Drilling at Ocean Drilling Program Sites 920 to 924 recovered core with a diverse set of pervasive structural elements. Site 920 recovered predominantly peridotitic rocks that display an early crystal-plastic fabric overprinted by at least five generations of veins. Sites 921 to 924 recovered gabbros that contain magmatic and metamorphic foliations and lineations developed to varying intensities throughout. Brittle features in the gabbro core include cataclastic zones, faults, and several generations of veins. The characteristic magnetization direction was used to estimate the in situ orientation of structural features within the core. Although significant uncertainty is associated with the unknown effects of anisotropy and tectonic rotations on the remanent declinations, the corrected attitudes of the dominant foliations at Site 920 dip gently east-northeast, parallel to other observations of seafloor structures in the area. Other vein generations and structural features in the rocks do not have a consistent orientation with respect to each other or a consistent variation with core depth. Sites 921-924 were drilled into a section of mostly gabbroic rocks that typically have complicated magnetic properties, with several remanence components identifiable during demagnetization. Reorientation of the gabbro cores is less certain because of the complexity of the remanent magnetization components, however, many structures in the gabbro from Hole 923A also seem to have gentle dips to the northeast after such a reorientation.
Date of initial receipt: 1 August 1995
Date of acceptance: 2 May 1996
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