10-10 Carbon and Water Devolatilization and Metamorphic Pathways in the Cucamonga Terrane

Session: Undergraduate and Graduate Geoscience Student Showcase (Posters)

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Abstract:

The Mesozoic Cordilleran arc in Southern California was formed by pulses of magmatism, culminating in a final Late-Cretaceous “flare-up” that caused expansive plutonism to create the Southern California Batholith (Schwartz et al., 2025). The local country rock includes both marbles and calc-silicates within the Cucamonga terrane (May and Walker, 1989). Thus, the heating of these carbon-bearing rocks during a volcanically and orogenically active era raises interest in the role of high-temperature metamorphism on carbon devolatilization and global carbon cycling.

Our study focuses on granulites dated from 86-72 Mya (Schwartz et al., 2023) collected from the Cucamonga Terrane in the San Gabriel Mountains. We aim to constrain the rocks’ Pressure-Temperature pathway as well as the degree of devolatilization of carbon and water in the samples. We will investigate these questions through analysis of thin sections on a Leica DM2700P petrographic microscope and scanning electron microscope in conjunction with thermodynamic pseudosections in Theriak Domino (de Capitani & Petrakakis 2010). Initial petrography reveals some samples with a quartz-plagioclase matrix containing pyroxenes, and others containing garnet porphyroblasts. Preliminary pseudosection results indicate equilibration temperatures and pressures reached at least 675°C and 9.5 kbar. This study aims to provide deeper insight into the mobilization of carbon and water during metamorphism with the broader goal of understanding how these processes contribute to climate change on a geologic time scale.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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