9712311 Hofmeister A multifaceted approach is needed to understand the dynamics of the 410 km discontinuity near subducting plates and its connection with non-equilibrium transitions from olivine to b- and g-spinel. The PIs propose: (1) to measure transformation kinetics, hydration, and thermodynamic properties from in situ (T up to ~900(C at P up to ~50 GPa) infrared spectra of various approximations to slab and mantle compositions and to elucidate mechanisms through TEM and petrographic studies of recovered samples; (2) to constrain olivine metastability and the elevation, sharpness, and velocity contrast of the 410 km discontinuity in and near five subduction zones from seismic traveltime and waveform modeling. (3) Construct a thermal-kinetic model to link mineral physics and seismic results. The sub-areas are strongly linked: Rate laws determined from the IR data form the basis for the geodynamical model which will provide the temperature distribution for calculating synthetic seismograms. Matching to seismic traveltimes and waveforms will provide feedback to the thermal-kinetic modeling in a highly-coupled manner. Model results will provide guidelines for new IR experiments. ***
