Pub Date : 2020-09-23DOI: 10.5800/gt-2020-11-3-0486
T. Romanyuk, N. Kuznetsov, S. Rud’ko, A. A. Kolesnikova, D. V. Moskovsky, A. S. Dubensky, V. Sheshukov, S. Lyapunov
The article presents the results of U-Pb isotope dating of detrital zircons from the Jurassic coarse rocks in the apex and the western slope of Mnt. Biyuk-Sinor (the southern wall of the Baidar basin, near the village of Orlinoe). These dates are compared with the detrital zircon dates obtained for sandy rocks from the Upper Jurassic coarse clastic strata composing the slopes of Mnt. Spilia near Balaklava Harbor and Mnt. Southern Demerdzhi near Alushta city, as well as the Middle Jurassic Bitak conglomerates near the village of Strogonovka (suburb of Simferopol city). The comparison shows a high degree of similarity of the averaged age characteristics of the main detrital zircon populations. Sandy rocks of Jurassic coarse clastic strata for zircon dating were sampled in four locations of the Mountaineous Crimea. Based on their dates and a summary set of ages of detrital zircon grains from sandstones of the Southern Coast of Crimea, spanning the stratigraphic interval from the Middle Jurassic to Neogene, we can provide a statistically reliable specification of the Carboniferous-Triassic time interval (360–200 Ma) of magmatic activity within the Black Sea region. This period was bounded in time by the Late Devonian and Early Jurassic relative magmatic lulls. None of the zircon grains of the Carboniferous-Triassic age has revealed Hf-isotopic characteristics indicating any significant contribution of crustal material older than the Mesoproterozoic into the protolith of the parent zircon rocks. Within the Carboniferous-Triassic interval of magmatic activity, three stages are distinguished: (I) 360–315 Ma, (II) 315–270 Ma, and (III) 270–200 Ma. Magmatic stage I (360–315 Ma) is related to the closure of the Reik ocean, which completed after the subducted slab ‘broke off’ into the mantle and was accompanied by the ubiquitously manifested HT-LP metamorphism. Zircon grains of stage I are characterized by peak ages of about 325–340 Ma and the dominance of negative eHf. Magmatic stages II (315–270 Ma) and III (270–200 Ma) correlate with functioning of the Scythian-Pontian volcanic suprasubduction belt. In these magmatic stages, zircon eHf values scatter from weakly negative to substantially positive (referred to the depleted mantle), which is typical for volcanic arcs. Fuzzy separation of stages II and III and strong variability of the peak ages of zircons from the studied samples (which we associate with these stages) can be due both to changes in magmatic activity in different segments of the belt, and to changes in the erosion intensity of crystalline complexes of the belt during the subsequent stages evolution caused by tectonic rearrangements within the Paleo-Tethys ocean and its peri-oceanic structures.
