Under this funding, the PI will carry out a petrological study of samples from igneous lower crust formed beneath oceanic spreading centers, in order to constrain lower crustal cooling rates as a function of depth and spreading rate. The proposed study will use samples and data from the PI's Oman work, supplemented by gabbro and peridotite from 14 to 16 degrees North on the Mid-Atlantic Ridge (MAR, ODP Leg 209), the SW Indian Ridge (SWIR, ODP Legs 118, 176 and179), and the East Pacific Rise (EPR, Hess Deep, ODP Leg 147). The PI will employ an array of "geospeedometry" techniques to determine closure temperatures and pressures for igneous and metamorphic equilibria, widths and compositions of exsolution lamellae, major and trace element diffusion profiles within mineral grains and outcrops, and crystal size distributions. Using these data, he will estimate relative and absolute cooling rates.
