The PI has done pioneering work on isotope diffusion in geologic materials. He proposes to use knowledge of diffusion rates combined with measurements of Sr and O isotopic compositions to determine the cooling histories of rock units that have been studied by other means. A key goal is to compare results based on the two district isotopic systems. The basic concept is to date a variety of minerals having different temperatures of Sr isotopic closure to obtain cooling curves. Then comparison predicted vs. observed O isotopic compositions will provide an independent test of the cooling model. This work is innovative and has high potential for understanding diffusion processes and thermal histories of igneous and metamorphic rocks.