Contrasts in the integrated strength of crustal blocks drive localized rock uplift and exhumation along the San Andreas fault system in the Santa Cruz Mountains, California, USA
Abstract
Deformation that develops along plate margins can accumulate in Earths crust over repeated earthquake cycles to build mountain ranges over millions of years. Crustal models with homogeneous rheologies can predict the evolution of broad, mountain-range-scale deformation through time, but geologic observations indicate that rheologic heterogeneities can localize deformation in Earths crust over spatial scales ranging from large crustal blocks down to the grain scale. To assess the relationship between strain localization and fault-block-scale crustal heterogeneities, we focus our study in the Santa Cruz Mountains (SCM), CA, where deformation surrounding a restraining bend in the strike-slip San Andreas fault has caused uplift of the mountain range since 4 Ma. In the SCM, regional faults divide the crust into distinct structural blocks with varying lithologic composition. Reconstructed rock uplift fields, 18 structural cross sections, and 34 low temperature apatite (U-Th)/He ages reveal that deformation, uplift, and exhumation histories differ between these fault-bounded structural blocks. Specifically, we find that uplift and exhumation are localized within structural blocks that host thick sedimentary successions atop previously extended crust, while uplift and exhumation in neighboring sediment-mantled plutonic terrane are demonstrably decreased. We infer that this pronounced difference in deformation likely developed due to contrasts in integrated crustal strength between juxtaposed structural blocks. Specifically, deformation and failure were concentrated in weaker crustal parcels in response to elevated compressive stresses surrounding the restraining bend in the San Andreas fault over the course of SCM formation. Our results suggest that deformation within strike-slip plate boundaries is strongly influenced by 110-km scale crustal heterogeneities, which result from the juxtaposition of parcels of crust with vastly different geologic histories within a complex, heterogeneous, and evolving plate margin.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.T11D..03B