Monazite fission-track thermochronology as a possible proxy for low-magnitude erosion

Conventional low-temperature thermochronology can resolve cooling typically associated with ~2 – 6 km of erosion. Lower magnitudes of erosion produced by surface processes and climatic variations are often difficult to quantify. Here, we apply a new, low-temperature thermochronometer (closure temperature <50 – 25 °C), monazite fission-track (MFT), to the Catalina-Rincon metamorphic core complex, Arizona, USA which has a well-constrained tectonic and paleoclimatic history. In the Catalina-Rincon, traditional low-temperature thermochronology (apatite and zircon fission-track and apatite and zircon [U-Th-Sm]/He) record timing of cooling related to metamorphic core complex detachment faulting and subsequent Basin and Range normal faulting (26 – 20 Ma and 15 – 12 Ma, respectively). We collected two monazite fission-track age-elevation profiles across southwestern and northeastern extent of the Catalina-Rincon. The southwestern profile (~ 1000 m relief) records a Plio-Pleistocene age-elevation trend, with older ages at higher elevations (4.5 – 1.5 Ma). Whereas the northwestern profile (~ 500 m) records a late Miocene-Pleistocene age-elevation trend, also with older ages at higher elevations (8.1 – 2.0 Ma). Across the two profiles these ages do not correlate with known tectonic activity in the region, they are consistent with Pliocene intensification of the North American Monsoon. However, such a low closure temperature could suggest that fission-tracks in monazite are not stable at surface temperatures and lie in the partial annealing zone.  Despite this concern, we attribute Plio-Pleistocene thermochronometric ages to record climate-enhanced erosion during a known period of enhanced precipitation. These results suggest that MFT has potential for dating low-magnitude erosion associated with climate and relief-forming processes.