Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0508
Y. Bashkuev, V. Khaptanov, M. Dembelov
Electrical resistivity (electrical conductivity) of water and bottom soil of the Barguzin Bay was studied by radio impedance soundings in VLF/LF bands, and the measurements were analysed. The georadar sounding method was used to investigate dielectric permittivity of freshwater ice (dielectric constant is ε=3.4). We developed the technique of radio impedance sounding from the ice surface of Lake Baikal for measuring the electrical resistance of bottom soil in the water area, and applied this technique to a layered model of a medium with a base showing poor/good conductivity. Geoelectric models were constructed for the Barguzin Bay coast and the southern Lake Baikal. The geoelectrical section (GES) of the water area can be useful for earthquake forecasting from electromagnetic data, as well as for analysing the physical and chemical causes of the occurrence of ring structures on the ice surface of Lake Baikal.
{"title":"GEOELECTRICAL SECTION OF THE BARGUZIN BAY OF LAKE BAIKAL ACCORDING TO GEORADAR AND RADIO IMPEDANCE SOUNDING DATA","authors":"Y. Bashkuev, V. Khaptanov, M. Dembelov","doi":"10.5800/gt-2020-11-4-0508","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0508","url":null,"abstract":"Electrical resistivity (electrical conductivity) of water and bottom soil of the Barguzin Bay was studied by radio impedance soundings in VLF/LF bands, and the measurements were analysed. The georadar sounding method was used to investigate dielectric permittivity of freshwater ice (dielectric constant is ε=3.4). We developed the technique of radio impedance sounding from the ice surface of Lake Baikal for measuring the electrical resistance of bottom soil in the water area, and applied this technique to a layered model of a medium with a base showing poor/good conductivity. Geoelectric models were constructed for the Barguzin Bay coast and the southern Lake Baikal. The geoelectrical section (GES) of the water area can be useful for earthquake forecasting from electromagnetic data, as well as for analysing the physical and chemical causes of the occurrence of ring structures on the ice surface of Lake Baikal.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75141913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0499
A. Kadashnikova, A. A. Sorokin, A. Ponomarchuk, A. Travin, V. Ponomarchuk
In our isotope-geochronological study, the age of ore metasomatites of the Unglichikan gold deposit is determined at 140–136 Ma. Magmatism of this age is absent in the study area, and it is thus unreasonable to relate the ore mineralization in the Unglichikan deposit to any magmatic process. We conclude that in the mobilization and redistribution of the ore material and the formation of the Unglichikan deposit, a significant role was played by dislocation processes accompanied by hydrothermal activity during the final stages of orogenesis in the Mongol-Okhotsk belt.
{"title":"THE FIRST 40Ar/39Ar GEOCHRONOLOGICAL DATA FOR ORE METASOMATITES OF THE UNGLICHIKAN GOLD DEPOSIT, EASTERN PART OF THE MONGOL-OKHOTSK FOLD BELT","authors":"A. Kadashnikova, A. A. Sorokin, A. Ponomarchuk, A. Travin, V. Ponomarchuk","doi":"10.5800/gt-2020-11-4-0499","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0499","url":null,"abstract":"In our isotope-geochronological study, the age of ore metasomatites of the Unglichikan gold deposit is determined at 140–136 Ma. Magmatism of this age is absent in the study area, and it is thus unreasonable to relate the ore mineralization in the Unglichikan deposit to any magmatic process. We conclude that in the mobilization and redistribution of the ore material and the formation of the Unglichikan deposit, a significant role was played by dislocation processes accompanied by hydrothermal activity during the final stages of orogenesis in the Mongol-Okhotsk belt.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75902913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0506
Y. Rebetsky, A. Marinin, S. Kuzikov, N. Sycheva, V. Sychev
An active fault was identified on the northern slope of the Kyrgyz ridge in the area near Research Scientific RAS in Bishkek. It belongs to a large system of crustal faults of the ridge. In our study, tectonophysical methods were used to analyse the regularities of the tectonic stress field reconstructed from seismological data on earthquake focal mechanisms. The stress distribution pattern near the investigated fault suggests its activity either in the recent past or at the present time. This conclusion is supported by the fact that at the eastern and western terminations of the fault, crustal stretching zones are located in a crosswise pattern. The Coulomb stresses on the fault surface were analysed, and the analysis results give grounds to state that its long section crossing the Alamedin river valley should be viewed as potentially hazardous. In the field, we observed abundant broken rock fragments and rock falls in the zone where the fault crosses the Alamedin and Aksu river valleys. It is known that rock falls have occurred more often in the last 3–5 years. The study results show slow movements along the fault. These strike-slip displacements have been going on for at least 10–15 years. According to the modern concepts of the preparation stage of an earthquake source, slow displacements along a fault gradually accelerate several years before an earthquake. Therefore, the studied fault (we named it Verkhovoi) should be considered a potentially hazardous zone wherein earthquakes can occur in future. A magnitude from 6.5 to 7.5 may be expected, depending on whether only the eastern part or the entire fault (i.e. 20 or 50 km, respectively) will be involved in a future seismic event. Further studies of the Verkhovoi fault are needed to clarify a trend in the development of slow sliding along the fault, which will allow understanding whether this process precedes dynamic rock failure (i.e. an earthquake) or tends to gradually decrease.
