Initial report of physical property measurements, ChikyuOman 2018: Crust-Mantle boundary and the mantle section from ICDP Oman Drilling Project Phase II

We report physical property measurements of core samples from the Samail ophiolite in Oman, drilled by the ICDP Oman Drilling Project. Onboard core logging was conducted on D/V Chikyu from July 5 to September 3, 2018. We analyzed 5 holes (CM1A, CM2B, BA1B, BA3A and BA4A) with a total core length of 1711m. The CM holes were drilled through the crust-mantle transition, from gabbroic lower crust, through dunite with minor gabbros, and in to residual mantle harzburgite. BA holes were taken from the mantle section and are composed of dunite and harzburgite intruded by minor gabbroic and pyroxenite dikes. Ultramafic rocks at both sites were extensively serpentinized, but the names of igneous protoliths are used here.

Whole-round data, including X-ray CT images, natural gamma radiation (NGR), gamma ray attenuation (GRA) density, magnetic susceptibility (MS), P-wave velocity (Vp) and noncontact electrical resistivity were obtained. Split core color spectroscopy data were also collected. Magnetic susceptibility, electrical resistivity under both nominally dry and brine-saturated conditions, P-wave velocity, bulk/grain density, porosity and thermal conductivity were measured in discrete samples. Nearly 100% core recovery allowed us to take a large data set of petrophysical data on the cores from Oman ophiolite including fault zones and highly altered intervals.

Generally, gabbroic rocktypes have higher density, P-wave velocity, and electrical resistivity, and lower porosity than ultramafic lithologies. Serpentinized dunite have lower density, P-wave velocity and electrical resistivity, and higher porosity than serpentinized harzburgite, and these physical properties are correlated with magnetic susceptibility, probably due to crystallization of magnetite during alteration. Average X-ray CT values are also correlated with many other physical properties in most lithologies.