4:00 PM - 4:15 PM
[S2-08] Differences in petrophysics of gabbroic rock in ocean drilling core samples from different regions
Keywords:Gabbro, IODP, Oceanic lower crust, compressional velocity, petrophysics
Previous scientific ocean drilling has penetrated various localities for gabbroic rocks, a component of the oceanic lower crust. Drilling has been carried out in the Atlantic Ocean with ODP Legs 153 (Kane FZ), Leg 209 (15°20'N FZ), and IODP Exp. 304 & 305 (Atlantis Massif), in the Indian Ocean with ODP Legs 118 & 176 and IODP Exp. 360 at a location known as Atlantis Bank. In the Pacific Ocean, speckled rock samples were collected from Hess Deep by ODP Leg 147 and IODP Exp. 345. These speckled rock core samples are valuable for elucidating the reality of the oceanic lower crust. We found a significant difference in seismic wave velocities from these regions. The Indian Ocean and Pacific Ocean specimens show a relationship between seismic wave velocity and the density of speckled rock, which is generally assumed to be the lower ocean crust. Still, the Atlantic Ocean speckled rock specimens have a seismic wave velocity of about one km/s slower than speckled rock from other localities with similar densities. Possible causes include (1) differences in mineral composition and degree of alteration, (2) differences in porosity (or crack density), (3) differences in degree of deformation, and (4) differences in formation age (temperature). We would like to present the results of our investigation of these causes and discuss the differences in elastic wave velocities.