卷 24, 编号 6 (2024)
Articles
Subduction and rifting ‒ reflect of oscillatory tectonic processes on boundaries of the lithosphere segments in the probable-deterministic gravity models
摘要
Research subject. Convergent boundaries of the Euroassian, North American, Pacific lithosphere plates and protooceanic plate of the South China Sea on the Eastern Asia. Aim. On the base of tectonic analysis of 3D rheological gravity models compared with another geologic-geophysical data to study deep structures in zones of joint of lithosphere plates and to define space-time relations between subducton and rift structures. Material and Methods. Land and seas gravity measurements on the Russian territory and Land Gravity Data.bgi.omp.obs-mip.fr, model: EGM08_CBA_global_2190_2.5m on the territories of South East China and Sea of Japan were used. Main method of research is the gravity method for modeling of rheological properties of the crust and upper mantle by distributions of the density contrast (differentiation) of geological media (authors method). Results. Analysis of 3D distributions of density inhomogeneities in a tectonosphere of the North East Russia, Japan Sea Region, Sikhote Alin and South East China is carried out, as a result of which in the Eastern margin of Asia identical traces of tectonic processes on boundaries of the lithosphere plates, reflected their directed-oscillatory character are revealed. Traces of the subduction processes has been founded in a shape of inclined rigid sheets (slabs) reflected by maximums of the density contrast and moved under continental margin and island arcs. However the subduction was not constant in time and periodically was interrupted by kickbacks and gaps of subducting slabs under influence of rifting and transform-shift processes. In time the rifts and attendant their shifts have been displaced in a direction from autochthonous to allochthonous segments: in the North East Asia from North Asian Craton to North American plate, on the Eastern Asia – from the continent to Pacific, and on the South East Asia – from the South China Sea Plate to Yangtze plate. Conclusions. Revealed features of a structure and geodynamic evolution of convergent zones are universal characteristics of upper rigid layers of the Earth (crust and lower lithosphere) moved above subcrustal viscous layer and astenosphere under influence of the oscillation tensions, caused, most likely, by deviation of the Earth rotation parameters. In all of four areas identical sequence of subductional and rifting processes has been revealed. A subduction accompanied by thrusting of the upper crust layer over autochthonous segments was repeatedly interrupted by gaps of crustal and lithosphere sheets and a formation of stretch-shift structures. Sudduction is not main and defining process in the convergent boundaries of lithosphere plate, bat represents a privet element of the oscillatory tectogenesis.
Lithosphere (Russia). 2024;24(6):943-961
943-961
New Early Frasnian stratas on the Middle Timan (Tsil’ma River basin)
摘要
Research subject. Rocks and paleontological fossils (spores of higher plants) of early Frasnian sedimentation within the Tsil’ma area (Middle Timan). Material and methods. The lithological and biostratigraphical methods were used to identify and describe lithological stratons, determine the composition of spore complexes of higher plants characteristic of each straton in the early Frasnian outcrops of the Tsil’ma area, as well as to correlate the latter with the zonal patterns of the Devonian of the East European Platform. Results. In the Middle Timan, within the Tsil’ma area, new stratons were described in various structural and facies zones, i.e., the Brusnichnaya, Rudyanskaya, and Paladinskaya formations, characterizing the early Frasnian period of sedimentation. The identified stratons have distinct lithological and palynological characteristics. A description of limitotypes and composite stratotypes was carried out. Conclusions. At present, the Brusnichnaya, Rudyanskaya, and Paladinskaya formations are the most complete sequence of early Frasnian sedimentation in the European North-East of Russia. Here, regional responses to the global events of Frasnes (soluta conodont zone) and Genundewa (rugosa conodont zone) are recorded. The formations are characterized by spore complexes; palynozones are correlated with conodont zones. This allowed correlation between the continental and marine early Frasnian deposits in the European North-East of Russia, along with establishment of their exact position in the Devonian stratigraphic scheme.
Lithosphere (Russia). 2024;24(6):962-977
962-977
Influence of Frasnian-Tournaisian reef massifs on halokinesis in the Solikamsk depression of the Pre-Ural trough
摘要
Research subject. Sedimentary strata of the Solikamsk depression of the Pre-Ural trough. The geological structure of the Solikamsk depression is characterized by the presence of a carbonate complex with a reef massif in the lower part of the sedimentary cover and a halogen stratum up to 500 m thick with salt uplifts formed in the roof in the upper part. The distance between the reef complex and the plastic salt strata ranges 1300–1700 m. Aim. Identification of the influence reef massifs on the formation of salt structures. Methods. Comparison and analysis of structural maps of the top of the reef-carbonate complex and the top of the salt strata, in the setting of the geodynamic conditions that existed at the border of the East European platform and the active Ural system. Results. One of the factors controlling the area distribution of salt uplifts of the Kungurian halogen sequence was established to be the presence of reef massifs in the Frasnian-Tournaisian sequence. Uplifts at the top of the salt mass are located in the spaces between the reef massifs. This is explained by the geodynamic influence of the capping structures of the reef massifs observed at the base of the salt strata. Uplifts in the base of the salt stratum under the action of general compressive stresses, due to its close position to the Urals, influenced the formation of a stress field in the plastic salt mass. As a result, the situation of a reduced mechanical stress in the areas between the enclosing structures of the salt mass developed. In these areas, during halokinesis, plastic salt masses were squeezed followed by formation of uplifts in the roof of the salt mass. Conclusions. In the Solikamsk depression, the capping structures above the Frasnian-Tournaisian reef massifs are a transmission link for the influence of the deep-seated strata on the plastic halogen strata located in the upper part of the sedimentary cover.
