Adakitic Volcanism in Sahand Region, Northwest Iran: Geochemical and Geodynamic Implications

Abstract

We present new whole major and trace elements data for a suite of adakitic dacite to rhyolite rocks from the Sahand region. These rocks formed in the Pliocene to Pleistocene during the the collision between the Arabian and Eurasian plates following subduction of Neo–Tethys Ocean. These subvolcanic intrusions were emplaced into late Cretaceous and Eocene sedimentary، volcano–clastic and volcanic rocks. Geochemical data indicate that the subalkaline dacitic to rhyodacitic rocks have an adakitic characteristics with Na₂O/K₂O (1.8–3.16), high Sr (391–804ppm), Mg# = (18–57) and low Y (3.6–20.8 ppm), low Yb (0.65–1.29 ppm), and low heavy rare earth element (HREE) abundances. Fractionated REE patterns with, (Ce/Yb)_N = 10–27, absence of negative Eu anomalies, low content of Y, Nb, Ti, and high Sr/Y ratios (74–265) suggest that the source was likely hydrous garnet–amphibolite or eclogite, possibly generated during subduction of the Neo–Tethyan oceanic slab beneath the Central Iran microplate. The adakitic volcanism was followed by eruption of alkaline magmatism in this area. Slab melting occurred after cessation of subduction, possibility cause by the collision. Transtensional tectonics accompanied by a locally extensional stress regime is account for magma genesis and ascent.