Tectonic settings and petrogenesis of Quaternary volcanic rocks of Sabalan

The Sabalan volcano is one of the youngest volcanic calderas in east of Turkish-Iranian Plateau and is a young member of the Alborz Magmatic Arc (AMA). This stratovolcano is located in northwest of Iran and northern of Bitlis- Zagros Suture Zone. Turkish–Iranian Plateau covers an area about 1.5-2 million km2, and it is marked by high elevations (typically1.5–2 km above sea level) and low relief compared with mountains ranges to the south and north, where convergent deformation is more active (e.g. Zagros, Alborz, Kopeh Dagh and Greater Caucasus ranges). Magmatism is an important feature on the Turkish–Iranian high plateau in the Arabia–Eurasia collision zone. The Arabia–Eurasia collision is the most recent Tethyan orogeny in southwest Asia. Some of the lavas are erupted close to the suture in the late Cenozoic initial Arabia–Eurasia collision (Kheirkhah et al., 2013). The reduction in magmatic production by the end of the Eocene and many of the recent centers in the Turkish–Iranian Plateau are indicated that the magmatism was activated since the Eocene. The Eocene and perhaps especially the Middle Eocene was a time of intensified magmatic activity within southwest Eurasia. The compositions of these rocks are typically calc-alkaline and the magmatism is interpreted as an example of arc and back-arc volcanism. Eocene and Oligo- Miocene lavas and plutonic rocks are also distributed in NW Iran and Ahar volcanic belt. The most magmatic in this plateau had activities in volcanic from the Late Miocene to Quaternary. Magmatism has occurred intermittently within SW Eurasia between the Oligocene and the present day, across much of the region north of the original suture (Kheirkhah et al., 2009). Materials and Methods Sabalan is a Plio-Quaternary stratovolcano spreading over about 700 km2 and with elevations up to 4821 m. It is one of the eight major volcanic cones of an Oligocene to Quaternary volcanic province, which covers more than 200,000 km2 in the border regions of Iran, Turkey and Azarbaijan. The Sabalan Quaternary volcanic structure is characterized by two stage development. A succession of ignimbritic and lava flows is ascribed the first stage. In the second stage, extrusion of conspicuous volcanic domes and the formation of minor pyroclastic and lava cones have taken place (Alberti et al., 1976). Results and Discussion The Quaternary Sabalan volcanic activities are indicated with trachy andesites which mostly are erupted from the main caldera and are interbedded with ignimberites. The youngest flows of these volcanic activities are predominated by pumice and scoria flows. Based on studied microscopic sections and geochemistry analyses by XRF and ICP methods, the young volcanic lavas consists of
andesite, trachy- andesite, trachy- dacite, dacite and rhyolite with pyroclastic flows (ignimbrites, volcanic ash), which show high-K calc-alkaline nature. The Quaternary Sabalan lavas show high K calc-alkaline to shoshonitic signatures. The calc-alkaline andesitic rocks of these volcanic activities have high contents of K, Sr and Ba and resemble the high-K andesites. The content of transition trace elements (Co, Ni and Sc) in the rocks of the Sabalan is low. The available geochemical data indicate that these rocks were derived from upper mantle garnet peridotite presumably overlying the subduction zone and enriched in LILE prior to partial melting. The magma probably underwent fractional crystallization of olivine and spinel lherzolite. Conclusions By Geochemical studies, it is suggested that this lavas indicate some properties of assimilation,
fractional and crystallization (AFC) process. These characteristics show that these lavas were erupted above an active continental margin. The data are consistent with the hypothesis of the volcanic rocks of this volcano probably being related by low-pressure fractionation involving geochemical investigations of these rocks such as LREE-enrichment compared with HREE, Pb positive anomalies, and depletions in Ta, Nb and high ratio of Ba/Nb. These characteristics indicate that the primitive magmas were related to an active continental margin, under affected of component’s subduction of Neotethyan ocean beneath central Iranian plate. It is assumed that these rocks are originated from low degree of partial melting (