177-5 Tracking the Tempo of Exhumation in the Sierra Nevada: Insights from Detrital Multi-Chronometer Thermochronology and Exhumation Modeling

Session: Chronology of Orogenesis: Unlocking the Timelines of Mountain Building

Presenting Author:

Authors:

Abstract:

Understanding long-term orogenic evolution requires constraining not just when exhumation occurred, but how exhumation rates varied through space and over time. Thermochronologic studies of mountain belts often rely exclusively on low-temperature chronometers, which constrain only the most recent exhumation events and overlook earlier histories. To address this, we apply a detrital multi-chronometer approach, combining zircon and apatite U-Th/He, apatite U-Pb, and hornblende ⁴⁰Ar/³⁹Ar data from modern catchments- with inverse thermal modeling (QTQt) and exhumation inversion (A2E) to investigate temporal and spatial exhumation patterns along the eastern Sierra Nevada.

In this contribution, we present results from catchments spanning the Mount Whitney region (36.542°N) south to the Garlock Fault (35.472°N), encompassing both the core of the southern Sierra Nevada batholith and its structurally complex southern margin. In the Mount Whitney area, models resolve rapid cooling and elevated exhumation rates (~0.3-0.4 km/Myr) beginning in the Late Cretaceous (~80-65 Ma), followed by a transition to slower, sustained exhumation (~0.1 km/Myr) through the Cenozoic. These results suggest near-contemporaneous cooling and exhumation following emplacement of the final arc-related intrusions, with a shift toward long-term erosion thereafter.

Although we do not resolve distinct late Cenozoic exhumation pulses across the full modeled catchments, our predicted ApHe dates align with low-temperature ages reported by Lee et al. (2023) in overlapping elevation ranges. For example, predicted ApHe ages from the Mount Whitney region range from ~40 to ~26 Ma between 2900 and 2300 m, closely matching the ~30 Ma signal in their 1900-2900 m ridgeline transects. Our models also predict older ApHe dates at higher elevations, representing greater bedrock relief than sampled by Lee et al., which may explain the absence of older signals in their data.

Preliminary results from catchments near the Garlock Fault suggest a pulse of ca. 50 Ma accelerated exhumation, potentially reflecting the effects of proto-Garlock faulting or early catchment reorganization. The contrasting exhumation histories of the two regions highlight the value of regional-scale thermochronology, paired with thermal-kinetic and kinematic modeling, to decipher complex signals. Ongoing work is expanding this approach latitudinally to test whether observed variations reflect structural segmentation, climate gradients, or lithospheric inheritance. This multi-chronometer, detrital framework provides a scalable method for tracking tectonic and surface processes over geologic time across orogenic systems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9472

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