EVOLUTION OF MESOZOIC MAGMATISM AND ORE-FORMING METASOMATIC PROCESSESIN THE SOUTHEASTERN TRANSBAIKAL REGION (RUSSIA)

Petrological analysis of magmatic and metasomatic rocks and their K-Ar and Rb-Sr isotope dating show that the multistage tectonomagmatic act ivization in the study area lasted from the Late Triassic to the Middl e Cretaceous. Four stages (impulses) of magmatic and hydrothermal acti vity were distinguished, each of which continued for 15-20 Ma and was characterized by specific magmatic and metasomatic rock associations. During the whole activization period the magmatism evolved from monzon ites, quartz diorites, and granosyenites to midalkaline leucogranites, including their lithium-fluorine varieties. The subsided tectonic blo cks were dominated by intrusive magmatic complexes, whereas in the upl ifted blocks the volcanic rocks were abundant. Hydrothermal metasomati c processes were cyclic, and some types of metasomatic rocks (skarns, greisens, beresites, feldspathites) were developed at different stages . The abundance of the low-temperature metasomatic processes (beresiti zation, argillization) and ore mineralization increased at the latest stages. The magmatic and hydrothermal activity was completed by the mi ddle of the Cretaceous. Space and time relations between the magmatic complexes, metasomatic rock associations, and ore types were also dete rmined.