Prehnite formation and metamorphic relations in the metagabbros of the Oreokastro ophiolite suite, Macedonia, Greece

Abstract

The gabbroic rocks of the Oreokastro ophiolite suite have been affected by an intensive sea‐floor hydrothermal metamorphism resulting in the formation of a mineral assemblage actinolite+epidote+chlorite+titanite+quartz, equivalent to an actinolite grade followed by a retrograde greenschist‐facies metamorphism. A subsequent intense brecciation of the rocks occurred locally in the oceanic environment. Ca‐enriched fluids were incorporated through the fracturing pattern and prehnite has developed as thin fracture fillings or as a stockwork. Mossbauer studies revealed that all iron in the prehnite structure is in ferric state and replaces A1 in the octahedral site. Electron microprobe study of prehnite from Oreokastro has shown the presence of as high as 14.3% mole of the Ca₂Fe₂Si₃O₁₀(OH)₂ end member in solid solution. Prehnite was the latest mineral to be formed under higher metamorphic conditions than the prehnite‐pumpellyite facies in an environment of high f_CO2‐ Mineral assemblages and textures indicate that during the metamorphic and metasomatic processes fluid composition and temperature were changing with time.

Michailidis, K., Kassoli‐Fournaraki, A., Ericsson, T., Filippidis, A. & Godelitsas, A., 1995: Prehnite formation and metamorphic relations in the metagabbros of the Oreokastro ophiolite suite, Macedonia, Greece. GFF, Vol. 117 (Pt. 1, March), pp. 15–21. Stockholm. ISSN 1103–5897.

Keywords:

• Prehnite
• Mossbauer
• metagabbro
• Greece
• sea‐floor metamorphism