TRACE ELEMENT AND SR-ND-PB- ISOTOPIC CONSTRAINTS on THE GENESIS OF CRETACEOUS GRANITOIDS IN CENTRAL ANATOLIA, TURKEY

There are numerous late Cretaceous (Cenomanian-Turonian to Campanian-Maastrictian) granitoids derived from protracted magmatism, generated in a post-obductional extension-related geodynamic setting. This extensional regime followed a continent-intra-oceanic island arc collision in central Anatolia in the Cenomanian, during the Neo-Tethyan evolution of Turkey. Textural and whole-rock geochemical data indicate that the central Anatolian granitoids (CAG) consist of (1) high-K, calc-alkaline, peraluminous, S-type, biotite- or two-mica leucogranite association, (2) high-K, calc-alkaline, metaluminous, I-type, quartz monzonitic-granodioritic association, and (3) high-K, alkaline, metaluminous, A-type, bi-modal, monzonitic-syenitic association. The S-type, calk-alkaline leucogranitic association was formed from purely crustal-derived felsic magmas. The I-type, calc-alkaline quartz monzonitic-granodioritic association was derived from a high-K, metaluminous, hybrid magma source, generated by mixing of coeval mantle and crustal derived melts. These rocks show imprints of subduction zone metasomatism with respect to trace and REE geochemical composition. The A-type, alkaline, bi-modal monzonitic-syenitic association has the same characteristics as I-type granites in terms of trace element geochemical composition. Radiogenic (Sr-Nd-Pb) isotope geochemistry data reveal an apparent crustal origin for the S-type granites, while a lithospheric mantle involvement appears likely for the genesis of hybrid magma sources of the I- and A-type granites. The mantle material was accreted into the collision zone as tectonic slices during the continent-oceanic island arc collision. During the post-collisional extensional regime, these mantle slices were remelted to give rise to the mafic magma source in the genesis of hybrid magmas.