Lithosphere (Russia). 2024;24(6):978-985
978-985
Depositional environment of the Middle- and Upper-Holocene sediments in the North-West of the Bol’shezemel’skaya tundra (in the Kuya river valley)
摘要
Research subject. The Holocene alluvium, lake-bog and oxbow-lake sediments in the lower reaches of the Kuya river valley, the right tributary of the Pechora river (Nenets Autonomous Okrug, northwest of the Bol`shezemel`skaya tundra). Aim. Investigation of the morphological types of fluvial formations, their lithostratigraphic subdivision, and reconstruction of the environmental conditions of sedimentation. Materials and methods. The sediments texture and structure features of the floodplain-channel complex were studied by granulometric and mineralogical analyses. The morphostructural features of the relief were identified by high-resolution satellite imagery and an ArcticDEM digital relief model. The spore-pollen and diatom analyses and radiocarbon dating results are presented. Results. The lithotypes of Holocene sediments that make up the valley in the lower reaches of the Kuya River are distinguished, and the chronology of paleogeographic events in the study area is presented. A geological and geomorphological scheme of the floodplain-channel complex of the Kuya River valley is constructed. The geological profile of alluvium and underlying sediments is constructed. Reconstructions of vegetation and climate dynamics in the mid- and late-Holocene based on the palynostratigraphic subdivision of alluvium sediments is carried out. The lower boundary of the late Sub-Atlantic period, correlated with the Little Ice Age, is clarified. Conclusions. The formation of the floodplain-channel complex occurred in four stages, with its constituent deposits being attributed to the channel, lacustrine, bog, and floodplain facies. According to morphometric features in the geomorphological structure of the river valley, an erosion-accumulative relief of the above-floodplain terraces of high and low floodplains is identified. The following stages of vegetation changes are traced: from tundra communities in the coldest conditions of the early Subboreal, which were replaced by forests of the middle taiga type to the Subboreal thermal maximum, dated 3360 ± 70 years ago (3602 cal. BP) to modern forest-tundra and south-tundra communities. The formation fluvial plain sediments occurred in shallow, slightly mineralized, and waterlogged reservoirs.
Lithosphere (Russia). 2024;24(6):986-1013
986-1013
New data on Quaternary deposits of the Pechora-Vychegda-Kama watershed
摘要
Research subject. Quaternary deposits in six wells. Two wells (No. 20830 and 20831) are located on the upper Pechora, and four wells (No. 20837, 20839, 20840 and 20841) are located in the upper reaches of the Vychegda River. Aim. Identification of the geological structure of Quaternary deposits in the research area and carrying out their facies-genetic division. Methods. The sediments were studied by granulometric and mineralogical methods, and in samples from well No. 20841, spores and pollen were isolated and palynological spectra were studied. Results. The facies-genetic division of Quaternary deposits was carried out based on changes in the structural features in the sections. The mineral composition of the heavy fraction of sediments is characterized by increased contents of ilmenite (up to 45%) and epidote (up to 38%), which are characteristic minerals of the North-Eastern terrigenous-mineralogical province, including Novaya Zemlya, Pai-Khoi and the Polar and Subpolar Urals. As a result of the palynological study of alluvial and lacustrine sediments in the well No. 20841 three spore-pollen complexes were identified. Conclusions. Alluvial, lacustrine (limny) and glacial deposits (moraines and fluvioglacial sediments) were identified in the well sections. The mineral composition of the heavy fraction indicates the participation of Ural igneous and metamorphic rocks in their formation, and the supply of minerals from the Kama, where Pliocene deposits are widely developed, seems very doubtful. Two palynological complexes were formed in the Middle Neopleistocene during the Rodionovian (Shklovian) interglacial, probably, and the third, characterizing rather harsh climatic conditions, in the initial phase of the Byzovian (Leningrad) megainterstadial of the Late Neopleistocene.
