Petrology and geochemistry of high temperature I type granitoids in Nusha region, Mazandaran province

The study area is located about 30 km south of Ramsar, in the central Alborz zone. In addition to the Nusha granitoids (with an age of about 56 million years), the outcrops in this area, mainly include Paleozoic and Mesozoic rock units. Petrographically, the Nusha granitoids have diorite, syenite, monzonite, monzodiorite, granodiorite and quartz monzonite compositions. Moreover, mineralogically, feldspar is the principal mineral, and the texture superiority in them belongs to the granular type. In terms of magmatic series these rocks are metaluminous and range from high K calcalkaline to shoshonitic. The geochemical characteristics of the major and rare elements, as well as the petrographic ones indicate that these granitoids are I type granites, and at the same time they belong to high temperature ones based on the behavior of Ba, Ce and Y elements. Enrichment in LILE and LREE and low concentrations of heavy rare earth elements HREE and high field strength elements HFSE, together with Nb and Ti negative anomaly in the spider diagrams are signs of magmas related to the subduction zone. The high temperature nature and characteristics such as Y/Nb, Rb/Sr and Rb/Ba ratios show that the Nusha granitoids have the geochemical properties of both crustal and mantle origin materials with different ratios. Based on tectonomagmatic discrimination diagrams and trace element compositions, these granitoids belong to an active continental margin environment. The parental magma has originated from melting of an enriched mantle source and contaminated with continental crust during ascent.