Density and Porosity of the Upper Oceanic Crust from Seafloor Gravity Measurements

The exposure of 1300 meters of upper oceanic crust at the Blanc0 Fracture Zone allows near-bottom gravity measurements to determine the in situ density of the seafloor as a function of depth. Gravity measurements along the north wall of the Blanc0 Depression indicate an outcrop density of 2530 * Kg/m3 for the upper 800 meters of crust and a calculated porosity of 23%. The lower 500 meters of crust (800 to 1300 meters below the sea floor) has a measured density of 2710 k 130 Kg/m3 and a porosity of 14%. These data indicate that most of the extrusive volcanic oceanic crust is highly porous and can act as an aquifer and large-scale reservoir for hydrothermal fluids. These direct crustal density measurements also support previous interpretations that low seismic velocities observed in Layer 2 are due to the high porosity of the upper extrusive section.