Russian Geology and Geophysics最新文献

{"title":"Calcium-Rich Ultramafites, Ankaramites, and Clinopyroxene–Porphyric Gabbro of the Birkhin Massif in the Ol’khon Region: Solution of the Problem of Primary Melt and Formation of Intrusion","authors":"E. Pushkarev, A. V. Lavrenchuk, I. Gottman, E. Sklyarov","doi":"10.2113/rgg20234571","DOIUrl":"https://doi.org/10.2113/rgg20234571","url":null,"abstract":"\u0000 ––The paper presents new data on the chemical and mineral compositions of ultramafic rocks and various gabbro of the Birkhin massif in the Ol’khon region. Porphyric phenocrysts and zoned grains of clinopyroxene have been first found and studied in gabbronorite, which made it possible to reconstruct the entire melt crystallization trend from ultramafic to gabbro parageneses. Similar clinopyroxene trends have been established for clinopyroxenites and subvolcanic ankaramites, whose bodies and dikes have been recently discovered within the massif and in its environment. The total petrological data show that the magnesian high-Ca ankaramite melt corresponds in composition to the assumed primary melt for the Birkhin massif.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43408300","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Preservation of Soft-Bodied Organisms in Early Cambrian Carbonates","authors":"V. Marusin, N. Bykova","doi":"10.2113/rgg20234595","DOIUrl":"https://doi.org/10.2113/rgg20234595","url":null,"abstract":"\u0000 —Preservation of soft-bodied organisms as casts is common in the Ediacaran fossil record and extremely rare in Cambrian rocks. Among the factors, limiting fossilization of soft tissues, there is bioturbation–sediment disturbance by burrowing organisms. It is the emergence of burrowing metazoans and associated sediment bioturbation that is thought to be one of the major causes for the disappearance of Ediacaran soft-bodied organisms from the fossil record around ~540 Ma. Here, we study an assemblage of fossils preserved as casts in the Fortunian carbonates of the Olenek Uplift (northeastern Siberian Platform) in association with a typical Fortunian ichnoassemblage. The overall morphology and preservation of the fossils reveal that they comprise microbially induced sedimentary structures and soft-bodied holdfasts. The latter are vaguely reminiscent of some Ediacaran holdfasts, though it is unlikely that they include their phylogenetic descendants. Three-dimensional preservation of the studied fossils was caused by authigenic crystallization of calcite and its further early-diagenetic dolomitization. Our study confirms the critical importance of specific environmental conditions ensuring preservation of soft-bodied organisms as three-dimensional molds and casts. This unique interplay of environmental factors became rare in the Cambrian Period, which was caused by intensification and expansion of bioturbation in marine basins.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45750735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Morphology and Composition Changes in Fluid Inclusions from Quartz under Progressive Deformation: Case Study of a Vein System in the Western Kelyan-Irokinda Fold Zone (Western Transbaikalia)","authors":"E. N. Kungulova, P. Tishin, D. Lychagin, A. Tomilenko, E. Moskvichev","doi":"10.2113/rgg20234546","DOIUrl":"https://doi.org/10.2113/rgg20234546","url":null,"abstract":"\u0000 —The behavior of fluids during plastic deformation is studied from the morphology and distribution of fluid inclusions in quartz grains of different microstructure types from a vein system controlled by thrusting and strike-slip faulting in the eastern Sayan–Baikal fold area. The analytical work includes electron backscatter diffraction (EBSD) for quartz microstructure and crystallography, as well as Linkam heating-and-freezing analysis and Raman spectroscopy for the composition of fluid inclusions. The studied fluid inclusions are of seven types that differ in morphology and position in the deformed quartz structure. A model is suggested to describe successive structural changes of quartz aggregates during dislocation sliding and subsequent creep-related recrystallization associated with redistribution of fluid. Fluid inclusions undergo qualitative and quantitative changes due to water leakage at all stages of plastic deformation. The changes occur by two main mechanisms: (i) mass transfer during dislocation sliding at medium temperatures and strain rates and (ii) diffusion creep at low strain rates and high temperatures. The contribution of creep increases gradually with temperature, which maintains the interaction of inclusions with migrating grain boundaries.