Pub Date : 2021-06-23DOI: 10.5800/gt-2021-12-2-0521
S. Kashubin, O. Petrov, S. Shokalsky, E. D. Milshtein, E. A. Androsov, I. Y. Vinokurov, O. Tarasova
The paper reports on the deep geophysical studies performed by the Geological Survey of Russia (VSEGEI) under the international project – Deep Processes and Metallogeny of Northern, Central and Eastern Asia. A model of the deep crustal structure is represented by a set of crustal thickness maps and a 5400-km long geotransect across the major tectonic areas of Northeastern Eurasia. An area of 50000000 km2 is digitally mapped in the uniform projection. The maps show the Moho depths, thicknesses of the main crustal units (i.e. the sedimentary cover and the consolidated crust), anomalous gravity and magnetic fields (in a schematic zoning map of the study area), and types of the crust. The geotransect gives the vertical section of the crust and upper mantle at the passive margin of the Eurasian continent (including submarine uplifts and shelf areas of the Arctic Ocean) and the active eastern continental margin, as well as an area of the Pacific plate.
{"title":"DEEP CRUSTAL STRUCTURE IN NORTHEASTERN EURASIA AND ITS CONTINENTAL MARGINS","authors":"S. Kashubin, O. Petrov, S. Shokalsky, E. D. Milshtein, E. A. Androsov, I. Y. Vinokurov, O. Tarasova","doi":"10.5800/gt-2021-12-2-0521","DOIUrl":"https://doi.org/10.5800/gt-2021-12-2-0521","url":null,"abstract":"The paper reports on the deep geophysical studies performed by the Geological Survey of Russia (VSEGEI) under the international project – Deep Processes and Metallogeny of Northern, Central and Eastern Asia. A model of the deep crustal structure is represented by a set of crustal thickness maps and a 5400-km long geotransect across the major tectonic areas of Northeastern Eurasia. An area of 50000000 km2 is digitally mapped in the uniform projection. The maps show the Moho depths, thicknesses of the main crustal units (i.e. the sedimentary cover and the consolidated crust), anomalous gravity and magnetic fields (in a schematic zoning map of the study area), and types of the crust. The geotransect gives the vertical section of the crust and upper mantle at the passive margin of the Eurasian continent (including submarine uplifts and shelf areas of the Arctic Ocean) and the active eastern continental margin, as well as an area of the Pacific plate.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2021-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91223721","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 : 2021-06-22DOI: 10.5800/gt-2021-12-2-0525
O. Udoratina, K. Kulikova, A. Shuyskiy, A. A. Sobolevа, V. Andreichev, I. Golubeva, V. A. Kapitanova
This work presents the summarization of U–Pb (SIMS, TIMS) zircon dates and petrogeochemical signatures of granitoids of the north of the Urals (Polar, Subpolar, and Northern Urals) obtained over the last decade. Granitе melts were formed from melting of different substrates, highly heterogeneous in composition and age, at all geodynamic stages distinguished in the studied area. Preuralides include island arc–accretionary (735–720 Ma, 670 Ma), collisional (650–520 Ma), and rift-related (520–480 Ma) granitoids. Uralides includes primitive island-arc granitoids (460–429 Ma), mature island-arc granitoids (412–368 Ma), early collisional (360–316 Ma) and late collisional (277–249 Ma) granitoids. As a result, the general trend of variations of oxygen (δ18OZrn, ‰), neodymium (εNd(t)wr), and hafnium (εHf(t)Zrn) isotope compositions identified in time. Mantle isotope compositions (δ18OZrn (+5.6), εNd(t)wr (+1.7), εHf(t)Zrn (+8.7...+10.6)), common for island arc granitoids (Preuralides) are changed by crustal–mantle ones (δ18OZrn (+7.2...+8.5), εNd(t)wr (–4.8...+1.8), εHf(t)Zrn (+2.1 to +13)), typical of collisional granites. According to this, the crustal matter played a significant role during the formation of the latter. The crustal-mantle isotope compositions are changed by the mantle ones, characteristic of rift-related (δ18OZrn (+4.7...+7), εNd(t)wr (+0.7...+5.6), εHf(t)Zrn (–2.04...+12.5)) and island-arc (Uralides; δ18OZrn (+4.2...+5.7), εNd(t)wr (+4.1...+7.4), εHf(t)Zrn (+12...+15.2)) granitoids.
