Collaborative Research: Depth-dependent decarbonation in a continental arc, Sierra Nevada, California

About This Grant

When hot magma interacts with Earth’s crust, it changes the minerals and textures of pre-existing rocks by the process of metamorphism. Conditions of metamorphism depend on the pressure, temperature, and the kinds of fluids present in magmas and the crust. These processes can also change rock chemistry by driving the release of elements including carbon which may be liberated from the rock by decarbonation. The process of decarbonation is important in Earth’s long-term natural geochemical cycles. Decarbonation also produces residual rocks called skarns. Skarn deposits are often enriched in base (W, Cu, Pb, Zn) and precious (Ag, Au) metals; thus, a deep understanding of these processes promotes our understanding of economically valuable mineral deposits with broad societal value. Through their work on the project, students will be prepared for vital roles in the geoscience workforce. In particular, they will gain skills in quantitative research methods and numerical modeling to assess the tempo and mode of metamorphic processes that transport energy, fluids, and metals as magmas intrude and crystallize in Earth's crust. Given the close association with critical minerals, the work and student training opportunities constitute a front-line effort to sustain our understanding of resources that are important for the development and advancement of modern technology and the national security of the United States. On-the-ground public outreach efforts include engaging community members in primary and secondary school settings in Florida’s Leon County School District and the development of an exhibit of ore-minerals from the historic Mineral King District in Sequoia National Park. This exhibit will be housed in the Three Rivers Historical Society Museum, near the entrance to the National Park, where thousands of public visitors may potentially see it each year. This work focuses on high-pressure and high-temperature decarbonation of marble and calc-silicate rocks that have been exposed by erosion into the deep lower crust of the Sierra Nevada mountains, California. To understand the influence that metamorphic pressure, temperature, and fluid availability have on decarbonation and mineralization, the investigators combine tools from field work, laboratory study of mineral textures and chemistry, and numerical modeling. Field studies, both ongoing and planned, will focus on key skarn occurrences. Textural analyses by both polarizing and electron microscopes will help identify characteristic features in skarn minerals that formed during metamorphism. Geochemical measurements, including X-ray Fluorescence Spectrometry (XRF), Electron Probe Micro-Analysis (EPMA), and Focused Ion Beam Scanning Electron Microscopy (FIB-SEM), will provide compositional insights at different scales—from whole-rock chemistry (XRF) down to micron-level details. Numerical modeling will further explore element and volatile migration in these lower crustal metamorphic settings, including carbon mobility and the geochemical processes controlling endowment of metals into ore deposits. 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.