CAREER: Investigating the tectono-magmatic response to a transitioning plate boundary: a case study of the California Borderlands

The California Borderlands is a submerged region directly west of Southern California and Baja Mexico. The region is unusual for its multiple basins (500-200 m deep) and ridges (some reach the surface and form the Channel Islands). It has experienced faulting, rotation, and volcanism over the past 30 million years while the approximate 1200 km tectonic boundary along the western limit of the North American tectonic plate transitioned from a subduction to a strike-slip orientation.

It is not well understood why significant faulting, rotation, volcanism, and the formation of a new triple junction are localized to the region off southern California and northern Baja. This project seeks to understand what caused the California Borderlands volcanism and how it is related to a change from subduction to strike-slip. Broader impacts include research opportunities for multiple graduate and undergraduate students, a long-term intensive mentoring program for students recruited from underrepresented groups, support for a URM early-career researcher, collaborations with world-class analytical facilities, and outreach to K-12 schools.

The goals of the project are to (1) investigate volcanic and tectonic processes not readily explained by standard plate boundary or hotspot dynamics. (2) Mentor and train a diverse pool of California State University Long Beach undergraduate and graduate students in ocean and geosciences. (3) Inspire and motivate a new generation of STEM professionals in the K-12 Norwalk School District. The PI proposes to define the timing and geochemical character of volcanic activity associated with processes uniquely recorded in the Borderland area off the coast of southern California that include the subduction of spreading centers and the transitioning from a subduction to transform boundary.

While the unique geology of this submerged region records these rarely observed events, the limited temporal and geochemical constraints currently available lack coverage required to characterize these complex tectonic events via their resulting volcanic feedbacks. Here the PI presents a new regional tectonic model based on modern kinematics that indicate the Borderland region would have been affected by ridge-trench interaction at 30 Ma and 18 Ma.

This proposal seeks to analyze previously retrieved seafloor volcanic samples to test the predictive consequences of the new tectonic model. This project will make use of these and other valuable samples from this area to answer transformative questions about the volcanic response prior to, during and after a plate boundary transition. The project will also train undergraduate student scientists from California State University Long Beach.

The scientific work is ideal for supporting multiple undergraduate and graduate researchers because it scales from observations and detailed characterization of igneous rocks to more advanced procedures of chemical analyses. The program is designed to increase retention through the implementation of a longer term (one and half years as compared to a typical summer research experience) intensive mentorship program utilizing the cohort model.

The proposed research and education activities are synergetic because they will (1) use the entirety of the proposed research as both undergraduate and graduate research projects (2) recruit graduate students from the undergraduate research program (3) incorporate weekly lab meetings to discuss research progress while also building a support network and providing mentorship. The undergraduate researchers supported by the PI will visit several local K-12 schools as community scientists to engage students and serve as role models striving for STEM careers.

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.