Pub Date : 2020-06-20DOI: 10.5800/gt-2020-11-2-0472
А. М. Mazukabzov, А. Fedorov, A. I. Nepomnyashchikh
The article presents the results of geological and structural studies of the northwestern part of the Gargan quartziferous province, wherein the Bural-Sardyk deposit is located. The early views on this deposit of high-quality siliceous raw materials have been amended using the new data. This deposit is associated with quartzites of the MesoProterozoic Irkut formation and discordantly overlaps the Gargan block. According to the detailed study results on the cover of the Oka-Urik interfluve area, its structure is predetermined by physical and mechanical properties of the rocks, and the degree of rock dislocation depends on the rock viscosity. Most of its section is composed of viscous quartzites that create the structural framework of the study area. Such viscous rocks are not prone to folding. An alternative is detachment taking place concordantly to layering. The only interlayer is composed of limestones that underwent intense plastic deformation reflected in multi-folding. Actually, limestones mark a zone of plastic detachment. The authors propose an interpretation of the formation of the deposit structure. The main deformation event was preceded by the sediment transformation stage in conditions of diagenesis and catagenesis due to the influence of a lithostatic load. Primary recrystallization under lithogenesis led to the formation of high-purity silicon rocks. At the next stage, the rocks were subjected to longitudinal compression in the PT conditions of green-shale metamorphism. This stage is mainly evidenced by sublayer detachments. In parallel with that process, quartzites experienced super-plastic flow and recrystallization, which led to the formation of super-quartzites. The bodies of super-quartzites tend to be layered and less discordant. Such a structural position suggests the possibility of detecting latent manifestations of super-quartzites at different levels in the quartzites of the Irkut formation. Tectonic detachments are observed in the sedimentary cover and do not reach the foundation. Based on these features, there are reasons to use the thin-skinned tectonic model. Rock deformation occurred under stress oriented from the northwest to the southeast. This is indicated by the position of the axial surfaces of the folds, as well as the orientations of the maximum compression axis and the crystallographic axes of quartz. Macroand microstructural data indicate that the tectonic transport of matter was directed to the southeast. The research results were used for compiling a new geological map of the deposit.
{"title":"STRUCTURE OF SUPER QUARTZITE AT THE BURAL-SARDYK DEPOSIT, EAST SAYAN MOUNTAINS","authors":"А. М. Mazukabzov, А. Fedorov, A. I. Nepomnyashchikh","doi":"10.5800/gt-2020-11-2-0472","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0472","url":null,"abstract":"The article presents the results of geological and structural studies of the northwestern part of the Gargan quartziferous province, wherein the Bural-Sardyk deposit is located. The early views on this deposit of high-quality siliceous raw materials have been amended using the new data. This deposit is associated with quartzites of the MesoProterozoic Irkut formation and discordantly overlaps the Gargan block. According to the detailed study results on the cover of the Oka-Urik interfluve area, its structure is predetermined by physical and mechanical properties of the rocks, and the degree of rock dislocation depends on the rock viscosity. Most of its section is composed of viscous quartzites that create the structural framework of the study area. Such viscous rocks are not prone to folding. An alternative is detachment taking place concordantly to layering. The only interlayer is composed of limestones that underwent intense plastic deformation reflected in multi-folding. Actually, limestones mark a zone of plastic detachment. The authors propose an interpretation of the formation of the deposit structure. The main deformation event was preceded by the sediment transformation stage in conditions of diagenesis and catagenesis due to the influence of a lithostatic load. Primary recrystallization under lithogenesis led to the formation of high-purity silicon rocks. At the next stage, the rocks were subjected to longitudinal compression in the PT conditions of green-shale metamorphism. This stage is mainly evidenced by sublayer detachments. In parallel with that process, quartzites experienced super-plastic flow and recrystallization, which led to the formation of super-quartzites. The bodies of super-quartzites tend to be layered and less discordant. Such a structural position suggests the possibility of detecting latent manifestations of super-quartzites at different levels in the quartzites of the Irkut formation. Tectonic detachments are observed in the sedimentary cover and do not reach the foundation. Based on these features, there are reasons to use the thin-skinned tectonic model. Rock deformation occurred under stress oriented from the northwest to the southeast. This is indicated by the position of the axial surfaces of the folds, as well as the orientations of the maximum compression axis and the crystallographic axes of quartz. Macroand microstructural data indicate that the tectonic transport of matter was directed to the southeast. The research results were used for compiling a new geological map of the deposit.