Small iron deposits at Kakopetros and Ravdoucha in western Crete are hosted by an extensional detachment zone at the roof of the high-pressure–low-temperature metamorphic core complex known as the Phyllite-Quartzite unit. The iron oxides occur in a brecciated layer of phyllite, quartzite, and marble up to tens of meters thick. They fill fractures and vugs in the breccia and partly impregnate the marble. The iron oxides, which were formerly mined in open pits, are predominantly composed of goethite and subordinate oxyhydroxides of the manganomelane group. The field relationships and microstructures indicate that precipitation of the iron-oxide minerals was related to fluid flow focussed along the detachment fault. δ18O values of goethite indicate crystallization at low temperatures (31°–40°C) and at a shallow depth of about 1 km. Microscopic investigations show that the deposition of iron oxides was syntectonic and occurred during deformation in the uppermost crust. Similar iron oxides are reported from low-angle brittle detachment horizons in the Cordilleran metamorphic core complexes of North America and suggest that small iron- and manganese-oxide deposits of this type may be a characteristic feature of detachment zones.

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