CAREER: Estimating Temperature and Water Content of the North American Mantle from Geophysical Observations

Northwestern University, Evanston IL

Investigators

Abstract

This project examines the roles of mantle temperature and hydrogen content in geodynamics and plate tectonics. Research products will be used for stimulation and education of kindergarten through graduate students. Tools developed for this purpose will be used in turn to have researchers explore the research products and to create student research projects. Convection patterns in the Earth's mantle, and how they couple with tectonic plate motion and deformation, are directed by spatial variations in viscosity. Mantle temperature and hydrogen content are principal parameters affecting viscosity. High temperatures will lower viscosity. Minerals with small percentages of hydrogen, obtained from water, are also significantly less viscous than pure mantle minerals. These two parameters can be estimated from a combination of geophysical, in particular seismological observations. Seismograms provide evidence for or against reduced seismic S-wave velocity and associated rigidity, anomalous Poisson ratios, and offset and altered mantle discontinuities beneath North America. These observables are affected differently by the two parameters and will be used simultaneously to estimate mantle temperature and hydrogen content. This effort will be aided by observed gravity, inferred attenuation, xenolith analyses, and measured heat flow. The proposed research is synergistic with Earthscope - a long-term national Earth Sciences facility in the United States. Teaching components are centered around a kiosk that will have three interactive components, useful at a wide range of educational levels and environments. The interaction will be centered around the products of the research summarized above. The proposed teaching capitalizes on the strong visual facets of the research products and integrates with the proposed research because 1) the research products are used to expose K-12 children hands-on and eyes-open to Earth Science, 2) the research assistants that will facilitate the kiosk to K-12 and undergraduate students are thus trained in teaching and public communication, 4) the interactions with the multi-level audience at the kiosks could help steer research, and 5) the interactive tool developed for the education & outreach kiosk will be used to explore and interpret the research products. Research products are three-dimensional seismic models and derivative models for temperature and hydrogen content in the mantle under North America.