GEODYNAMIC MODELING OF EDGE-DRIVEN CONVECTION IMAGED BY SIEDCAR (SEISMIC INVESTIGATION OF EDGE DRIVEN CONVECTION ASSOCIATED WITH THE RIO GRANDE RIFT)

University Of Houston, Houston TX

Investigators

Abstract

SIEDCAR (Seismic Investigation of Edge driven Convection Associated with the Rio Grande Rift) is a 2D array of 75 broadband seismographs deployed along the western edge of the Great Plains. SIEDCAR was designed to determine whether small-scale, edge-driven convection is occurring along the edge of the Great Plains, east of the Rio Grande rift zone, and if so, what its lateral dimensions are. The SIEDCAR proposal did not include a request for funding for a geodynamic modeling component to address its two other questions: 1) what conditions lead to edge-driven convection, and 2) what (if any) are tectonic (surface) effects of edge-driven convection and how do they match geologic observations. Although no funding was requested for the Geodynamic Modeling, it was considered a critical component of the SIEDCAR proposal by the PI?s, by the reviewers, and by the Program Officer. The present proposal serves to pursue funding for the geodynamic modeling component of SIEDCAR, and was developed in collaboration with SIEDCAR PIs Pulliam and Grand. Numerical experiments show that an abrupt change in the thickness of the lithosphere can have a profound effect on upper mantle flow. There is a downwelling at the lithospheric discontinuity, and upwelling below the thinner lithosphere. Whether such small-scale convective flow (edge-driven convection) in the mantle is a significant, real world phenomenon and, if so, what the effects on surface geology are, is unknown. SIEDCAR will provide tomographic images of the upper mantle along the edge of the Great Plains, where edge-driven convection supposedly occurs. Our goal of this proposal is to answer the following questions: 1) Regarding the process of edge-driven convection: When does edge-driven convection occur? What rheological or other parameters influence this process? How does edge-driven convection look like in 3D? Which part of the lithosphere may detach and sink into the asthenosphere (only mantle lithosphere or also lower crust?) What are surface effects? Where (if any) is partial melting expected? 2) Regarding the fast-velocity structure imaged by SIEDCAR: Is this fast-velocity structure related to edge driven convection? What is the nature of the fast-velocity anomaly? 3) Regarding crustal and surface effects: How does edge-driven convection relate to tectonics, surface processes (vertical movements), and volcanism in southeastern New Mexico? We will use the numerical software Citcom for a Geodynamic Modeling study of edge-driven convection. In addition, our PhD student will do waveform modeling to validate and calibrate the tomography produced previously. Our proposed research would overlap one year with SIEDCAR. Ten High-school teachers have participated in SIEDCAR field and data analysis efforts and workshops. The SIEDCAR project includes a component that provides field and data analysis experiences for minority-serving teachers in Texas and New Mexico in collaboration with separate E&O projects that aim to increase diversity in the geosciences. By partnering with UT Austin's GeoFORCE Texas public/private consortium and the project entitled Strengthening Pathways to Diversity Through Professional Development for Minority-Serving K-12 Science Educators (funded by NSF's Opportunities for Enhancing Diversity in the Geosciences (OEDG) Program), we accessed the Texas Regional Collaboratives for Excellence in Science Education to recruit the high school teachers. The SIEDCAR project has assembled a strong cadre of teachers who are enthusiastic and engaged. We propose to extend the program by one more summer, in order to add a geodynamic component to the teacher workshops and to ensure that final products are finalized: organized and well-documented. We thus propose to conduct a single, ten-days workshop for ten teachers in year one of this project which follows up on a SIEDCAR workshop. These lessons will be well-organized, well-documented, and self-contained and will be broadly distributed to interested teachers. They will be performed in collaboration with the SIEDCAR PIs.