The objective of this project is to investigate fluid inclusions in high temperature veins of hydrothermal origin in oceanic rocks. Samples recovered by dredging from the mid- Atlantic Ridge and the western Pacific will be examined and classified using standard heating/freezing techniques. Data will be used to infer the temperatures, fluid compositions, and the pressures within the ancient hydrothermal systems. These results will be combined with petrography and mineral chemical analysis to determine the sample histories from the primary igneous stage through metamorphism/metasomatism and hydrothermal veining. The project is unique because the fluid inclusion technique provides a method of "sampling" deep hydrothermal fluids in sub-crustal oceanic systems. The research to be performed under this award will be done in an undergraduate institution.