The 117.38 m of gabbroic core drilled during the Ocean Drilling Program (ODP) Leg 153 at Sites 921-924 in the Mid-Atlantic Ridge between 23°N and the Kane Fracture Zone exhibits a remarkable primary compositional heterogeneity, such as magmatic layering, intrusive contacts, and late magmatic veining, which expresses a succession of magmatic events. Magmatic features include random shape fabric and magmatic layering; the successive deformative overprint occurred in metamorphic conditions. The ductile deformation, generally concentrated in the discrete domain of the gabbro, is associated with the metamorphic assemblages (1) olivine + clinopyroxene + orthopyroxene + plagioclase + ilmenite + Ti-magnetite, (2) olivine + clinopyroxene + plagioclase + ilmenite + Ti-magnetite + red hornblende. At lower temperatures, brittle deformation prevails, and the following assemblages develop: (3) clinopyroxene + plagioclase + red-brown hornblende + Ti-magnetite + magnetite(?) + ilmenite, (4) plagioclase + brown hornblende + Ti-magnetite + magnetite + hematite + titanite ± Ti-oxide, (5) plagioclase + green hornblende + magnetite + titanite, (6) plagioclase + actinolite + chlorite + titanite + magnetite, (7) albite + actinolite + chlorite + prehnite ± epidote ± titanite, and (8) albite + prehnite + chlorite ± smectite.

Date of initial receipt: 3 August 1995
Date of acceptance: 26 January 1996

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