Petrographic features and provenance reconstruction of the Lower Riphean sandstones of the Mukun Group of the south-eastern Anabar shield

Research subject. Lower Riphean terrigenous rocks of the Mukun Group of the East Anabar basin. Aim. Reconstruction of provenance, identification of petrographic features, and restoration of sedimentation environments of these terrigenousrocks. Materials and methods . The upper part of the Mukun Group section located in the lower reaches of the Bolshaya Kuonamka River (southeast of the Anabar Shield) was studied, as well as a set of Lower Riphean sandstone samples of the same level. Reconstruction of provenance and formation environments of terrigenous rocks was based on U-Pb dating of detrital zircons, as well as field observations and study of the mineral composition of these rocks using petrographic, X-ray phase and X-ray spectral analyses. Results. The studied sandstones are characterized by a bimodal granulometric composition (sand-siltstone), dominated by angular grains of potassium feldspar with intense secondary alterations, as well as medium and well-rounded grains of quartz and zircon. The U-Pb dating of detrital zircon (69 grains) showed the presence of several different-aged provenances, represented by igneous and metamorphic rocks, the age of which corresponds to the main peaks of the dating distribution spectrum: 1965±5, 2095 ± 14, 2750 ± 7, and 2891 ± 9 Ma (weighted average). Conclusions. The deposition of Lower Riphean terrigenous rocks of the Mukun Group of the East Anabar Basin occurred in a shallow, calm environment during the erosion of a stable continental block of local origin. The most representative (more than 50%) is the age cluster of detrital zircon ~1965 Ma, which reflects the widespread occurrence of Proterozoic regional granulite metamorphism rocks on the Anabar Shield. In addition to metamorphosed Archean-Proterozoic rocks, the following igneous complexes might have been the source of zircon: Archean Anabar enderbite-charnockite-migmatite and Proterozoic Magan alaskite-leucogranite-migmatite together with Billyakh granodiorite-granitegranosyenite. The absence of detrital zircon younger than 1890 Ma in the studied sandstone indicates different provinces for the West and East Anabar sedimentation basins.