{"title":"Stages of Carboniferous-Triassic magmatism in the Black Sea region based on isotope-geochronological study of detrital zircons from jurassic coarse clastic strata of the Mountainous Crimea","authors":"T. Romanyuk, N. Kuznetsov, S. Rud’ko, A. A. Kolesnikova, D. V. Moskovsky, A. S. Dubensky, V. Sheshukov, S. Lyapunov","doi":"10.5800/gt-2020-11-3-0486","DOIUrl":"https://doi.org/10.5800/gt-2020-11-3-0486","url":null,"abstract":"The article presents the results of U-Pb isotope dating of detrital zircons from the Jurassic coarse rocks in the apex and the western slope of Mnt. Biyuk-Sinor (the southern wall of the Baidar basin, near the village of Orlinoe). These dates are compared with the detrital zircon dates obtained for sandy rocks from the Upper Jurassic coarse clastic strata composing the slopes of Mnt. Spilia near Balaklava Harbor and Mnt. Southern Demerdzhi near Alushta city, as well as the Middle Jurassic Bitak conglomerates near the village of Strogonovka (suburb of Simferopol city). The comparison shows a high degree of similarity of the averaged age characteristics of the main detrital zircon populations. Sandy rocks of Jurassic coarse clastic strata for zircon dating were sampled in four locations of the Mountaineous Crimea. Based on their dates and a summary set of ages of detrital zircon grains from sandstones of the Southern Coast of Crimea, spanning the stratigraphic interval from the Middle Jurassic to Neogene, we can provide a statistically reliable specification of the Carboniferous-Triassic time interval (360–200 Ma) of magmatic activity within the Black Sea region. This period was bounded in time by the Late Devonian and Early Jurassic relative magmatic lulls. None of the zircon grains of the Carboniferous-Triassic age has revealed Hf-isotopic characteristics indicating any significant contribution of crustal material older than the Mesoproterozoic into the protolith of the parent zircon rocks. Within the Carboniferous-Triassic interval of magmatic activity, three stages are distinguished: (I) 360–315 Ma, (II) 315–270 Ma, and (III) 270–200 Ma. Magmatic stage I (360–315 Ma) is related to the closure of the Reik ocean, which completed after the subducted slab ‘broke off’ into the mantle and was accompanied by the ubiquitously manifested HT-LP metamorphism. Zircon grains of stage I are characterized by peak ages of about 325–340 Ma and the dominance of negative eHf. Magmatic stages II (315–270 Ma) and III (270–200 Ma) correlate with functioning of the Scythian-Pontian volcanic suprasubduction belt. In these magmatic stages, zircon eHf values scatter from weakly negative to substantially positive (referred to the depleted mantle), which is typical for volcanic arcs. Fuzzy separation of stages II and III and strong variability of the peak ages of zircons from the studied samples (which we associate with these stages) can be due both to changes in magmatic activity in different segments of the belt, and to changes in the erosion intensity of crystalline complexes of the belt during the subsequent stages evolution caused by tectonic rearrangements within the Paleo-Tethys ocean and its peri-oceanic structures.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73408765","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 : 2020-09-23DOI: 10.5800/gt-2020-11-3-0489
E. Dubinin, A. Grokholsky
. The study was focused on the tectonic structure features of the Gulf of Aden, which includes three provinces. The western, central and eastern provinces differ in morphostructural segmentation of the spreading ridge of the Gulf of Aden, which took place in different geodynamic regimes of their formation and development. In our study, physical modeling was performed to investigate the segmentation mechanisms of the three parts and the formation of the marginal plateau and the island of Socotra. In experiments, an elastic-plastic plate lying on a liquid base (simulating melt) was subjected to normal or oblique stretchig. Plate sections imitating the continental or oceanic lithosphere in the model had different thicknesses. Various heterogeneities, such as cuts, linear weakened zones (rift heating zones) etc., were set in the plate sections in accordance with natural analogues. The modeling results show that morphostructural segmentation of the spreading axis in the Gulf of Aden depends on the degree of heating and the thickness of the lithosphere, associated with different distances from the Afar plume and local thermal anomalies, spreading obliquity and the existence of structural inhomogeneities with increased lithosphere strength, which are associated in this case with the presence of Mesozoic grabens on the pre-breakup basement. The smaller is the lithosphere thickness, the smaller is the size of the segments. The sharper is the angle, the more pronounced is segmentation. The study of the connection of the Gulf of Aden continental rift with the rift zone of the Carlsberg ridge suggests that during their development, these rift fractures propagated towards each other. The experiment results show that in case of a «sharp» boundary between blocks that differ in thickness, a shear zone is likely to occur. Such a case is applicable, for example, to the Alula-Fartak fracture zone, or to Owen’s fracture zone. With a less ‘sharp’ boundary, overlapping structures are often formed, such as microplates or microblocks enclosed between two rift fissures. In such case, one microblock then dies, while the other develops into a spreading ridge. Apparently, such a microblock is represented by the marginal plateau and the island of Sokotra. As shown by the modeling, propagation of the two rifts towards each other was important for the formation of the plateau and the island of Socotra. Moreover, a significant role was played by the initial geometry of the rift zones and their initial positioning separate from each other. the Arabia and Somalia plates started ≈20 Ma ago, shortly before anomaly 6 (19.7 Ma), the oldest magnetic anomaly recognized in the Gulf of Aden; ( б–г ) – fast propagation (350 km/Ma on average) of the rift fault to the west and the formation of the oceanic crust all along the Gulf of Aden. The Sheba ridge propagation in most of the Gulf of Aden was completed at chron 5C (16.0 Ma); ( д ) – current position of the spreading ridge.
