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Geological Society, London, Special Publications; 1984; v. 13; p. 121-130;
DOI: 10.1144/GSL.SP.1984.013.01.11
© 1984 Geological Society of London

Fracture Zones

Occurrence and significance of gneissic amphibolites in the Vema fracture zone, equatorial Mid-Atlantic Ridge

J. Honnorez, R.S.M.A.S., C. Mevel & R. Montigny, I.P.G.

University of Miami, 4600 Rickenbacker Causeway, Miami, FA 33149, USA
Laboratoire de Pétrologie, Université Pierre et Marie Curie, 4 place Jussieu, 75230 Paris Cedex 05, France
Laboratoire de Paléomagnétisme, 5 rue René Descartes, 67084 Strasbourg, France

Numerous gneissic amphibolites were recovered together with variably deformed and metamorphosed gabbros and serpentinites in the Vema fracture zone during two separate cruises. Petrological studies and K/Ar dating show that these rocks result from recrystallization of gabbros under stress, at temperatures consistent with amphibolite facies, probably in the vicinity of the ridge axis. We suggest that gneissic amphibolites were formed in a large subvertical shear zone related to transform fault movement which favoured penetration of seawater in oceanic layer 3. Less deformed metagabbros recrystallized away from the fault zone under static conditions from interaction with evolved seawater-derived fluids.