زمين شناسي و سنگ زايي مجموعه آتشفشاني قليايي - نيمه قليايي شمال ايران مركزي: نقش فرايندهاي تفريق بلوري و غني شدگي سنگهاي اسيدي تا بازي در يك محيط پشت كمان

Geochemistry and Petrogenesis of an Alkaline-Calc Alkaline Volcanic Suite North Central Iran: The Role of Crystal Fractionation and Enrichment Processes in a Back-arc Environment

South Kahrizak volcanic rocks with Eocene age are located in the north part of Central Iran. These rocks are mainly composed of pyroclastics (tuff and ignimbrites) and lava flows (rhyolite, trachyandesite, basaltic trachyandesite and basalt). Petrographic evidence such as: zoning, sieve texture and rounded crystals in plagioclase and pyroxene phenocrysts show the non-equilibrium conditions between melt and crystals during magma cooling. Geochemical characteristics indicate that these rocks locate in the subalkaline to alkaline domain. The highly enrichment of LREE compared to HREE, high content of LILE relative to HFSE and significant anomalies of Nb, Ta and Ti reveal the characteristics of a subduction - related volcanism. Whereas, the alkaline affinity of rocks shows that they may have formed in an extentional region, most probably a back-arc basin.