{"title":"Specific features of structure formation during the development of the lithosphere of the Gulf of Aden (physical modeling)","authors":"E. Dubinin, A. Grokholsky","doi":"10.5800/gt-2020-11-3-0489","DOIUrl":"https://doi.org/10.5800/gt-2020-11-3-0489","url":null,"abstract":". The study was focused on the tectonic structure features of the Gulf of Aden, which includes three provinces. The western, central and eastern provinces differ in morphostructural segmentation of the spreading ridge of the Gulf of Aden, which took place in different geodynamic regimes of their formation and development. In our study, physical modeling was performed to investigate the segmentation mechanisms of the three parts and the formation of the marginal plateau and the island of Socotra. In experiments, an elastic-plastic plate lying on a liquid base (simulating melt) was subjected to normal or oblique stretchig. Plate sections imitating the continental or oceanic lithosphere in the model had different thicknesses. Various heterogeneities, such as cuts, linear weakened zones (rift heating zones) etc., were set in the plate sections in accordance with natural analogues. The modeling results show that morphostructural segmentation of the spreading axis in the Gulf of Aden depends on the degree of heating and the thickness of the lithosphere, associated with different distances from the Afar plume and local thermal anomalies, spreading obliquity and the existence of structural inhomogeneities with increased lithosphere strength, which are associated in this case with the presence of Mesozoic grabens on the pre-breakup basement. The smaller is the lithosphere thickness, the smaller is the size of the segments. The sharper is the angle, the more pronounced is segmentation. The study of the connection of the Gulf of Aden continental rift with the rift zone of the Carlsberg ridge suggests that during their development, these rift fractures propagated towards each other. The experiment results show that in case of a «sharp» boundary between blocks that differ in thickness, a shear zone is likely to occur. Such a case is applicable, for example, to the Alula-Fartak fracture zone, or to Owen’s fracture zone. With a less ‘sharp’ boundary, overlapping structures are often formed, such as microplates or microblocks enclosed between two rift fissures. In such case, one microblock then dies, while the other develops into a spreading ridge. Apparently, such a microblock is represented by the marginal plateau and the island of Sokotra. As shown by the modeling, propagation of the two rifts towards each other was important for the formation of the plateau and the island of Socotra. Moreover, a significant role was played by the initial geometry of the rift zones and their initial positioning separate from each other. the Arabia and Somalia plates started ≈20 Ma ago, shortly before anomaly 6 (19.7 Ma), the oldest magnetic anomaly recognized in the Gulf of Aden; ( б–г ) – fast propagation (350 km/Ma on average) of the rift fault to the west and the formation of the oceanic crust all along the Gulf of Aden. The Sheba ridge propagation in most of the Gulf of Aden was completed at chron 5C (16.0 Ma); ( д ) – current position of the spreading ridge.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84499626","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 : 2020-09-23DOI: 10.5800/gt-2020-11-3-0493
K. Ghazaryan, R. Sargsyan
The study is focused on searching for spatial regularities in the occurrence of earthquake hypocenters in different geological settings in Northern Armenia. Tectonic-geomorphological indices are applied to define the tectonic activity of blocks composing the study area, which was manifested within a long period of time, starting from the neotectonic development period. The blocks are classified accordingly. The regional seismic activity is analysed considering the block structure of the study area. Earthquake focal mechanisms are determined, and dominant displacement trends are identified. Based on the comparative analysis of the blocks’ tectonic activity indicators and the locations of seismic events differing in strength, regular patterns of spatial distribution of seismic events are identified. It is established that the earthquake hypocenters of different strength occur in certain block structures; and the predominant types of movements in the earthquake hypocenters are largely determined by types of fault structures. It is emphasized that investigating the blocks’ neotectonic activity is important for discovering the general patterns of spatial distribution of seismic events.
