Density and porosity of the upper oceanic crust from seafloor gravity measurements

Abstract

The exposure of 1300 meters of upper oceanic crust at the Blanco 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 Blanco 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 ± 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.