Speaker: Prof. Josh Schwartz
Affiliation: CSU Northridge, Department of Geological Sciences
Date: Wednesday, October 7, 2026
Time: 12:00 PM
Abstract
The lower crust of continental arcs is a key environment for magma differentiation, crustal recycling, high-temperature metamorphism, and ductile deformation, yet direct observations of these processes remain rare. The Cucamonga and San Antonio terranes of southern California expose a remarkable lower- to middle-crustal section of the Southern California batholith, a major segment of the Mesozoic California arc between the Sierra Nevada and Peninsular Ranges batholiths. This deep-crustal record documents progressive underthrusting of a late Paleozoic–Mesozoic sedimentary basin beneath the arc, approximately 100 million years of magmatism from 175 to 75 Ma, and multiple episodes of high-grade metamorphism and deformation. During a major Late Cretaceous magmatic flare-up, voluminous tonalitic and granodioritic magmas transferred heat into the lower crust, driving granulite-facies metamorphism and partial melting of the underthrust metasedimentary sequence. Geochemical, petrochronologic, and structural data reveal how mantle-derived magmatism, crustal melting, inherited fabrics, and evolving rheological contrasts interacted to construct and reorganize the deep crust of Southern California.
About the Speaker
Dr. Joshua Schwartz is a Professor of Geology in the California State University Northridge Department of Geological Sciences, where he serves as the faculty director of the LA-ROCS mentoring program and co-director of the Geological Sciences Laser Ablation Laboratory. He received his B.A. degree in Geology from Brown University (Minors in Ancient Languages and Near Eastern Archaeology), M.S. in Geology from Brown University, and Ph.D. in Geology from the University of Wyoming. He is a field- and laboratory-based petrologist who focuses his research on arc magmatic processes. Dr. Schwartz’s expertise lies in using field observations and laboratory techniques to understand the magmatic construction of arcs, particularly in deep-crustal exposures. His research group is currently working on arc systems in the western United States, Argentina, and New Zealand.