Volume 13, Nº 2 (2019)
- Ano: 2019
- Artigos: 9
- URL: https://journals.rcsi.science/1819-7140/issue/view/13144
Article
New Age Data on the Volcanic Rocks of the Alazey Plateau (Northeastern Yakutia)
Resumo
The age of the rocks of the Cretaceous volcanogenic sequence of the Alazey Plateau, Kolyma–Indigirka Orogen of Northeastern Russia, is determined using U–Pb zircon dating on trachydacites and K–Ar feldspar–groundmass dating on dacites and basalts. The dacites of the Severnaya Sededema Formation, which was formed within volcanic belts, are dated as Aptian–Cenomanian (106–97 Ma), while the basalts of the Khangatas Formation yield the Paleocene age (59 Ma). These rocks mark the extension and rifting stage in the evolution of the region.
Geochemical Features of Early Mesozoic Metabasalts of the Western Part of the Tukuringra Terrane, Mongol–Okhotsk fold belt
Resumo
The paper presents the results of geochemical and Sm–Nd isotope study of the metavolcanic rocks of the western part of the Tukuringra Terrane, one of the largest terranes of the Mongol–Okhotsk fold belt. It is shown that among the metavolcanics of the Teplokluchevskaya, Garmakan, and Algaja formations there are varieties similar to OIB and N-MORB, yet no rocks revealing features characteristic of the subduction origin are found. Being of Early Mesozoic age, the studied metabasalts are the youngest rocks within the Mongol–Okhotsk belt. The Lower Mesozoic deposits of the western part of the Tukuringra Terrane, including the volcanics of the OIB and N-MORB types, may have been relics of the residual ocean basin. The data obtained reflect the absence of subduction processes in the Late Triassic–Middle Jurassic at the final stages of the formation of the Mongol–Okhotsk fold belt. The closure of the Early Mesozoic basin was probably due to large-scale shear displacements.
Rare-Metal Mineralization of Sn Occurrences in the Area of Li–F Granites, Verkhneurmiysky Ore Cluster, Amur Region
Resumo
The by-products of the Far East Sn deposits related to Li–F granites include trace elements. The petrography and mineral composition of the Sn-bearing metasomatites of the Verkhneurmiysky ore cluster (VUOC) of the Amur region (feldspatites, greisens, zwitters, turmalinites, and chloritites) and the multistage complex rare-metal (RM) mineralization of the Sn occurrences in area of Li–F granites are studied. The minerals of strategic metals (Nb, Ta, W, Y, REE (from La to Lu), Be, Li, Rb, Zr, Hf, In, Sc, Se, Cd, and Te) are found. The RMs occur as minerals (fergusonite, plumbopyrochlore, allanite, monazite, roquesite, sakuraiite, etc.) and isomorphic substitution in the ore (wolframite; cassiterrite; Cu, Sn, Fe, Mo, Zn, and Pb sulfides; native bismuth; etc.) and rock-forming (fluorite, siderophyllite, muscovite, and epidote) minerals. Some RMs (Y, REEs, Nb, In, and Sc) most frequently occur in Sn-bearing metasomatites. The RM minerals formed during the VUOC evolution (from the premineral feldspatite to the postmineral chloritite stage) with decreasing intensity of RM mineral formation and compositional evolution from lithophile to chalcophile RMs: (LREE, Zr, Hf) → (W, Nb, Ta, Y, HREEs, Sc) → (Sn, In, Cd, Se, Te). The formation of the VUOC RM mineralization was caused by magmatic, metasomatic, and crystal chemical factors. The possible complex exploration of the Far East Sn deposits is shown for areas of Li–F granites.
Conodont Assemblage from the Upper Part of the Lower Olenekian Abrek Bay Section, South Primorye
Resumo
This paper describes the conodont species found for the first time in Abrek Bay in the upper part of the Lower Triassic deposits, which are provisionally assigned through ammonoids to the Anasibirites nevolini zone. The study of the conodonts from these layers has made it possible to identify the assemblage composed of the species Concervatella concervativa (Müller), Ellisonia triassica Müller, Foliella gardenae (Staesche), Neospathodus novaehollandiae McTavish, N. posterolongatus Zhao et Orchard, N. spitiensis Goel, and Novispathodus waageni (Sweet) occurring in both the Anasibirites nevolini zone and the Mesohedenstroemia bosphorensis underlying zone, belonging to the Olenekian bottom, and also the species Triassospathodus aff. homeri (Bender) and T. cf. symmetricus (Orchard) that are more characteristic for the overlying ammonite zones of the Olenekian top.
