Exhumation of the central Wasatch Mountains, Utah: 1. Patterns and timing of exhumation deduced from low‐temperature thermochronology data

Abstract

[1] The Wasatch Mountains are often cited as an example of normal fault growth and footwall flexure. They represent a tilted footwall at the edge of the Basin and Range extensional province, a major rift basin. Thus understanding the detailed spatial and elevation changes in coupled thermochronometer data, and how these changes can be interpreted, may aid in the analysis of thermochronometer data from other extensional regions around the world. We present a dense data set from the Cottonwood Intrusive Belt (CIB) of the Wasatch that includes apatite fission track (AFT), zircon fission track (ZFT), and apatite (U-Th)/He ages. ZFT, AFT, and apatite (U-Th)/He ages are 10, 5, and 3 Ma, respectively, adjacent to the Wasatch fault. AFT and (U-Th)/He ages increase slightly with distance east of the fault until about 15-20 km, where a more abrupt increase in these ages occurs at or near the Silver Fork-Superior fault zone. ZFT and AFT ages are concordant with 31-38 Ma pluton emplacement ages on the eastern side of range. Modeling of the data leads to the following interpretation: (1) Early cooling and $3-4 km of exhumation for the middle and eastern parts of the range occurred in the late Oligocene-middle Miocene. (2) Beginning at 10-12 Ma, the locus of exhumation shifted westward toward the present range front, where the rocks cooled from >200°C in the last 10-12 Myr. Our data and interpretations are consistent with a model in which the locus of faulting and exhumation shifted opposite the direction of tilt, similar to that predicted by rolling-hinge extensional models. However, this westward shift and rapid Miocene to recent exhumation may be a local effect superimposed on lower fault displacement and exhumation rates elsewhere along the Wasatch.

Pattern and timing of late Cenozoic rapid exhumation and uplift of the Helan Mountain, China

“…The spatial distribution of the AFT ages indicates that the exhumation is greatest at the EHSF, and lessens away from the EHSF. Previous studies have demonstrated that in extensional tectonic regimes, most exhumation occurs in the footwalls of normal-fault bounded ranges, and results in the upward lateral advection of mass and heat in the footwall [26][27][28][29][30]. Therefore, the spatial variation of exhumation may reflect a component of tilt related to the normal faulting of the EHSF.…”

Evaluation of detrital thermochronology for quantification of glacial catchment denudation and sediment mixing

“…These methods are able to record processes that affect the upper 2-6 km of the crust, depending on the geothermal gradients. Many studies have successfully identified patterns of cooling ages across a region that could be interpreted with respect to tectonics, erosion, landscape evolution, and climate (e.g., Armstrong et al, 2003;Reiners et al, 2007;Huntington et al, 2007;Barnes et al, 2012).…”

U-Th zonation-dependent alpha-ejection in (U-Th)/He chronometry

“…Since the modern resurgence of (U-Th)/He dating (Zeitler et al, 1987;Farley et al, 1996;Wolf et al, 1996), numerous studies have used (U-Th)/He thermochronometry to study a wide range of geomorphic and tectonic processes (House et al, 1998;Reiners et al, 2000;Stockli et al, 2000;House et al, 2001;Stockli et al, 2002;Armstrong et al, 2003;Ehlers et al, 2003;Reiners et al, 2003). More recent studies have exploited the relatively rapid ingrowth of He to date young volcanic deposits Aciego et al, 2003;Davidson et al, 2004;Min et al, 2005), and to understand diffusive loss of He associated with wildfires (Mitchell and Reiners, 2003) and shock metamorphism of meteroites (Min et al, 2004).…”