ELECTRICAL-RESISTIVITY OF OCEANIC BASALTS

The electrical resistivity of a large number of ocean crust basalt samples obtained by the Deep Sea Drilling Project has been studied, including the effect of temperature and pressure, the correlation with porosity, and the changes with degree of dehydration. The data are compared to those of samples from several oceanic islands and a few gabbros that might be representative of the lower oceanic crust. The geometric mean resistivity of 153 ocean crust basalts, seawater saturated, at 22oC and atmospheric pressure is 190 ohm m. There is no significant change with thw low-temperature weathering or halmyrolysis characteristic of the upper part of old oceanic crust. Higher-temperature hydrothermal alteration such as that experienced by subaqueous Bermuda lavas appears to reduce the porosity and thus increase the resistivity. In contrast, subaerial basalts such as those from the Azores have high porosity and thus low resistivity, but Azores subaqueous samples of similar composition have the same resistivity as deepsea basalts. The gabbros have low porosity and resistivity an order of magnitude higher than the basalts. -Authors