{"title":"TECTONOPHYSICAL STUDY OF THE VERKHOVOI FAULT ACTIVITY ON THE NORTHERN SLOPE OF THE KYRGIZ RIDGE","authors":"Y. Rebetsky, A. Marinin, S. Kuzikov, N. Sycheva, V. Sychev","doi":"10.5800/gt-2020-11-4-0506","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0506","url":null,"abstract":"An active fault was identified on the northern slope of the Kyrgyz ridge in the area near Research Scientific RAS in Bishkek. It belongs to a large system of crustal faults of the ridge. In our study, tectonophysical methods were used to analyse the regularities of the tectonic stress field reconstructed from seismological data on earthquake focal mechanisms. The stress distribution pattern near the investigated fault suggests its activity either in the recent past or at the present time. This conclusion is supported by the fact that at the eastern and western terminations of the fault, crustal stretching zones are located in a crosswise pattern. The Coulomb stresses on the fault surface were analysed, and the analysis results give grounds to state that its long section crossing the Alamedin river valley should be viewed as potentially hazardous. In the field, we observed abundant broken rock fragments and rock falls in the zone where the fault crosses the Alamedin and Aksu river valleys. It is known that rock falls have occurred more often in the last 3–5 years. The study results show slow movements along the fault. These strike-slip displacements have been going on for at least 10–15 years. According to the modern concepts of the preparation stage of an earthquake source, slow displacements along a fault gradually accelerate several years before an earthquake. Therefore, the studied fault (we named it Verkhovoi) should be considered a potentially hazardous zone wherein earthquakes can occur in future. A magnitude from 6.5 to 7.5 may be expected, depending on whether only the eastern part or the entire fault (i.e. 20 or 50 km, respectively) will be involved in a future seismic event. Further studies of the Verkhovoi fault are needed to clarify a trend in the development of slow sliding along the fault, which will allow understanding whether this process precedes dynamic rock failure (i.e. an earthquake) or tends to gradually decrease.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79471137","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0507
N. Sycheva, A. Mansurov
The intracontinental collision zone including the Pamir and Tien Shan is of particular interest for investigating geodynamic processes in the crust and lithosphere. We analysed seismotectonic deformation (STD) in this area, using the method of calculations proposed by Yu.V. Riznichenko and S.L. Yunga. Seismicity distribution patterns across the area and in depth and average annual STD velocity rates (STD intensity, IƩ) were estimated from the data published in the ISC Catalogue (International Seismological Center, London), that includes the information on more than 56000 earthquakes recorded in the study area in 1902–2018. Areas of intense seismotectonic deformation are identified for different depth ranges. The estimated STD intensity IƩ has a maximum value of 1.76⋅10–7 year–1 in the southwestern part of the Pamir-Hindu Kush seismic zone (depth 100–300 km). In the junction zone of the West Tien-Shan and the Pamir (western Alai and Trans-Alai ridges, depth 0–50 km), it amounts to 1.25⋅10–7 year–1. Locations of seismically active zones migrate de pending on the depth. At a depth of 0–50 km, two active seismic zones are identified – the eastern Trans-Alai ridge and the central part of the Pamir–Hindu Kush. At depths below 50 km, the southern part of the Pamir–Hindu Kush seismic zone is seismically active. Earthquakes of the highest magnitudes occurred at depths of 100–300 km. We investigated the STD direction patterns using the focal mechanisms of 3276 earthquakes (1949–2018) and constructed the diagrams showing the main stress axes. For the majority of the analysed seismic events, the compression axis changed its direction in the 300–360° azimuth sector. Maps were constructed to show averaged source mechanisms and STD values calculated for the crust and upper mantle. From representative data sets, averaged mechanisms were reconstructed