Turkish Journal of Earth Sciences




The Yildizdag gabbroic pluton intrudes the Paleocene-Eocene Yakupoğlan formation which is imbricated with the ophiolitic melange of the northern branch of the Neo-Tethyan ocean, and the crustal metasediments of Kırsehir block or Central Anatolian Crystalline Complex. It is subdivided into some mapable subunits such as gabbroic main body, dioritic marginal facies and microdioritic dykes. Mineralogical-geochemical (major, some trace and REE) data reveal that the magnetite + olivine + augite + calcic plagioclase, and hornblende + biotite + intermediate (or sodic) plagioclase fractionation/accumulation has formed the gabbroic main body and dioritic rocks, respectively, during the solidification of a single mafic magma source. The fractionation/accumulation of these mineral associations has also caused to possess tholeiitic and calc-alkaline characters for the gabbroic main body and dioritic rocks, respectively. The high contents of some crustal elements like Pb and Nb in some dioritic rocks also remark the evidences of crustal contamination by digestion of crustal rocks during ascending/cooling of magma. The mafic-tholeiitic magma source of the Yildizdag gabbroic pluton is proposed to be derived from the non-modal Rayleigh type partial melting of upper mantle source rocks with a partial melting degree of up to 25 % on the basis of REE geochemical modeling. Mineralogical-petrological and regional geology data on the Yildizdag gabbroic pluton can suggest the following petrogenesis model. The magma source of the Yildizdag gabbroic pluton has been derived from the partial melting of upper mantle source rocks by adiabatic decompression mechanism under the tensional regime due to lithospheric attenuation. Such a tectonic regime can be created after the crustal thickening, i.e. imbrication, formed by the Upper Cretaceous collision of Anatolides and Pontides after the consumption of the northern branch of Neo-Tethyan oceanic crust along the Ankara-Erzincan suture zone. This juxtaposition of Anatolides and Pontides made them to behave as a single plate, so that, the magma genesis can be identified as a post-collisional, within plate magmatism.

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