(Table T1) Orientation estimates for oxide-bearing lithologies of ODP Hole 179-1105A

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 ~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.

在大洋钻探计划（Ocean Drilling Program）第179航次的锤钻测试间隙期间，研究人员于西南印度洋中脊距735B钻孔约1.3公里处对1105A钻孔进行取芯，取芯深度达海底以下158米（158 mbsf）。本次取芯作业不仅实现了超过80%的高岩心回收率，还采集了一套连续的井下测井数据。此种组合为验证测井技术在硬岩环境中的实用性提供了难得契机。以岩心作为参照标准，我们得以识别出代表岩心不同构造特征的特定地层微扫描测井仪（Formation MicroScanner, FMS）成像特征：含浸染状氧化物的辉长岩在FMS成像中呈现斑驳外观；在面理化层段中，可通过FMS的方位信息确定面理产状。我们还提供了相关实证：在具有强破碎电阻率特征的层段中，岩心回收率会降低且质量更差；部分岩性单元在FMS记录中呈现出显著不同的特征，这有助于更精准地估算层段厚度。本研究表明，至少在本次航次中，所采集的样品（尽管并非全部）始终取自取芯段的顶部，而取芯段的岩性特征在仅数厘米的尺度上就存在差异。因此，所获取的岩心未必能按比例反映整个取芯段的情况。将岩心及FMS成像测得的构造数据与古地磁数据进行重定向后可知，亚特兰蒂斯地块（Atlantis Bank）在结晶与变形历史中所受的主应力方向与西南印度洋中脊轴平行。