New Evidence of Eocene Ingression in Grabens of the Tan-Lu Fault System (East Asia): An Important Event Level
Resumo
New evidence of Eocene ingression in the area of the present-day Russian–Chinese border is provided. It was previously believed that Cenozoic grabens of the Tangcheng–Lujiang (Tan-Lu) Fault Zone, located in China and also traced in Russia, were filled predominantly by continental, rarely, lagoonal sediments. In 2015, drilling in the Huadian Basin (graben), which is part of the Tan-Lu system, recovered the Hydrobia zhuoxianensis gastropod in the black shales among the continental fauna. This finding indicates coastal marine conditions and therefore specifies the extent of the Eocene ingression. This gastropod can also be used in interregional stratigraphic correlation.
Geological Conditions of Gas Accumulation in the Coastal–Shelf Zone of the Peter the Great Bay, Sea of Japan
Resumo
The results of the study of natural gas in Peter the Great Bay from 2009 to 2014 are reported. The data on the distribution of natural gas in the water and bottom sediments are obtained. High concentrations of gas in the bottom water and sediments are registered in some areas of the bay. The probable sources of methane and other natural gases are suggested.
Natural and Technogenic Mineral Formation in the Aquifer of the Amur-Tunguska Interfluves
Resumo
Changes in mineralogical composition occurring in the course of preparation of drinking water in-situ are studied based on the data from the monitoring wells of the Tunguska groundwater intake. Intensive dissolution of feldspars, pyroxenes, siderite, and, to a lesser extent, quartz with the formation of secondary minerals (amorphous silica, clay minerals, and secondary siderite) occur in the aquifer of the Tunguska intake. In addition, solid products of the destruction are formed, including microfragments of minerals, which together with the primary clay, secondary minerals, and oxides and hydroxides of iron and manganese that originated in the process of intralayer oxidation of water, participate in the colmatation of cracks and the slit space of the well filters. Regeneration actions result only in a partial recovery of the specific flow rate of the wells, since the hydrochloric acid used in them leaches only the oxide–hydroxide part of the colmatant, leaving virtually unchanged its aluminosilicate component.
Geochemistry and Conditions of the Formation of the Ulsk Thermal Spring (Coasts of the Sea of Okhotsk, Khabarovsk Krai)
Resumo
The report presents original data on the isotope and chemical composition of the nitric thermal, cold underground, and surface natural waters, along with the water-enclosing rocks, of the Ulsk occurrence of thermal mineral waters (coasts of the Sea of Okhotsk, Khabarovsk krai). The data on the concentrations of oxygen and nitrogen isotopes and rare-earth elements, as well as on the volume activity of radon, in the treated underground and surface waters are obtained for the first time. Based on the data of automated monitoring of the physical parameters, the hydrogeological characteristics of the thermal waters are determined and the balneal properties are evaluated. The results obtained show the atmospheric origin of the nitric thermal waters of the Ulsk spring; however, the indicative chemical elements occurring in the considered waters represent the effects of deep-seated high-temperature processes as well. It is found that the waters warmed to 31°C within fractured Paleocene granites do not show significant variations of temperature, and the chemical composition varies exclusively under the interaction with the water-enclosing rocks. The profiles of the distribution of rare-earth elements (REEs) in the thermal waters represent the REE distribution in the water-enclosing granitoids and point to the limitation of the thermal water circulation with the area of the occurrence of the Paleocene granites of the Bekchi–Ul Massif. The temperature of the deep-seated reservoir measured by geothermometers was 80°C or below, which may indicate a depth of water circulation of 1–2 km or less.
Reconstruction of Sources in River Sediments in the Lower Part of the Bureya River Based on Geochemical Indices
Resumo
The results of studies of the macro- and microelement composition of the riverbed sediments of the Bureya River are presented. Analysis of the changes in the distribution of microelements (rare-earth elements), as well as in the values of geochemical indices (WIP, STI, R, CIA, CIW, PIA, and V), shows that the sediments in different parts of the river were formed by various sources. Thus, the values of the mentioned indices, as well as their trends, allow one to assume that the primary matter sources in the upper (mountain) reaches of the Bureya River are granitoids occurring within the bounds of the river valley. This part of the river shows downstream a regular increase in the fraction of more weathered matter in the erosion area. The indices of chemical weathering in the riverbed deposits of the lower reaches of the Bureya River (the river reaching the submountain plain) do not follow the trend appearing in the upper reaches. The riverbed sediments as such in the lower reaches of the Bureya River are similar in chemical composition to the sediments of the Amur River. The author assumes in view of these facts that the riverbed sediments of the lower reaches of the Bureya River are mainly constituted by the substance supplied by the Amur River.