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47488713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mineral–Geochemical and Geotectonic Features of the Lotmvara-II Ultrabasic Sill, Serpentinite Belt (Kola Peninsula)","authors":"A. Barkov, A. A. Nikiforov, V. Korolyuk, R. Martin","doi":"10.2113/rgg20234538","DOIUrl":"https://doi.org/10.2113/rgg20234538","url":null,"abstract":"\u0000 —In this paper, we present a description of the characteristics of the Lotmvara-II sill, which is a representative of the Serpentinite Belt (SB) composed of a series of shallowly emplaced ultrabasic intrusive bodies. The Paleoproterozoic SB complexes were derived from a large-scale mantle plume of komatiitic melt. The sill consists predominantly of fine-grained (locally nearly micrograined) harzburgites with subordinate zones of dunites and orthopyroxenites, located in the central and marginal parts, respectively. It formed from an Al-undepleted komatiitic magma of extremely high Mg content and may represent a near-surface laccolithic “ridge.” In general, the sill is comparatively homogeneous and does not have distinct zoning in the distribution of Mg# values in rock compositions (Mg# = 84.2–88.9, average 86.7). Detailed studies show that olivine, chromian spinel, and ilmenite are the most strongly magnesian in the central part of the body. The maximum values of Mg# equal to 90.7–91.4 in the compositions of olivine at the center of the sill are interpreted as “centers of initial crystallization”. The low values of Mg# equal to 73.4–76.4 are attributed to manifestations of the recurrent generation of olivine. The values of Mg# of orthopyroxene in the sill are within the range 84.6 to 92.3. Orthopyroxene grains in a porphyritic texture are surrounded by a rim of calcic amphibole (autometasomatic in origin); they do not differ compositionally from normal grains. The Zn content of the chromian spinel generally decreases toward the marginal parts of the sill. There is an insignificant degree of magmatic differentiation in the sill with respect to the principal components, but incompatible elements (REE and HFSE) locally show increased levels of their relative enrichment, which is reflected in the nature of the mineral associations described. Thus, the sill has a cryptic zonal structure, which is consistent with its overall crystallization from the center to the edges. The data gathered suggest the presence and significant development of volatile components, halogens, CO2, and especially magmatic H2O, which are capable of strongly lowering the liquidus and reducing the density and viscosity of the high-magnesium melt, thereby improving its mobility during ascent from the mantle to the near-surface level of the crust. An increase in fO2 is observed during in situ subvolcanic crystallization of the sill, as noted earlier in the related complexes of the belt. The relatively small volume of the komatiitic magma in the sill crystallized fairly quickly, resulting in unusual mineral intergrowths. Thus, the Lotmvara-II sill is a novel member in the Serpentinite Belt–Tulppio Belt (SB–TB) in the Paleoproterozoic SB–TB megastructure of the Fennoscandian Shield.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46327173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Integration of Geophysical Methods to Study Deep Structure of the Angara Fault, the Largest in the Baikal Rift","authors":"I. Seminsky, А.K. Seminsky, А. Pospeev, F.R. Rustamova","doi":"10.2113/rgg20234539","DOIUrl":"https://doi.org/10.2113/rgg20234539","url":null,"abstract":"\u0000 —The Angara regional fault which is transversal to the Baikal basin totals about 150 km in length and ranks as a major strike-slip fault with the normal component in the seismically active rift zone. Given that its vicinities represent an area with high population density, the emphasis needs to be placed primarily on the study of its structural features. At this, the Angara fault has been poorly studied by geophysical methods. Results of the specialized mapping carried out in the 1990s revealed the block structure of the Angara fault zone, however without a reliable identification of the fault plane, which leaves its position still to be debatable. To establish the Angara fault plane and studying its deep structure, the integration of such geophysical methods as magnetotelluric (MT) sounding, radon emanation and fieldwalking magnetic surveys was required. Their application in the study of the deep structure of the southern parts of the Angara fault allowed revealing anomalies in all of the measured fields, accordingly. The anomaly-forming object, which the authors associate with the deep penetrated Angara fault plane, was expressed in the most distinct way by the magnetotelluric data (as a high-resistivity region (ER = 8500 Ohm∙m) relative to the host rock) and radon emanation survey (radon volumetric activity index RAI ≥ 20). The fact that the magnetic field received only minor distortions from the object may indicate either moderate magnetic characteristics of the latter or a significant occurrence depth. The identified anomaly-forming object localized within the crystalline basement tends to be more sharply expressed in the left bank of the Irkutsk Reservoir, while in the upper part of the cross-section it is overprinted by rocks of the sedimentary cover.