Abstract

Sabalan is a voluminous stratovolcano situated in the northwestern part of Alborz-Azerbaijan zone, 25 km from Meshkinshahr. It is separated by a fault creating a tectonic boundary from Sarab plain and Meshkinshahr. The composition of Sabalan volcanic rocks ranges from andesite, trachyandesite to dacite. The rocks have hypocrystalline porphyritic texture with a glassy matrix and microlite . Plagioclase, amphibole, pyroxene, biotite, and oxides are the main phenocryst phase of the rocks. Some plagioclases show disequilibrium textures (sieve texture and oscillatory zoning). The sieve texture and oscillatory zoning in the plagioclases may be indicative of magma mixing processes in the genesis of the Sabalan volcanic rocks. Geochemical data reveal that the Sabalan lavas exhibit calk-alkaline major-oxide trends with a sodic character and they range in composition from andesite to dacite. Pre-caldera and post-caldera volcanic rocks have similar geochemical features with enrichments in LILE and LREE relative to HFSE and HREE, respectively, and have negative Ti, Nb, and Ta anomalies. Ba/Ta ratios higher than 450 and La/Nb ratios ranging between 2 and 3 indicate a volcanic arc setting for the studied rocks. Based on field and geochemical studies, Sabalan is a subduction-related volcano, occurred as a result of subduction of Neo-Tethyan oceanic crust beneath the Iranian microplate.

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