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76751798","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 : 2020-06-20DOI: 10.5800/gt-2020-11-2-0473
A. Hassan, S. Rasskazov, I. Chuvashova, T. Yasnygina, L. Titova, N. Kulagina, M. Usoltseva
. We present results of lithogeochemical, diatomic and palynological studies of sediments from the Tunka-13 well that was drilled in the southeastern part of dry Tunka basin in the Baikal rift zone. At the base of the section, there is an eroded basaltic flow of 16–15 Ma. From lithogeochemical signatures, we identify nine sedimentary units. The seven lower ones (interval 7.2–86.5 m) belong to the Tankhoi formation, the eighth (interval 2.7–6.6 m) to the Anosov formation, the ninth (interval <2.4 m) to the sandy stratum. We determined local sources of clastic material of basaltic and silicic compositions for units 1 and 2, respectively, and remote sources of silicic compositions for the overlaying units. The section shows a change from alluvial facies (units 1–3) through avandelta (unit 4) and lacustrine ones (units 5–7), again to alluvial facies (unit 8) and then to lacustrine-eolian ones (unit 9). Spore and pollen spectra from sediments of units 1–7 are divided into three palynozones (PZ), reflecting the vegetation change in the Late Miocene – Early Pliocene: PZ-1 – coniferous and deciduous forests with a small participation of thermophilic broadleaved species in moderately warm, humid climatic conditions; PZ-2 – enhancing the role of hemlock and more diverse thermophilic deciduous rocks in more humid and warm conditions; PZ-3 – a gradual reduction in the number of hemlock and other dark coniferous species, removing broadleaved species by birch and alder, growing grassy communities in wetlands due to climate cooling. We identified layers of lacustrine facies by occurrence of fossil diatoms that are absent in the layers of the alluvial and avandelta facies. In lacustrine sediments, we distinguish four diatom zones: DZ-1 denotes a relatively deep Late Miocene paleolake, marked by planktonic species, DZ-2, DZ-3 and DZ-4 – a shallow Early Pliocene lake with a developed littoral zone and short transgression. The Late-Miocene paleolake transgression, indicated by changing facies, is associated with structural reorganization, accompanied by volcanic extinction in the Tunka valley about 9–8 Ma, and the Early Pliocene short transgression with a new reorganization, reflected in volcanic rejuvenation about 4.0 Ma. shows no Eu-anomaly, unit 2 – weak anomaly, unit 3 – interbedded layers with and without anomaly. In all the overlying sediments, the anomaly is clearly defined.
{"title":"IDENTIFYING UPPER MIOCENE – LOWER PLIOCENE LACUSTRINE SEDIMENTS IN DRY TUNKA BASIN OF THE BAIKAL RIFT ZONE","authors":"A. Hassan, S. Rasskazov, I. Chuvashova, T. Yasnygina, L. Titova, N. Kulagina, M. Usoltseva","doi":"10.5800/gt-2020-11-2-0473","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0473","url":null,"abstract":". We present results of lithogeochemical, diatomic and palynological studies of sediments from the Tunka-13 well that was drilled in the southeastern part of dry Tunka basin in the Baikal rift zone. At the base of the section, there is an eroded basaltic flow of 16–15 Ma. From lithogeochemical signatures, we identify nine sedimentary units. The seven lower ones (interval 7.2–86.5 m) belong to the Tankhoi formation, the eighth (interval 2.7–6.6 m) to the Anosov formation, the ninth (interval <2.4 m) to the sandy stratum. We determined local sources of clastic material of basaltic and silicic compositions for units 1 and 2, respectively, and remote sources of silicic compositions for the overlaying units. The section shows a change from alluvial facies (units 1–3) through avandelta (unit 4) and lacustrine ones (units 5–7), again to alluvial facies (unit 8) and then to lacustrine-eolian ones (unit 9). Spore and pollen spectra from sediments of units 1–7 are divided into three palynozones (PZ), reflecting the vegetation change in the Late Miocene – Early Pliocene: PZ-1 – coniferous and deciduous forests with a small participation of thermophilic broadleaved