{"title":"GRANITOID MAGMATISM IN THE NORTH OF THE URALS: U–Pb AGE, EVOLUTION, SOURCES","authors":"O. Udoratina, K. Kulikova, A. Shuyskiy, A. A. Sobolevа, V. Andreichev, I. Golubeva, V. A. Kapitanova","doi":"10.5800/gt-2021-12-2-0525","DOIUrl":"https://doi.org/10.5800/gt-2021-12-2-0525","url":null,"abstract":"This work presents the summarization of U–Pb (SIMS, TIMS) zircon dates and petrogeochemical signatures of granitoids of the north of the Urals (Polar, Subpolar, and Northern Urals) obtained over the last decade. Granitе melts were formed from melting of different substrates, highly heterogeneous in composition and age, at all geodynamic stages distinguished in the studied area. Preuralides include island arc–accretionary (735–720 Ma, 670 Ma), collisional (650–520 Ma), and rift-related (520–480 Ma) granitoids. Uralides includes primitive island-arc granitoids (460–429 Ma), mature island-arc granitoids (412–368 Ma), early collisional (360–316 Ma) and late collisional (277–249 Ma) granitoids. As a result, the general trend of variations of oxygen (δ18OZrn, ‰), neodymium (εNd(t)wr), and hafnium (εHf(t)Zrn) isotope compositions identified in time. Mantle isotope compositions (δ18OZrn (+5.6), εNd(t)wr (+1.7), εHf(t)Zrn (+8.7...+10.6)), common for island arc granitoids (Preuralides) are changed by crustal–mantle ones (δ18OZrn (+7.2...+8.5), εNd(t)wr (–4.8...+1.8), εHf(t)Zrn (+2.1 to +13)), typical of collisional granites. According to this, the crustal matter played a significant role during the formation of the latter. The crustal-mantle isotope compositions are changed by the mantle ones, characteristic of rift-related (δ18OZrn (+4.7...+7), εNd(t)wr (+0.7...+5.6), εHf(t)Zrn (–2.04...+12.5)) and island-arc (Uralides; δ18OZrn (+4.2...+5.7), εNd(t)wr (+4.1...+7.4), εHf(t)Zrn (+12...+15.2)) granitoids.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2021-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74986281","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 : 2021-03-21DOI: 10.5800/GT-2021-12-1-0517
F. Zhimulev, E. Pospeeva, I. Novikov, V. Potapov
The Salair fold-nappe terrane (a.k.a. Salair orogen, Salair) is the northwestern part of the Altai-Sayan folded area of the Central Asian Orogenic Belt. It is composed of Cambrian – Early Ordovician volcanic rocks and island-arc sedimentary deposits. In plan, Salair is a horseshoe-shaped structure with the northeast-facing convex side, which is formed by the outcrops of the Early Paleozoic folded basement. Its inner part is the Khmelev basin composed of Upper Devonian – Lower Carboniferous sandstones and siltstones. The Early Paleozoic volcanic rocks and sediments of Salair are overthrusted onto the Devonian-Permian sediments of the Kuznetsk basin. The Paleozoic thrusts, that were reactivated at the neotectonic stage, are observed in the modern relief as tectonic steps. Our study of the Salair deep structure was based on the data from two profiles of magnetotelluric sounding. These 175-km and 125-km long profiles go across the strike of the Salair structure and the western part of the Kuznetsk basin. Profile 1 detects a subhorizontal zone of increased conductivity (100–500 Ohm·m) at the depths of 8–15 km. At the eastern part of Profile 1, this zone gently continues upward, towards a shallow conducting zone that corresponds to the sediments of the Kuznetsk basin. Two high-resistance bodies (1000–7000 Ohm⋅m) are detected at the depths of 0–6 km in the middle of the section. They are separated by a subvertical conducting zone corresponding to the Kinterep thrust. The main features are the subhorizontal positions and the flattened forms of crustal conductivity anomalies. At the central part of Profile 2, there is a high-resistance block (above 150000 Ohm⋅m) over the entire depth range of the section, from the surface to the depths of about 20 km. In the eastern part of Profile 2, a shallow zone of increased conductivity corresponds to the sediments of the Kuznetsk basin. The subhorizontal mid-crust layer of increased conductivity, which is detected in the Salair crust, is typical of intracontinental orogens. The distribution pattern of electrical conductivity anomalies confirms the Salair thrust onto the Kuznetsk basin. The northern part of the Khmelev basin is characterized by high resistivity, which can be explained by abundant covered Late Permian granite massifs in that part of the Khmelev basin. The Kinterep thrust located in the northeastern part of the Khmelev basin is manifested in the deep geoelectric crust structure as a conducting zone, which can be considered as an evidence of the activity of this fault.