for the junction zone of the South Tien Shan, North Pamir and Tarim (depths of 0–50 km) and for the southwestern part of the Pamir–Hindu Kush seismic zone (depths more than 50 km). Using the STD maps, the directions of shortening and extension axes were determined, and different deformation settings were described. Based on the STD tensors calculated for depths of 0–50 km (crust), we estimated Lode – Nadai coefficients με, plane strain angles ω (according to S.L. Yunga) and the vertical component of the STD tensors, and determined their distribution patterns. Compression (0.6≤με≤1) takes place in the major part of the study area, while the Central and South Pamirs are subjected to extension with shear (–0.6<με<–0.2) and pure shear (–0.2≤με≤+0.2). The study area (except the Central and South Pamirs) is uplifting. A comparison shows that deformation models based on the STD technique and GPS data are fully consistent.
{"title":"SEISMOTECTONIC DEFORMATION OF THE LITHOSPHERE IN THE PAMIR AND ADJACENT TERRITORIES","authors":"N. Sycheva, A. Mansurov","doi":"10.5800/gt-2020-11-4-0507","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0507","url":null,"abstract":"The intracontinental collision zone including the Pamir and Tien Shan is of particular interest for investigating geodynamic processes in the crust and lithosphere. We analysed seismotectonic deformation (STD) in this area, using the method of calculations proposed by Yu.V. Riznichenko and S.L. Yunga. Seismicity distribution patterns across the area and in depth and average annual STD velocity rates (STD intensity, IƩ) were estimated from the data published in the ISC Catalogue (International Seismological Center, London), that includes the information on more than 56000 earthquakes recorded in the study area in 1902–2018. Areas of intense seismotectonic deformation are identified for different depth ranges. The estimated STD intensity IƩ has a maximum value of 1.76⋅10–7 year–1 in the southwestern part of the Pamir-Hindu Kush seismic zone (depth 100–300 km). In the junction zone of the West Tien-Shan and the Pamir (western Alai and Trans-Alai ridges, depth 0–50 km), it amounts to 1.25⋅10–7 year–1. Locations of seismically active zones migrate de pending on the depth. At a depth of 0–50 km, two active seismic zones are identified – the eastern Trans-Alai ridge and the central part of the Pamir–Hindu Kush. At depths below 50 km, the southern part of the Pamir–Hindu Kush seismic zone is seismically active. Earthquakes of the highest magnitudes occurred at depths of 100–300 km. We investigated the STD direction patterns using the focal mechanisms of 3276 earthquakes (1949–2018) and constructed the diagrams showing the main stress axes. For the majority of the analysed seismic events, the compression axis changed its direction in the 300–360° azimuth sector. Maps were constructed to show averaged source mechanisms and STD values calculated for the crust and upper mantle. From representative data sets, averaged mechanisms were reconstructed for the junction zone of the South Tien Shan, North Pamir and Tarim (depths of 0–50 km) and for the southwestern part of the Pamir–Hindu Kush seismic zone (depths more than 50 km). Using the STD maps, the directions of shortening and extension axes were determined, and different deformation settings were described. Based on the STD tensors calculated for depths of 0–50 km (crust), we estimated Lode – Nadai coefficients με, plane strain angles ω (according to S.L. Yunga) and the vertical component of the STD tensors, and determined their distribution patterns. Compression (0.6≤με≤1) takes place in the major part of the study area, while the Central and South Pamirs are subjected to extension with shear (–0.6<με<–0.2) and pure shear (–0.2≤με≤+0.2). The study area (except the Central and South Pamirs) is uplifting. A comparison shows that deformation models based on the STD technique and GPS data are fully consistent.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77718590","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0500
V. Savel'eva, Yu. V. Danilova, E. P. Bazarova, B. Danilov
