CSEDI Collaborative Res.: Composition and Seismic Structure of the Mantle Transition Zone

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Bass Grand The investigators propose a collaborative effort between a mineral physicist (J Bass, University of Illinois Urbana-Champaign) and a seismologist (S. Grand, University of Texas, Austin) aimed at elucidating the seismic structure and mineralogy of the Earth's transition zone, from 300-1000 km in depth. The seismic structure will be determined in several regions with unprecedented resolution of the velocity jumps across transition zone discontinuities and the seismic velocity gradients between the jumps. The available mineral elasticity data and phase relations for relevant mineral systems will be used to calculate the compositions and proportions of individual phases, and the properties of candidate mantle assemblages as a function of depth for a range of bulk compositions. Two key experiments on the high temperature and pressure elasticity of beta phase and aluminous perovskite will be done to fill in the most pressing gaps in the elasticity data base. A new waveform inversion code will be used to determine acceptable fits of mineralogic models directly to the seismic data within certain imposed constraints. For example, with the percent olivine component and size of discontinuities fixed, they can search for allowable models of gradients that satisfy seismic constraints. Other initial conditions will be tried as well. In this way the investigators propose to define both the structure of the transition zone and the range of mineralogical models which are compatible with the seismic data in a more formal quantitative way than has been done before. This research will involve one student working on mineral physics aspects of the project at UIUC, and a student working on the seismological aspects at UTA.