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

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Abstract

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

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