{"title":"General regularities of seismic activity of Northern Armenia in connection with block structure and tectonic activity","authors":"K. Ghazaryan, R. Sargsyan","doi":"10.5800/gt-2020-11-3-0493","DOIUrl":"https://doi.org/10.5800/gt-2020-11-3-0493","url":null,"abstract":"The study is focused on searching for spatial regularities in the occurrence of earthquake hypocenters in different geological settings in Northern Armenia. Tectonic-geomorphological indices are applied to define the tectonic activity of blocks composing the study area, which was manifested within a long period of time, starting from the neotectonic development period. The blocks are classified accordingly. The regional seismic activity is analysed considering the block structure of the study area. Earthquake focal mechanisms are determined, and dominant displacement trends are identified. Based on the comparative analysis of the blocks’ tectonic activity indicators and the locations of seismic events differing in strength, regular patterns of spatial distribution of seismic events are identified. It is established that the earthquake hypocenters of different strength occur in certain block structures; and the predominant types of movements in the earthquake hypocenters are largely determined by types of fault structures. It is emphasized that investigating the blocks’ neotectonic activity is important for discovering the general patterns of spatial distribution of seismic events.","PeriodicalId":44925,"journal":{"name":"Geodynamics & Tectonophysics","volume":null,"pages":null},"PeriodicalIF":0.7,"publicationDate":"2020-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77294182","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-2020-11-2-0470
V. Andreichev, A. Soboleva, O. Udoratina, Y. Ronkin, M. Coble, E. Miller
. The Northern Timan is an uplifted block of Late Precambrian basement of the Timan Ridge, where Neoproterozoic sedimentary-metamorphic rocks of the Barmin Group are cut by intrusive rocks of different composition and all unconformably overlain by Lower Silurian limestone. To determine the age of granites, U-Pb dating of zircons was carried out using secondary ion mass spectrometry (SIMS). Two episodes of Neoproterozoic granite magmatism were es-tablished. Granite rocks of the Bolshoy Kameshek (613 ± 6 Ma) and Cape Bolshoy Rumyanichny (614 ± 11 Ma) plutons are interpreted to be associated with the formation of Central Iapetus Magmatic Province and record the Ediacaran stage of Rodinia breakup. The granites of the Sopki Kamennyie pluton (723‒727 Ma) formed in Cryogenian time and are assumed to represent an earlier episode of Rodinia breakup. Their ages correlate with the age of the Franklin LIP that existed in Northern Laurentia and is believed to have spread to South Siberia.
