Biotite in olivine gabbros from Atlantis Bank, SW Indian Ridge: Evidence for amphibolite-facies metasomatic alteration

Abstract

Olivine gabbros from IODP/ODP Hole U1473A and 735B at Atlantis Bank contain significant amounts of biotite and biotite-chlorite (B/C) mixtures in coronitic aggregates around olivine grains. The B/C mixtures are different from previously reported chlorite-smectite mixtures in K content and crosscutting texture. The close relationship of the biotite with felsic veins, the high F contents of biotite, and estimated temperatures for amphibole and vein formations suggest a widespread amphibolite-facies metasomatic alteration by felsic magmatic fluids in the lower oceanic crust.