The ductile to brittle deformation and the associated hydrothermal mineralogical record in Holes 920B and 920D peridotites are complex. Remnants of a high-temperature phase (brown hornblende, talc) are preserved in the serpentinized harzburgites. Primary chromites in the harzburgite are altered to ferritchromite. Magnetite, which originated from olivine breakdown during serpentinization, (1) recrystallizes, mimicking mesh and ribbon textures, and (2) reorganizes in veins and trails. Primary sulfide minerals rarely survive the extensive serpentinization, and are affected by significant mobilization.

An ilvaite + chlorite + fibrous salitic pyroxene ± carbonate ± grandite garnet + magnetite ± sulfides (pyrite > pyrrhotite > chalcopyrite) assemblage that developed in pyroxenite veins is cut by later serpentine veins. Late hydrothermal veins, pyrite (+ silicates) precipitate in veins, which are cut in turn by pyrrhotite + chalcopyrite (+ phyllosilicate) veins.

Date of initial receipt: 3 August 1995
Date of acceptance: 22 March 1996

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