{"title":"Deep structure of the Salair fold-nappe terrane (NW CAOB) according to magnetotelluric sounding","authors":"F. Zhimulev, E. Pospeeva, I. Novikov, V. Potapov","doi":"10.5800/GT-2021-12-1-0517","DOIUrl":"https://doi.org/10.5800/GT-2021-12-1-0517","url":null,"abstract":"The Salair fold-nappe terrane (a.k.a. Salair orogen, Salair) is the northwestern part of the Altai-Sayan folded area of the Central Asian Orogenic Belt. It is composed of Cambrian – Early Ordovician volcanic rocks and island-arc sedimentary deposits. In plan, Salair is a horseshoe-shaped structure with the northeast-facing convex side, which is formed by the outcrops of the Early Paleozoic folded basement. Its inner part is the Khmelev basin composed of Upper Devonian – Lower Carboniferous sandstones and siltstones. The Early Paleozoic volcanic rocks and sediments of Salair are overthrusted onto the Devonian-Permian sediments of the Kuznetsk basin. The Paleozoic thrusts, that were reactivated at the neotectonic stage, are observed in the modern relief as tectonic steps. Our study of the Salair deep structure was based on the data from two profiles of magnetotelluric sounding. These 175-km and 125-km long profiles go across the strike of the Salair structure and the western part of the Kuznetsk basin. Profile 1 detects a subhorizontal zone of increased conductivity (100–500 Ohm·m) at the depths of 8–15 km. At the eastern part of Profile 1, this zone gently continues upward, towards a shallow conducting zone that corresponds to the sediments of the Kuznetsk basin. Two high-resistance bodies (1000–7000 Ohm⋅m) are detected at the depths of 0–6 km in the middle of the section. They are separated by a subvertical conducting zone corresponding to the Kinterep thrust. The main features are the subhorizontal positions and the flattened forms of crustal conductivity anomalies. At the central part of Profile 2, there is a high-resistance block (above 150000 Ohm⋅m) over the entire depth range of the section, from the surface to the depths of about 20 km. In the eastern part of Profile 2, a shallow zone of increased conductivity corresponds to the sediments of the Kuznetsk basin. The subhorizontal mid-crust layer of increased conductivity, which is detected in the Salair crust, is typical of intracontinental orogens. The distribution pattern of electrical conductivity anomalies confirms the Salair thrust onto the Kuznetsk basin. The northern part of the Khmelev basin is characterized by high resistivity, which can be explained by abundant covered Late Permian granite massifs in that part of the Khmelev basin. The Kinterep thrust located in the northeastern part of the Khmelev basin is manifested in the deep geoelectric crust structure as a conducting zone, which can be considered as an evidence of the activity of this fault.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2021-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89482831","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 : 2021-03-21DOI: 10.5800/GT-2021-12-1-0516
M. N. Kondratyev
Tectonic fracturing of the Mesozoic and Cenozoic structures was studied in the Northern Priokhotie (Magadan region). The cataclastic analysis method and the statistical method of fracture density analysis were used to reconstruct their state of stress. It is revealed that the folded structures of the Arman’-Viliga synclinorium are subjected to horizontal shearing; the axis of maximum compression is sublatitudinal (azimuth 67°, angle 12°); extension is submeridional (azimuth 161°, angle 19°). In the Uda-Murgal volcanic arc, horizontal extension with shear takes place; the compression axis is directed to NW (azimuth 259°, angle 29°), and the extension axis to NE (azimuth 152°, angle 26°). In the Okhotsk-Chukotka volcanogenic belt, volcanic structures are in the field of varying tectonic stresses, from predominant horizontal extension to horizontal shear. The Cenozoic intermontane depressions of the Miocene – Pliocene ages are subjected to horizontal shear; the compression axis is directed to NE (azimuth 214°, angle 29°), and the extension axis to NW (azimuth 121°, angle 4°). The results of the comparative analysis of the stress states in the above-mentioned areas reliably show that the diversity of the stress state types is statistically related to the structural positions of the studies sites. Such diversity cannot be explained by an influence of active faults, or by any consecutive superposition of deformations at different stages, despite the fact that the deformations have complicated the observed pattern of the stress states. We conclude that each subsequent geodynamic stage only introduced additional elements into the previous structure, but did not completely transform it.