Lithosphere (Russia). 2024;24(6):1014-1028
1014-1028
Noble-metal mineralization and conditions of formation of Au-Ag epithermal veins from Kyzik-Chadr Au-Mo-Cu porphyry deposit, Eastern Tuva
摘要
Research object. The results of mineralogical-geochemical, fluid inclusion and isotopic studies of Au-Ag epithermal veins of Kyzik-Chadr Au-Mo-Cu porphyry deposit (Eastern Tuva) are considered. The aim of the study is to examine mineralogical and geochemical peculiarities and conditions of formation of gold-sulfide-quartz veins from Kyzik-Chadr deposit to identify their ore-formation. Methods. The chemical composition of minerals was determined by SEM (Tescan MIRA 3 LMU with XMax 80 and INCA Wave 500 (Oxford Instruments Nanoanalysis Ltd). Fluid inclusion study in quartz were carried out using a Linkam TMS-600 thermostage with LinkSystem 32 DV-NC software and an Olympus BX51 optical microscope. The oxygen isotopic composition of quartz was determined on a FINNIGAN MAT 253 gas mass spectrometer. The isotopic composition of sulfur in sulfides was determined using a Finnigan MAT Delta gas mass spectrometer in the double-infusion mode. Results. A wide variety of Au-Ag minerals in gold-sulfide-quartz veins due to variations of fO2, fS2, fSe2 and fTe2 during ore formation was diagnosed: gold, Hg-gold, Hg-electrum, Hg-kustelite, weishanite (Au,Ag)1.2Hg0.8, sylvanite AgAuTe2, petzite Ag3AuTe2, hessite Ag2Te, schützite Ag5Te3, empressite AgTe, fischerite Ag3AuSe2, Se-uytenbogaardtite Ag3AuS2, acanthite Ag2S, which are associated with altaiite PbTe, coloradoite HgTe, claustalite PbSe, fahlores of tennantite-tetrahedrite series and barite. The study of fluid inclusions (thermometry, Raman spectroscopy) in quartz and mineral thermometry (petzite–hessite–native Au paragenesis) determined that the ore veins were formed due to CO2-water Na-K ± Mg-chloride fluid with salinity of 5.7–10.0 wt % NaCl eq with temperatures decreasing from 360 to 230°C and variations in fO2, fS2, fSe2, and fTe2. Oxygen isotopy in quartz indicates mixing of magmatic fluid with meteoric water (δ18O of fluid from +3.5 to +7.1‰). The δ34SH2S values of the fluid from +7.1 to +5.2‰ suggest that some sulfur was extracted from the host rocks. Conclusions. According to mineralogical and geochemical peculiarities and conditions of formation of gold-sulfide-quartz veins from Kyzik-Chadr Au-Mo-Cu porphyry deposit can be attributed to epithermal Au-Ag veins of intermediate sulfidation type, which are the product of a single porphyry-epithermal ore-magmatic system in the Kyzik-Chadr ore field.
Lithosphere (Russia). 2024;24(6):1029-1045
1029-1045
Mössbauer spectroscopy of ore-forming chromium spinels of the Polar Urals
摘要
Research subject. The work studied the heterogeneity of the chemical and phase composition of chromitites and ore-forming chromium spinels of the Polar Ural massifs Rai-Iz and Voikaro-Syninsky. Its influence on the value of the oxidation state of iron (Fe# = Fe3+/(Fe3+ + Fe2+)), determined by the calculation method, from the stoichiometric formula of the mineral, and using Mössbauer spectroscopy, is analyzed. The purpose of the study is to determine the degree of influence of various manifestations of the heterogeneity of the chemical composition of spinel on the results of determining Fe3+/(Fe3+ + Fe2+) using Mössbauer spectroscopy. Methods and materials. Monofractions of ore-forming chromium spinels were studied by Mössbauer spectroscopy (SM2201 spectrometer). The study of the heterogeneity of chromium spinel grains was carried out using microprobe analysis (electron probe microanalyzer Cameca SX-100) in polished sections and blocks, as well as X-ray phase analysis (powder diffractometer SHIMADZU XRD-6000) in samples analyzed on a Mössbauer spectrometer. Results. The studied ore-forming spinels exhibit three types of compositional heterogeneity, which determine the Fe#Möss– Fe#stoich discrepancy and influence its value: 1) chemical zoning of grains; 2) multiphase, associated with the presence of two generations of mineral grains with varying degrees iron oxidation; 3) hidden multiphase, manifested in broadening of diffraction peaks. In all cases, there is variability in the degree of iron oxidation in the mineral grains. Conclusions. The studied ore-forming spinels of the main ore bodies of the Rai-Iz massif and the northern part of the Voykar-Synya massif have a normal, unconverted structure, and the distribution of cations over its positions corresponds to the crystal chemical formula. Deviations in the distribution of iron cations, established during the study of the mineral by Mössbauer spectroscopy, are associated with the chemical heterogeneity of its grains and the presence in the ore of several spinel phases of different compositions.
