Basic magmatism in the geological history of the Elbrus Neovolcanic area, greater Caucasus: Evidence from K-Ar and Sr-Nd isotope data

Abstract

The age and genesis of basic rocks in the magmatic evolutionary series are of principal significance for regions with predominant acid, mainly crustal volcanism. The appearance of basic volcanic rocks in the rhyolite‐dacite volcanic sequences is usually a sensitive indicator of a change in the conditions of magma generation, the involvement of different mantle and/or crustal reservoirs, or a change in the geotectonic and geodynamic settings of the volcanic activity. This is evident from the abundance of Neogene‐Quaternary acid and moderately acid volcanism in the Elbrus neovolcanic area, Greater Caucasus. The Neogene‐Quaternary magmatic centers of the Greater Caucasus are localized within three (Kazbek, Central Georgian, and Elbrus) neovolcanic areas. The Elbrus area located in the central part of the northern slope of the Greater Caucasus is bounded by the upper reaches of the Kuban River in the west, the Kuma River in the north, the Cherek River in the east, and the Main Caucasus Range in the south (Fig. 1). Evolution of the young magmatism in the Greater Caucasus is divided into three stages [1] with age boundaries determined by isotope‐geochronological investigations [2‐8]. The first (Late Miocene) stage (9.5‐8.3 Ma) is represented by subalkaline acid intrusive rocks of the Caucasian Mineral’nye Vody area of the Elbrus volcanic area [2, 3]. Products of the second (Pliocene) stage are found in the central sector (Chegem and Tyrnyauz regions). In the Chegem region, the products are represented by acid and moderately acid volcanic rocks of the Upper Chegem caldera and Lower Chegem highland (2.9‐2.7 Ma) [2, 5, 6], andesites of the postcaldera Kumtyube and