The Origin of the Rhyolite Massif of the Upper Chegem Highland (North Caucasus)

摘要

Based on new materials, the structure and origin of a huge (up to 2-km-thick) massif of acid volcanic rocks, which occur in the volcanotectonic depression in the upper reaches of the Chegem River in the North Caucasus, is considered. The issue of the lava, rather than the pyroclastic origin of the main part of the massif, is discussed. This massif was formed due to multiple eruptions of lava flows that composed a series of the acid volcanic rocks without gaps and with a well-pronounced columnar jointing in a limited volume of a deep volcanotectonic depression formed synchronously to eruptions in the Late Pliocene. The volcanic rocks were formed as a result of the boiling of a silicate melt and its exit from the vent of the volcano, which could be due to the phase transition of a supercritical aqueous fluid.