{"title":"Tectonic stress in the structures of the Northern Priokhotie (Magadan region) according to geological data","authors":"M. N. Kondratyev","doi":"10.5800/GT-2021-12-1-0516","DOIUrl":"https://doi.org/10.5800/GT-2021-12-1-0516","url":null,"abstract":"Tectonic fracturing of the Mesozoic and Cenozoic structures was studied in the Northern Priokhotie (Magadan region). The cataclastic analysis method and the statistical method of fracture density analysis were used to reconstruct their state of stress. It is revealed that the folded structures of the Arman’-Viliga synclinorium are subjected to horizontal shearing; the axis of maximum compression is sublatitudinal (azimuth 67°, angle 12°); extension is submeridional (azimuth 161°, angle 19°). In the Uda-Murgal volcanic arc, horizontal extension with shear takes place; the compression axis is directed to NW (azimuth 259°, angle 29°), and the extension axis to NE (azimuth 152°, angle 26°). In the Okhotsk-Chukotka volcanogenic belt, volcanic structures are in the field of varying tectonic stresses, from predominant horizontal extension to horizontal shear. The Cenozoic intermontane depressions of the Miocene – Pliocene ages are subjected to horizontal shear; the compression axis is directed to NE (azimuth 214°, angle 29°), and the extension axis to NW (azimuth 121°, angle 4°). The results of the comparative analysis of the stress states in the above-mentioned areas reliably show that the diversity of the stress state types is statistically related to the structural positions of the studies sites. Such diversity cannot be explained by an influence of active faults, or by any consecutive superposition of deformations at different stages, despite the fact that the deformations have complicated the observed pattern of the stress states. We conclude that each subsequent geodynamic stage only introduced additional elements into the previous structure, but did not completely transform it.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2021-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89916951","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 : 2021-03-21DOI: 10.5800/GT-2021-12-1-0511
B. G. Golionko, A. Ryazantsev
The study is focused on mesostructural folded parageneses of the Taldyk antiform (a.k.a. Taldyk block) located in the East Mugodzhar zone. The sequence of their formation is established; the structural evolution of the study area is investigated, and four stages of deformation are identified. The NW-trending folds F1 with SE-vergence formed during the first stage of deformation, DI. The geodynamics and timeline of this stage remain unclear. The W-E-trending folds F2 with E-vergence are related to tectonic movements that took place at stage DII. In the western limb of the antiform, stage DII is evidenced by folds overturned towards the south-east. In the eastern limb, folds plunge to the east and northeast. These fold structures are probably related to the Devonian subduction-obduction processes. At stage DIII, thrusting of the Taldyk antiform over the West Mugodzhar zone and folding F3 with W-vergence is related to the Ural continental collision in the Late Paleozoic, which completed the geodynamic evolution of the Ural paleo-ocean. At stage DIV, postcollisional shearing is evidenced by folds F4 with steeply dipping hinges, which completed the structural evolution of the study area.