species in moderately warm, humid climatic conditions; PZ-2 – enhancing the role of hemlock and more diverse thermophilic deciduous rocks in more humid and warm conditions; PZ-3 – a gradual reduction in the number of hemlock and other dark coniferous species, removing broadleaved species by birch and alder, growing grassy communities in wetlands due to climate cooling. We identified layers of lacustrine facies by occurrence of fossil diatoms that are absent in the layers of the alluvial and avandelta facies. In lacustrine sediments, we distinguish four diatom zones: DZ-1 denotes a relatively deep Late Miocene paleolake, marked by planktonic species, DZ-2, DZ-3 and DZ-4 – a shallow Early Pliocene lake with a developed littoral zone and short transgression. The Late-Miocene paleolake transgression, indicated by changing facies, is associated with structural reorganization, accompanied by volcanic extinction in the Tunka valley about 9–8 Ma, and the Early Pliocene short transgression with a new reorganization, reflected in volcanic rejuvenation about 4.0 Ma. shows no Eu-anomaly, unit 2 – weak anomaly, unit 3 – interbedded layers with and without anomaly. In all the overlying sediments, the anomaly is clearly defined.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73956994","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 : 2020-06-20DOI: 10.5800/gt-2020-11-2-0471
A. Khotylev, A. V. Tevelev, Y. Bychkova, A. Latyshev, M. Anosova
Among the Riphean–Vendian dyke complexes of the basic composition, which intersect the Precambrian strata of the Bashkirian meganticlinorium (Southern Urals), one of the most common is the Kurgas gabbro-dolerite complex dated to the Early – Middle Riphean. This article presents the isotopic dating, petrological and geochemical features of the rocks belonging to the Kurgas complex. It gives the first description of the regional geochemical zoning that is reflected in a decrease in SiO2 contents from the north to the south along the Bashkirian meganticlinorium, and an increase in MgO contents in the same direction, which is attributed by the authors to an increase in the permeability of the crust to the south during opening of the Mashak riftogenic structure. New data on isotopic ages were obtained for the dyke that cuts the Satka formation of the Lower Riphean – 1318±10 (40Ar/39Ar), the intrusion in the exocontact zone of the Berdyaush rapakivi granite massif – 1349±11 Ma (U-Pb), and the andesite dyke among the metamorphic rocks of the Taratash complex – 1365.6±6.6 Ma (U-Pb). These ages, in combination with the previously obtained data, suggest that the complex formed during a rather long period of time (from 1385 to 1318 Ma, as a minimum), which corresponds to the beginning of the Middle Riphean. Isotopic U-Pb age of the dyke that cuts the contact zone of the Berdyaush massif, suggests that the major portion of the massif had already crystallized by that time and was exhumed into the shallow zone of brittle deformation.
在与南乌拉尔地区巴什基利亚巨型背斜前寒武纪地层相交叉的里芬—文迪安基性岩脉复合体中，最常见的是早—中里芬期的库尔加斯辉长—白云岩复合体。本文介绍了库尔加斯杂岩的同位素定年、岩石学和地球化学特征。首次描述了区域地球化学分带的特征，主要表现为沿巴什基里亚巨型背斜由北向南SiO2含量减少，而沿同一方向MgO含量增加，认为这是由于马沙克造裂构造打开时地壳向南渗透性增加所致。获得了切割下里芬河萨特卡组的岩脉- 1318±10 (40Ar/39Ar)、Berdyaush rapakivi花岗岩地块外接触带侵入物- 1349±11 Ma (U-Pb)和Taratash杂岩变质岩中的安山岩岩脉- 1365.6±6.6 Ma (U-Pb)的同位素年龄新数据。这些年龄与先前获得的数据相结合，表明该复合体的形成时间相当长(至少从1385年到1318年)，对应于中Riphean的开始。切断别尔佳什地块接触带的岩脉的同位素U-Pb年龄表明，此时该地块的主要部分已经结晶，并被挖掘到浅脆性变形带。
{"title":"MEZOPROTEROZOIC BASITE MAGMATISM OF THE BASHKIRIAN MEGANTICLINORIUM (SOUTHERN URALS): AGE CONSTRAINTS, PETROLOGICAL AND GEOCHEMICAL FEATURES","authors":"A. Khotylev, A. V. Tevelev, Y. Bychkova, A. Latyshev, M. Anosova","doi":"10.5800/gt-2020-11-2-0471","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0471","url":null,"abstract":"Among the Riphean–Vendian dyke complexes of the basic composition, which intersect the Precambrian strata of the Bashkirian meganticlinorium (Southern Urals), one of the most common is the Kurgas gabbro-dolerite complex dated to the Early – Middle Riphean. This article presents the isotopic dating, petrological and geochemical features of the rocks belonging to the Kurgas complex. It gives the first description of the regional geochemical zoning that is reflected in a decrease in SiO2 contents from the north to the south along the Bashkirian meganticlinorium, and an increase in MgO contents in the same direction, which is attributed by the authors to an increase in the permeability of the crust to the south during opening of the Mashak riftogenic structure. New data on isotopic ages were obtained for the dyke that cuts the Satka formation of the Lower Riphean – 1318±10 (40Ar/39Ar), the intrusion in the exocontact zone of the Berdyaush rapakivi granite massif – 1349±11 Ma (U-Pb), and the andesite dyke among the metamorphic rocks of the Taratash complex – 1365.6±6.6 Ma (U-Pb). These ages, in combination with the previously obtained data, suggest that the complex formed during a rather long period of time (from 1385 to 1318 Ma, as a minimum), which corresponds to the beginning of the Middle Riphean. Isotopic U-Pb age of the dyke that cuts the contact zone of the Berdyaush massif, suggests that the major portion of the massif had already crystallized by that time and was exhumed into the shallow zone of brittle deformation.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89824173","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 : 2020-06-20DOI: 10.5800/gt-2020-11-2-0477
