Russian Journal of Earth Sciences
Vol. 3, No. 3, August 2001
Evolution of magmatism in the zone of junction
between granite-greenstone and granulite-gneiss regions, Sayan mountains, Siberia
V. I. Levitskii, A. I. Melnikov, and G. P. Sandimirova
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.