14 Unraveling Structural Complexity along the San Andreas Fault Zone, Southern California: Using Geochronology in Conjunction with Geologic and Geomorphic Mapping

Tuesday, 5 April 2016
8:30 AM - 12:30 PM
Meeting Room 203 C

A COMPILATION OF OSL GEOCHRONOLOGY COLLECTED BY THE U.S. GEOLOGICAL SURVEY FROM SOUTHERN CALIFORNIA: WHAT THE DATES TELL US AND HOW THEY WILL BE USED

Paper number: 14-9
Program: Theme Sessions
Time: 10:50 AM – 11:10 AM

Authors

Abstract

Over the last decade, the U.S. Geological Survey has investigated the geochronology of southern California surficial deposits associated with the San Andreas Fault system (SAF) and the Eastern California Shear Zone (ECSZ) using optically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) dating. Over fifty five luminescence sites and dates elucidate ongoing landscape evolution and active tectonics, especially near intersections between the fault systems, and span multiple physiographic provinces.

Within the Transverse Ranges, the study areas included the Cottonwood Mountains, the Cottonwood Pass-Cottonwood Springs area, and strands of the Chiriaco Fault where it crosses the north piedmont of the Orocopia Mountains west of Chiriaco Summit. Within the Mojave Desert Province we focused on the Twentynine Palms area, at the intersection between the ECSZ and the Pinto Mountain Fault.

At the boundary between the Transverse Ranges and Peninsular Ranges Provinces, we highlighted complexities within the SAF associated with San Gorgonio Pass. Sample targets included terraces in the canyons of San Gorgonio River; Little San Gorgonio River; the Banning Bench; the alluviated Beaumont Plain at the west end of the San Gorgonio Pass Fault zone; the intersection of the Yucaipa horst-and-graben complex, the San Bernardino strand of the SAF (Wilson Creek area); and a nested alluvial-fan complex astride strands of the SAF at the mouth of Mission Creek at the northwestern head of Coachella Valley. Coachella Valley, particularly the Devers Hill area, and basins within the sinistral fault complex of the Eastern Transverse Ranges were also dated. Samples were selected to help constrain the age of last movement on the Chiriaco fault, a major sinistral fault zone in the eastern Transverse Ranges province, and to begin to document the ages of major alluvial events and pop-up structures in that province.

While most of the luminescence dates are destined for maps, SCEC compilations, or investigative reports, individual local sites where intensive systematic sampling was possible can provide new and useful age control for the latest Pleistocene to Holocene deposits and future investigations will be able to use the database that has accumulated from this study.

Geological Society of America Abstracts with Programs. Vol. 48, No. 4

doi: 10.1130/abs/2016CD-274589

© Copyright 2016 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.