Ar-Ar Dating and Petrogenesis of the Early Miocene Taskapi-Mecitli (ercis-Van) Granitoid, Eastern Anatolia Collisional Zone, Turkey

Abstract

The Early Miocene Taskapi-Mecitli granitoid that is located in the northern section of the Eastern Anatolia Collision Zone has typical I-type, metaluminous and calk-alkaline characteristics. It also contains mafic micro-granular / magmatic enclaves (MMEs). New Ar-Ar dating results show that the age of the Taskapi-Mecitli granitoid is similar to 23 Ma and it crystallised in the Early Miocene, in contrast to its previously known Cretaceous age. Identical crystallisation ages (similar to 23 Ma), similar mineral assemblages and geochemical compositions, and indistinguishable isotopic compositions of MMEs and host rocks imply that the MMEs are most consistent with a cumulate origin formed at earlier stages of the same magmatic system that produced the Taskapi-Mecitli granitoid. MELTS modelling suggests that magma of the Taskapi-Mecitli granitoid was the result of fractionation under a crustal pressure of 4 kbar, with a H2O content of 1.5%. EC-AFC model calculation reveals that the Taskapi-Mecitli granitoid includes from 0.5% to 2% crustal assimilation rates. These rates indicate that crustal contamination can be negligible when compared to fractional crystallisation in the evolution of the magma beneath the Taskapi-Mecitli granitoid. The partial melting model calculations and MORB-normalised trace element concentrations of the least evolved samples of the Taskapi-Mecitli granitoid are consistent with those of mafic melts obtained from partial melting of interacting mantle- lower crust with a melting degree of 18%. The age (23 Ma) of the post- or syn-collisional Taskapi-Mecitli granitoid suggests that the collision between Arabian and Eurasian plates could be before/around similar to 23 Ma (Late Oligocene to Early Miocene).