P. Dyadkov, O. Kuchay, Y. Romanenko, Z. S. Dzhumagaliyeva
. Seismotectonic deformations in the Middle America Trench and their features in the area of preparation of the Chiapas earthquake, М W =8.2, 08 September 2017, were determined using the data on 2244 focal mechanisms of earthquakes for the period of 1977–2017. The distribution of seismicity with depth was studied in detail. The decrease in the depth of the Benioff zone in the north-western subduction segments and the increase in the south-eastern segments is associated with the age of the subducting parts of the Cocos plate and the angle of their immersion. The latter mechanism can also explain the presence of earthquakes with normal focal mechanism on the oceanic uplift in the south-eastern segments of the subduction zone and their absence in the north-western ones. In general, the typical character of subduction deformations has a number of features in the Middle America Trench. The predominance of shortening by horizontal components and elongation by vertical ones at depths up to 35 km is replaced by the transitional type with mosaic distribution of deformations of different signs in the depth range of 36–70 km. Even lower, in the depth range of 70–105 km, the type of deformation changes to the opposite with respect to the upper horizon. The Chiapas earthquake occurred on the border of regions with different types of deformation, which indicates softening of the block’s medium to the west of the hypocenter and its hardening to the east. Such a state of the lithospheric medium may indicate the presence of a deformation shadow zone in the Chiapas earthquake preparation area.
． 利用1977-2017年2244次震源机制资料，确定了2017年9月8日恰帕斯地震М W =8.2预备区的中美洲海沟地震构造形变及其特征。详细研究了地震活动性随深度的分布。贝尼奥夫带在西北俯冲段深度减小而在东南俯冲段深度增大，与Cocos板块俯冲部分的年龄及其浸没角度有关。后一种机制也可以解释在俯冲带的东南段海洋隆起有正常震源机制的地震而在西北段海洋隆起没有正常震源机制的地震。总的来说，中美洲海沟典型的俯冲变形特征具有许多特征。35 km以下以水平分量缩短和垂直分量延长为主，在36 ~ 70 km范围内以不同标志的变形马赛克分布为主。在更低的70-105 km深度范围内，变形类型与上层相反。恰帕斯地震发生在不同变形类型区域的边界，这表明震源西部的块体介质软化，东部的块体介质硬化。这样的岩石圈介质状态可能表明恰帕斯地震准备区存在变形阴影带。
{"title":"DEFORMATIONS IN THE MIDDLE AMERICA TRENCH ACCORDING TO EARTHQUAKE FOCAL MECHANISMS AND THEIR FEATURES IN THE AREA OF THE 2017 МW 8.2 CHIAPAS EARTHQUAKE, MEXICO","authors":"P. Dyadkov, O. Kuchay, Y. Romanenko, Z. S. Dzhumagaliyeva","doi":"10.5800/gt-2020-11-2-0477","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0477","url":null,"abstract":". Seismotectonic deformations in the Middle America Trench and their features in the area of preparation of the Chiapas earthquake, М W =8.2, 08 September 2017, were determined using the data on 2244 focal mechanisms of earthquakes for the period of 1977–2017. The distribution of seismicity with depth was studied in detail. The decrease in the depth of the Benioff zone in the north-western subduction segments and the increase in the south-eastern segments is associated with the age of the subducting parts of the Cocos plate and the angle of their immersion. The latter mechanism can also explain the presence of earthquakes with normal focal mechanism on the oceanic uplift in the south-eastern segments of the subduction zone and their absence in the north-western ones. In general, the typical character of subduction deformations has a number of features in the Middle America Trench. The predominance of shortening by horizontal components and elongation by vertical ones at depths up to 35 km is replaced by the transitional type with mosaic distribution of deformations of different signs in the depth range of 36–70 km. Even lower, in the depth range of 70–105 km, the type of deformation changes to the opposite with respect to the upper horizon. The Chiapas earthquake occurred on the border of regions with different types of deformation, which indicates softening of the block’s medium to the west of the hypocenter and its hardening to the east. Such a state of the lithospheric medium may indicate the presence of a deformation shadow zone in the Chiapas earthquake preparation area.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87929620","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 : 2020-06-20DOI: 10.5800/gt-2020-11-2-0479
V. Bragin, L. Sverdlik
