Petrogenesis of the Refahiye Ophiolite and its Tectonic Significance for Neotethyan Ophiolites Along the İzmir-Ankara-Erzincan Suture Zone

Abstract

The Refahiye ophiolite, situated near Erzincan in the eastern part of the İzmir-Ankara-Erzincan Suture Zone (İAESZ), is one of the best exposures of oceanic lithosphere in the northern branch of the Neotethyan Ocean. The ophiolite, mainly thrust southwards, transported on an ophiolitic mélange, over the Early Triassic-Campanian Munzur Limestone of the Anatolide-Tauride Platform, was also emplaced by north-directed backthrusting onto the Pontides in the Late Cretaceous. It displays an almost complete ophiolite series unconformably overlain by Tertiary volcano-sedimentary units. The mantle peridotites are dominated by harzburgites, with dunite bands and lenses locally cut by isolated diabase dykes, whereas the mafic-ultramafic cumulates of the mantle-crust transitional zone consist of dunites, wehrlites, pyroxenites and gabbros. The diabase dykes of the sheeted-dyke complex show a magmatic boundary with the underlying massive gabbros which are in places crosscut by plagiogranite dykes. The basic and leucocratic rocks exhibit greenschist facies assemblages of ocean floor metamorphism. The spilitic pillow basalts and cover sediments (radiolarites, pelagic limestones) of the upper units of the oceanic crust are preserved as megablocks in the ophiolitic mélange. Petrological features of the ophiolitic rocks show that the ultramafic, mafic and leucocratic rocks belong to a co-magmatic differentiated tholeiite series. The crystallization order is olivine-clinopyroxene (locally with orthopyroxene)-plagioclase. The gabbros and diabases are tholeiitic (Nb/Y= 0.05-0.5). Whereas the LIL elements (K, Sr, Rb, Ba), with the exception of Th, show variable scatter because of ocean floor hydrothermal alteration, the HFSE (Nb, Ti, Zr, Y) and the LREE (La, Ce, Nd) have been depleted relative to N-MORB. The ratios of the selected trace elements (Ti/V, Zr/Y, Th/Y, Ti/Zr) and the tectonomagmatic discrimination diagrams for Ti-poor gabbros and dykes suggest that the Refahiye ophiolite has island arc tholeiitic (IAT) and possibly boninitic affinities. The mantle peridotites have very low REE concentrations, showing U-shaped REE patterns. The isotropic gabbros and plagiogranites exhibit high REE concentrations with positive and negative Eu anomalies respectively, patterns typical of SSZ magmatism. The ultramafic-mafic and leucocratic rocks of the Refahiye ophiolite were formed in the earliest stages of island arc development in a suprasubductional, forearc tectonic setting in the northern branch of the Neotethyan Ocean, similar to most of the Cretaceous Eastern Mediterranean ophiolites.