Age and origin of the Kitoi sillimanite schist deposit,eastern Siberia

Doklady Earth Sciences -     

Age stages of metamorphism at the Kitoi Sillimanite schist deposit, southeastern Prisayan’e

The Irkut Block with dominant rocks of the Sharyzhalgai Series and Kitoi Block with prevalence of the Kitoi Series rocks are the main structures of the Presayanian basement elevation of the Siberian Craton. Two stages of metamorphism, Neoarchean (2.6–2.7 Ga) and Paleoproterozoic (1.85–1.87 Ga), were established for the granulitic complexes of these blocks. The rocks of the Kitoi sillimanite schist deposit composed of sillimanite, andalusite-sillimanite, and garnet-sillimanite schists and gneisses underwent by intense ultrametamorphic transformations which led to the formation of sillimanite- and garnet-bearing plagioclase and feldspar migmatites, and also granites, sienites, and granite-pegmatites. The geochronological study of melanocratic schists and leucocratic plagiogneisses-the typical rocks of the Kitoi deposit-showed the manifestation of metamorphism only at the Archean and Proterozoic boundary (2450–2550 Ma).     

The first data on mass-independent fractionation of sulfur isotopes in sulfides from rocks of the eastern part of the Fennoscandian Shield

The first data on the multi-isotope composition of sulfur (³²S, ³³S, ³⁴S) in samples from the Fennoscandian Shield were obtained by the laser local method. An anomalous concentration of the stable isotope ³³S was registered in some samples. Δ³³S ranges from–0.45 to +0.24‰, which indicates the mass-independent fractionation of S isotopes and provides evidence for the processes of primarily sedimentary accumulation of sulfides in the Archean oxygen-free atmosphere.     

Age of Granulites of the Cheremshanskaya Unit (Sharyzhalgai Uplift,Siberian Craton,Russia): New Data

Doklady Earth Sciences - The present paper presents new U–Pb and Sm–Nd age data obtained for granulites of the Cheremshanskaya Unit enclosing metamorphosed volcano-sedimentary sulfide...     

Geochemistry of stable oxygen and hydrogen isotopes in minerals and corundum-bearing rocks in northern Karelia as an indicator of their unusual genesis

The paper presents newly obtained data on the oxygen and hydrogen isotopic composition of minerals in corundum occurrences and their host rocks in northern Karelia. Minerals in the Khitoostrov and Varaka corundum-bearing zones have extremely low δ¹⁸O (lower than ?26‰) and δ D (lower than ?215‰), which suggest that the mineral-forming process involved glacial waters and that the minerals preserve the isotopic ratios of their protolith. Aluminous corundum plagioclasites were produced by high-pressure Svecofennian (1.9-1.8 Ga) metamorphism of Paleoproterozoic rocks that had been metasomatized with the involvement of meteoric waters during the Guronian glaciation epoch.     

The famennian-lower carboniferous reference section Geran-Kalasi (Nakhichevan Autonomous Region,Azerbaijan)

One of the most complete sections of the Upper Devonian-Lower Carboniferous in the Nakhichevan Autonomous Region in Azerbaijan is described bed-by-bed. The section is located on the northeastern slope of Geran-Kalasi Mountain. The section features a continuous succession of marine beds and abundant fossils, including foraminiferans, bryozoans, tabulates, rugoses, brachiopods, ostracodes, crinoids, conodonts, and algae. A few ammonoids found in the section have not yet been identified. In the process of composing the 1:25000 scale geological map, a complex brachiopod zone is for the first time accepted as a major stratigraphic unit (indicating the stratotype and an assemblage of zonal brachiopod species).     

Regions of the Earth with the best-pronounced annual period of seismic activity

A number of relatively small regions of the Earth have been found where the annual periodicity of seismic activity is most prominent, i.e., the Balkans and Turkey, an isthmus between North and South Americas, Alaska and the Aleutians, and some others. In both hemispheres, these regions are associated with subduction zones or intensely faulted segments of the continental crust.     

Lazurite: Validation as a Mineral Species with the Formula Na7Ca(Al6Si6O24)(SO4) $${\text{S}}_{3}^{{\bullet - }}$$ ⋅H2O and New Data

Geology of Ore Deposits - The status of lazurite as a valid mineral species has been confirmed. The neotype specimen from the Malaya Bystraya gem lazurite deposit, Baikal Lake area has been studied...     

Age constraints of high-temperature metamorphic events in crystalline complexes of the Irkut block,the Sharyzhalgai ledge of the Siberian platform basement: Results of the U-Pb single zircon dating

Geochronological data obtained in this work and previously known results of U-Pb geochronology suggest that principal metamorphic events, which took place in eastern part of the Irkut block (the Sharyzhalgai marginal ledge of the Siberian platform basement), correspond in age to (1) about 2.8 Ga, (2) 2649 ± 6 to 2562 ± 20 Ma, and (3) 1865 ± 4 to 1855 ± 5 Ma. Structural and metamorphic reworking of the earliest event originated under conditions of the granulite facies, whereas conditions of granulite and amphibolite facies were characteristic of the second and third events. Metasomatites after carbonate rocks originated in eastern part of the Sharyzhalgai ledge during the Early Proterozoic metamorphic event that lasted approximately 20 m.y. Being combined with age data, which are known at present for the reference syn-and post-collision granitoids in the Siberian platform basement and flanking foldbelts, new geochronological results show that accretion of basement blocks to the Siberian craton progressed from the east to the west between 1900 and 1840 Ma. To a first approximation, this geochronological interval characterizes time span of the Paleoproterozoic ocean closure and ultimate time, when the craton and supercontinent Columbia became amalgamated.