Petrochemical and Sr-Nd isotope investigations of A-type granites in the east of Misho, NW Iran

Abstract

The Misho plutonic complex consists of a series of granitic bodies which range from syenogranite, alkali granite to monzogranites. They include metaluminous to peraluminous compositions. The garnitoid bodies are intruded into the unmetamorphosed late Paleozoic rocks and are located between two dextral, oblique-slip fault systems along which they have been uplifted as a major positive flower structure. The Misho granitoid belongs to the alkaline granitoid series that have been attributed to a Late Permian post-collisional setting. The studied granitoid displays high SiO2 contents between 67.71 and 76.4 wt%. On both FeO/(FeO + MgO) and [(Na2O + K2O) − CaO] vs. SiO2 diagrams, the samples, plot in the ferroan and alkaline fields, therefore, show an A-type granitoid signature. Trace and rare earth elements distribution patterns for the Misho rocks indicate a distinctive depletion in Nb, Sr, Ba, P, and Ti relative to other trace elements and a greater enrichment in large-ion lithophile elements compared to high field strength elements that are also typical features of A-type granites. The granitoid samples are geochemically similar to typical A2-type granites, e.g., high K2O + Na2O, FeO/MgO, Ga/Al, and Y/Nb values and low CaO, Ba, Sr, and Eu contents. They have initial Sr isotopic ratios in the range >0.712 and negative e Ndt values of −1 to −3.2 for a time of generation of 232 Ma. We suggest that shear zones play an important role in providing suitable conduits for ascending asthenospheric material and heat influx in the lower crust continental. It is proposed that the Misho parental granitoid magmas were produced by the partial melting of the lower crust continental at extensional setting in active continental margin setting that was formed after the collision of the Eurasia plate and Iranian plate following closure of paleo-Tethyan oceanic crust during Middle Jurassic times.