{"title":"GRANITES OF THE NORTHERN TIMAN – PROBABLE INDICATORS OF NEOPROTEROZOIC STAGES OF RODINIA BREAKUP","authors":"V. Andreichev, A. Soboleva, O. Udoratina, Y. Ronkin, M. Coble, E. Miller","doi":"10.5800/gt-2020-11-2-0470","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0470","url":null,"abstract":". The Northern Timan is an uplifted block of Late Precambrian basement of the Timan Ridge, where Neoproterozoic sedimentary-metamorphic rocks of the Barmin Group are cut by intrusive rocks of different composition and all unconformably overlain by Lower Silurian limestone. To determine the age of granites, U-Pb dating of zircons was carried out using secondary ion mass spectrometry (SIMS). Two episodes of Neoproterozoic granite magmatism were es-tablished. Granite rocks of the Bolshoy Kameshek (613 ± 6 Ma) and Cape Bolshoy Rumyanichny (614 ± 11 Ma) plutons are interpreted to be associated with the formation of Central Iapetus Magmatic Province and record the Ediacaran stage of Rodinia breakup. The granites of the Sopki Kamennyie pluton (723‒727 Ma) formed in Cryogenian time and are assumed to represent an earlier episode of Rodinia breakup. Their ages correlate with the age of the Franklin LIP that existed in Northern Laurentia and is believed to have spread to South Siberia.","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":"77169544","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-2020-11-2-0476
S. Sokolov, N. Chamov, M. Khutorskoy, S. Silantiev
Seismicity, heat flow, seismic tomography data, prerift and synrift magmatism are considered as intensity indicators of geodynamic processes along the Atlantic-Arctic rift system (AARS). In this rift system, several large (over 100 km ) sub-latitudinal displacements of the rift axis are due to left-lateral strike-slip faulting. The AARS segments are distinguished by the age of splitting of continental plates from each other. A dependence is revealed between the current thermal state of the mantle under the AARS and the age of spreading start. This dependence is established from both seismic tomography and heat flow data. In section δ(Vp/Vs), the locations of the main segmenting faults and ‘cold’ anomalies in the upper mantle are coincident. Distributions of total seismic moments are practically synchronous in the depth intervals of 0–13, 13–35, and >35 km. The maximum values above the plumes are represented by higher seismic moments in the surface layer. The main demarcation zones differ in maximum energy release values in the AARS with shearing features. Comparison of these values against the age of the start of spreading processes shows trends of heat flow and medium field tomography in the AARS segments. The trends confirm the thermal interpretation of the seismic tomography data and suggest mantle cooling with age and a decrease in the mean temperatures of the mantle. The main factor causing the sublatitudinal asymmetry of heat flow in the AARS is the impact of Coriolis forces on the magma in the asthenospheric source. Most of the synrift igneous formations seem to be related to the influence of long-lived anomalies in the mantle, which had lower rates of magma generation than those typical of the formation of magmatic provinces. In conditions for spreading and the formation of the oceanic crust, the process followed the principle of energy cost minimization, and the prerift magmatic provinces with the pre-processed crust contributed to the choice and positioning of the AARS trajectory. The plume branches are imposed in the tomographic section and thus ‘concealing’ the relationship between the age and the thermal state. However, that does not change the trend to cooling of the mantle beneath the AARS, proportionally to the time since the start of spreading.
{"title":"INTENSITY INDICATORS OF GEODYNAMIC PROCESSES ALONG THE ATLANTIC-ARCTIC RIFT SYSTEM","authors":"S. Sokolov, N. Chamov, M. Khutorskoy, S. Silantiev","doi":"10.5800/gt-2020-11-2-0476","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0476","url":null,"abstract":"Seismicity, heat flow, seismic tomography data, prerift and synrift magmatism are considered as intensity indicators of geodynamic processes along the Atlantic-Arctic rift system (AARS). In this rift system, several large (over 100 km ) sub-latitudinal displacements of the rift axis are due to left-lateral strike-slip faulting. The AARS segments are distinguished by the age of splitting of continental plates from each other. A dependence is revealed between the current thermal state of the mantle under the AARS and the age of spreading start. This dependence is established from both seismic tomography and heat flow data. In section δ(Vp/Vs), the locations of the main segmenting faults and ‘cold’ anomalies in the upper mantle are coincident. Distributions of total seismic moments are practically synchronous in the depth intervals of 0–13, 13–35, and >35 km. The maximum values above the plumes are represented by higher seismic moments in the surface layer. The main demarcation zones differ in maximum energy release values in the AARS with shearing features. Comparison of these values against