Broadband marine MT exploration of the East Pacific Rise at 9 50 0

[1] We present the first use at a mid-ocean ridge of a recently developed broadband marine magnetotelluric (MT) instrument. The extended high frequency performance of the instrument allows resolution of electrical resistivity structure at shallower depths than traditional marine MT sensors. Our two-dimensional inversion model from data collected at four MT sites on the East Pacific Rise (EPR) at 9 500N demonstrates the viability of the method to image electrical resistivity structure in both the crust and shallow mantle. While our pilot experiment falls far short of the coverage needed to provide rigorous constraints on structure, a low resistivity zone in the crustal portion of the inversion model agrees well with seismic tomography and seafloor compliance results. Resistivities beneath the ridge imply a crustal partial melt fraction of 1–20%. A total melt volume of about 0.75 km per kilometer of ridge implies an average melt residence time of about 1000 years.