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 ∼10⁶ 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.