122 From the Cosmos and Back: Quantifying Processes and Rates of Landscape Change

This session explores how methods such as cosmogenic nuclides, apatite (U-Th)/He thermochronometry, U-series geochemistry, luminescence, and chemical mass balances quantify relationships between climate, tectonics, and erosion.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 212AB

Investigating Landscape Response to Tectonic Reorganisation in the San Gorgonio Pass Region Using Thermoluminescence (TL) Thermochronology

Paper number: 122-7
Program: Technical Sessions
Time: 3:20 PM – 3:35 PM

Authors

Abstract

The San Gorgonio Pass (SGP), situated within the southern San Andreas Fault zone, is a tectonically complex region exerting primary control on earthquake–rupture propagation, making it crucial for seismic‐hazard assessment. Due to its multistranded configuration, substantial uncertainty remains regarding slip partitioning across the SGP and the activity of individual fault strands during the Late Pleistocene and Holocene. Previous investigations have utilised low‐temperature thermochronometers such as Apatite U–Th/He (AHe) cooling ages and cosmogenic ¹⁰Be catchment‐wide erosion rates to infer fault activity. While the million‐year resolution of AHe tends to average out short‐term tectonic and climatic perturbations, the millennial resolution of catchment-averaged ¹⁰Be measurements may be biased by stochastic landslides in the region's steep terrain. In this study, we employ thermoluminescence (TL) thermochronology, a novel ultra-low temperature thermochronometer, to derive in-situ bedrock exhumation rates spanning 10–100 ka across the Mill Creek, Mission Creek, Galena Peak, and San Bernardino San Andreas fault strands. We utilise these exhumation rate measurements to characterise the influence of the SGP on earthquake dynamics and slip partitioning among the aforementioned fault strands in the southern San Bernardino Mountains. To ascertain the relative contributions of tectonic uplift versus local geological controls, we compare exhumation rates with topographic metrics including hillslope angle, local relief, elevation, curvature, distance to fault strands, and precipitation data derived from the 30-year PRISM dataset. Our findings reveal that the most rapid exhumation occurs in steep, high-relief concave reaches situated low in the landscape. Samples exhibit higher erosion rates closer to the Galena Peak, western Mill Creek, and San Bernardino San Andreas fault strands, potentially indicating active tectonic uplift along these faults. For samples collected near the Mill Creek catchment headwall, the spatial pattern of exhumation rates indicates a transient erosional response manifested as an upstream-migrating knickpoint, indicative of fluvial adjustment to base-level fall likely driven by tectonic reorganisation. This study demonstrates the efficacy of TL thermochronology-derived exhumation rates for resolving slip partitioning in tectonically intricate settings and elucidating landscape responses to spatially and temporally variable tectonic uplift.

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

doi: 10.1130/abs/2025AM-413058

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