The study of the Bol’shaya Tagna alkaline-carbonatite massif and adjacent areas was focused on the mineral and chemical compositions of minerals, the distribution of petrogenic and trace elements in pyroxene-free alkaline picrites in veins and dikes dated at the late Riphean (circa 645 Ma), and comparison with the Bushkanai kimberlite-picrite dike. Phenocrysts in the pyroxene-free picrites are represented by olivine (replaced with serpentine) and phlogopite; the bulk is formed by serpentine, phlogopite, monticellite, calcite, etc .; xenocrysts of pyrope and chrome diopside are absent. Phlogopite and Cr-spinel from the picrites are chemically similar to these minerals in kimberlites, but the evolution of the spinel compositions corresponds to the titanomagnetite trend; monticellite is depleted in forsterite (Mg2SiO4). The rocks contain strontianite, burbankite, titanium andradite, calcirtite and Mn-ilmenite, which are not typical of kimberlites, but are inherent in carbonate-bearing ultramafic lamprophyres, ayllikites. The pyroxene-free picrites have low contents (wt %) of SiO2 (28.4‒33.2), Al2O3 (3.2‒5.6), and Na2O (0.01‒0.05); relatively high contents of TiO2 (2.0‒3.3), and К2О (0.45‒1.33); varying contents of MgO (16.1‒24.1), СаО (12.9‒22.8), СО2 (1.1‒12.2), Ni (260‒850 ppm), and Cr (840‒2200 ppm); and Mg#=0.73‒0.80. The contents of Th, U, Nb, Ta, La, and Ce in the veins are approximately two orders higher than those in the primitive mantle; the spectra of trace elements differ from the spectra of the South African and Yakuian kimberlites. In the pyroxene-free picrites and the rocks of the Bushkanai dike, the Nb/U, Nb/Th, Th/Ce, La/Nb, and Zr/Nb ratios are similar to those in ocean island basalts (OIB) and thus give evidence of the leading contribution of the recycled component into the source melt. In experiments conducted to investigate melting of carbonated garnet lherzolite, the pyroxene-free alkaline picrites melted at 5–6 GPa.
{"title":"KIMBERLITE-LIKE ROCKS OF THE URIK-IYA GRABEN, EASTERN SAYAN REGION: MINERAL COMPOSITION, GEOCHEMISTRY AND FORMATION CONDITIONS","authors":"V. Savel'eva, Yu. V. Danilova, E. P. Bazarova, B. Danilov","doi":"10.5800/gt-2020-11-4-0500","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0500","url":null,"abstract":"The study of the Bol’shaya Tagna alkaline-carbonatite massif and adjacent areas was focused on the mineral and chemical compositions of minerals, the distribution of petrogenic and trace elements in pyroxene-free alkaline picrites in veins and dikes dated at the late Riphean (circa 645 Ma), and comparison with the Bushkanai kimberlite-picrite dike. Phenocrysts in the pyroxene-free picrites are represented by olivine (replaced with serpentine) and phlogopite; the bulk is formed by serpentine, phlogopite, monticellite, calcite, etc .; xenocrysts of pyrope and chrome diopside are absent. Phlogopite and Cr-spinel from the picrites are chemically similar to these minerals in kimberlites, but the evolution of the spinel compositions corresponds to the titanomagnetite trend; monticellite is depleted in forsterite (Mg2SiO4). The rocks contain strontianite, burbankite, titanium andradite, calcirtite and Mn-ilmenite, which are not typical of kimberlites, but are inherent in carbonate-bearing ultramafic lamprophyres, ayllikites. The pyroxene-free picrites have low contents (wt %) of SiO2 (28.4‒33.2), Al2O3 (3.2‒5.6), and Na2O (0.01‒0.05); relatively high contents of TiO2 (2.0‒3.3), and К2О (0.45‒1.33); varying contents of MgO (16.1‒24.1), СаО (12.9‒22.8), СО2 (1.1‒12.2), Ni (260‒850 ppm), and Cr (840‒2200 ppm); and Mg#=0.73‒0.80. The contents of Th, U, Nb, Ta, La, and Ce in the veins are approximately two orders higher than those in the primitive mantle; the spectra of trace elements differ from the spectra of the South African and Yakuian kimberlites. In the pyroxene-free picrites and the rocks of the Bushkanai dike, the Nb/U, Nb/Th, Th/Ce, La/Nb, and Zr/Nb ratios are similar to those in ocean island basalts (OIB) and thus give evidence of the leading contribution of the recycled component into the source melt. In experiments conducted to investigate melting of carbonated garnet lherzolite, the pyroxene-free alkaline picrites melted at 5–6 GPa.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83181282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0501