The RAS Research Station started geodynamical research at the Bishkek Geodynamic Test Area (BGTA) in 1980s. This test area is located in the Northern Tien Shan, one of most seismically active zones of Central Asia. The distribution patterns of crustal deformation in space and time are investigated by a complex of geophysical, seismological and geodesic methods. Long-offset transient electromagnetic (LOTEM) technique is an important component of the geophysical research carried out at BGTA with the focus on forecasting of seismic activity dynamics. LOTEM is considered to be one of the most informative methods for obtaining data on multilayered conductive anisotropic geologic environment. This article presents the results of integrated interpretation of LOTEM sounding data recorded at permanent electromagnetic monitoring stations, Ak-Suu and Shavai. The time series of specific electrical resistance are analyzed to reveal a correlation with the stress-strain state of the geologic environment and seismic process in the study region in the period from January 2016 to October 2018. It is established that the deformation process taking place at a depth of more than 8.0 km is reflected in the time series of specific electrical resistance in the form of bay-shaped negative variations. A decrease of apparent resistance is observed when the receiver dipoles of the measurement unit are arranged in the meridian (N-S) direction. The periods of compression in the submeridional direction coincide with the periods with the highest density of seismic events. A comparison of earthquake hypocenter locations against the topographic relief and the data on regional faults shows the maximum density of hypocenters at the axial parts of Northern Tien Shan ridges.
{"title":"ESTIMATES OF RELATIONSHIP BETWEEN THE DYNAMICS OF GEOPHYSICAL PARAMETERS AND THE STRESS-STRAIN STATE OF GEOENVIRONMENT","authors":"V. Bragin, L. Sverdlik","doi":"10.5800/gt-2020-11-2-0479","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0479","url":null,"abstract":"The RAS Research Station started geodynamical research at the Bishkek Geodynamic Test Area (BGTA) in 1980s. This test area is located in the Northern Tien Shan, one of most seismically active zones of Central Asia. The distribution patterns of crustal deformation in space and time are investigated by a complex of geophysical, seismological and geodesic methods. Long-offset transient electromagnetic (LOTEM) technique is an important component of the geophysical research carried out at BGTA with the focus on forecasting of seismic activity dynamics. LOTEM is considered to be one of the most informative methods for obtaining data on multilayered conductive anisotropic geologic environment. This article presents the results of integrated interpretation of LOTEM sounding data recorded at permanent electromagnetic monitoring stations, Ak-Suu and Shavai. The time series of specific electrical resistance are analyzed to reveal a correlation with the stress-strain state of the geologic environment and seismic process in the study region in the period from January 2016 to October 2018. It is established that the deformation process taking place at a depth of more than 8.0 km is reflected in the time series of specific electrical resistance in the form of bay-shaped negative variations. A decrease of apparent resistance is observed when the receiver dipoles of the measurement unit are arranged in the meridian (N-S) direction. The periods of compression in the submeridional direction coincide with the periods with the highest density of seismic events. A comparison of earthquake hypocenter locations against the topographic relief and the data on regional faults shows the maximum density of hypocenters at the axial parts of Northern Tien Shan ridges.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85931209","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 : 2020-06-20DOI: 10.5800/gt-2020-11-2-0475
I. V. Buchko, A. Rodionov, E. Salnikova
. The first geochronological data have been obtained for Amnunakta massif composed of monzogabbro-monzodiorite and located in the southeastern part of the Selenga-Stanovoy superterrane. It was found that the age of Amnunakta massif (240 ± 1 Ma) is almost similar to that of quartz porphyry of the Kuitun formation and alkaline granites of the Nerchugan complex, which were sampled from the eastern flank of the Selenga-Vitim Volcano-Plutonic belt. Taking into account the geological position and geochemical features of the Amnunakta massif, there are grounds to suggest that the formation of this massif (as well as of quartz porphyry of the Kuitun formation and alkaline granites of the Nerchugan complex) was associated with one of the impulses of bimodal intraplate magmatism during the evolution of the Selenga-Vitim belt.
