Collaborative Research: Using Mineral Physics to Interpret Seismic Anisotropy of the Basin and Range Crust

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Proposal: 0745588 Collaborative Research: Using Mineral Physics to Interpret Seismic Anisotropy of the Basin and Range CrustThe tectonics-scale purpose of this research is to interpret the anisotropy of the lower crust in the Basin and Range using measurements of the anisotropy of local rocks. Understanding the anisotropy of the lower crust is important to geodynamicists, geodesists, petrologists, structural geologists and seismologists who seek to understand its role in processes as diverse as the rheology of the lithosphere, the generation of magmas, geochemical cycling between the crust and mantle, and the formation and genesis of the entire crust. The broader scale purpose of this research is to improve understanding of the causes of anisotropy of the lower crust in general by using mineral-physics based knowledge about the causes of anisotropy as a predictive tool. Rock samples are being studied from two xenolith pipes and three crustal sections in the Basin and Range. Electron-backscatter diffraction is used to measure orientations of all crystals in representative samples. Single-crystal stiffness data are used to calculate the elasticities of the samples. These elasticities are then combined with rock abundance and structure data collected in the field to yield bulk km-scale elasticities for each of the five study sites. Armed with km-scale elasticities for the five study sites plus elasticities for the constituent lithologies we interpret the anisotropy of the Basin and Range lower crust measured from EarthScope's USArray. For the anisotropy studies, we search for anisotropy signals in the receiver functions from the stations closest to the localities of the field samples. Finally, we use what we learn from the site-specific studies to investigate province-wide anisotropy and its tectonic implications.