Crustal resistivity structure at 9°50′N on the East Pacific Rise: Results of an electromagnetic survey

Abstract

We report the first results of an extensive electromagnetic survey of the East Pacific Rise (EPR) at 9°50′N, which used the magnetometric resistivity (MMR) technique to measure the electrical resistivity structure of the seafloor in the vicinity of the spreading center. Ten seafloor magnetometers were deployed in areas of known hydrothermal activity, in axial sites devoid of venting, and further off‐axis to a distance of approximately 4 km. Data collected at off‐axis sites show higher seafloor resistivities than at axial sites. This response is opposite to that expected from porosity controlled resistivity structure, with a thicker high‐porosity extrusive layer 2A off‐axis, as required by seismic data. An explanation for the reduced axial resistivities is that the uppermost few hundred meters of crust are much hotter beneath the ridge crest than a few kilometers off‐axis, lowering the pore‐fluid resistivity.