Precambrian Granitoids of the Nechera and Tonoda Uplifts in the Baikal Orogenic Region ( Geochemistry and Zircon Geochronology )

The granitoids of the Nechera and Tonoda uplifts have been classified on the basis of complex geochemical and geochronological investigations by the thermoemission zircon method. It is proven that there are the Kodar orogenic (1900± 50 Ma), Nichatka active (1750± 50 Ma) granitoid complexes and related silica-alkaline metasomatites. The Kodar granites (granite formation) have Th-rare-earth-rare-metal specialization and the Nichatka granites (subalkaline granite formation) have rare-alkaline-metal geochemical specialization. The Istanakh pegmatite-granite complex (about 1550± 50 Ma) is described for the first time. This complex marks the stage of Early-Riphean tectonic-magmatic activity of the Baikal orogenic region.