{"title":"AGE OF THE AMNUNAKTA MONZOGABBRO-MONZODIORITE MASSIF IN THE SOUTHERN FRAMING OF THE SIBERIAN CRATON","authors":"I. V. Buchko, A. Rodionov, E. Salnikova","doi":"10.5800/gt-2020-11-2-0475","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0475","url":null,"abstract":". The first geochronological data have been obtained for Amnunakta massif composed of monzogabbro-monzodiorite and located in the southeastern part of the Selenga-Stanovoy superterrane. It was found that the age of Amnunakta massif (240 ± 1 Ma) is almost similar to that of quartz porphyry of the Kuitun formation and alkaline granites of the Nerchugan complex, which were sampled from the eastern flank of the Selenga-Vitim Volcano-Plutonic belt. Taking into account the geological position and geochemical features of the Amnunakta massif, there are grounds to suggest that the formation of this massif (as well as of quartz porphyry of the Kuitun formation and alkaline granites of the Nerchugan complex) was associated with one of the impulses of bimodal intraplate magmatism during the evolution of the Selenga-Vitim belt.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84317398","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 : 2020-06-20DOI: 10.5800/gt-2020-11-2-0484
K. Seminsky, S. Bornyakov, A. Bobrov, A. Shagun
The complex of geophysical methods was successfully applied in the Alakit-Markha kimberlite field of the Yakutsk diamondiferous province. A pipe was identified in the local forecast area specified within the field at the previous stage of prospecting. The studies using electric tomography (ET), radon survey (RS) and microseismic sounding (MS) covered an area of ≈1000⨯500 m. Based on the jointly processed ET and RS plan images and MS profiles, a tubular body was detected in the sedimentary cover. It is confined to a fault node and stands out among the host rocks by low electrical resistivity, increased soil radon concentrations and high spectral ratios of the horizontal and vertical components of microseisms. Its complex shape is manifested at the ground surface by two isometric structures (each being several hundred meters long), which jointly form a dike-like body at a depth of ≈40 m, as shown by the electrical tomography images. According to the MS data, its root part is detected to comprise one or two fractured narrow zones that are traceable to a depth of 2 km and below. The structure of the identified body and its chemical composition will be determined after exploratory drilling is complete. Today there are grounds to conclude that using ET, RS and MS methods jointly as a complex described in the article proved effective for identifying pipes controlled by fault zones in the sedimentary cover areas.
{"title":"EXPERIENCE OF USING ELECTRICAL TOMOGRAPHY, RADON SURVEY AND MICROSEISMIC SOUNDING IN SEARCH FOR PIPES CONTROLLED BY FAULT ZONES","authors":"K. Seminsky, S. Bornyakov, A. Bobrov, A. Shagun","doi":"10.5800/gt-2020-11-2-0484","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0484","url":null,"abstract":"The complex of geophysical methods was successfully applied in the Alakit-Markha kimberlite field of the Yakutsk diamondiferous province. A pipe was identified in the local forecast area specified within the field at the previous stage of prospecting. The studies using electric tomography (ET), radon survey (RS) and microseismic sounding (MS) covered an area of ≈1000⨯500 m. Based on the jointly processed ET and RS plan images and MS profiles, a tubular body was detected in the sedimentary cover. It is confined to a fault node and stands out among the host rocks by low electrical resistivity, increased soil radon concentrations and high spectral ratios of the horizontal and vertical components of microseisms. Its complex shape is manifested at the ground surface by two isometric structures (each being several hundred meters long), which jointly form a dike-like body at a depth of ≈40 m, as shown by the electrical tomography images. According to the MS data, its root part is detected to comprise one or two fractured narrow zones that are traceable to a depth of 2 km and below. The structure of the identified body and its chemical composition will be determined after exploratory drilling is complete. Today there are grounds to conclude that using ET, RS and MS methods jointly as a complex described in the article proved effective for identifying pipes controlled by fault zones in the sedimentary cover areas.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85142201","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 : 2020-03-19DOI: 10.5800/gt-2020-11-1-0460
L. A. Sim
Spatial reconstruction of tectonic stresses within the Subpolar Ural quartz crystal-containing province was conducted by the kinematic method [Gushchenko, 1973, 1979] based on the main indicators of tectonic stresses on slickensides. Local stress states (LSS) and general stress fields for large blocks were reconstructed by the method described in [Sim, Marinin, 2015]. In the blocks with numerous occurrences of quartz crystal (Pelingichey and Omega-Shor blocks), the general stress fields is characterized by a stress state close to uniaxial tension, i.e. the Lode-Nadai coefficient µ=–1. In these blocks, thick quartz veins are perpendicular to the tension axis of the general stress field. In the block without quartz crystal (West Saled), the general stress field is characterized by a triaxial stress state or pure shear state (–1˂µσ˂+1). The LSS of the quartz crystal deposits show the following: the stress state of µ=–1 is typical of quartz veins without quartz crystal nests, and a special kind of stress state is reconstructed near the nests with piezoelectric material. It is named a variation of the type of stress state (VTSS), which means that within one tectonic stage, the type of stress state changes approximately as follows: µσ=+1 (40 %), µσ=–1 (40 %), and –1˂µσ˂+1. It means that in the piezoelectric mineral deposits, pulsating tectonic stresses provided for a fluid flow of hydrothermal solutions at the intersection of ore-bearing and ore-controling faults when tension (µ=–1) was replaced with compression (µ=+1), while the orientations of compression and tension axes remained unchanged. Apparently, such a regime was caused by alternating activation of the above-mentioned faults. The tectonic stress reconstructions were performed for 33 mineral deposits and occurrences of quartz crystal. VTSS was determined in 32 deposits; one mineral occurrence is characterized by uniaxial tension. Therefore, we propose using VTSS (variation of the type of stress state) as a criterion for predicting the locations of quartz crystal deposits.
