taylor & Bartley, 1992).…”