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43115314","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Two Millennia of Climate History for the Russian Altai: Integrated Reconstruction from Lake Sediment Data","authors":"V. V. Babich, A. Daryin, N. Rudaya, T. Markovich","doi":"10.2113/rgg20234585","DOIUrl":"https://doi.org/10.2113/rgg20234585","url":null,"abstract":"––A continuous history of annual air temperatures in the Russian Altai for the past 2000 years has been reconstructed for the first time by integrating climate archives stored in the bottom sediments of four lakes in Gorny Altai (Teletskoye, Kucherla, Lower Multa, and Middle Multa). The integrated chronology comprises all known climate events of the two milennia time span: Roman warm epoch (~200 to 500 AD), Dark Age cold epoch (~500 to 750 AD), medieval warming (~750 to 1300 AD), and Little Ice Age (~1300 to 1850 AD). The events distinguished in the integrated climate reconstruction agree perfectly in number and time with the events reconstructed from other climate proxies for the Altai and adjacent areas of West Siberia, Tyva, and West Mongolia. Therefore, the temperature patterns represent a common course of the 2000-year climate evolution over a large part of Central Asia. Similar synchronicity is observed with the available quantitative climate reconstructions for the Northern Hemisphere and its different regions. It means that the climate change in Central Asia over the past two millennia has followed the general global scenario.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47340895","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Carbonate Sedimentation in High-Mineralized Lake Bolshoi Bagan (South of West Siberia): Dependence on Holocene Climate Changes","authors":"P. A. Solotchin, É. Solotchina, A. Maltsev, G. Leonova, S. Krivonogov, A. Zhdanova, I. Danilenko","doi":"10.2113/rgg20234567","DOIUrl":"https://doi.org/10.2113/rgg20234567","url":null,"abstract":"\u0000 ––We present the results of comprehensive studies of Holocene bottom sediments from the shallow hypersaline (mineralization up to 282 g/L) Lake Bolshoi Bagan, located in the East Baraba lowland (south of Western Siberia). The research methods include X-ray diffractometry (XRD), IR spectroscopy, laser granulometry, scanning electron microscopy, elemental analysis of sediments and pore water, radiocarbon (14C AMS) dating. It has been found that during the Holocene an intensive authigenic mineral formation took place in the lake basin; gypsum, halite and carbonates of calcite-dolomite series dominate among the newly formed mineral phases. Mg-calcites with different Mg contents, excess-Ca dolomites, aragonite and occasionally Mg-siderite have been found in the assemblage of carbonate minerals by mathematical modeling of complex XRD patterns. Mineralogical and crystallochemical studies, supplemented by the results of geochemical analyses, allowed us to identify four stages of the evolution of Lake Bolshoi Bagan in the Holocene, due to regional climate variations. The boundaries of the stages in general correspond to the boundaries of the climatostratigraphic phases by the Blytt–Sernander system: Stage I (the end of the Boreal) – the lake formation, humid climate; Stage II (Atlantic) – climate aridization, shallowing of the lake; Stage III (Subboreal) – unstable climate, frequent change of conditions; Stage IV (Subatlantic) – moderately cool and dry climate.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46367246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distribution and Cocrystallization Coefficients of a Wide Range of Typomorphic Elements in Magnetite, Hematite, and Sphalerite in Hydrothermal Systems","authors":"V. Tauson, S. Lipko, N. Smagunov, D. Babkin, O. Belozerova","doi":"10.2113/rgg20234576","DOIUrl":"https://doi.org/10.2113/rgg20234576","url":null,"abstract":"\u0000 —Distribution of a wide range of elements in the systems with magnetite, hematite and sphalerite is studied by the method of thermogradient hydrothermal synthesis combined with internal fluid sampling at 450 °C temperature and 100 MPa pressure. The distribution and cocrystallization coefficients are determined; the literature and original data on these coefficients are summarized. The possibility of obtaining the reproducible data on elements distribution in the mineral − solution system in the occurrence of many typomorphic elements is substantiated. This considerably increases the experiment efficiency. A significant advantage of