T238 Tectonic and Climatic Disruption of Hydrological Systems as a Driver for Evolution of Biota and Ecosystems

Wednesday, 25 September 2019
8:00 AM - 12:00 PM
Room 224A, North Building

REGIONAL-SCALE DETACHMENT FAULTING AS A MECHANISM FOR CRUSTAL EXTENSION IN THE NORTHERN PORTION OF THE EASTERN CALIFORNIA SHEAR ZONE

Paper number: T238-3
Program: Technical Sessions
Time: 8:30 AM – 8:45 AM

Authors

Abstract

Palinspastic reconstructions show that the northern portion of the Eastern California Shear Zone (north of the Garlock fault and west of the Spring Mountains) has undergone ~200% crustal extension since 16 Ma. However, the specific structures accommodating this extension are still unclear. Strain-rate models based on published fault slip rates fall far short of matching either the strain rates inferred from the geological reconstructions or those indicated by contemporary geodetic velocities. We use fault outcrop data, geodetic data, and earthquake hypocenter distributions to evaluate three conceptual models for northern ECSZ faulting. These are (1) traditional high-angle ‘Basin-and-Range’ block faulting, (2) a regional low-angle detachment, and (3) a two-episode model of low-angle faulting in the Miocene subsequently replaced by a modern system of high-angle strike-slip faults. Block normal faulting requires much deeper basins than are observed. Both geodetic and geological analyses indicate that dilation is currently underway and thus contradicts the modern shear-faulting model. However, hypocenter distributions are consistent with displacement on a regional low-angle detachment that crops out along the Death Valley fault system and dips northwest underneath the Sierra Nevada. This conceptual model is compatible with the various lines of evidence that we considered. Modern crustal extension in the region thus appears to be a perpetuation of the faulting style initiated in the Miocene, rather than an evolution from low-angle normal faulting to deep-seated strike-slip faulting.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-335431

© Copyright 2019 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.