In situ permeability and pore-pressure measurements near the Mid- Atlantic Ridge, Deep Sea Drilling Project Hole 395A ( Leg 78B).

Abstract

The in situ permeability and pore pressure of 7.2Ma ocean crust were measured in a 664m deep hole near the Mid-Atlantic Ridge. These measurements indicate that the bulk permeability from 583-664m below the sea floor (490-571m sub-basement) at this site is very low, about 3-9 microdarcies, and that the pore pressure in the interval from 180-664m sub-bottom is at least 1.5bars below the oceanic hydrostat. The measured permeability is so low that it virtually precludes significant hydrothermal convection between 583-664m sub-bottom, although substantial hydrothermal convection is probably occurring at shallower depths. If this low-permeability zone is pervasive it places strong constraints on the vertical extent of convective transfer in cooling oceanic lithosphere.-from Authors