using cocrystallization coefficients rather than “conventional” distribution coefficients expressed by the ratio of the element concentrations in crystal and solution (fluid) is shown. The features of behavior and occurrence of elements in hydrothermal systems are provided with physico-chemical evidence, through application of cocrystallization coefficients. The examples of the behavior of typomorphic trace elements in sphalerite are considered, which support the theoretical analysis. The major (Fe, Mn, Zn and possibly Cu) and secondary (Ti, V, Al, and Co) components of ore-forming solutions are estimated according to the compositions of magnetite and hematite from hydrothermal ore deposits of various types. The similarity in compositions of magnetite and hematite does not prove their coformation from a single fluid, quite the reverse, and this fact indicates different compositions of fluids from which the minerals were deposited.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45828175","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Late Paleozoic–Cenozoic Tectonothermal Evolution of Transbaikalia: Thermochronology of the Angara–Vitim Granitoid Batholith","authors":"A. Travin, M. M. Buslov, Y. Bishaev, A. A. Tsygankov, E. Mikheev","doi":"10.2113/rgg20234577","DOIUrl":"https://doi.org/10.2113/rgg20234577","url":null,"abstract":"\u0000 —The tectonothermal evolution of Transbaikalia is reconstructed using U/Pb, 40Ar/39Ar, and apatite fission track thermo-chronology of samples from the Late Paleozoic Angara–Vitim granitoid batholith (AVB). Successive closure of the zircon and amphibole isotope systems provides evidence that the AVB rocks cooled down rapidly soon after crystallization and 7–4 km of rocks were denuded subsequently during an extensive late Paleozoic orogeny in southern Siberia. The isotopic system of feldspar closed in the Middle Jurassic–Early Cretaceous (170–140 Ma) after a period of tectonic stability and slow closure of the biotite isotopic system in the early Permian–Middle Jurassic (295–170 Ma). The 170–140 Ma span was the time when the Mongol–Okhotsk orogen began its evolution, and the orogeny caused denudation of ~3 km of rocks. Denudation was slow in the Paleogene–Miocene (60–5 Ma) but accelerated over the past 5 million years (a ~3–2 km thick layer) during rapid cooling of rocks and activity under a far-field effect of the India–Eurasia collision.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48159566","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental Study of the Process of Interaction of Hydrogen with Igneous Melts in the Conditions of the Earth’s Crust","authors":"E. Persikov, P. G. Bukhtiyarov, L. Aranovich, O. Shaposhnikova, A. Nekrasov","doi":"10.2113/rgg20234562","DOIUrl":"https://doi.org/10.2113/rgg20234562","url":null,"abstract":"\u0000 —We report new experimental data on the interaction of igneous melts with hydrogen at temperatures of 1100–1250 °C and hydrogen pressures of 1–100 MPa in strongly reducing conditions: fO2=10−12−10−14. The experiments were conducted using an original high-gas-pressure unit equipped with a unique device that provides long-term experiments at high temperatures and pressures of hydrogen. The experiments used natural samples of igneous rocks: the magnesian basalt of the Northern Breakthrough of the Tolbachik Volcano (Kamchatka) and the andesite of the Avacha Volcano (Kamchatka). On the basis of the experiments, the following features of the process of interaction of hydrogen with igneous melts have been established: (1) Despite the high reduction potential of the H2–igneous melt system, the reactions of hydrogen oxidation and complete reduction of oxides of metals of variable valence in the melt do not go to the end. The cessation of redox reactions in basaltic and andesitic melts is due to the formation of H2O in the melt, which buffers the reduction potential of hydrogen; (2) The initially homogeneous igneous melt becomes heterogeneous: The formed H2O dissolves in the melt and in the fluid phase (at first pure hydrogen), and melts of variable, more acidic composition and small metallic isolations of the liquation structure are formed; (3) The complex process of metal–silicate liquation in magmatic melts when they interact with hydrogen can be carried out at real magma temperatures in nature (≤1200 °C), significantly lower than the corresponding melting points of iron and its alloys with nickel and cobalt; (4) The structure and dimensions of the experimentally established metal isolations are consistent with natural data on the finds of small quantities of native metals, primarily iron and its alloys with nickel and cobalt, in igneous rocks of different compositions and genesis.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42669502","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}