An Assessment of Monazite Fission‐Track Thermochronology as a Proxy for Low‐Magnitude Cooling, Catalina‐Rincon Metamorphic Core Complex, AZ, USA

Abstract Conventional low‐temperature thermochronology can resolve rock cooling over geological timescales (>1 Myr) typically associated with ∼6–2 km of erosion, often induced by tectonic processes. Lower magnitude erosional events, however, produced by surface processes remain difficult to resolve. Here, we apply monazite fission‐track (MFT) thermochronometry to the tectonically well‐constrained Catalina‐Rincon metamorphic core complex (MCC) to assess its ability to resolve low‐temperature cooling in the upper‐crust over ∼10 6 years timescales. Established low‐temperature thermochronology (apatite fission‐track [AFT] and apatite and zircon [U‐Th‐Sm]/He) record timing of MCC and subsequent Basin and Range tectonic exhumation (26–20 Ma and 15–12 Ma, respectively). Monazite fission‐track data were obtained from samples collected in two vertical elevation profiles. The eastern transect displays a Late Miocene—Pliocene age‐elevation trend and implies a two‐stage cooling history related to late‐stage footwall uplift associated with Basin and Range normal faulting (∼7.5–5.1 Ma) and subsequent Pliocene—Pleistocene erosion (∼4.0–3.0 Ma). The northwestern transect data suggest a single period of rapid Pliocene—Pleistocene cooling (∼2.8–1.0 Ma). Thermal history modeling, however, fails to find a solution that satisfies the MFT annealing model with the AFT annealing and (U‐Th‐Sm)/He diffusion models. This suggests that the present MFT thermal annealing model does not account for all sources of annealing. We suggest that Pliocene—Pleistocene MFT ages may record a period of climate‐enhanced erosion during a known phase of increased precipitation associated with the development of the North American Monsoon.