Geochemistry and Tectono-magmatic setting of Eshkavarat A1-type granitoid in Southern Caspian Sea: Derived from underplated rocks related to oceanic Plume in Northern Iran

The Eshkavarat intrusive bodies, consisting of monzonite, quartz monzonite and syenite to granite composition, with late Cretaceous age, are located east of Gilan province in western Alborz and formed as 4 large bodies, in the southern part of the study area. Petrographically they show perthitic and micrographic textures and are composed of K-feldspar, quartz, plagioclase and biotite as main minerals with accessory iron oxides and apatite. These rocks have high SiO2, alkalis, FeO(total)/MgO. In the spider diagram show subparallel, linear, and homogeneous REE profiles with enrichment of LILE. Granitoid show high Ga/Al, Zr, Th, Rb, and rare earth elements (REE) (except Eu), low CaO, MgO and strong depletion in Ba, Eu and Sr. They have the typical geochemical characteristics of A1-type granites. Tectonic discrimination diagrams show the tectonic setting of the within-plate granite (WPG). According to the tectonic model presented for the study area, a tectonic window and an extensional regime above the supra-subduction zone appear to have been created by the subduction of the oceanic crust of the southern Caspian Sea after the end of the Upper Cretaceous. The mantle magma then rose up through the tectonic window. Direct release of this mantle magma has generated oceanic plume-like (OIB) rocks in the region. This mantle magma, arrest under the crust, causing its partial melting, and finally, fractionational crystalisation of mafic minerals and minor crustal assimilation, primarily parent magma of A1 granitoids and syenitic A1 rocks was generated, then, by fractionation felsic minerals A1-type granitic magmas were created.