Lithosphere (Russia). 2024;24(6):1046-1059
1046-1059
Mineralogy and genesis of apocarbonate serpentinites of the Pitkäranta mining district, Northern Ladoga region. Part 1. Ophicalcite of the Hopunvaara ore field
摘要
Research subject. Serpentinites of the apocarbonate type in the contact aureole of the Salmi Batholith. Aim. Mineralogical and genetic description of the calcite-serpentine rocks of the Hopunvaara ore field. Materials and methods. Thirty samples of ophicalcite were studied using scanning electron microscopy, electron probe analysis, powder X-ray diffraction, FTIR and Raman spectroscopy, as well as differential thermal analysis. Results. The ophicalcite of the Hopunvaara ore field is represented by two types. The first variety was studied on samples from the Izvestkovyi quarry (“Lime Break”). It consists of thin-fibrous aggregates of clinochrysotile and lizardite (or only lizardite) intergrowing with calcite, with subordinate amounts of phlogopite and fluorapatite, as well as with veins of magnetite. Serpentine contains a small amount of impurities – up to 1.0 wt % FeO, up to 0.7 wt % Al2O3 and not more than 0.1 wt % MnO. Calcite is chemically pure. Ophicalcite of the second type, described in the Klara mining, is composed mainly of lizardite, which forms complete pseudomorphs after crystals of forsterite and/or minerals of the humite group enclosed among a carbonate matrix. Serpentine contains 0.4–2.5 wt % FeO, 0.0–1.6 wt % Al2O3, 0.1–0.2 wt % MnO, and 0.9–2.1 wt % F. In the carbonate matrix, along with almost pure calcite, there is dolomite containing 1.4 wt % MnO. Minor minerals are represented by fluorite, phlogopite and sphalerite. Such a rock is sectioned by antigorite-carbonate-fluorite-hematite veins with cassiterite, the formation temperature of which is estimated at 300–350°C. Conclusions. The formation of ophicalcite of the first type occurred through the interaction of dolomite with acidic SiO2-rich 200–300°C hydrothermal solutions. The microfiber structure of apodolomite serpentine aggregates is due to the mechanism of their crystallization in a porous medium that occurs during carbonate leaching. Ophicalcite of the second type was formed as a result of serpentinization of forsterite calciphyres at the regressive stage of skarnification process at T < 370°C.
Lithosphere (Russia). 2024;24(6):1060-1083
1060-1083
Minerals of spinel group from izrandites of the Alexandrovsky polymetamorphic complex in the Southern Urals
摘要
Object of research. Spinelides of izrandites of the Aleksandrov polymetamorphic complex in the Southern Urals. Purpose of research. Studying of composition of spinel group minerals and coexisting ilmenite in single grains and in different phases in unmixing structures after decomposition of solid solutions, reconstruction of primary compositions of oxide minerals and comparison with the same minerals from Ural-Alaskan-type complexes having an ankaramine affinity. Methods. The study was performed on a Tescan Mira scanning electron microscope at the “Geoanalitic” Center of Common Use (Ekaterinburg). The images were obtained in backscattered electron mode. The composition of minerals was determined in points and using an area scanning facilities of SEM for the unmixing structures of spinels. Results. Chrome spinel containing more than 25 wt % Cr2O3 and corresponding to the earliest stage of crystallization has been discovered in izrandites of the Alexandrovsky polymetamorphic complex in the Southern Urals. The several stages of Cr-Fe-Ti-oxide and rock-forming silicates crystallization were determined. It was shown that during cooling and subsolidus transformation, oxide minerals undergo complex multistage decomposition of the solid solution with the formation of phases enriched in aluminum and ferric iron in equilibrium with ilmenite. The compositions of these phases are distributed along the Cr-spinel solvus. The earliest primary hypersolvus spinels form inclusions in olivine and clinopyroxene. They are characterized by 3–4 wt % of TiO2 and 15–20 wt % of Cr2O3. The late spinel forms inclusions in kaersutite and are situated in the intergranular space. Their compositions are poor in Cr2O3 < 7%, but rich in TiO2 10–25 wt %, corresponding to titanomagnetite and ulvospinel. Conclusions. The composition of rocks, silicate minerals and Cr-Fe-Ti-oxides confirm the similarity of izrandites with ankaramites and tilaites from complexes of Ural-Alaskan-type. High titanium content in izrandites in comparison with similar rocks of the Ural Platinum Belt reflect the geochemical peculiarities of the primary melt which was formed by melting of the metasomatically transformed Mesoproterozoic mantle under the influence of a plume.
Lithosphere (Russia). 2024;24(6):1084-1102
1084-1102