Mafic and ultramafic rock fragments on Chios Island, Greece: puzzling pieces within the Tethyan ophiolite belts of the Eastern Mediterranean

In the southeastern part of Chios Island, Greece, exotic blocks of amphibolites and serpentinized peridotite can be found within a narrow, approximately N–S elongated area adjacent to non-metamorphosed sedimentary strata of Triassic age to its west and of Cenozoic age to its east. In this work, we present for the first time petrological and mineral chemical data for the amphibolites and ultramafic rock fragments from SE Chios Island, describe their possible origin and estimate the metamorphic pressure–temperature conditions and the age of metamorphic overprint. The protoliths of the amphibolites were mafic rocks of enriched (Type I amphibolite) and normal (Type II amphibolite) mid-ocean ridge character metamorphosed under upper amphibolite-facies conditions at 640–780 °C and 5–7 kbar. U–Pb isotopic data from titanite from three amphibolites yielded early Middle to early Late Jurassic lower intercept ages, which we interpret as the age of metamorphism during oceanic lithosphere emplacement. The peridotite is strongly serpentinized, mainly containing lizardite, which implies low-grade metamorphic conditions. With the exception of alteration rims, Cr- and Mg-numbers of the chrome spinel from the serpentinized peridotite range from 10–26 and 69–79, respectively, a range similar to abyssal peridotites of the subcontinental lithospheric mantle. We suggest that the amphibolites and ultramafic rocks represent separate fragments within a mélange, most likely of tectonic rather than accretionary origin. Metamorphism of the amphibolites took place prior to their presumed emplacement in the mélange. The mafic and ultramafic rock fragments of Chios preserve a different sort of subcontinental signature than that largely reported elsewhere within the Eastern Mediterranean ophiolite belts. A correlation with rocks of mélange units in western Turkey or in the northern and/or southern Aegean region is discussed.