Geochemical and petrogenetic features of plagiogranite dykes in the Koziakas ophiolitic mélange (W. Thessaly, Greece)

Abstract

Plagiogranite and dolerite dykes with boninitic affinities intrude thrust-bounded blocks of serpentinized harzburgite at the eastern part of the Koziakas ophiolitic melange. Geochemically they are characterized as oceanic plagiogranites with trondhjemitic composition and metaluminous affinities. Low ΣREE and trace element contents indicate derivation from a depleted mantle source. Geochemical modelling shows that the Koziakas plagiogranites could have originated by 5–20 % partial melting of a gabbro precursor. Locally, an early-stage high-T hydrothermal alteration event seems to have caused the anorthitization of magmatic plagioclase. This hydrothermal event was overprinted by a low-T retrograde alteration. The overall field data and geochemical affinities suggest a supra-subduction zone origin for the studied plagiogranite dykes, which is compatible with the geotectonic environment of the Koziakas ophiolite.