Geochemistry and petrology of volcanic rocks in the south of Natanz (The middle part of Urumieh-Dokhtar Magmatic Arc)

Abstract

The south Natanz volcanic zone located in the central part of Urumieh-Dokhtar magmatic arc and the north of Isfahan. The area is dominated by the Eocene volcanic rocks ranging from acidic to intermediate and relatively basic affinity. Petrologically, they consist of rhyolite, dacite, andesite, basaltic trachyandesite and basaltic andesite. Mineralogically speaking, except for the acidic rocks, the other rocks are mainly made of plagioclase and clinopyroxene up. According to EPMA, the composition of clinopyroxene and plagioclase is augite and andesine to bytownite. Having features such as zoning and sieve texture in phenocrysts of plagioclase, roundness, and corrosion gulf in minerals belonging to the volcanic rocks reflecting the existence of unequilibrium during magma solidification. Considering geochemical features of these rocks, we can realize that they are calc-alkaline with potassium from intermediate to high LILE enrichment, and negative Nb-Ti anomalies. On the spider diagram, primitive mantle- normalized with Pb-enrichment can be seen which may be attributed to crustal assimilation. The negative anomalies of Nb and Ti on the spider diagram reflect subduction process, the crustal involvement in magmatism processes, or an indication of deficiency of these elements at the origin, the stability of Nb-Ti bearing phases during partial melting or separating these elements in the course of fractional crystallization process. The chondrite- normalized REE pattern points to LREE enrichment in comparison with HREE. The volcanic rocks studied have been originated in a magmatic arc.

Keywords

• volcanic rocks
• calc-alkaline
• magmatic arc
• geochemistry
• natanz