University of Tokyo, Japan

During a lull in hammer drill testing during Ocean Drilling Program Leg 179, Hole 1105A was cored to 158 mbsf on the Southwest Indian Ridge within approximately 1.3 km of Hole 735B. This coring operation resulted in not only high recovery (in excess of 80%) but in the collection of a suite of continuous downhole logging data. This combination allows the rare opportunity to demonstrate the utility of logging in hard rock environments. By using the core as a reference, we have been able to recognize specific Formation MicroScanner (FMS) image characteristics that represent different structural aspects of the core. Gabbro with disseminated oxide has a mottled appearance in the FMS images, and in foliated intervals, the attitude of the foliation can be determined from FMS orientation. We also present evidence of decreased and poorer quality core recovery from intervals that have resistivity characteristics indicative of intense fracturing and that certain lithologic units can have markedly different characteristics in the FMS record, improving estimates of interval thickness. This study shows that, at least for this expedition, the material sampled is consistently (albeit not universally) from the top of the cored interval, which varies in lithologic character on scales as small as a few centimeters. Therefore, the core recovered does not necessarily proportionally represent the cored interval. Reorientation of structural data measured on cores and on FMS images to paleomagnetic data indicates the direction of principle stress during the crystallization and deformation history of the Atlantis Bank was parallel to the Southwest Indian Ridge axis.