Oceanic crust generation in an island arc tectonic setting, SE Anatolian orogenic belt (Turkey)

Abstract

A number of Late Cretaceous ophiolitic bodies are located between the metamorphic massifs of the southeast Anatolian orogenic system. One of them, the Göksun ophiolite (northern Kahramanmaraş), which crops out in a tectonic window bounded by the Malatya metamorphic units on both the north and south, is located in the EW-trending nappe zone of the southeast Anatolian orogenic belt between Göksun and Afşin (northern Kahramanmaraş). It consists of ultramafic–mafic cumulates, isotropic gabbro, a sheeted dyke complex, plagiogranite, volcanic rocks and associated volcanosedimentary units. The ophiolitic rocks and the tectonically overlying Malatya–Keban metamorphic units were intruded by syn-collisional granitoids (∼ 85 Ma). The volcanic units are characterized by a wide spectrum of rocks ranging in composition from basalt to rhyolite. The sheeted dykes consist of diabase and microdiorite, whereas the isotropic gabbros consist of gabbro, diorite and quartzdiorite. The magmatic rocks in the Göksun ophiolite are part of a co-magmatic differentiated series of subalkaline tholeiites. Selective enrichment of some LIL elements (Rb, Ba, K, Sr and Th) and depletion of the HFS elements (Nb, Ta, Ti, Zr) relative to N-MORB are the main features of the upper crustal rocks. The presence of negative anomalies for Ta, Nb, Ti, the ratios of selected trace elements (Nb/Th, Th/Yb, Ta/Yb) and normalized REE patterns all are indicative of a subduction-related environment. All the geochemical evidence both from the volcanic rocks and the deeper levels (sheeted dykes and isotropic gabbro) show that the Göksun ophiolite formed during the mature stage of a suprasubduction zone (SSZ) tectonic setting in the southern branch of the Neotethyan ocean between the Malatya–Keban platform to the north and the Arabian platform to the south during Late Cretaceous times. Geological, geochronological and petrological data on the Göksun ophiolite and the Baskil magmatic arc suggest that there were two subduction zones, the first one dipping beneath the Malatya–Keban platform, generating the Baskil magmatic arc and the second one further south within the ocean basin, generating the Göksun ophiolite in a suprasubduction zone environment.