Nesa-e-pain shoshonitic intrusion, an evidence of the Tertiary magmatism in the Central Alborz, Iran



The studied intrusion is located in the Central Alborz tectonic zone of Iran, in the south of Taleghan valley near the Nesa-e-pain village. The Nesa-e-pain post Eocene intrusion is composed mainly of monzonite along with some gabbro and syenitic dykes. This intrusion is emplaced in the acidic tuff of Karaj Formation with a chilled margin in the contact. The intrusive rocks with a granular texture are mainly composed of plagioclase, alkali feldspar and clinopyroxene as rock forming minerals. These rocks are metaluminous and belong to SH (shoshonitic) type granites. High Zr/Nb, Nb/Ta and Rb/Zr ratios with accompanying the sample position on Sm/Yb vs Sm and La/Sm diagrams display that the intrusive rocks have probably originated from an enriched mantle (Sp-gran lherzolite). According to the discrimination and spider diagrams, it seems that the magma of these rocks was generated in a subduction zone because of their enrichment in LILE and depletion