An Archaean Tonalite–Trondhjemite–Granodiorite Association of the Kursk Block (Voronezh Massif): Composition,Age, and Correlation with the Ukrainian Shield

Doklady Earth Sciences - Framing of the Archaean greenstone belts of the Kursk Block (KB) of the East Sarmatia preserves rocks of the TTG association: those do not form massifs with distinct...     

Phase relations of REE-bearing minerals during the metamorphism of carbonaceous shales in the Tim-Yastrebovskaya structure,Voronezh Crystalline Massif,Russia

Paleoproterozoic carbonaceous shales in the Tim-Yastrebovskii ancient rift, which underwent zonal metamorphism at 350–550°C, contain REE mineralization of silicates (allanite, thorite, and Ce-P huttonite) fluorcarbonates (bastnaesite and synchysite), phosphates (monazite and xenotime), and REE-bearing apatite. The reason for the wide occurrence of bastnaesite and other REE minerals is relatively high REE concentrations in the sulfide-bearing carbonaceous shales, with these elements accumulated in the organic matter in the course of diagenesis. Reaction textures with REE-bearing chlorite, bastnaesite, and allanite suggest that REE-bearing chlorite and bastnaesite provided REE for the forming of higher temperature allanite and monazite. This is corroborated by the REE patterns of the monazite, allanite, and bastnaesite, which are almost identical and are characterized by the strong predominance of LREE. The replacements of REE minerals during metamorphism at 350–550°C took place via a number successive transitions: (1) Mnz → Aln, Chl _REE → Bst, Chl _REE → Aln, Bst → Aln and (2) Bst → Mnz and Ap _LREE → Mnz. These replacements can be accounted for by prograde metamorphic reactions.     

Archean Carbonatites and Alkaline Rocks of the Kursk Block,Sarmatia: Age and Geodynamic Setting

Doklady Earth Sciences - Neoarchean intraplate granitoid (2.61 Ga) and carbonatite magmatism are established in the Kursk block of Sarmatia in close spatial association. Alkaline pyroxenites,...     

The Paleoprotherozoic Volcanics of the Tim Formation within the Kursk Block,Sarmatia: Age and Geodynamic Setting

Doklady Earth Sciences - The volcanic–terrigenous Tim Formation in the Kursk Block of Sarmatia occurs in the Paleoproterozoic synforms. The Tim Formation volcanics are represented by...