Site 976 was the first site of Leg 161 to address the tectonic objectives of the drilling campaign. Hole 976B penetrated 267.0 m into high-temperature metamorphic basement with well-developed foliations. The main lithologic units identified in the core are recognized in downhole measurements and high-resolution borehole wall images, allowing us to extend the lithologic description over missing intervals (about 80% of the section). Azimuths of foliation planes and tectonic structures are obtained from FMS image analyses. As images are oriented in space with respect to true north, an analysis of the dip directions of the detected events can be obtained, which is not possible with nonoriented cores.
This study provides a first draft of the structural environment within which these metamorphic rocks have evolved. FMS and BHTV images reveal that low-angle foliation planes are mainly dipping to the west. The most fractured part of the basement is in the upper 100 m, with steep planes dipping to the east. The ruptures identified and mapped in the 820.0 to 880.0 mbsf interval are coherent with the presence of an extensional to transtensive strike-slip stress regime at this site, with S3 trending in a N080° direction. As Hole 976B is located in the western part of the Alboran Basin, this new result indicates a present-day N080° directed extensional or transtensional stress component. This result is compatible with the actual kinematics of Europe-Africa plate convergence in the westernmost Mediterranean.