LATE COLLISION RHYOLITIC VOLCANISM IN THE NORTH-EASTERN PART OF THE ARMENIAN HIGHLAND

Abstract

Plio-Pleistocene acidic volcanism of the northeastern part of the Armenian highland is related to a continental collision zone as a result of convergence between Eurasia and Arabia lithosphere plates. The development of volcanism is divided into three stages of 10–17, 4.5–7.5 and 0.1–2.8 Ma. A crustal origin model is proposed to explain the geochemical and petrogenetic aspects of the acidic volcanism formation. Spatially separated Ba-rich and Rb-rich geochemical types of rhyolites were revealed, indicating more evolved and primitive rhyolitic magma types, respectively. The variation interval of the primary 87Sr/86Sr ratio was found to be from 0.70438 to 0.70636. Age and lateral variation of geochemical and isotopic parameters were determined by differences of initial substrates and degrees of their partial melting. The mechanisms of rhyolitic magma evolution were the remelting of heterogeneous sialitic materials and low-pressure fractional crystallization in isolated magmatic chambers. These facts confirm the model of crustal anatexis origin of the eutectic melts. The eutectic rhyolitic magma was generated by an open-system melting in the presence of deep-horizon mobile K–Rb fluids, initiated by mantle resources.