Permeability Estimates at Mid Ocean Ridge Sites

Abstract

Measurements of the heat and mass flow from geothermal fields on Mid Ocean Ridges (MOR), together with estimates of the dimensions and thermal profiles of the geothermal plumes and certain assumptions concerning the isotropic and uniform nature of the porous medium, are used to obtain approximate values for largescale vertical permeability of the MOR system. As no drill-hole pressure and temperature data is available, an estimate is obtained for the near-surface pressure gradient imposed on each geothermal plume using a simplified model for the flow of cold seawater onto the MOR hotplate. This hotplate, at a depth h below the sea bed, produces a linear chain of such plumes of cross sectional area A at a distance L apart and is assumed to be a dense brine layer, just on the boil, conducting heat from a deeper magmatic heat source.