Pliocene granitoid massif in the Kazbek volcanic center: First geochronological and isotope-geochemical data

Abstract

Detailed study of Late Cenozoic intrusive magmatism in the Earth remains one of the most pressing and interesting geological problems of both regional and fundamental significance. For example, data on recent plutonic rocks with a short-term modern history can be used to solve important problems, such as the duration of crystallization and cooling of different (in volume and composition) intrusive bodies, recognition of discrete intrusive phases for plutons formed in geologically short intervals, determination of subtle isotope‐ geochemical differences between rocks of different intrusive phases, and so on. The present paper is devoted to the geochronological and isotope‐geochemical study of one of the reference (but insufficiently studied) terranes of young granitoid magmatism in the Kazbek neovolcanic area of the Greater Caucasus. Data obtained suggests the existence of a single intrusive massif in the area. They make it possible to determine its timing, major petrochemical characteristics of granitoids, and possible sources of magmatic melts. At the Greater Caucasus and its northern periphery, one can distinguish three stages of Late Cenozoic activity (Late Miocene, Pliocene, and Anthropogene) [1‐7 and others]. Pliocene magmatism was mainly expressed in the formation of hypabyssal granite or granodiorite intrusions, as well as usually differentiated (from diorite to granites) intrusive massifs. The Elbrus neovolcanic area incorporates two granitoid massifs (Eldzhurtu and Dzhungusu), for which a great number of isotope, geochronological, isotope‐geochemical, and thermochronological data are available [3, 4, and others]. Pliocene intrusive massifs in the Kazbek volcanic area, including the most well-known Tepli and Songuti-Don massifs, have been studied less. In the Kazbek area, plutonic bodies are typically localized in the sublatitudinal zone between Skalistyi Ridge in the north and the Main Caucasus Range in the south. The zone is extended from Mt. Shkhara in the west to Kazbek Volcano in the east. In addition, several small massifs are known on the southern slope of the Main Caucasus Range (Tsurungal, Karobi, and Kalkva). This vast area also includes numerous dikes varying in composition from granite porphyries to subalkaline diabases. Probably, some of them mark the paleovolcanic edifices