SGER: Testing the Viability of (U-Th)/He Thermochronology in Complex Tectonic Systems

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Exhumation in the northern California Coast Ranges, and orogens in general, results fromthe interplay of geodynamic processes that drive uplift and surface processes that respond to therates and patterns of uplift. A variety of approaches have been used to determine patterns ofexhumation, but placing robust, quantifiable constraints on these estimates is difficult because ofthe feedbacks and linkages among large scale geodynamic, thermal, and landscape evolutionprocesses. There is a critical need for a technique to constrain the trajectory of rocks at shallow-crustal (low-temperature) levels to constrain uplift and exhumation in active orogenic belts. Mostrecently, (U-Th)/He thermochronometry has been identified as a potential tool to helpquantitatively constrain exhumation and uplift. The (U-Th)/He system has the advantage of a lowclosure temperature (~ 60-70 C for apatite) and thus in principal it records the last fewkilometers of unroofing. As a low-T thermochronometer the same characteristics that make (U-Th)/He so appealing for geomorphic studies also raise questions about its utility in regions ofcomplex thermal and/or tectonic histories. It is uncertain whether this tool can extract meaningfulinformation from a complex signal that incorporates both the exhumation history and theinevitable thermal feedbacks driven by that exhumation. In this project we will apply (U-Th)/Hethermochronometry coupled with landscape evolution, thermal and geodynamic modeling, toevaluate if (U-Th)/He dating can be confidently applied in regions of active tectonism that are notin thermal or geomorphic steady-state.