N. K. Gayday, N. Goryachev, I. M. Khasanov, E. Goshko
Ore deposits of the Magadan region are now in the focus of comprehensive studies as information on their deep structure is needed for both subsoil prospecting and regional development planning. This article presents the research results for the southeastern flank of the Yana-Kolyma orogenic belt. This area located at the junction with the Okhotsk-Koryak orogenic belt was investigated using the northeastern segment of the regional geophysical profile 3-DV. We analyzed the frequency-energy sections of the crust along the profile, 3D crustal density model of the entire study area, and magnetic, geoelectric and gravimagnetic characteristics of the crust. Complex data interpretation allowed tracing the crustal fault zones, areas wherein the crust material was strongly reworked, and zones of quasi-horizontal stratification. Considering the revealed features of the physical parameters of the crust material, we conclude that the currently accepted boundaries of individual tectonic blocks in the study area need to be adjusted. The northern boundary of the Balygychan uplift should be mapped along the Pautov fault. The Srednekansky branch of the Inyali-Debinsky synclinorium should be considered a transitional block that belongs to the Sugoi synclinorium, and its name should be changed to the Orotukan block.
{"title":"STRUCTURAL FEATURES OF THE DEEP STRUCTURE OF THE SOUTHEASTERN YANA-KOLYMA FOLD SYSTEM FROM COMPLEX GEOPHYSICAL DATA","authors":"N. K. Gayday, N. Goryachev, I. M. Khasanov, E. Goshko","doi":"10.5800/gt-2020-11-4-0501","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0501","url":null,"abstract":"Ore deposits of the Magadan region are now in the focus of comprehensive studies as information on their deep structure is needed for both subsoil prospecting and regional development planning. This article presents the research results for the southeastern flank of the Yana-Kolyma orogenic belt. This area located at the junction with the Okhotsk-Koryak orogenic belt was investigated using the northeastern segment of the regional geophysical profile 3-DV. We analyzed the frequency-energy sections of the crust along the profile, 3D crustal density model of the entire study area, and magnetic, geoelectric and gravimagnetic characteristics of the crust. Complex data interpretation allowed tracing the crustal fault zones, areas wherein the crust material was strongly reworked, and zones of quasi-horizontal stratification. Considering the revealed features of the physical parameters of the crust material, we conclude that the currently accepted boundaries of individual tectonic blocks in the study area need to be adjusted. The northern boundary of the Balygychan uplift should be mapped along the Pautov fault. The Srednekansky branch of the Inyali-Debinsky synclinorium should be considered a transitional block that belongs to the Sugoi synclinorium, and its name should be changed to the Orotukan block.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90110988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0509
V. Plotkin, V. Potapov
Many minerals have semiconductor properties. It is known that petroleum reservoir rocks permeated with hydrocarbon fluids can sometimes behave as semiconductors. In the Earth’s magnetic field, the electrical conductivity of such materials becomes anisotropic, and the Hall effect is quite possible in rocks in natural conditions and detectable by magnetotelluric sounding. In the anisotropic medium, the field is subject to normal mode splitting, and its components show different attenuation coefficients and phase velocities. The modes differ due to polarization and rotation of the field vectors (clockwise in one mode, and counterclockwise in another). With account of the Hall effect, responses of the medium can be different when the medium is excited by a single normal wave. To detect the Hall effect in MTS surveys, we use the polarization analysis method and select the spectra of modes with right and left circular polarization. Special experiments were carried out to detect the contribution of the Hall effect during the MTS surveys. This article presents the first estimates of the Hall conductivity for the studied rocks.
{"title":"HALL CONDUCTIVITY ESTIMATES FROM MAGNETOTELLURIC SOUNDING DATA","authors":"V. Plotkin, V. Potapov","doi":"10.5800/gt-2020-11-4-0509","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0509","url":null,"abstract":"Many minerals have semiconductor properties. It is known that petroleum reservoir rocks permeated with hydrocarbon fluids can sometimes behave as semiconductors. In the Earth’s magnetic field, the electrical conductivity of such materials becomes anisotropic, and the Hall effect is quite possible in rocks in natural conditions and detectable by magnetotelluric sounding. In the anisotropic medium, the field is subject to normal mode splitting, and its components show different attenuation coefficients and phase velocities. The modes differ due to polarization and rotation of the field vectors (clockwise in one mode, and counterclockwise in another). With account of the Hall effect, responses of the medium can be different when the medium is excited by a single normal wave. To detect the Hall effect in MTS surveys, we use the polarization analysis method and select the spectra of modes with right and left circular polarization. Special experiments were carried out to detect the contribution of the Hall effect during the MTS surveys. This article presents the first estimates of the Hall conductivity for the studied rocks.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81257437","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0505
V. Burtman, S. Y. Kolodyazhny
Directions of 683 faults located in the southeastern part of the Fennoscandian (Baltic) shield were statistically analyzed, and three orthogonal associations of fault systems were identified in the study area. According to the dynamic analysis of the fault systems and their associations, the main NW-striking faults belong to the fault network originating mainly from the early Paleoproterozoic. These faults functioned in the Paleoproterozoic during four main deformation stages: D1 – sinistral shear transtension and asymmetric rift genesis (2.1–1.9 Ga); D2 – sinistral shear transpression under oblique accretion and convergence (1.9 Ga); D3 – sinistral shear transpression under oblique collision (1.89–1.80 Ga); D4 – dextral strike-slip displacements at the background of complex escape tectonics of the late collision stage (1.80–1.78 Ga). The regional stress field changed as follows: D1 – northeast- or east-trending extension; D2 – northeast compression; D3 – sub-latitudinal compression; D4 – sub-meridian compression. Changes in dynamic loading conditions led to multiple kinematic inversions of the fault networks. Widespread transtension and transpression settings in the southeastern parts of the Baltic Shield give evidence of asymmetric rifting, oblique accretion and collision in the Paleoproterozoic, which must be taken in to account in geodynamic reconstructions.
