ABSTRACT

Thermal convection in the Earth's mantle drives plate tectonics which generates natural hazards, such as volcanic eruptions and earthquakes. Understanding mantle flows has, thus, strong societal relevance. Seismology is a major tool when investigating mantle flows. Differences in seismic velocities, called seismic anisotropy, reflect the elastic anisotropy of mantle rocks. This anisotropy results from the properties of their constitutive minerals and from their deformation by convective flows. Here, the PI will experimentally measure the elastic anisotropy of various mantle minerals at the extreme pressures and temperatures prevailing in the Earth. From the data, rock seismic anisotropies can be calculated and compared with field observations. The experiments will be carried out at a national synchrotron facility, where powerful X-rays are generated, and in the PI's laser laboratory at University of New Mexico (UNM). The lasers and X-rays will be guided toward small mineral specimens pressurized in-between two diamonds. Mineral elastic properties can be extracted by quantifying the interaction between X-ray/laser beams and specimens which induces elastic waves in the minerals. Results from this project will improve the understanding of three critical zones in the Earth's mantle, located near plate boundaries and within the first few hundred kilometers underneath the surface. The project outcomes will be integrated into educational outreaches towards high-school students in Albuquerque (NM), notably from under-represented groups, as well as in a new introductory course at UNM. The project will also support two early-career scientists and provide training to one graduate student at UNM.

This proposal aims at better understanding the seismic anisotropy observed in three critical regions of the Earth's upper mantle: the lithosphere-asthenosphere boundary, the mid-lithosphere discontinuity and the mantle wedge in subduction zones. The goal is to link the anisotropy to the elastic properties of the relevant minerals. The PI will perform experiments in the diamond-anvil cell at the high pressures and temperatures prevailing in the mantle. Single-crystal Brillouin spectroscopy at PI's laser spectroscopy laboratory and a national synchrotron facility, the Advance Photon Source (IL), will allow measuring the elastic constants of hydrogen-bearing olivine and pyroxenes and minerals from the amphibole and serpentine groups. Specimens will be prepared by focused ion beam and a novel scattering geometry will be implemented to ensure the success of the project. The research outcomes will be integrated into educational and outreach activities. The PI, an early-career female scientist, will work with teachers from Albuquerque high schools to encourage students to pursue STEM studies. A new introductory geoscience course will provide fun movie-discussion-exploration style learning experiences at University of New Mexico. The objective is to engage at an early stage more female and students from underrepresented groups into Earth Sciences careers. The project will also support a postdoctoral associate and provide training to one graduate student at UNM.

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.

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