{"title":"Tectonophysical criteria for forecasting the locations of quartz crystal deposits (case of Subpolar Ural)","authors":"L. A. Sim","doi":"10.5800/gt-2020-11-1-0460","DOIUrl":"https://doi.org/10.5800/gt-2020-11-1-0460","url":null,"abstract":"Spatial reconstruction of tectonic stresses within the Subpolar Ural quartz crystal-containing province was conducted by the kinematic method [Gushchenko, 1973, 1979] based on the main indicators of tectonic stresses on slickensides. Local stress states (LSS) and general stress fields for large blocks were reconstructed by the method described in [Sim, Marinin, 2015]. In the blocks with numerous occurrences of quartz crystal (Pelingichey and Omega-Shor blocks), the general stress fields is characterized by a stress state close to uniaxial tension, i.e. the Lode-Nadai coefficient µ=–1. In these blocks, thick quartz veins are perpendicular to the tension axis of the general stress field. In the block without quartz crystal (West Saled), the general stress field is characterized by a triaxial stress state or pure shear state (–1˂µσ˂+1). The LSS of the quartz crystal deposits show the following: the stress state of µ=–1 is typical of quartz veins without quartz crystal nests, and a special kind of stress state is reconstructed near the nests with piezoelectric material. It is named a variation of the type of stress state (VTSS), which means that within one tectonic stage, the type of stress state changes approximately as follows: µσ=+1 (40 %), µσ=–1 (40 %), and –1˂µσ˂+1. It means that in the piezoelectric mineral deposits, pulsating tectonic stresses provided for a fluid flow of hydrothermal solutions at the intersection of ore-bearing and ore-controling faults when tension (µ=–1) was replaced with compression (µ=+1), while the orientations of compression and tension axes remained unchanged. Apparently, such a regime was caused by alternating activation of the above-mentioned faults. The tectonic stress reconstructions were performed for 33 mineral deposits and occurrences of quartz crystal. VTSS was determined in 32 deposits; one mineral occurrence is characterized by uniaxial tension. Therefore, we propose using VTSS (variation of the type of stress state) as a criterion for predicting the locations of quartz crystal deposits.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74363754","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 : 2020-03-19DOI: 10.5800/gt-2020-11-1-0462
A. Sobisevich, L. Sobisevich, D. Likhodeev
Observations reflecting the structure and conditions of the seismogravitational process in the lithosphere were analyzed using the data on the catastrophic tsunamigenic earthquake of Maule (Chile) [Sobisevich et al., 2019]. Seismogravitational processes were first identified by a group of Soviet scientists from the city of Leningrad (now St. Petersburg) under the leadership of Professor E.M. Linkov [Linkov et al., 1982, 1990]. The study of these processes continues at the North Caucasus Geophysical Observatory of IPE RAS, which was established in 2004. Experiments are carried out using unique quartz tiltmeters designed by D.G. Gridnev, which ensure the stable registration of long–period seismogravitational processes on the scale of the Earth [Sobisevich, 2013; Sobisevich et al., 2017].
