Luminescence thermochronology reveals Late Pleistocene exhumation history near the Mill Creek strand of the San Andreas fault

Nathan D. Brown, Marina O. Argueta, Seulgi Moon, Ed J. Rhodes, Michael E. Oskin, & Alex E. Morelan

Submitted September 11, 2022, SCEC Contribution #12401, 2022 SCEC Annual Meeting Poster #098

Recent work suggests that the Mill Creek, Galena Peak, and Mission Creek strands of the southern San Andreas fault system near the southern San Bernardino Mountains may have been active in the late Pleistocene and Holocene with implication for seismic hazards in southern California. However, past efforts to resolve offset along the Mill Creek and Galena Peak faults have been limited by poor fault exposure and few datable offset units. Here we apply thermoluminescence (TL) ultra-low-temperature thermochronology to show an erosion rate contrast across these two fault strands during the late Pleistocene, consistent with dip-slip motion along these faults. Erosion rates in this region show a general deceleration of erosion from 100 to 10 ka, with the exception of samples from the western Yucaipa Ridge tectonic block, which maintain erosion rates near 10^3 mm/ka during this interval. Comparison with nearby apatite (U-Th)/He ages and catchment-averaged cosmogenic Be-10 erosion rates reveals general agreement among all techniques. Yet, the in situ TL erosion rates capture spatial variability obscured in the other datasets, including greater erosion rates at low elevations, and lower erosion rates above a knickpoint and on a relict surface. Our results support a recently active western Mill Creek - Galena Peak fault configuration, compatible with unfaulted late Pleistocene sediments observed across the eastern Mill Creek fault and with recent claims for Holocene activity on the Mission Creek fault.

Key Words
luminescence, thermochronology, Mill Creek, San Gorgonio Knot, Mission Creek

Citation
Brown, N. D., Argueta, M. O., Moon, S., Rhodes, E. J., Oskin, M. E., & Morelan, A. E. (2022, 09). Luminescence thermochronology reveals Late Pleistocene exhumation history near the Mill Creek strand of the San Andreas fault. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology