1 شاهرود- بلوار دانشگاه- دانشگاه صنعتی شاهرود- دانشکده علوم زمین
2 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China
3 Department of Petrology, School of Geosciences, Shahrood University of Technology, Shahrood, Iran
The post-ophiolite igneous rocks with dacite/rhyolite composition outcropped in the ophiolitic complex of Sabzevar zone. The calc-alkaline and high silica adakitic nature of these rocks has been proved previously. The rocks display initial 87Sr/86Sr ratios and εNd(t) values of 0.70444 to 0.70382 and +5.30 to +6.18 respectively, as same as these values in MORB compositions. These isotopic signatures are corresponding to adakitic compositions derived from melting of the Cenozoic oceanic subducted slabs. The emplacement age of these rocks into the Sabzevar ophiolitic zone obtained about 48 Ma by SHRIMP II U–Pb method on separated zircons. The results show that parental magma of the Sabzevar adakitic rocks generated by partial melting of a garnet-amphibolite or eclogite source derived from metamorphism of Sabzevar subducted oceanic lithosphere in early Eocene time. Magma differentiation via amphibole fractionation was the main factor in the manifestation of more adakitic signatures in more-evolved rocks (rhyolites).