Using Magma Mixing/Mingling Evidence for Understanding Magmatic Evolution at Mount Bidkhan Stratovolcano (South-East Iran)

Abstract

Mount Bidkhan stratovolcano is located in the central Iranian volcanic belt. It is composed of several types of pyroclastic deposits, lava flows and intrusive bodies. Textural and chemical characteristics of plagioclase phenocrysts from the eruptive products volcanic edifice, record complex magma mixing events over the lifetime of the volcano. Evidences such as xenocrystic high Al+Ti clinopyroxene and calcic cored plagioclase phenocrysts (An 75) in andesites, sieve-textured, dusty, and oscillatory zoned plagioclase together with clear normally zoned ones in the same sample and the wide compositional range of the plagioclase rims, show that magma mixing events have been playing an important role in the origin of Bidkhan eruptive products . Based on whole evidences, we propose a model for the evolution of Bidkhan parent magmas. According to the model, it is likely that mantle derived basic melts are injected into the lower crust, cause partial melting and produced acidic primitive melts. These two melts are then, mixed and resulted hybrid magmas, ascend toward the shallower reservoirs. Repeated magma injection gives rise to a second mixing event. Thus eruptive products at Mount Bidkhan have been originated from the mixing of intermediate hybrid magmas within shallow magma chambers. Sometimes, two melts have been erupted simultaneously as mingled melts. This model can be tested for other volcanic province of central Iranian volcanic belt.