This project is exploring the link between mantle dynamics and magmatism through an integrated seismic and petrologic study across the Basin and Range of the Western US. Many hypotheses exist for what drives melting during lithosphere extension, hydration, heating and convective removal, but there is as yet no consensus on which of these processes is dominant in the western US, nor even where melting occurs.
New seismic data emerging from Earthscope/USArray are providing an unprecedented view of upper mantle structure. Developments in the inversion of Rayleigh waves are allowing the best resolution of lateral and vertical variations in phase velocities to depths of ~ 200 km. The interpretation of seismic velocity and attenuation, however, is still debated as to the relative importance of mantle temperature, water and melt content. The best approach to resolving these variables is to obtain independent constraints from young mantle-derived magmas and xenoliths from the region. Preliminary data show for the first time large variations in the water content of magmas and xenoliths derived from the mantle of the western US. By integrating such observations with other petrologic and seismic predictions of mantle temperature and melting depth, our goals are to determine 1) the lithosphere/asthenosphere boundary, 2) the shape of the melting region, and 3) the water content of the continental lithospheric mantle and underlying asthenosphere beneath the B&R.
This project involves three integrated activities: 1) inversion of surface waves for velocity, attenuation and anisotropy, 2) measurement of the water content of magmas from melt inclusion studies, and 3) study of mantle xenoliths, including thermobarometry, seismic velocities, and water content. Results from this project will be shared with the EarthScope and GeoSwath communities, the NavDat database, and the interested public with a web interface.
