Geochemistry of a meta-ophiolite suite; an associated metagabbros, eclogites and glaucophanites on the island of Syros, Greece

Geochemical and Sr-isotopic constraints are placed on the geotectonic setting in which the magmatic protoliths of the famous association of the Syros high-P metamorphic ophiolitic suite were formed. A compositional gap exists between the metagabbros with mg 0.75-0.88 and eclogites and garnet glaucophanites with mg 0.35-0.62. Metagabbros from various localities and glaucophanites from around Manna form geochemically coherent groups with smooth correlations between compatible as well as immobile incompatible elements and mg. By contrast, the behaviour of these elements is very non-systematic in the eclogites and garnet glaucophanites. From a strong correlation of Ni and Cr with mg and the flat REE patterns lacking Eu anomalies, a cumulus nature is inferred for olivine, clinopyroxene and spinel associated with intercumulus formation of plagioclase in the magmatic protoliths of the metagabbros. There is no direct genetic link between these rocks and the precursors of the Manna-type glaucophanites with REE characteristics typical of N- to T-type MORB. The individual evolution of the protoliths of the eclogites and garnet glaucophanites is thought to have occurred in small magma bodies as suggested for superferric eclogites from elsewhere. The initial (super 87) Sr/ (super 86) Sr ratios of the metagabbros (0.7031-0.7033) and an epsilon (sub Nd) value of 7.7 from a garnet glaucophanite are taken to infer a magmatic setting for the protoliths in a back-arc setting.