Vol 73, No 6 (2018)
- Year: 2018
- Articles: 13
- URL: https://journals.rcsi.science/0145-8752/issue/view/10703
Article
Assessment of the Contribution of Secondary Metachronous Magnetization Components to the Precambrian Paleomagnetic Poles of the Karelian Craton
Abstract
The secondary (metachronous) magnetization components identified in the Precambrian complexes of the Karelian Craton have been analyzed. The average directions of high-temperature components (deviations from the true direction) have been calculated based on the contribution of secondary magnetization components resulting from tectonomagmatic events of uneven ages. The Precambrian key poles often coincide with the vector sum of the Phanerozoic magnetization components of uneven ages. The conclusion on the primary/secondary origin of the Precambrian paleomagnetic poles should be made on the basis of the integrated petro- and paleomagnetic and isotope data and geological correlations, rather than based on only the paleomagnetic reliability tests.
The Neotectonics and Seismicity of the Island of Cuba and its Surroundings
Abstract
Studies using structural-geomorphic analysis of the island of Cuba and its surroundings and the 3D geodynamic modeling of the formation mechanism of recent dislocations in the region yielded the following results: a roof block style of recent dislocations was revealed; the relationship of dislocations with Mesozoic structures and seismicity was determined; orientations of axes and zones of the maximum stresses were calculated; tendencies of morphostructure evolution at the recent stage were specified; and a seismic forecast was made. As a result, high statistical values of correlation between neotectonic parameters and seismicity have been obtained.
The First Evidence for Mesozoic Magmatism on the Western Slope of the Southern Urals
Abstract
Numerous Riphean mafic dykes cross-cut Precambrian clastics and carbonates on the western slope of the Southern Urals. An andesite dyke with an isotope age of 71 ± 1 Ma (U–Pb SHRIMP II on zircons) encountered among metamorphic rocks of the Taratashskii complex (Archean–Early Proterozoic) at the northern terminus of the Bashkirian meganticlinorium along with two gabbro bodies with zircons of similar ages near the town of Bakal provides the first evidence of Mesozoic magmatism in this region.
Calcareous Nanoplankton in the Paleogene Deposits of the Bakhchisaray District (Southwest Crimea)
Abstract
The calcareous nannoplankton of the Upper Paleocene and Eocene deposits from the Bakhchisaray district of the Southwest Crimea has been studied. It has been compared with the coeval complexes studied earlier and the following zones have been identified: the Kacha Formation corresponds to zones NP6–NP8 (?), the Bakhchisaray Formation is NP12, and the Simferopol Formation is NP13–NP14. According to the species composition, calcareous nannoplankton inhabited the normal salty shelf sea in the tropical belt.
The Metasomatic Zoning and Sb Mineralization of the Yuzhnoe Ore Occurrence, Shilka Area, Transbaikalia
Abstract
The results of a study of wall-rock metasomatites are presented on the basis of a complex mineralogical–structural approach, including the study of numerous publications, as well as original macro- and microscopic and X-ray diffraction data. The rocks are classified and the metasomatic column is presented; conclusions are made based on studying the hydrothermal–metasomatic processes related to the discharge of endogenic energy and redistribution of flows of material in the upper part of the crust.
The Details of a Method for the Preparation of Solid Geological Samples for ICP-MS Multielement Analysis
Abstract
The technique of decomposition of samples with a poorly soluble complex matrix (sintering with sodium carbonate) for subsequent determination of trace element composition by the method of high resolution inductively-coupled plasma-mass spectrometry (ICP-MS) was improved and tested. Analytical and methodical problems that arise during the preparation of samples for analysis are described and directions for their solution are indicated. The correctness of the developed sample preparation procedure has been verified by comparative analysis of various procedures applied to the international certified rock reference samples.
The Distribution and Speciation of PGEs in Chromitite from the Svetloborsky, Veresovoborsky, and Kamenushensky Clinopyroxenite–Dunite Massifs (Middle Urals)
Abstract
The mineralogical and geochemical patterns of platinum-bearing vein–impregnated and massive chromitite from dunite of the Svetloborsky, Veresovoborsky, and Kamenushensky clinopyroxenite–dunite massifs (Middle Urals) are reported. Platinum is characterized by an extremely uneven distribution in chromitite and is concentrated in the form of Pt–Fe intermetallic compounds. The structural and textural patterns of chromitite from these massifs, the PGE distribution in it, and the composition of chrome spinels are similar to those in well-studied chromitite from the zoned clinopyroxenite–dunite massifs of the Urals (Nizhny Tagil) and Koryakia (Gal’moenansky).
