Constraining Rifting and Magmatism in the West Antarctic Rift using Geodynamic Modeling

Colorado State University, Fort Collins CO

Investigators

Abstract

Nontechnical Project Description This project uses computer models to investigate the processes that controlled formation of the West Antarctic Rift System (WARS), one of the world's largest continental rift zones, over the past 100 million years. An enigmatic feature of the WARS is its transition from a broad rift system during its early history, to a narrow rift more recently. Both broad and narrow rifts are common features on Earth. The proposed research leverages the unique behavior of the WARS to examine the factors that determine how and why these styles of rift behavior develop. Computer models will be developed to match the style of extension in the WARS with the space-time patterns of volcanism and magmatism in the rift. These models will constrain temperatures in the crust and mantle beneath the rift, which are thought to exert strong controls on the style of rift behavior, and will test several hypotheses for the causes of rift-related magmatism. The project contributes to advancing basic science through improved understanding of how continents break apart and how continental rifts and rift sedimentary basins evolve. Improved understanding of these processes provides foundational knowledge that informs assessment of volcano, earthquake, and landslide hazards common in modern rift systems such as the broad cordilleran rift in the western U.S. and the narrow East African Rift. Project outcomes will also provide a process-based geological context for exploration of geothermal energy resources in active rifts and fossil energy resources in sedimentary basins formed by ancient rift systems such as those bounding the eastern U.S. and Gulf of Mexico continental margins. Research conducted during this project will become the basis for development of a hands-on science experiment designed to demonstrate rift behaviors for junior high school and high school science classes. Science kits containing materials for the experiment will be created and added to a K-12 science materials ?lending library? maintained by Colorado State University (CSU). K-12 teachers will be trained to use the science kit during summer teacher workshops that are regularly held on the CSU campus. The research will be conducted with help from one Ph.D. student and one undergraduate student, both of whom will also participate in the K-12 teacher?s workshops and development of the classroom science kit. Technical Project Description This project will produce new constraints on the thermal evolution of the Earth's mantle beneath the West Antarctic Rift System (WARS) since the onset of extension ca. 105 million years ago. This is critical to understanding WARS extension, as contrasting models have argued for active rifting driven by rising hot mantle plumes, and passive rifting driven by intraplate gravitational forces and far-field boundary forces applied at the edges of the tectonic plate. A suite of finite element models will be developed to examine alternative rifting scenarios in order to determine if models with a hot mantle are consistent with the WARS structural evolution. Multiple simulations will be created to identify warmest and coolest rifting scenarios. These warm and cool end-member temperature fields will be used to test the hypothesis that a plume or plumes are responsible for rifting in the WARS. Various petrogenetic models for rift-related magmatism will be tested by computing the potential magma contribution from each hypothetical source using the P-T fields from the end-member models. The project will produce two self-consistent models of rifting and magmatism in the WARS (warm and cool end members), constrained by the dual requirements of matching the structural evolution of the rift and space-time patterns of magma production and composition.