Pulsed Mesozoic Deformation in the Cordilleran Hinterland and Evolution of the Nevadaplano: Insights from the Pequop Mountains, NE Nevada

Abstract

<jats:title>Abstract</jats:title> <jats:p>Mesozoic crustal shortening in the North American Cordillera’s hinterland was related to the construction of the Nevadaplano orogenic plateau. Petrologic and geochemical proxies in Cordilleran core complexes suggest substantial Late Cretaceous crustal thickening during plateau construction. In eastern Nevada, geobarometry from the Snake Range and Ruby Mountains-East Humboldt Range-Wood Hills-Pequop Mountains (REWP) core complexes suggests that the ~10–12 km thick Neoproterozoic-Triassic passive-margin sequence was buried to great depths (&amp;gt;30 km) during Mesozoic shortening and was later exhumed to the surface via high-magnitude Cenozoic extension. Deep regional burial is commonly reconciled with structural models involving cryptic thrust sheets, such as the hypothesized Windermere thrust in the REWP. We test the viability of deep thrust burial by examining the least-deformed part of the REWP in the Pequop Mountains. Observations include a compilation of new and published peak temperature estimates (n=60) spanning the Neoproterozoic-Triassic strata, documentation of critical field relationships that constrain deformation style and timing, and new 40Ar/39Ar ages. This evidence refutes models of deep regional thrust burial, including (1) recognition that most contractional structures in the Pequop Mountains formed in the Jurassic, not Cretaceous, and (2) peak temperature constraints and field relationships are inconsistent with deep burial. Jurassic deformation recorded here correlates with coeval structures spanning western Nevada to central Utah, which highlights that Middle-Late Jurassic shortening was significant in the Cordilleran hinterland. These observations challenge commonly held views for the Mesozoic-early Cenozoic evolution of the REWP and Cordilleran hinterland, including the timing of contractional strain, temporal evolution of plateau growth, and initial conditions for high-magnitude Cenozoic extension. The long-standing differences between peak-pressure estimates and field relationships in Nevadan core complexes may reflect tectonic overpressure.</jats:p>

The Role of Shortening in the Sevier Hinterland Within the U.S. Cordilleran Retroarc Thrust System: Insights From the Cretaceous Newark Canyon Formation in Central Nevada

“…Our shortening timing compilation from central Nevada (Figure 14; Table 1), when combined with the results of studies in northeastern Nevada and northwestern Utah that lie to the east of Figure 14a (Allmendinger & Jordan, 1984; Miller & Hoisch, 1995; Thorman et al., 1991, 1992; Zuza et al., 2020), demonstrate that Late Jurassic contractional deformation, though generally of a low magnitude (i.e., limited upper‐crustal shortening) and often spatially isolated (i.e., accommodated by aerially restricted structures that cannot be correlated for significant distances along‐strike or across‐strike), was distributed across a broad region of the northern Sevier hinterland (Figure 15c). Deformation was often spatially associated with ∼155–165 Ma granitic intrusions and associated metamorphism, which defines an episode of retroarc magmatism that extended as far east as western Utah (Figure 15c) (e.g., Allmendinger & Jordan, 1984; Barton et al., 1988; Miller & Hoisch, 1995; Zuza et al., 2020). In addition, the onset of thickening at mid‐crustal levels in northwestern Utah is interpreted as Late Jurassic (∼150 Ma) on the basis of initial prograde metamorphism within deeply exhumed rocks now exposed in the Raft River core complex (Cruz‐Uribe et al., 2015; Kelly et al., 2015).…”

“…Camilleri and Chamberlain (1997) proposed that peak metamorphism was achieved by structural burial beneath a thick thrust sheet carried by the hypothesized east‐vergent Windermere thrust, which can be bracketed between ∼154 Ma, the timing of dike emplacement that pre‐dated metamorphism, and ∼84 Ma, the timing of peak metamorphism. However, because several aspects of the Windermere thrust model have been criticized by more recent studies (e.g., see arguments in Henry et al., 2011; Long, 2012; Zuza et al., 2020), we instead focus on geochronology that constrains the timing of metamorphism and burial of rocks in this region, which is bracketed between the initiation of prograde metamorphism at ∼97 Ma (Hallett & Spear, 2015) and peak metamorphism between ∼89 and 77 Ma (Hallett & Spear, 2014, 2015; McGrew et al., 2000). In our compilation, we interpret ∼97–77 Ma as an approximate window for the timing of crustal thickening at mid‐crustal levels in northeastern Nevada.…”

“…In the Pequop Mountains, the southeast‐vergent Independence thrust (Camilleri & Chamberlain, 1997) has recently been interpreted by Zuza et al. (2020) to have been emplaced during the Late Jurassic, as it is cut by a ∼160 Ma lamprophyre sill. However, we note that Camilleri and Chamberlain (1997) originally interpreted that the Independence thrust cuts and deforms this lamprophyre sill, which suggests a younger motion age.…”

“…The LFTB was constructed during the Middle‐Late Jurassic closure of a back‐arc basin (e.g., Oldow, 1984; Wyld, 2002). In the Sevier hinterland, Middle‐Late Jurassic magmatism and associated contractional deformation have been documented in several areas of northeastern Nevada (e.g., Miller & Hoisch, 1995; Smith & Ketner, 1977; Zuza et al., 2020) and northwestern Utah (e.g., Allmendinger & Jordan, 1984).…”

Heterogenous late Miocene extension in the northern Walker Lane (California-Nevada, USA) demonstrates vertically decoupled crustal extension

“…Coupled magmatism and intra-arc and retroarc shortening led to crustal thickening as part of an inferred high-elevation orogenic plateau, termed the Nevadaplano, which was located within the hinterland of the Sevier foreland thrust belt observed in central Utah (DeCelles, 2004;Dickinson, 2006;Ernst, 2010;Henry et al, 2012). Growth of this plateau probably started in the Middle-Late Jurassic (Wyld, 2002;Miller and Hoisch, 1995;Zuza et al, 2020aZuza et al, , 2021, and crustal shortening, magmatism, and thickening peaked in the Late Cretaceous (Coney and Reynolds, 1977;Dickinson and Snyder, 1978;Humphreys et al, 2003;DeCelles and Graham, 2015;Yonkee and Weil, 2015). Estimates for the thickness of this plateau are derived from structural restorations, geochemical proxies, and inferences from stable isotope paleoaltimetry, which all suggest that much of the Nevadaplano was ≥60 km thick (e.g., Coney and Harms, 1984;Chapman et al, 2015;Cassel et al, 2009Cassel et al, , 2014.…”