{"title":"Deformation and structural evolution of metamorphic complexes of the Taldyk antiform in the East Mugodzhar zone of Urals (West Kazakhstan)","authors":"B. G. Golionko, A. Ryazantsev","doi":"10.5800/GT-2021-12-1-0511","DOIUrl":"https://doi.org/10.5800/GT-2021-12-1-0511","url":null,"abstract":"The study is focused on mesostructural folded parageneses of the Taldyk antiform (a.k.a. Taldyk block) located in the East Mugodzhar zone. The sequence of their formation is established; the structural evolution of the study area is investigated, and four stages of deformation are identified. The NW-trending folds F1 with SE-vergence formed during the first stage of deformation, DI. The geodynamics and timeline of this stage remain unclear. The W-E-trending folds F2 with E-vergence are related to tectonic movements that took place at stage DII. In the western limb of the antiform, stage DII is evidenced by folds overturned towards the south-east. In the eastern limb, folds plunge to the east and northeast. These fold structures are probably related to the Devonian subduction-obduction processes. At stage DIII, thrusting of the Taldyk antiform over the West Mugodzhar zone and folding F3 with W-vergence is related to the Ural continental collision in the Late Paleozoic, which completed the geodynamic evolution of the Ural paleo-ocean. At stage DIV, postcollisional shearing is evidenced by folds F4 with steeply dipping hinges, which completed the structural evolution of the study area.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2021-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89323548","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 : 2021-03-21DOI: 10.5800/GT-2021-12-1-0519
K. Ghazaryan, R. Sargsyan
The territory of Armenia, although relatively small, is geologically and tectonically complex. Its complexity is not only due to a dense network of faults. It results from a complicated history of tectonic development including several phases of mountain formation and planation, and the extensive development of fold-block, tectonic and magmatic processes. An important scientific task is identification of earthquake-prone structural blocks by analysing seismotectonic data on geotectonic zones in Armenia. This article describes the seismotectonic analysis of geological and geophysical data on the Viraayots-Karabakh zone.We used a wide spectrum of modern tectonic-geomorphological indices and GIS technologies in order to assess the neotectonic (Neogene – Quaternary) activity of the main block units of the study area and to classify the block units by their tectonic activity levels. Tectonics of the study area is contrasting, and many tectonically active blocks are in the immediate neighbourhood with passive blocks.Based on the records of seismic events of various magnitudes and historic earthquake data, we analysed modern seismicity of the block units. For each block, a quantitative analysis of its total seismic energy release was performed, and relationships between the released seismic energy values and the number of recorded earthquakes were analyzed. Based on such analysis, we identify a group of blocks wherein the total released seismic energy values are high, but the numbers of seismic events recorded in these blocks are rather limited. In the context of block tectonic activity, analysing these data makes it possible to detect the blocks with the highest probability of the occurrence of strong earthquakes.
{"title":"Seismotectonic analysis of the Viraayots–Karabakh zone (Armenia) and the adjacent areas of Lesser Caucasus","authors":"K. Ghazaryan, R. Sargsyan","doi":"10.5800/GT-2021-12-1-0519","DOIUrl":"https://doi.org/10.5800/GT-2021-12-1-0519","url":null,"abstract":"The territory of Armenia, although relatively small, is geologically and tectonically complex. Its complexity is not only due to a dense network of faults. It results from a complicated history of tectonic development including several phases of mountain formation and planation, and the extensive development of fold-block, tectonic and magmatic processes. An important scientific task is identification of earthquake-prone structural blocks by analysing seismotectonic data on geotectonic zones in Armenia. This article describes the seismotectonic analysis of geological and geophysical data on the Viraayots-Karabakh zone.We used a wide spectrum of modern tectonic-geomorphological indices and GIS technologies in order to assess the neotectonic (Neogene – Quaternary) activity of the main block units of the study area and to classify the block units by their tectonic activity levels. Tectonics of the study area is contrasting, and many tectonically active blocks are in the immediate neighbourhood with passive blocks.Based on the records of seismic events of various magnitudes and historic earthquake data, we analysed modern seismicity of the block units. For each block, a quantitative analysis of its total seismic energy release was performed, and relationships between the released seismic energy values and the number of recorded earthquakes were analyzed. Based on such analysis, we identify a group of blocks wherein the total released seismic energy values are high, but the numbers of seismic events recorded in these blocks are rather limited. In the context of block tectonic activity, analysing these data makes it possible to detect the blocks with the highest probability of the occurrence of strong earthquakes.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2021-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87806159","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 : 2021-01-01DOI: 10.5800/gt-2021-12-1-0513
S. Efremov, A. Travin
The 40Ar/39Ar dating of ultrapotassic rocks from Central Chukotka shows that these rocks are Early Cretaceous, and yields a narrow range of age variations (109 to 107 Ma), which correlates fairly well with the range of age variations of granitoids typical of the study area (117–105 Ma). There are thus grounds to suggest that the ultrapotassic magmas and granitoids resulted from the same geological process that can be identified from the material characteristics of the ultrapotassic magmas.In the modern concepts of the regional geological development, the formation of the granitoid and ultrapotassic magmas can be related to the continental lithosphere extension due to the collision of Eurasian plate and the Chukotka – Arctic Alaska continental block.Using modern genetic models based on the interpretations of the material characteristics of ultrapotassic magmas, it is possible to limit the number of genetic hypotheses and to relate the continental lithosphere extension to the processes that took place in the upper mantle of the study area.
