ELECTRICAL-PROPERTIES OF MIDOCEAN RIDGE BASALT AND IMPLICATIONS FOR THE STRUCTURE OF THE UPPER OCEANIC-CRUST IN HOLE 504B

The electrical resistivity, porosity, and cation exchange capacity (CEC) of mid-ocean ridge basalt (MORB) samples from Deep Sea Drilling Project hole 504B have been measured in the laboratory. During Leg 111 of the Ocean Drilling Program, the Joides Resolution D.V. returned in the equatorial Pacific to deepen hole 504B and to perform a series of downhole experiments. A continuous electrical resistivity profile permitted to discriminate the large-scale seismic layers of the upper oceanic crust and to isolate individual lithologic units. In the extensive part of the crust, the massive flows (10-m thick or more) are found to constitute permeability barriers and, subsequently, to constrain fluid circulation. The relationship between morpohology, hydrological regime, and therefore alteration of the basaltic basement is proposed to be related to the accretion process of the upper oceanic crust. -from Author