Collaborative Project: Seismic Petrology of the Lower Oceanic Crust: An Investigation of Seismic Velocity, Modal Mineralogy and Water Content in Oceanic Diabase and Gabbro

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Under this award, the PIs will measure the seismic velocities, modal mineralogy, water content, and mineral and rock elastic properties in order to understand what controls the seismic velocity variation with depth in the lower ocean crust. Whereas conventional wisdom suggests that the observed velocity changes with depth in lower ocean crust (seismic layer 3) and the observed velocity gradients are controlled by increasing pressure and decreasing alteration (chlorite) with depth, recent evidence by the PIs indicates these factors are unlikely to exert major control. Instead, preliminary data suggest that the presence of hydrous minerals and the overall water content of the rocks may control the seismic velocities. The additional measurements for samples from ODP holes 504B, 735B, 894G, and 923A will be used to test this hypothesis and extend the findings to answer several specific questions about the relationships between mineralogy, cracks, water content, and hydrous phases, on the seismic velocities and velocity gradients in the lower ocean crust.