Genesis of Cr-bearing hydrogrossular-rich veins in a chromitite boulder from Ayios Stefanos, West Othris, Greece: A paradigm of micro-rodingites formation at the late stages of oceanic slab emplacement

•Gabbro intrusions penetrate a chromitite boulder in the Ayios Stefanos mine area.•The boulder is crossed by antitaxial veins filled mainly with hydrogrossular, clinochlore and serpentine.•Tremolitization of clinopyroxene in gabbros and dissolution of Cr-spinel in the veins provided the essential substances for all vein-filling minerals.•Veins have recorded a general T decrease in the obducting slab via transport away from the spreading center.