{"title":"Isotopic age and paleogeodynamic position of ultrapotassic magmatism of Central Chukotka","authors":"S. Efremov, A. Travin","doi":"10.5800/gt-2021-12-1-0513","DOIUrl":"https://doi.org/10.5800/gt-2021-12-1-0513","url":null,"abstract":"The 40Ar/39Ar dating of ultrapotassic rocks from Central Chukotka shows that these rocks are Early Cretaceous, and yields a narrow range of age variations (109 to 107 Ma), which correlates fairly well with the range of age variations of granitoids typical of the study area (117–105 Ma). There are thus grounds to suggest that the ultrapotassic magmas and granitoids resulted from the same geological process that can be identified from the material characteristics of the ultrapotassic magmas.In the modern concepts of the regional geological development, the formation of the granitoid and ultrapotassic magmas can be related to the continental lithosphere extension due to the collision of Eurasian plate and the Chukotka – Arctic Alaska continental block.Using modern genetic models based on the interpretations of the material characteristics of ultrapotassic magmas, it is possible to limit the number of genetic hypotheses and to relate the continental lithosphere extension to the processes that took place in the upper mantle of the study area.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80931502","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 : 2021-01-01DOI: 10.5800/gt-2021-12-1-0515
P. V. Makarov, I. Smolin, V. Zimina
The paper describes numerical modeling of the generation and propagation of the fronts of moving deformation autosolitons in a loaded nonlinear strong medium. It presents solving a system of dynamic equations for solid mechanics, using an equation of state written in a relaxation form that takes into account both an overload of the solid medium and subsequent stress relaxation. The structure of a deformation autosoliton front is investigated in detail. It is shown that the front of a deformation autosoliton that is moving in an elastoplastic medium is a shear band (i.e. a narrow zone of intense shearing strain), which is oriented in the direction of maximum shear stress. Consecutive formation of such shear bands can be viewed as deformation autosoliton perturbations propagating along the axis of loading (compression or extension). A fine structure of a deformation autosoliton front is revealed. It is shown that slow autosoliton dynamics is an integral component of any deformation process, including the seismic process, in any solid medium. In contrast to fast autosoliton dynamics (when the velocities of stress waves are equal to the speed of sound), slow deformation autosoliton perturbations propagate at velocities 5–7 orders of magnitude lower than the velocities of sound. Considering the geomedium, it should be noted that slow dynamics plays a significant role in creating deformation patterns of the crust elements.
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Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0503
V. Sankov, A. Parfeevets
This article gives a chronological review of the main published research results concerning the Cenozoic crustal stress-strain state in Mongolia and adjacent territories. The studies commenced in the southern Baikal rift zone in the 1970s and were extended further southwards to cover mobile regions neighbouring the Siberian platform. Geological, structural and morphostructural data were collected and analysed to define the crustal stress types and spatial characteristics. The authors have consolidated their reconstructions of the crustal stress-strain state of Mongolia, which were based on tectonic fracturing data and displacements along fractures in fault zones active in the Cenozoic. We consolidated a database of reconstructed stress tensors, which now contains more than 750+ solutions. The Late Cenozoic stress field was mapped. The map shows domains differing in types of the paleostress state of the crust. The reconstructions were compared to our calculations of the present-day crustal stress state, which were based on earthquake focal mechanisms, and to calculations by other authors. At the Late Cenozoic and current stages, the maximum horizontal compression axis (SHmax) has varying orientations, from submeridional (Western Mongolia) to NE and ENE (Eastern Mongolia). The role of compression increases from the northern domains, where the reconstructions show shear and transtension, to the southern domains with prevailing transpression and compression. Regular changes occur in the stress state and rupture parageneses along the largest latitudinal faults, North Khangai and Dolinoozersky; such changes are related to left-lateral strike-slip faulting. We analysed the sequence of the occurrence of stress fields differing in types and spatial characteristics, and revealed the main regularities in the evolution of the crustal stress-strain state in time. In the Cenozoic history of crust deformation in Mongolia, we can distinguish several episodes that differ in the dominant impacts of various tectonic force sources or combinations of such impacts. At the beginning of the Cenozoic, tectonic structures developed mainly under the influence of the interaction of East Asia and the Pacific Plate, which was manifested in the southeastern domains of the study area. The long-term SE-trending asthenospheric flow caused crustal stretching, which initiated the formation of tectonic structures comprising the Baikal rift system. Starting from the Pliocene, crustal stretching took place in combination with NNE compression caused by the India–Eurasia convergence. As a result, shearing occurred along the large faults. At this background, the Khangai and Khentei uplifts (including crust extension zones at their crests) are large structures that developed due to the dynamic effect of local mantle anomalies.
