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GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 386-6
Presentation Time: 9:00 AM-6:30 PM

CONTRASTS IN INTEGRATED CRUSTAL STRENGTH DRIVE STRAIN LOCALIZATION WITHIN THE SANTA CRUZ MOUNTAINS RESTRAINING BEND IN THE THE SAN ANDREAS FAULT, NORTHERN CALIFORNIA


BADEN, Curtis William, Department of Geological and Environmental Sciences, Stanford University, 455 Serra Mall, Building 320, Stanford, CA 94305-2115, HILLEY, George E., Department of Geological Sciences, Stanford University, 455 Serra Mall, Building 320, Stanford, CA 94305-2115, SHUSTER, David L., Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA 94720 and HOURIGAN, Jeremy, Earth and Planetary Sciences, University California Santa Cruz, Santa Cruz, CA 94305, cbaden@stanford.edu

The Santa Cruz Mountains juxtapose compliant and rigid crust in the vicinity of asymmetric topography and deformation surrounding the Santa Cruz Mountains restraining bend, and this juxtaposition appears to strongly modulate the topography and deformation within the range. The asymmetric, high elongate crest of topography northwest of the restraining bend resides within a severely folded and faulted sequence of sedimentary basin deposits on the order of 5-10 km thick. Apatite (U-Th)/He ages sampled along this topographic crest are recently reset, implying substantial recent exhumation (~2-3 km) within the last 5 Ma. Additionally, exhumation appears to have occurred more recently in the proximity of the restraining bend relative to locations farther away within these units. These sedimentary deposits are sharply bounded to the southwest by Salanian granitic terrains, and to the northeast by volcanic and metasedimentary units of the Franciscan Complex across the San Andreas Fault. Samples from the Salinian terrains exhibit older ages than the sedimentary samples to which they are juxtaposed, suggesting that less exhumation and inferred deformation has taken place. Trends in crustal displacement fields derived from the 3D geologic model agree with this result. Together, these observations argue for localization of strain within compliant crustal blocks within the deforming plate margin. While topographic advection and fault interaction may influence the distribution of topography and deformation observed surrounding the bend, we propose that contrasts in integrated strength of the crust may fundamentally control the localization of plastic deformation and the subsequent development of asymmetric crustal displacement fields and topographic distributions we observe. In actively deforming regions, the juxtaposition of weak and strong crustal units may localize deformation and plastic strain in relatively weak parcels of crust.

Session No. 386--Booth# 380

T210. Challenges in Tectonics: Beyond Steady State: New Developments in Understanding Strain Localization Processes and the Rheology of the Lithosphere (Posters)
Wednesday, 25 October 2017: 9:00 AM-6:30 PM
Halls 4EF (Washington State Convention Center)
Geological Society of America Abstracts with Programs. Vol. 49, No. 6
doi: 10.1130/abs/2017AM-306514
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