Adakite magmatism within the Sabzevar ophiolite zone, NE Iran: U-Pb geochronology and Sr-Nd isotopic evidences

Numerous post-ophiolite intrusions exposed into the late Cretaceous–Paleocene Sabzevar ophiolite belt, northeast Iran. The intrusions consist of calc-alkaline intermediate to felsic rocks with metaluminous to peraluminous in nature and adakitic affinities. Based on U-Th-Pb dating on separated zircons by SHRIMP Ⅱ, the emplacement age of these rocks into the ophiolite zone is constrained to ~45 Ma. All intrusions show similar MORB –like initial Nd and Sr values of 0.512911 to 0512846 and 0.704758 to 0.703790, respectively, with positive εNd (45 Ma) values of .26 to .45 implying their cogenetic nature. These isotopic signatures combined with geochemical evidences are corresponding to parental adakitic magmas derived from wet partial melting of a garnet-amphibolite source from Sabzevar subducted oceanic lithosphere. After emplacement in the deep magma storage region (equal to 700-900 MPa), this magma evolved to intensify adakitic signatures via amphibole–dominated magma fractionation.