EVOLUTION OF MAGMATISM IN THE ZONE OF JUNCTION BETWEEN GRANITE-GREENSTONE AND GRANULITE-GNEISS REGIONS, SAYAN MOUNTAINS, SIBERIA

Abstract

The crust in the south of the Siberian Craton includes the tonalite-trondhjemite complex of the basement, the highly metamorphozed rocks of the Kitoi Suite, the rocks of the Onot greenstone belt, ultrametamorphic rocks, the gabbroids of the Arban Complex, the metaultramafics of the Ilchira Complex, the rocks of the postultrametamorphic phase, and the metasomatic rocks of deep fault zones. The continental sialic tonalite-trondhjemite crust and the oceanic basaltic crust coexisted during the Early Archean. The rocks of the Onot greenstone belt are restricted to the linear troughs (paleorifts) of the early sialic tonalite-trondhjemite crust. The bottom of the belt is dominated by calc-alkalic bimodal rocks, the middle, by carbonate rocks, and the top, by clastic rocks and flysch. The processes of ultrametamorphic and postultrametamorphic allochemical transformations altered significantly the preexisting rocks. The junction zones of the Baikal granulite-gneiss and East Sayan granite-greenstone regions are marked by the wide development of the rapakivi-like granites of the Shumikha Complex, similar petrogeochemically to the maritime complex of the West Baikal region. The subconcordant linear distribution of the rocks of the Onot Belt, the ultrametamorphic and postultrametamorphic rocks, the granites of the Shumikha Complex, and the metasomatic rocks of deep fault zones testifies to their long-lasting connections with mantle sources.