Plio-Quaternary Adakite Genesis and Post-collisional Processes: Whole Rock Constraints and Sr, Nd Isotopic Compositions in Alborz Magmatic Belt, Ardabil, Iran

The Plio-quaternary sub-volcanic domes are the products of magmatism in the Turkish-Iranian plateau in the collision zone between Eurasia and Arabia. Intermediate-felsic volcanic rocks are found ۵۰ km west of Ardabil. These volcanic domes make a significant part of the Sabalan volcanic, a Plio-quaternary stratovolcano in northwest Iran. The igneous rocks (adakitic) include dacite, trachyte, andesite, trachy-andesite, and trachydacite, associated with ignimbrite and pyroclastic equivalents. They mainly comprise phenocrysts and a microcrystalline groundmass of pyroxene, amphibole, and plagioclase, with biotite and titanomagnetite. These rocks are enriched in Light Rare Earth Elements (LRREs) and Large Ion Lithophile Elements (LILEs) and depleted from Heavy Rare Earth Elements (HRREs) and High-Field Strength Elements (HFSEs). In these rocks, the SiO۲ content is ۵۶-۶۶ wt%, Na۲O is > ۳.۵ wt%, Al۲O۳  > ۱۵ wt%, Yb < ۰.۲ ppm, and Y < ۷ ppm, which are typical of high silica adakitic rocks. The initial ratios of the ۱۴۳Nd/۱۴۴Nd range from ۰.۵۱۲۷ to ۰.۵۱۲۹ and the initial ratios of ۸۷Sr/۸۶Sr for the adakites range from ۰.۷۰۳۵ to ۰.۷۰۶۰, reflecting the heterogeneity of the mantle and different degrees of crystallization. These geological, geochemical, and Sr, and Nd isotopic data indicate that these rocks belong to the post-collisional adakite type, and are derived from low-degree partial melting of a subduction-metasomatized continental lithospheric mantle (eclogite or amphibolite garnet). In the studied area, mineralization related to Plio-quaternary adakitic rocks has not been observed.

کلیدواژه ها:

Alborz magmatic belt ، Sr-Nd isotopic ، Adakite ، Sabalan ، Iran