利用智利Maule (Chile)灾难性海啸地震资料，分析了反映岩石圈地震重力过程结构和条件的观测结果[Sobisevich et al.， 2019]。在E.M. Linkov教授的领导下，来自列宁格勒(现在的圣彼得堡)的一组苏联科学家首先发现了地震引力过程[Linkov等人，1982,1990]。2004年建立的北高加索地球物理观测站继续对这些过程进行研究。实验使用D.G. Gridnev设计的独特石英倾斜仪进行，确保了地球尺度上长周期地震重力过程的稳定配准[Sobisevich, 2013;Sobisevich et al.， 2017]。
{"title":"Seismogravitational processes accompanying the evolution of seismic focal structures in the lithosphere","authors":"A. Sobisevich, L. Sobisevich, D. Likhodeev","doi":"10.5800/gt-2020-11-1-0462","DOIUrl":"https://doi.org/10.5800/gt-2020-11-1-0462","url":null,"abstract":"Observations reflecting the structure and conditions of the seismogravitational process in the lithosphere were analyzed using the data on the catastrophic tsunamigenic earthquake of Maule (Chile) [Sobisevich et al., 2019]. Seismogravitational processes were first identified by a group of Soviet scientists from the city of Leningrad (now St. Petersburg) under the leadership of Professor E.M. Linkov [Linkov et al., 1982, 1990]. The study of these processes continues at the North Caucasus Geophysical Observatory of IPE RAS, which was established in 2004. Experiments are carried out using unique quartz tiltmeters designed by D.G. Gridnev, which ensure the stable registration of long–period seismogravitational processes on the scale of the Earth [Sobisevich, 2013; Sobisevich et al., 2017].","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86918867","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 : 2020-03-19DOI: 10.5800/gt-2020-11-1-0459
Y. Rebetsky
The current state of crustal stresses in the Caucasus and adjacent territories has been reconstructed. Stress inversion was performed by the cataclastic analysis of earthquake focal mechanisms considered as seismological strain indicators. The data were taken from the unified catalogue of focal mechanisms of the Northern Eurasia, which was consolidated by the Laboratory of Tectonophysics of IPE RAS in the early 1990s. It contains the information from many seismological data sources of various authors who worked both in the USSR and abroad. Seismological data for the last years after the collapse of the USSR were taken from Global CMT catalogue. The study area has been quite densely covered by reconstructions of the principal stress axes. At the same time, the area of stress averaging has been considerably reduced by the iterative use of a window for stress averaging, which was gradually expanded for zones with reduced densities of earthquake epicenters. The revealed regularities of the current stress field based on the unified catalogue of focal mechanisms collected by different authors correlate with the reconstructions performed according to the Global CMT catalogue. The cataclastic analysis of displacements along fractures allowed estimating the stress magnitudes, and the crust of the study area was zoned with respect to the intensity of normalized values of the lowest and highest stresses of horizontal compression, as well as to the normalized values of shear stresses acting on the crustal basement. In all cases, the values were normalized to the rock strength. The stress parameters are presented in “Tectonic Stresses of Eurasia”. This new Internet resource created by the Laboratory of Tectonophysics on the IPE RAS website shows the stress data in different scales and levels of details.
{"title":"The current state of crustal stresses in the Caucasus according to the unified catalogue of earthquake focal mechanisms","authors":"Y. Rebetsky","doi":"10.5800/gt-2020-11-1-0459","DOIUrl":"https://doi.org/10.5800/gt-2020-11-1-0459","url":null,"abstract":"The current state of crustal stresses in the Caucasus and adjacent territories has been reconstructed. Stress inversion was performed by the cataclastic analysis of earthquake focal mechanisms considered as seismological strain indicators. The data were taken from the unified catalogue of focal mechanisms of the Northern Eurasia, which was consolidated by the Laboratory of Tectonophysics of IPE RAS in the early 1990s. It contains the information from many seismological data sources of various authors who worked both in the USSR and abroad. Seismological data for the last years after the collapse of the USSR were taken from Global CMT catalogue. The study area has been quite densely covered by reconstructions of the principal stress axes. At the same time, the area of stress averaging has been considerably reduced by the iterative use of a window for stress averaging, which was gradually expanded for zones with reduced densities of earthquake epicenters. The revealed regularities of the current stress field based on the unified catalogue of focal mechanisms collected by different authors correlate with the reconstructions performed according to the Global CMT catalogue. The cataclastic analysis of displacements along fractures allowed estimating the stress magnitudes, and the crust of the study area was zoned with respect to the intensity of normalized values of the lowest and highest stresses of horizontal compression, as well as to the normalized values of shear stresses acting on the crustal basement. In all cases, the values were normalized to the rock strength. The stress parameters are presented in “Tectonic Stresses of Eurasia”. This new Internet resource created by the Laboratory of Tectonophysics on the IPE RAS website shows the stress data in different scales and levels of details.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89902042","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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