Petrogenesis and geodynamics of plagiogranites from Central Turkey (Ekecikdağ/Aksaray): new geochemical and isotopic data for generation in an arc basin system within the northern branch of Neotethys

Abstract

In the Late Cretaceous, throughout the closure of the Neotethys Ocean, ophiolitic rocks from the Izmir–Ankara–Erzincan ocean branch were overthrusted the northern margin of the Tauride-Anatolide Platform. The ophiolitic rocks in the Ekecikdag (Aksaray/Central Turkey) region typify the oceanic crust of the Izmir–Ankara–Erzincan branch of Neotethys. The gabbros in the area are cut by copious plagiogranite dykes, and both rock units are intruded by mafic dykes. The plagiogranites are leucocratic, fine- to medium-grained calc-alkaline rocks characterized mainly by plagioclase and quartz, with minor amounts of biotite, hornblende and clinopyroxene, and accessory phases of zircon, titanite, apatite and opaque minerals. They are tonalite and trondhjemite in composition with high SiO2 (69.9–75.9 wt%) and exceptionally low K2O (<0.5 wt%) contents. The plagiogranites in common with gabbros and mafic dykes show high large-ion lithophile elements/high-field strength element ratios with depletion in Nb, Ti and light rare-earth elements with respect to N-MORB. The plagiogranites together with gabbros and mafic dykes show low initial 87Sr/86Sr ratios (0.70419–0.70647), high ƐNd(T) (6.0–7.5) values with 206Pb/204Pb (18.199–18.581), 207Pb/204Pb (15.571–15.639) and 208Pb/204Pb (38.292–38.605) ratios indicating a depleted mantle source modified with a subduction component. They show similar isotopic characteristics to the other supra-subduction zone (SSZ) ophiolites in the Eastern Mediterranean to East Anatolian–Lesser Caucasus and Iran regions. It is suggested that the Ekecikdag plagiogranite was generated in a short time interval from a depleted mantle source in a SSZ/fore-arc basin setting, and its nature was further modified by a subduction component during intra-oceanic subduction.