the age of the start of spreading processes shows trends of heat flow and medium field tomography in the AARS segments. The trends confirm the thermal interpretation of the seismic tomography data and suggest mantle cooling with age and a decrease in the mean temperatures of the mantle. The main factor causing the sublatitudinal asymmetry of heat flow in the AARS is the impact of Coriolis forces on the magma in the asthenospheric source. Most of the synrift igneous formations seem to be related to the influence of long-lived anomalies in the mantle, which had lower rates of magma generation than those typical of the formation of magmatic provinces. In conditions for spreading and the formation of the oceanic crust, the process followed the principle of energy cost minimization, and the prerift magmatic provinces with the pre-processed crust contributed to the choice and positioning of the AARS trajectory. The plume branches are imposed in the tomographic section and thus ‘concealing’ the relationship between the age and the thermal state. However, that does not change the trend to cooling of the mantle beneath the AARS, proportionally to the time since the start of spreading.","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":"83532164","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-2020-11-2-0478
Y. Gatinsky, T. Prokhorova, D. Rundquist
. Ample geologic and geophysical data provide the basis for distinguishing the 102–104° E geodivider in the North, Central and South Asia. The geodivider’s central part is confirmed by the data on seismicity, seismically active faults and the modern crust block structure. These data and historical and instrumentally identified earthquake epicenters were used for a more correct definition of the block boundaries and interblock zones in the central part of the geodivider and in its wings. Seismic energy is considerably increased (to 10 J) in the eastern part of the geodivider’s western wing, and rarely increased directly in the geodivider itself. Near the geodivider, a seismic energy increase is detected east of it only at the western border of the South-Eastern China Block. The authors analyzed deep seismic sections and constructed energy dissipation graphs along transects crossing the geodivider and its western wing. The analysis and the graphs show the predomination of left-lateral NW-striking slips in the north, thrusts to the east and southeast in the center, and right-lateral NE-striking slips in the south. The total seismic energy increases constantly to the west. In the central and northern segments of the geodivider’s central part and west of it, horizontal blocks displacements cause a direct influence on seismicity level increasing and changes in geodynamic regimes within the investigated territory of Central Asia. Changes in the horizontal displacement vector are accompanied by the change of tectonic strain regimes. Increased heat flow values to the east from the geodivider within the East Asian transit zone are probably related to the change of the geodynamic regimes in the same direction under the influence of the submerged Pacific slab. The data obtained by the Chinese and Russian researchers confirm delamination (stratification) processes in the Southeast Tibet crust during its interaction with the colder and thicker lithosphere of Southeast China, and displacement of its upper layers to the southeast and south, as we supposed in our earlier publications.
{"title":"CENTRAL ASIAN GEODYNAMIC REGIMES WEST AND EAST 102–104° GEODIVIDER","authors":"Y. Gatinsky, T. Prokhorova, D. Rundquist","doi":"10.5800/gt-2020-11-2-0478","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0478","url":null,"abstract":". Ample geologic and geophysical data provide the basis for distinguishing the 102–104° E geodivider in the North, Central and South Asia. The geodivider’s central part is confirmed by the data on seismicity, seismically active faults and the modern crust block structure. These data and historical and instrumentally identified earthquake epicenters were used for a more correct definition of the block boundaries and interblock zones in the central part of the geodivider and in its wings. Seismic energy is considerably increased (to 10 J) in the eastern part of the geodivider’s western wing, and rarely increased directly in the geodivider itself. Near the geodivider, a seismic energy increase is detected east of it only at the western border of the South-Eastern China Block. The authors analyzed deep seismic sections and constructed energy dissipation graphs along transects crossing the geodivider and its western wing. The analysis and the graphs show the predomination of left-lateral NW-striking slips in the north, thrusts to the east and southeast in the center, and right-lateral NE-striking slips in the south. The total seismic energy increases constantly to the west. In the central and northern segments of the geodivider’s central part and west of it, horizontal blocks displacements cause a direct influence on seismicity level increasing and changes in geodynamic regimes within the investigated territory of Central