Plate boundary trench retreat and dextral shear drive intracontinental fault-slip histories: Neogene dextral faulting across the Gabbs Valley and Gillis Ranges, Central Walker Lane, Nevada

Abstract

The spatial-temporal evolution of intracontinental faults and the forces that drive their style, orientation, and timing are central to understanding tectonic processes. Intracontinental NW-striking dextral faults in the Gabbs Valley–Gillis Ranges (hereafter referred to as the GVGR), Nevada, define a structural domain known as the eastern Central Walker Lane located east of the western margin of the North American plate. To consider how changes in boundary type along the western margin of the North American plate influenced both the initiation and continued dextral fault slip to the present day in the GVGR, we combine our new detailed geologic mapping, struc­tural studies, and 40Ar/39Ar geochronology with published geologic maps to calculate early to middle Miocene dextral fault-slip rates. In the GVGR, Meso­zoic basement is nonconformably overlain by a late Oligocene to Miocene sequence dominated by tuffs, lavas, and sedimentary rocks. These rocks are cut and offset by four primary NW-striking dextral faults, from east to west the Petrified Spring, Benton Spring, Gumdrop Hills, and Agai Pah Hills–Indian Head faults. A range of geologic markers, including tuff- and lava-filled paleovalleys, the southern extent of lava flows, and a normal fault, show average dextral offset magnitudes of 9.6 ± 1.1 km, 7.0 ± 1.7 km, 9.7 ± 1.0 km, and 4.9 ± 1.1 km across the four faults, respectively. Cumulative dextral offset across the GVGR is 31.2 ± 2.3 km. Initiation of slip along the Petrified Spring fault is tightly bracketed between 15.99 ± 0.05 Ma and 15.71 ± 0.03 Ma, whereas slip along the other faults initiated after 24.30 ± 0.05 Ma to 20.14 ± 0.26 Ma. Assuming that slip along all four faults initiated at the same time as the Petrified Spring fault yields calculated dextral fault-slip rates of 0.4 ± 0.1–0.6 ± 0.1 mm/yr, 0.4 ± 0.1–0.5 ± 0.1 mm/yr, 0.6 ± 0.1 mm/yr, and 0.3 ± 0.1 mm/yr on the four faults, respectively. Middle Miocene initiation of dextral fault slip across the GVGR overlaps with the onset of normal slip along range-bounding faults in the western Basin and Range to the north and the northern Eastern California shear zone to the south. Based on this spatial-temporal relationship, we propose that dextral fault slip across the GVGR defines a kinematic link or accommodation zone between the two regions of extension. At the time of initiation of dextral slip across the GVGR, the plate-boundary setting to the west was characterized by subduction of the Farallon plate beneath the North American plate. To account for the middle Miocene onset of extension across the Basin and Range and dextral slip in the GVGR, we hypothesize that middle Miocene trench retreat drove westward motion of the Sierra Nevada and behind it, crustal extension across the Basin and Range and NW-dextral shear within the GVGR. During the Pliocene, the plate boundary to the west changed to NW-dextral shear between the Pacific and North American plates, which drove continued dextral slip along the same faults within the GVGR because they were fortuitously aligned subparallel to plate boundary motion.

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

“…Lee et al (2020) interpreted westward trench retreat at this time, which, when coupled with elevated GPE of the thickened crust, would have allowed for an early phase of fast extension. This initial burst of high-strain-rate extension of thickened crust would have occurred as plate boundary stresses relaxed due to subduction rollback (e.g., Colgan and Henry, 2009;Lee et al, 2020). Alternatively, Nicholson et al (1994) speculated that consumption and capture of oceanic microplates could lead to discrete jumps of transform-margin elongation, and it is possible that such events could have led to punctuated continental extension (e.g., Stock and Lee, 1994).…”

“…Plate reconstructions demonstrate that the westward propagation of Basin and Range extension and inception of the Walker Lane coincides with the transition of the Pacific-North American convergent plate boundary to a right-lateral transform boundary, with increased relative plate motion and changing plate convergence directions from west-northwest to north-northwest at ca. 12 Ma (Atwater and Stock, 1998;Faulds and Henry, 2008;Cashman et al, 2009;Busby, 2013;DeMets and Merkouriev, 2016;Lee et al, 2020).…”

“…When the first-observed phase of rapid extension (~10 −14 s −1 ) initiated ca. 15 Ma, the Mendocino triple junction was still significantly south of the study area (DeMets and Merkouriev, 2016), and thus deformation would have been controlled by plate-boundary stresses across the Juan de Fuca-North American plate boundary (e.g., Atwater, 1970;Faulds and Henry, 2008;Lee et al, 2020). Lee et al (2020) interpreted westward trench retreat at this time, which, when coupled with elevated GPE of the thickened crust, would have allowed for an early phase of fast extension.…”

“…15 Ma, the Mendocino triple junction was still significantly south of the study area (DeMets and Merkouriev, 2016), and thus deformation would have been controlled by plate-boundary stresses across the Juan de Fuca-North American plate boundary (e.g., Atwater, 1970;Faulds and Henry, 2008;Lee et al, 2020). Lee et al (2020) interpreted westward trench retreat at this time, which, when coupled with elevated GPE of the thickened crust, would have allowed for an early phase of fast extension. This initial burst of high-strain-rate extension of thickened crust would have occurred as plate boundary stresses relaxed due to subduction rollback (e.g., Colgan and Henry, 2009;Lee et al, 2020).…”

“…Domain b includes the Singatse and Wassuk Ranges, which have extended >150% (Dilles and Gans, 1995;Surpless et al, 2002;Long, 2019). Finally, domain c includes the Gillis Range, which accommodates significant right-lateral shear in the Walker Lane (e.g., Faulds and Henry, 2008;Lee et al, 2020) on approximately four northwest-striking right-slip faults. Long (2019) constructed a cross section across this region based on mapping by Hardyman (1980) and estimated ~4.9 km of extension (13% extensional strain) (Figs.…”