Middle Paleozoic adakite granitoids of the crystalline basement of the Foreland Range of the Greater Caucasus

Abstract

Relevance. The study of granites in the Foreland Range of the Greater Caucasus, which were formed in the middle Paleozoic, is an interesting and important task due to the fact that ore objects with molybdenum and tungsten mineralization are associated with them in the region. The aim of the study is to obtain analytical data and to clarify the geodynamic position and ore specialization of middle Paleozoic granitoids. The objects of research were the granitogneiss masses exposed in the crystalline basement of the Foreland Range of the Greater Caucasus in the interfluve of the Bolshaya and Malaya Laba rivers. The research methods included: study the composition of the selected samples by XRF, ICP-MS methods, their petrographic description, calculating geochemical characteristics, and analyzing discrimination diagrams. Results. It has been established that granitogneisses are normally and moderately alkaline, moderately and highly magnesian, and moderately potassium formations. It has been shown that they are adakitic granitoids characterized by high contents of Na2O, Ba, Sr, LiLe, LREE, and high Sr/Y 60–190 and Laн/Ybн13 – 40 ratios, with low CaO, HFSE, HREE, Y, and Yb. It is assumed that their initial melts were formed in supra-subduction conditions at significant depths (P15–16 kbar). The melting protolith was a lower-crustal garnet amphibolite, with thermal and fluid participation of the subducted oceanic crust. It has been noted that the hydrothermal mineralization of the quartz-scheelite formation is associated with the rocks.