Permeability Profiles Across the Crust-Mantle Sections in the Oman Drilling Project Inferred From Dry and Wet Resistivity Data

Abstract

Permeability profiles in the crust-mantle sequences of the Samail ophiolite were constructed based on onboard measurements of the electrical resistivity of cores recovered during the Oman Drilling Project. For each sample, we measured dry and brine-saturated resistivity during the description campaign on the drilling vessel Chikyu. Owing to the conductive brine in the pore space, wet resistivity is systematically lower than dry resistivity. The difference between dry and wet resistivity is attributed to the movement of dissolved ions in brine that occupies the pore space. We applied effective medium theory to calculate the volume fraction of pores that contribute to electrical transport. Using an empirical cubic law between transport porosity and permeability, we constructed permeability profiles for the crust-mantle transition zone and the serpentinized mantle sections in the Samail ophiolite. The results indicate that (1) the gabbro sequence has a markedly lower permeability than the underlying mantle sequence; (2) serpentinized dunites have higher permeability than serpentinized harzburgites; and (3) discrete sample permeability is correlated with ultrasonic velocity, suggesting that the permeability variations predominately reflect crack density and geometry.