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Pub Date : 2020-12-15DOI: 10.5800/gt-2020-11-4-0504
D. Safonov
Earthquake focal mechanisms in the Southern Kuril-Kamchatka and Northern Japan subduction zones were analysed to investigate the features of the tectonic stress field inside the Pacific lithospheric plate subducting into the upper mantle. Earthquake focal mechanism (hypocenter depths of more than 200 km) were taken from the 1966– 2018 NIED, IMGiG FEB RAS and GlobalCMT catalogues. The tectonic stress field was reconstructed by the cataclastic analysis method, using a coordinate system related to the subducting plate. In most parts of the studied seismic focal zone, the axis of the principal compression stress approximately coincides with the direction of the Pacific lithospheric plate subduction beneath the Sea of Okhotsk. It slightly deviates towards the hinge zone separating the studied regions. The principal tension stress axis is most often perpendicular to the plate movement, but less stable in direction. This leads to compression relative to the slab in some parts of the studied regions, and causes shearing in others. The hinge zone is marked by the unstable position of the tension axis and high values of the Lode–Nadai coefficient, corresponding to the conditions of uniaxial compression, while the compression direction remains the same, towards the slab movement. Two more areas of uniaxial compression are located below the Sea of Japan at depths of 400–500 km.
分析了南千岛群岛-堪察加半岛和日本北部俯冲带的地震震源机制，探讨了太平洋岩石圈板块俯冲至上地幔的构造应力场特征。地震震源机制(震源深度超过200公里)取自1966 - 2018年NIED、IMGiG FEB RAS和GlobalCMT目录。采用与俯冲板块相关的坐标系，采用碎裂分析方法重建了构造应力场。在地震震源带的大部分地区，主压应力轴线与鄂霍次克海下的太平洋岩石圈板块俯冲方向大致重合。它稍微偏离分离研究区域的铰链区。主拉应力轴通常垂直于板块运动，但方向不太稳定。这导致研究区域的某些部分相对于板的压缩，并导致其他部分的剪切。铰区受拉轴位置不稳定，Lode-Nadai系数值较高，对应于单轴受压条件，而受压方向不变，即向板移动方向。另外两个单轴压缩区位于日本海以下400-500公里的深度。
{"title":"RECONSTRUCTION OF THE TECTONIC STRESS FIELD IN THE DEEP PARTS OF THE SOUTHERN KURIL-KAMCHATKA AND NORTHERN JAPAN SUBDUCTION ZONES","authors":"D. Safonov","doi":"10.5800/gt-2020-11-4-0504","DOIUrl":"https://doi.org/10.5800/gt-2020-11-4-0504","url":null,"abstract":"Earthquake focal mechanisms in the Southern Kuril-Kamchatka and Northern Japan subduction zones were analysed to investigate the features of the tectonic stress field inside the Pacific lithospheric plate subducting into the upper mantle. Earthquake focal mechanism (hypocenter depths of more than 200 km) were taken from the 1966– 2018 NIED, IMGiG FEB RAS and GlobalCMT catalogues. The tectonic stress field was reconstructed by the cataclastic analysis method, using a coordinate system related to the subducting plate. In most parts of the studied seismic focal zone, the axis of the principal compression stress approximately coincides with the direction of the Pacific lithospheric plate subduction beneath the Sea of Okhotsk. It slightly deviates towards the hinge zone separating the studied regions. The principal tension stress axis is most often perpendicular to the plate movement, but less stable in direction. This leads to compression relative to the slab in some parts of the studied regions, and causes shearing in others. The hinge zone is marked by the unstable position of the tension axis and high values of the Lode–Nadai coefficient, corresponding to the conditions of uniaxial compression, while the compression direction remains the same, towards the slab movement. Two more areas of uniaxial compression are located below the Sea of Japan at depths of 400–500 km.","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":"88689903","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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