Investigating the nature and timing of development of the Eastern California shear zone (ECSZ) in southeastern California

University Of Texas At El Paso, El Paso TX

Investigators

Abstract

The boundary between the Pacific and North American plates includes the San Andreas fault and a wider region of deformation called the Eastern California shear zone, which contains active and inactive segments. This project investigates faults in the inactive Eastern California shear zone to constrain the timescales and styles of faulting through time. This information will help to understand the structural narrowing of the plate boundary and abandonment of the inactive segment, which is important for constraining the evolution of earthquake-producing faults in southern California. This project combines field studies, detailed fault analysis, and geochronology to study rocks that were deformed during evolution of the inactive segment. To do this, the project will include a team of graduate, undergraduate, and community college students from a largely Hispanic population who will each gain valuable experience in conducting science and scientific communication. Students will also be involved with outreach opportunities at local earth science events to interact with the community. Relative transform motion across the Pacific-North America plate boundary is accommodated by the San Andreas fault system, with a lesser, but substantial, portion occurring within a broad zone of distributed deformation known as the Eastern California shear zone (ECSZ). The ECSZ can be subdivided into an active segment that currently takes up 20-25% of the relative plate motion, and a paleo-ECSZ that is largely inactive today. The goal of this project is to constrain the timescales and styles of deformation within the paleo-ECSZ through field studies, structural analysis, and geo/thermochronology applied to the well-characterized Bear Canyon conglomerate (BCC) that formed coeval with evolution of the paleo-ECSZ. 40Ar/39Ar sanidine ages on tephra layers coupled with detrital sanidine 40Ar/39Ar of the BCC will constraint timescales of deposition. Thermochronology of basement rocks coupled with structural and thin section analysis of fault rocks will document changing strain fields as the paleo-ECSZ became active, and U-Pb dating of fault calcite will constrain timescales of faulting. Documenting this somewhat cryptic earlier history is crucial for understanding structural narrowing of the ECSZ into an active belt and abandonment of the paleo-ECSZ. This project will fund graduate and undergraduate students who will reflect the largely Hispanic population of UTEP. Students will gain valuable experience with field work, structural analysis, geo/thermochronology, modeling techniques, and scientific communication. Outreach opportunities at local earth science events will be used to build relationships with the community and community college. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.