Asia. Changes in the horizontal displacement vector are accompanied by the change of tectonic strain regimes. Increased heat flow values to the east from the geodivider within the East Asian transit zone are probably related to the change of the geodynamic regimes in the same direction under the influence of the submerged Pacific slab. The data obtained by the Chinese and Russian researchers confirm delamination (stratification) processes in the Southeast Tibet crust during its interaction with the colder and thicker lithosphere of Southeast China, and displacement of its upper layers to the southeast and south, as we supposed in our earlier publications.","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":"85707210","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-2020-11-2-0480
K. Markovich
АBSTRACT. The paper presents the results of the study aimed at predicting velocities of modern vertical movements of the Earth’s crust, which used the approach developed by Professor G.I. Karataev. This approach is based on mathematical simulation of geological and geophysical phenomena and an axiomatic correlation model for predicting various parameters of the crust from the data on gravitational anomalies. We pioneer in using this approach to study the territory of Belarus on the basis of geodetic, geological, geophysical and seismological data, as well as modern models showing gravitational fields and topography. This paper presents regression equations between the modern vertical movement velocities, gravitational and magnetic fields, crust thickness, and topography data. These equations give reasonably accurate data for constructing a map of forecasted modern vertical movement velocities for the territory of Belarus. Our map proves that the approach based on a correlation model and a complex of geodetic, geological, geophysical and seismological data for predicting the modern vertical movement velocities is very promising and capable of improving the reliability of forecast mapping. It should be noted that other maps of modern vertical crustal movement velocities for territories, including the geostructural elements of different ages and different types, were constructed using the method of simple linear interpolation, which is highly likely to cause prediction errors. In such case, prediction of modern vertical crustal movement velocities should be based on established patterns and correlations between the crustal movements, geophysical fields, and development history of geological structures and their elements.
{"title":"PREDICTION OF VELOCITIES OF MODERN VERTICAL MOVEMENTS OF THE EARTH’S CRUST FROM GEODETIC, GEOPHYSICAL AND SEISMOLOGICAL DATA","authors":"K. Markovich","doi":"10.5800/gt-2020-11-2-0480","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0480","url":null,"abstract":"АBSTRACT. The paper presents the results of the study aimed at predicting velocities of modern vertical movements of the Earth’s crust, which used the approach developed by Professor G.I. Karataev. This approach is based on mathematical simulation of geological and geophysical phenomena and an axiomatic correlation model for predicting various parameters of the crust from the data on gravitational anomalies. We pioneer in using this approach to study the territory of Belarus on the basis of geodetic, geological, geophysical and seismological data, as well as modern models showing gravitational fields and topography. This paper presents regression equations between the modern vertical movement velocities, gravitational and magnetic fields, crust thickness, and topography data. These equations give reasonably accurate data for constructing a map of forecasted modern vertical movement velocities for the territory of Belarus. Our map proves that the approach based on a correlation model and a complex of geodetic, geological, geophysical and seismological data for predicting the modern vertical movement velocities is very promising and capable of improving the reliability of forecast mapping. It should be noted that other maps of modern vertical crustal movement velocities for territories, including the geostructural elements of different ages and different types, were constructed using the method of simple linear interpolation, which is highly likely to cause prediction errors. In such case, prediction of modern vertical crustal movement velocities should be based on established patterns and correlations between the crustal movements, geophysical fields, and development history of geological structures and their elements.","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":"80841991","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-2020-11-2-0483
Yanshuang Guo, Yanqun Zhuo, Peixun Liu, Shunyun Chen, Jin Ma
