GEOLOGICAL STRUCTURE AND FORMATION CONDITIONS OF THE CHELYABINSK GRANITOID MASSIF (SOUTHERN URALS)

Abstract

The Chelyabinsk granitoid massif is located in the northern part of the East-Ural megazone and it is about 1100 km2 in area. It is an integral part of the Main granite belt of the Urals. The massif is one of polyformational, polychronous and is a close analogue of the granite-gneiss domes: Varlamovsky, Borisovsky, Yeremkinsky, Sanarsky (Kochkarsky anticlinorium) and Beloretsky (Bashkirsky meganticlinorium). Four main granitoid complexes are distinguished in the Chelyabinsk pluton by age and petrographic parameters: smolensky (Є?S) diorite-tonalite (migmatite), warshavsky (C2v) granite-granitegneiss, poletayevsky (C2pl) granodiorite-granite and kremenkulsky (P2kr) granite-leucogranite. It is established that smolensky granite-gneisses, warshavsky granites, poletaevsky granodiorites and granites belong to the tonalite-granodiorite formation. The first of them were formed in the intracontinental geodynamic setting, and the second and third - on the marginal continental setting. Warshavsky granite-gneisses are close to the granitemigmatite formation in petrogeochemical features, and the kremenkulsky leucogranites are close to granite. The geodynamic setting of their formation corresponded to the interior of the continents. The igneous group includes warshavsky granites and kremenkulsky leucogranites, in the quartz of which melt inclusions are established, as well as granodiorites and granites of the poletayevsky complex, having formation temperatures of 800 °C and 700 °C and a pressure of 6.1 and 4.3 kbar (abyssal zone), respectively based on the study of the chemical composition of biotite and garnet. The smolensky and warshavsky gneisses and migmatites apparently have a metasomatic genesis and subsequently underwent a transformation under the conditions of the green shale and epidote-amphibolite facies (400 - 460 °С and 490 - 510 °С