{"title":"FAULT SYSTEMS IN THE UPPER CRUST OF THE FENNOSCANDIAN SHIELD, THE EAST EUROPEAN PLATFORM","authors":"V. Burtman, S. Y. Kolodyazhny","doi":"10.5800/gt-2020-11-4-0505","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0505","url":null,"abstract":"Directions of 683 faults located in the southeastern part of the Fennoscandian (Baltic) shield were statistically analyzed, and three orthogonal associations of fault systems were identified in the study area. According to the dynamic analysis of the fault systems and their associations, the main NW-striking faults belong to the fault network originating mainly from the early Paleoproterozoic. These faults functioned in the Paleoproterozoic during four main deformation stages: D1 – sinistral shear transtension and asymmetric rift genesis (2.1–1.9 Ga); D2 – sinistral shear transpression under oblique accretion and convergence (1.9 Ga); D3 – sinistral shear transpression under oblique collision (1.89–1.80 Ga); D4 – dextral strike-slip displacements at the background of complex escape tectonics of the late collision stage (1.80–1.78 Ga). The regional stress field changed as follows: D1 – northeast- or east-trending extension; D2 – northeast compression; D3 – sub-latitudinal compression; D4 – sub-meridian compression. Changes in dynamic loading conditions led to multiple kinematic inversions of the fault networks. Widespread transtension and transpression settings in the southeastern parts of the Baltic Shield give evidence of asymmetric rifting, oblique accretion and collision in the Paleoproterozoic, which must be taken in to account in geodynamic reconstructions.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80921049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0502
M. I. Gyokche, A. Plyusnin
In the Earth studies, discoveries and investigations of impact craters buried beneath thick sediments are sporadic so far and may still remain inefficient, unless geophysical surveys of the areas of interest are initiated. Such studies can provide useful data to develop the knowledge about cosmic events of the past geological eras, as well as contribute to industrial development of the areas. It is known that an impact crater is filled with layered deposits that create specific sequences and are generally thicker that deposits outside the crater. We have investigated a Precambrian crater located in the southern part of the Nepa-Botuoba anteclise of the Siberian platform. This impact crater called Nepsky-1 was discovered by seismic surveys using the common depth point method (CDPM). In our study, we used the geological and geophysical deep-drilling data of three wells, including gamma-ray and neutron logs and lithological core descriptions. With reference to the concepts of regional geological conditions, we reconstructed the conditions of sedimentation in the study area based on a comprehensive analysis of the structural and textural features of the rocks, and logging and seismic survey data. By processing and interpretation of the CDPM 3D seismic survey data, we obtained the structural images and cross-sections of the impact crater and analysed the thickness of its fill deposits. The Nepsky-1 crater is a bowl-shaped structure with a rim composed of allogenic breccia. In the area around the crater, fault systems are detected. Based on the core sample analysis, we identified the lithological members of the crater and its rim and described them in detail. Active compensation with lacustrine-delta sediments took place in the Nepa period of the late Vendian. By the end of the Tira time, the crater was completely leveled up. In our study, we obtained the first data on the structure of the crater section of the Vendian deposits. Sedimentation in the study area was controlled by the sea level changes. The main terrigenous productive horizons are confined to sandstones that accumulated during the sea level low stand, and found at the bottoms of the lower and upper Nepa subsuites, as well as at the bottoms of the lower and upper Tira subsuites. It is established that the study area was tectonically active in the late Tira time. As a result, the sediments filling the crater were removed to subaerial conditions, and the edges of the allogenic breccia rim were partially destroyed and formed granite breccia outgrowths observed in the rim’s cross-section. We conclude that in the Nepa and Tira times, tectonic vertical movements initiated relatively fast weathering and transportation of the terrigenous material from the adjacent hills into the sedimentation basin. The Nepsky-1 crater gives evidence of meteorite bombing of the Siberian paleocontinent in Precambrian. Finding similar crater structures can be reasonably expected in the study region. Considering the
