Abstract: Earth is unique among the rocky planets of the solar system in having compositionally evolved continental crust—the reason for life as we know it. Many differentiation processes have been proposed to explain its existence. Starting with mafic, mantle-derived basalt, differentiation produces a diverse range of more evolved compositions that erupt at subduction zones and form the continental crust. However, quantifying and evaluating the role of pre-existing crust in these processes remains challenging. Focusing on the well-studied Sierra Nevada batholith which provides a framework, I document mafic compositions that reflect an early stage of differentiation in a Mesozoic arc. Transecting the central Sierra Nevada in a regional study of mafic intrusions across the batholith, I show that their ages, geochemistry, and field relationships with the rest of the batholith vary systematically, as the mafic magmas interacted with heterogeneous crustal belts.
 

Bio: Juliet is a Postdoctoral Fellow at Massachusetts Institute of Technology, studying base metal sulfide deposits and the associated mafic intrusion in northern Maine. As a field-based petrologist, her research forges connections between observations from the rock record and pressing societal issues, including the global supply of critical metals, volcanic hazards, and geoethics. For her MS and PhD at Caltech, she pursued more fundamental questions about the formation and evolution of subduction zone magmas. Prior to graduate school, her career took her far and wide. She spent several years as a Geologist at the U.S. Geological Survey in Menlo Park, CA, where she did fieldwork at volcanoes mainly in California but also in Oregon, Washington, and abroad in Chile and Saudi Arabia. She also spent time as an AmeriCorps member serving in the Sierra Nevada, California for a non-profit and for the National Park Service. She will be starting as an Assistant Professor at Boston College in Fall 2026.

* For the Zoom link, please email Xueyao Cheng  > xc272@stanford.edu