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Vol 73, No 5 (2018)
- Year: 2018
- Articles: 9
- URL: https://journals.rcsi.science/0145-8752/issue/view/10699
Article
Theoretical Modeling of the Regular Olivine Intergrowths in Mimetic Paramorphs from Ringwoodite and Wadsleyite
Abstract
This work presents the results of theoretical modeling of regular misorientations of olivine grains in mimetic paramorphs from ringwoodite and wadsleyite, whose formation is expected during the rise of material from the mantle transition zone. The coordinates of the axes and angles of misorientation, which characterize ten operations of alignment in the pair intergrowths of olivine grains, eight of which are twins, are calculated. Possible conditions for the formation of the predicted mimetic paramorphs and the chances of their preservation are discussed. The calculated orientations are compared with the known olivine twin laws.
397-406
Granulite Gneiss Belts: The Geodynamic Aspect
Abstract
The features of the structure and tectonic evolution of granulite gneiss belts (GGBs) are analyzed and summarized from the present-day data. Their continent–continent collision tectonic origin is supported, as well as multicycle and an inherited style of evolution expressed in multiple manifestations of granulite facies metamorphism of the belt separated by few 100 Ma. GGBs are permanently mobile structures that exhibit endogenic activity during all stages of their evolution, including intraplate conditions. Their relationship with supercontinental cyclicity is evident from (i) the spatial location of most GGBs in the margins of young oceans that originated during the breakup of Pangea, (ii) the amalgamation and breakup of ancient supercontinents along the GGBs, and (iii) the correlation between various types of granulite metamorphism of these belts and stages of supercontinental cycle. The evolution of these belts leads to complex interaction of plate and mantle plume tectonics, which is expressed in combination of continent–continent collision and underplating. The possible use of GGBs in paleotectonic analysis along with other indicators of geodynamic settings is shown.
407-415
The Geological History of the Kerch–Taman Area Based on a Reconstructed Regional Balanced Section
Abstract
The geological framework and tectonics of the East Black Sea region is characterized through balancing a geological cross-section and paleoreconstruction during the Paleogene–Neogene period. The studied area includes the Kerch–Taman trough, the Anapa Swell (a continuation of the immersed part of the Greater Caucasus Orogen), the Tuapse trough, and the Shatsky Swell. This paper is mainly focused on the Russian shelf zone of the Black Sea. The results are important for understanding the trap formation time and the preservation of hydrocarbon deposits in the Russian sector of the Black Sea shelf.
416-422
The Cyclic and Sequence Stratigraphic Characteristics of the Visean–Serpukhovian Deposits in the Southern Part of the Moscow Syneclise
Abstract
The composition and origin of the Visean–Serpukhovian deposits in the southern part of the Moscow Syneclise have been characterized based upon generalizations of our own results and analysis of published and unpublished data. The levels of karst-influenced rocks correspond to the shallowest biogenic carbonate organogenic-clastic sediments of the initial and final phases of the eustatic cycle, i.e., the early transgression (transgressive system tract) and the late regression (the second half of the high-standing tract). Alluvial sands of the Oka River have been found in the karst cavities. A generalized model of the sequence has been proposed and a sequence stratigraphic interpretation of the studied section has been carried out.
423-433
Permian Fossil Plants from the Sediments of the Vorkuta Series at the Pechora Coal Basin in the Collection of the Earth Science Museum of Moscow State University
Abstract
Permian plant remains from the Vorkuta 1 location collected at the Earth Science Museum of the Moscow State University were characterized (at outcrop 38 at the left bank of the Vorkuta River within the boundaries of Vorkuta town opposite the Rudnik settlement). The collection includes equisetophytes Paracalamites decoratus (Eichwald) Zalessky, P. frigidus Neuburg, Paracalamitina cf. striata Zalessky emend. Naug.; Annulina neuburgiana (Radczenko) Neuburg, the leaves of ferns (Pecopteris anthriscifolia (Goeppert) Zalessky, P. helenaeana Zalessky, P. vorcutana Zalessky, and P. cf. leptophylla Bunbury), as well as the leaves of Vojnovskyales Rufloria spp. and, probably, of ginkgophytes. In terms of stratigraphy, the considered plant remains originated from the Inta formations of the Vorkuta series (the Ufa stage of the Biarmian (Middle) subdivision of the Permian system). The collection is characterized by significant scientific, exhibition, and didactic potentialities.
434-443
The Timescales of Magma Mixing in the Plumbing System of Bezymianny Volcano (Kamchatka): Insights from Diffusion Chronometry
Abstract
Intrusion of magma of contrasting composition into a magma chamber often triggers eruptions of arc volcanoes. Application of the diffusion chronometry method allowed us to determine the time when fresh magma was supplied to the shallow chamber of Bezymianny volcano in the case of six eruptions in 2006–2012 and to compare them to the recorded seismic activity of this volcano. Two types of eruptions of Bezymianny volcano were distinguished, with a contrasting orthopyroxene rim being formed in the respective magmas (a) up to 3 years and (b) up to 2 months before the beginning of an eruption. It was shown that these differences are caused by two different paths of magma supply to the shallow chamber of Bezymianny volcano.
444-450
Fractionation of Rare-Earth Elements in the Processes of Hydrothermal Ore Formation
Abstract
The data on the distribution of elements in the Pb–Zn cross-section of the Gatsirovskaya vein (the Upper Zgid deposit, North Ossetia, Russia) have shown that the spectra of rare-earth elements (REEs) changed significantly in the ore samples during the vein formation. The sharp growth of the LaN/YbN, LaN/NdN, GdN/HoN, and GdN/YbN ratios is confined to the vein intervals, where the maximum amount of ore components is deposited. The comparison of the REE spectra of ores to the characteristics of the spectra of the rocks surrounding the vein and the host rocks suggests that the vein material deposited from the solutions in which the REE ratio changed with time. REE fractionation occurred due to the mobilization of components by hydrothermal solutions during their interaction with the Paleozoic host granites.
451-456
Composition of Pore Solutions. A Study Using the Indirect Method of Water Extracts
Abstract
We have compared quantitative characteristics of the macro- and microcomponent composition of pore solutions in bottom sediments obtained by their direct analysis and those calculated on the basis of the composition of water extracts taking into account water content of the samples. In the result of the study it was shown that the method of water extracts may be used to determine salinity and chemical composition of natural pore waters in low-permeable argillaceous deposits with different lithification rates. It was also shown that an analysis of water extracts does not allow determining the exact composition of the natural pore solution, but may be used for the evaluation (within the measurement error) of chlorine, sodium, and bromine content.
457-466
Experimental Research on the Photodegradation of the Organic Compounds of Natural Waters
Abstract
The photodegradation of organo-mineral complexes in natural conditions was studied using samples of soil and swamp waters to study the effect of sunlight on the composition and properties of organic matter and metal forms dissolved in natural waters. The total contents of certain aliphatic and aromatic carboxylic acids increased in the samples after irradiation. Photodegradation of organic matter of the natural waters with the high Fe content is accompanied by the formation of colloidal particles (Fe hydroxides). The number of negatively-charged complexes of Ni, Cu, Zn, and Cd increased under insolation in swamp waters and decreased in soil waters.
467-471