Zirconolite, Baddeleyite, Zircon, and Thorite of Island-Arc Quartz Gabbronorite-Dolerites of the Ayu-Dag Intrusive, Crimean Mountains
Abstract
The Early Bajocian island-arc quartz gabbronorite-dolerites of the Ayu-Dag intrusive contain syngenetic zirconolite and baddeleyite. Zirconolite includes Ca-dominant and atypical Y-dominant (Y, Ca, Th, REE)2FeZr2Ti3O14 varieties. Two genetic types of zircon and thorite occur. The dominant xenogenic zircon-I with thorite inclusions and numerous melting traces (lacunes) is enriched in Hf, Th, Y, and P (up to 6 wt % HfO2, 5 wt % ThO2, 6 wt % Y2O3, 3 wt % P2O5). Thorite contains 7–9 wt % UO2. Zircon-I and thorite-I of similar compositions are typical minerals of highly radioactive granites. The isotope age of xenogenic zircon is more than 2 Ga. Rare syngenetic zircon-II is extremely depleted in Th, U, Y, and Hf. Thus, the Ayu-Dag basic magma was contaminated by Early Precambrian highly radioactive granites, whose bodies probably occur in the basement of Crimean Mountains.
Acid Mobilization of Aluminum from Minerals and Rocks
Abstract
The leaching of aluminum with acidified riverine waters from minerals (hornblende, biotite, muscovite, microcline, labradorite, and albite) and rocks (granite, tuffosandstone, and crystalline schist) was studied experimentally. The relationship between the aluminum concentration and solution acidity was found: log[Al] = A–BpH, where the angular coefficient B was approximately equal for all the samples, 0.74 ± 0.06. It was concluded that polymeric hydroxocomplexes of aluminum prevailed in the solutions. The pH value below which the content of dissolved aluminum should exceed the maximum allowable concentration for fishery water bodies is 6.6 ± 0.3.
The Spatial Distribution of Sands of Different Ages and Geneses on the Territory of Russia
Abstract
In engineering geology sands are studied from different aspects, including features of their spatial distribution. The latter is especially important for the vast territory of Russia. Schematic maps of the distribution of Pre-Quaternary and Quaternary sandy soils on the Russian territory were compiled. The patterns of their distribution by area and section within the platform and mountain regions are described.
Distinguishing Oil Generation Zones by IR Spectra of Chloroform Bitumens within Mezozoic and Cenozoic Deposits of the Azov–Kuban Oil-and-Gas Basin
Abstract
The use of IR spectrometry for examining the structural and group composition of chloroform bituminous components of dispersed organic matter in Mesozoic and Cenozoic deposits of the Azov–Kuban oil-and-gas basin resulted in obtaining significant information on the conditions of sedimentation and diagenesis of the deposits that enclose organic matter, as well as on its degree of katagenetic transformation. The IR spectra, which conformed to 15 genetic types of chloroform bitumen, allow one to distinguish the zones that contain no oil-and-gas source rocks, along with those with generation of hydrocarbons and those with completed processes.
Salinity and Macrocomponent Composition of Pore Water of the Bazhenov, Achimov, and Georgiev Formations from Analysis of Aqueous Extracts
Abstract
This paper presents a reliable dataset on formation water salinity (mineralization) and salt composition for low-permeable (tight) shale rocks of the Bazhenov, Achimov and Georgiev formations for the first time. The data were obtained via laboratory analysis of aqueous extracts from rock samples before and after hydrocarbon extraction (cleaning). Thermodynamic modeling of the obtained solutions with a number of minerals was carried out and a correlation analysis of the Na/Cl, Ca/SO4, Mg/SO4, Ca/Cl, Ca/HCO3, and Fe/SO4 ratios was performed. It was established that the concentrations of certain macro-components, including Ca, Mg, Fe, hydrocarbonate, and sulfate ion in pore water cannot be reliably determined using aqueous-extract data, while at the same time, a reliable estimate of the minimal formation water salinity could be made. The need to use non-extracted core samples with the maximum preserved residual water saturation to study a pore water composition of tight shale rocks is shown.
Newly Discovered Hydrate-Bearing Structure in Lake Baikal
Abstract
A new deep-water hydrate-bearing structure, named after Moscow State University (MSU), has been discovered on July 29, 2018 during the geological-geophysical research of the Class@Baikal project. The structure lies on a fault scarp at the bottom of the central basin of Lake Baikal at a water depth of 1380 m (coordinates N 52°52′/E 107°07′). The “MSU” structure is sub-isometric in planar view, 500 m in diameter, and reveals a multi-summit morphology. Results of initial investigations show an active fluid seepage and gashydrate formation within the discovered structure. Laboratory analyses of the sampled gases indicate a significant concentration of thermogenic hydrocarbons.