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4-D Geodynamic Modeling With Data Assimilation: Origin Of Intra-Plate Volcanism In The Pacific Northwest

Lijun Liu, University of Illinois at Urbana-Champaign

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Continental volcanism represents a major natural hazard on Earth. Understanding the formation mechanism of volcanism is of high interest to the scientific community. The proposed work aims to clear out the existing confusions on the interpretation of surface volcanic features, mantle seismic images, and the systems overall evolution with time. This proposed research will be broadly transformative due to its multidisciplinary nature. For example, understanding past mantle evolution will help identify the tectonic origin of various mantle seismic structures, an important goal of geophysics; a better constrained mantle thermal structure will provide a new context for explaining geochemistry data associated with volcanism; linking plate motion history and mantle dynamics will lead to new insights of surface tectonic deformation, which may provide a new perspective for interpreting geological records. Most importantly, long-term Earth evolution models like the one proposed here will provide a framework for establishing physical connections among different fields of geoscience research and linking dynamic processes occurring at different spatial and temporal scales. Additionally, the proposed research will produce excellent lecture materials for general education. The PI plans to participate in outreach activities such as the iRISE program to deliver K-12 lectures through online teaching.

Origin of the Pacific Northwest intra-plate volcanic province, including the mid-Miocene Steens-Columbia River flood basalt and subsequent Yellowstone and Newberry hotspot tracks, still remains heavily debated after decades of research. One popular hypothesis is that this volcanic province formed from a mantle plume originating from the core-mantle boundary region. Alternatively, many models argued for a shallow origin, without involving a mantle plume. However, most of these earlier conceptual models did not consider observational constraints from the mantle, which only became available recently with the help of USArray. The tomography inversions generated from these data reveal unprecedented details on the mantle structure of western U.S., which in turn provide important information on the corresponding mantle dynamics and its temporal evolution over time. These seismic images also present a new perspective on the origin of Pacific Northwest volcanic history. The proposed project will use the Blue Waters supercomputer to quantitatively evaluate the origin of the Pacific Northwest volcanic province by simulating the sub-lithosphere dynamic evolution of western United States in the context of Mesozoic-Cenozoic subduction history of the Farallon plate below North America. The PI proposes to, first, calculate the detailed mantle flow since the Miocene using forward and adjoint methods based on recent seismic tomography and then to explore three hypotheses on the generation of observed slow seismic anomalies and surface volcanism including: 1) a mantle plume in a subduction environment, 2) slab-generated mantle upwelling, and 3) entrainment and intrusion of hot oceanic asthenosphere. High-resolution geodynamic models with realistic initial and boundary conditions will be used to calculate mantle flow and test hypotheses.