- © The Mineralogical Society Of America
Exhumation is a primary phenomenon used to characterize geomorphic and tectonic histories. The motion of rock with respect to the earth’s surface is produced by erosion and tectonic denudation. Unroofing by erosion redistributes crustal mass and is a major accommodator of shortening in orogenic belts (Brandon et al. 1998; Zeitler et al. 2001; Willett et al. 2003). Tectonic denudation, typically associated with crustal extension, brings rocks to the surface at rapid rates from significant crustal depths (Hodges et al. 1998; Hacker et al. 2003; Vanderhaeghe et al. 2003). Quantifying exhumation using thermochronology is thus an important element in investigations of long-term, crustal-scale geomorphic and tectonic processes.
The thermochronometers most appropriate for estimating exhumation related to landscape or neotectonic history are apatite (U-Th)/He and fission-track dating. Given their low closure temperatures and the typical geothermal gradient of the continents, these cooling ages generally record exhumation from ~1–4 km depths (Farley 2002; Ehlers and Farley 2003; Naeser 1979; Gleadow et al. 1986). The accuracy of the exhumation history inferred from these data is limited by how well the spatially and temporally variant geothermal gradient is known or modeled (Mancktelow and Grasemann 1997; Ehlers and Farley 2003). Beyond these limitations, thermochronology is often hindered by what the rocks in a given study area record. Cooling ages may be “too old” and predate the tectonic or erosional history of interest. Or, topography, accessibility, bedrock lithology, and exposure may hinder collection of a robust sample set. In many studies, experimental design is determined by logistics, available funding and time, and prior analytical training of the investigator. Thus, some studies may not obtain the optimal results to address a given question. Although many papers deal with technical aspects of thermochronometry, the purpose of this paper is to explore …