{"title":"THE NEPSKY-1 IMPACT CRATER AND ITS FILL DEPOSITS ON THE BASEMENT ROOF OF THE SIBERIAN PLATFORM","authors":"M. I. Gyokche, A. Plyusnin","doi":"10.5800/gt-2020-11-4-0502","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0502","url":null,"abstract":"In the Earth studies, discoveries and investigations of impact craters buried beneath thick sediments are sporadic so far and may still remain inefficient, unless geophysical surveys of the areas of interest are initiated. Such studies can provide useful data to develop the knowledge about cosmic events of the past geological eras, as well as contribute to industrial development of the areas. It is known that an impact crater is filled with layered deposits that create specific sequences and are generally thicker that deposits outside the crater. We have investigated a Precambrian crater located in the southern part of the Nepa-Botuoba anteclise of the Siberian platform. This impact crater called Nepsky-1 was discovered by seismic surveys using the common depth point method (CDPM). In our study, we used the geological and geophysical deep-drilling data of three wells, including gamma-ray and neutron logs and lithological core descriptions. With reference to the concepts of regional geological conditions, we reconstructed the conditions of sedimentation in the study area based on a comprehensive analysis of the structural and textural features of the rocks, and logging and seismic survey data. By processing and interpretation of the CDPM 3D seismic survey data, we obtained the structural images and cross-sections of the impact crater and analysed the thickness of its fill deposits. The Nepsky-1 crater is a bowl-shaped structure with a rim composed of allogenic breccia. In the area around the crater, fault systems are detected. Based on the core sample analysis, we identified the lithological members of the crater and its rim and described them in detail. Active compensation with lacustrine-delta sediments took place in the Nepa period of the late Vendian. By the end of the Tira time, the crater was completely leveled up. In our study, we obtained the first data on the structure of the crater section of the Vendian deposits. Sedimentation in the study area was controlled by the sea level changes. The main terrigenous productive horizons are confined to sandstones that accumulated during the sea level low stand, and found at the bottoms of the lower and upper Nepa subsuites, as well as at the bottoms of the lower and upper Tira subsuites. It is established that the study area was tectonically active in the late Tira time. As a result, the sediments filling the crater were removed to subaerial conditions, and the edges of the allogenic breccia rim were partially destroyed and formed granite breccia outgrowths observed in the rim’s cross-section. We conclude that in the Nepa and Tira times, tectonic vertical movements initiated relatively fast weathering and transportation of the terrigenous material from the adjacent hills into the sedimentation basin. The Nepsky-1 crater gives evidence of meteorite bombing of the Siberian paleocontinent in Precambrian. Finding similar crater structures can be reasonably expected in the study region. Considering the ","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91137159","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-12-14DOI: 10.5800/gt-2020-11-4-0498
D. Gladkochub, A. Mazukabzov, T. Donskaya
We analyzed new geological and geochronological data on sedimentation and metamorphism in the junction area of the Aldan and Stanovoy Superterranes comprising the southern flank of the Siberian craton. The analysis was focused on early Proterozoic deposits belonging to the Udokan group. It is confirmed that highly metamorphosed rocks at the base of the Udokan group (Kolar subgroup of the Stanovoy suture zone) differ sharply from other rock associations included in this group (Chiney and Kemen subgroups of the Aldan Superterrane). They differ in the degree of metamorphic alterations, style of tectonic deformation, igneous complexes intruding them, and show a complete lack of copper mineralization. There are thus grounds to exclude the Kolar subgroup from the Udokan group. According to our data, the age of the sediments in the Udokan group, including the Chiney and Kemen subgroups, is 1.90‒1.87 Ga, i.e. in the study area, sedimentation lasted for no more than 30 Ma and proceeded simultaneously with the copper mineralization within the intracontinental extensional basin at the stage of collapse of the early Proterozoic orogen.
{"title":"THE PHENOMENON OF RAPID ACCUMULATION OF SEDIMENTS BELONGING TO THE UDOKAN GROUP AND THE FORMATION OF THE UNIQUE UDOKAN COPPER DEPOSIT (ALDAN SHIELD, SIBERIAN CRATON)","authors":"D. Gladkochub, A. Mazukabzov, T. Donskaya","doi":"10.5800/gt-2020-11-4-0498","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0498","url":null,"abstract":"We analyzed new geological and geochronological data on sedimentation and metamorphism in the junction area of the Aldan and Stanovoy Superterranes comprising the southern flank of the Siberian craton. The analysis was focused on early Proterozoic deposits belonging to the Udokan group. It is confirmed that highly metamorphosed rocks at the base of the Udokan group (Kolar subgroup of the Stanovoy suture zone) differ sharply from other rock associations included in this group (Chiney and Kemen subgroups of the Aldan Superterrane). They differ in the degree of metamorphic alterations, style of tectonic deformation, igneous complexes intruding them, and show a complete lack of copper mineralization. There are thus grounds to exclude the Kolar subgroup from the Udokan group. According to our data, the age of the sediments in the Udokan group, including the Chiney and Kemen subgroups, is 1.90‒1.87 Ga, i.e. in the study area, sedimentation lasted for no more than 30 Ma and proceeded simultaneously with the copper mineralization within the intracontinental extensional basin at the stage of collapse of the early Proterozoic orogen.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72440557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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