Supra-Subduction Zone Mantle Peridotites in the Tethyan Ocean (East Anatolian Accretionary Complex-Eastern Turkey): Petrological Evidence for Melting and Melt-Rock Interaction

Abstract

The East Anatolian Accretionary Complex formed as a result of the natural process of collision between the Arabian and Eurasian plates and the subduction of the Neotethys oceanic lithosphere located between them, covers a broad area, largely east of Lake Van. This study presents new information about the formation environment of mantle peridotites located within the East Anatolian Accretionary Complex and its rock-melt interactions. According to petrographic and geochemical investigations, peridotites comprise olivine, orthopyroxene, and chromite with low modal content in clinopyroxene (<1 vol%) while whole rock geochemical data indicates that they contain a high MgO (40.56-43.31 wt%) and low Al2O3 (0.16-0.48 wt%) and CaO (0.02-0.38 wt%) content. These values show that these rocks have a high degree of depletion, revealing typical arc peridotite features. Studies on olivine and pyroxene minerals, which are commonly observed in peridotites, show that these rocks are related to the arc. When peridotites are normalized to chondrite, partial enrichment takes place in light and heavy rare earth elements, while partial depletion occurs in medium rare earth elements. The enrichment of the rare earth elements is considered sufficient proof that the mantle peridotites underwent a boninitic mantle-induced enrichment during subduction. Analysis of chromites in the main melt, and its contents (Al2O3, TiO2 and FeO/MgO) suggest boninitic effects in peridotites. All data obtained from peridotites reveal formation of a subduction zone within the Neotethys oceanic lithosphere with an advanced degree of melting leading to re-enrichment of forearc peridotites in advancing periods. These features compare with southern Neotethys and Iran ophiolites.