K-Ar age, whole-rock and isotope geochemistry of A-type granitoids in the Divrigi-Sivas region, eastern-central Anatolia, Turkey

The bimodal, A-type Dumluca and Murmana granitoids consist of felsic monzonitic/syenitic and mafic gabbroic/dioritic and monzogabbroic/monzodioritic rocks, which were intruded into the Cenomanian-Turonian supra subduction zone-type Divrigi ophiolitic melange. New homblende and biotite K-Ar dates yield cooling ages ranging from 72 to 77 Ma, and from 68 to 77 Ma for the felsic and mafic rocks, respectively, in the Dumluca and Murmana granitoids. Felsic and mafic rocks of these intrusions have a metaluminous, high-K alkaline composition, however, highly evolved members of the felsic rocks are peraluminous in character. Trace element geochemistry data indicate that mafic and felsic rocks have their own geochemical characteristics which show different sources. The combined evidence of the trace element, radiogenic and stable isotope geochemistry from the Dumluca and Murmana granitoids suggest that the mafic rocks were derived exclusively from an enriched mantle mafic magma (EM 11), but the felsic rocks were derived from a hybrid felsic magma. The hybrid felsic magma was generated by the mixing of the mantle-derived mafic with another crustal-derived silicic melt. The composition of some mafic rocks from Murmana granitoid suite is thought to be derived from an enriched mantle source that may have been metasomatized by earlier subduction-derived fluids, thus carrying the subduction signature in the source material. The local and regional geology suggest an early Late Cretaceous post-collisional extension-related geodynamic setting, following the collision between the Tauride-Anatolide platform and an oceanic island arc comprising the supra subduction zone-type central Anatolian ophiolite. (c) 2006 Elsevier B.V. All rights reserved.