Geomorphic evidence for enhanced Pliocene–Quaternary faulting in the northwestern Basin and Range

Abstract

Mountains in the U.S. Basin and Range Province are similar in form, yet they have different histories of deformation and uplift. Unfortunately, chronicling fault slip with techniques like thermochronology and geodetics can still leave sizable, yet potentially important gaps at Pliocene-Quaternary (~10 5-10 6 yr) time scales. Here, we combine existing geochronology with new geomorphic observations and approaches to investigate the Miocene to Quaternary slip history of active normal faults that are exhuming three footwall ranges in northwestern Nevada: the Pine Forest Range, the Jackson Mountains, and the Santa Rosa Range. We use the National Elevation Dataset (10 m) digital elevation model (DEM) to measure bedrock river profiles and hillslope gradients from these ranges. We observe a prominent suite of channel convexities (knickpoints) that segment the channels into upper reaches with low steepness (mean k sn = ~182; q ref = 0.51) and lower, fault-proximal reaches with high steepness (mean k sn = ~361), with a concomitant increase in hillslope angles of ~6°-9°. Geologic maps and field-based proxies for rock strength allow us to rule out static causes for the knickpoints and interpret them as transient features triggered by a drop in base level that created ~20% of the existing relief (~220 m of ~1050 m total). We then constrain the timing of base-level change using paleochannel profile reconstructions, catchment-scale volumetric erosion fluxes, and a stream-power-based knickpoint celerity (migration) model. Low-temperature thermochronology data show that faulting began at ca. 11-12 Ma, yet our results estimate knickpoint initiation began in the last 5 Ma and possibly as recently as 0.1 Ma with reasonable migration rates of 0.5-2 mm/yr. We interpret the collective results to be evidence for enhanced Pliocene-Quaternary fault slip that may be related to tectonic reorganization in the American West, although we cannot rule out climate as a contributing mechanism. We propose that similar studies, which remain remarkably rare across the region, be used to further test how robust this Plio-Quaternary landscape signal may be throughout the Great Basin.

Testing fault growth models with low‐temperature thermochronology in the northwest Basin and Range, USA

“…At the catchment scale, channel knickpoint migration velocities in tectonically active environments can be related to uplift rate [ Niemann et al , ; Attal et al , ; Whittaker , ], such that knickpoint elevations should mimic a displacement profile consistent with the tip propagation model (Figure a [ Whittaker , ]). In the Pine Forest Range, where the thermochronometer data show that fault lengthening may have ceased by ~8 Ma, knickpoint height is rather uniform across the range [ Ellis et al , ]; this mimics, instead, a displacement profile more consistent with the constant fault‐length model (Figure c). In conclusion, observed spatial patterns of Pine Forest Range fluvial knickpoints also support the thermochronologic evidence that shows that fault development best aligns with the constant fault‐length model.…”

A paleoseismic transect across the northwestern Basin and Range Province, northwestern Nevada and northeastern California, USA

“…Thermochronologic studies indicate unroofing and initial extension in the region ca. 12 Ma (Colgan et al, 2006b), and recent analysis of the tectonic geomorphology of the Santa Rosa Range indicates renewed uplift 5 Ma to 0.1 Ma (Ellis et al, 2014). Quaternary activity along the SRRFZ was described in Michetti and Wesnousky (1993), Narwold and Pezzopane (1997), Narwold (2001), Personius et al (2004), and Personius and Mahan (2005).…”

“…Recent analysis of the tectonic geomorphology of the Pine Forest Range suggest a pattern of renewed uplift 5 Ma to 0.1 Ma, although the knickpoint retreat data from the PFR is less convincing than similar data from the Jackson Mountains fault zone (JMFZ; Ellis et al, 2014).…”

“…A comparison between longer term (hundreds of thousands to millions of years) measures of slip rate and the rates from Narwold (2001), Personius and Mahan (2005), and those presented herein leads us to infer that slip rates on the SSRFZ declined significantly in the late Quaternary. Longer term rate estimates include post-12 Ma exhumation rates of 0.3-0.5 mm/yr based on thermochronology (Colgan et al, 2006b), slip rate estimates of 0.3-0.9 mm/yr based on the heights of faceted spurs along the footwall of the SRRFZ ( dePolo, 1998), and a post-0.5 Ma period of increased slip on the SRRFZ inferred from analysis of rates of knickpoint retreat in the Santa Rosa Range (Ellis et al, 2014). The long recurrence intervals (~17-65 k.y., determined by Personius and Mahan, 2005) also support low rates of slip in the late Quaternary.…”

“…Thermochronologic studies indicate unroofing and initial extension in the region ca. 12 Ma (Colgan et al, 2006b), and recent analysis of the tectonic geomorphology of the Jackson Mountains indicates renewed uplift from 5 Ma to 0.1 Ma (Ellis et al, 2014). Parts of the fault are included in reconnaissance mapping by Dohrenwend and Moring (1991b, scale 1:250,000) and despite significant topographic relief (1-1.5 km) and a very steep range front, the fault is only classified as Quaternary in compilations (dePolo, 2008;U.S.…”