1. Fault meta-instability is a key observable deformation stage to identify seismic precursor information. 2. Local preslips or micro-ruptures happen in few segments of fault, but there is only one nucleation zone. 3. The preslip areas first occur in the segments of low volume strain, but fast instability of the fault starts in the high volume strain area. ABSTRACT. According to the steady state of fault and energy balance, we provided a new idea to observe the precursors for a stressed fault. The meta-instability (or sub-instability) state of a fault is defined as the transition phase from peak stress to critical stress of fast instability (earthquake generation) during a full period of slow loading and fast unloading. The accumulative deformation energy begins to release in this stage. Identifying its deformation before fast instability would be beneficial to obtain premonitory information, and to evaluate the seismic risks of tectonic regions. In this study, we emphasized to analyze deformation process of the meta-instable stage with stain tensor data from a straight precut fault in granite at a slow loading rate, and observed the tempo-spatial features during the full deformation process of the fault. Two types of tectonic zones and instabilities occur on the stick-slip fault. The low- and high-value segments in the volume strain component appear along the fault strike with a load increment. The former first weakens and then becomes initial energy release segments; the latter forms strong stress-interlocking areas and finally turns into the initial region of fast instability. And there are two stages in the entire instable process of the fault: the initial stage is associated with the release of the low volume strain segments, which means fault pre-slips, slow earthquakes or weak earthquakes. The second one characterizes a strong earthquake through the release of high volume strain parts. The rupture acceleration in the first stage promotes the generation of the second. Moreover, fault instability contains two types of strain adjustments along the fault: the front-like strain change along the transition segments from low- to high- strain portions with volume strain release, and the compressive strain pulse of fault instability after the volume strain release extends to a certain range with loading increment. In laboratory experiments, the front-type strain occurs about 12 seconds before fast fault instability; the compressive pulse initiates within less than 0.1 second, and then the fault turns quickly into a dynamic strain adjustment, which appears quasi-synchronously between different measurement points, and, finally, an earthquake is generated.
{"title":"EXPERIMENTAL STUDY OF OBSERVABLE DEFORMATION PROCESS IN FAULT META-INSTABILITY STATE BEFORE EARTHQUAKE GENERATION","authors":"Yanshuang Guo, Yanqun Zhuo, Peixun Liu, Shunyun Chen, Jin Ma","doi":"10.5800/gt-2020-11-2-0483","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0483","url":null,"abstract":"1. Fault meta-instability is a key observable deformation stage to identify seismic precursor information. 2. Local preslips or micro-ruptures happen in few segments of fault, but there is only one nucleation zone. 3. The preslip areas first occur in the segments of low volume strain, but fast instability of the fault starts in the high volume strain area. ABSTRACT. According to the steady state of fault and energy balance, we provided a new idea to observe the precursors for a stressed fault. The meta-instability (or sub-instability) state of a fault is defined as the transition phase from peak stress to critical stress of fast instability (earthquake generation) during a full period of slow loading and fast unloading. The accumulative deformation energy begins to release in this stage. Identifying its deformation before fast instability would be beneficial to obtain premonitory information, and to evaluate the seismic risks of tectonic regions. In this study, we emphasized to analyze deformation process of the meta-instable stage with stain tensor data from a straight precut fault in granite at a slow loading rate, and observed the tempo-spatial features during the full deformation process of the fault. Two types of tectonic zones and instabilities occur on the stick-slip fault. The low- and high-value segments in the volume strain component appear along the fault strike with a load increment. The former first weakens and then becomes initial energy release segments; the latter forms strong stress-interlocking areas and finally turns into the initial region of fast instability. And there are two stages in the entire instable process of the fault: the initial stage is associated with the release of the low volume strain segments, which means fault pre-slips, slow earthquakes or weak earthquakes. The second one characterizes a strong earthquake through the release of high volume strain parts. The rupture acceleration in the first stage promotes the generation of the second. Moreover, fault instability contains two types of strain adjustments along the fault: the front-like strain change along the transition segments from low- to high- strain portions with volume strain release, and the compressive strain pulse of fault instability after the volume strain release extends to a certain range with loading increment. In laboratory experiments, the front-type strain occurs about 12 seconds before fast fault instability; the compressive pulse initiates within less than 0.1 second, and then the fault turns quickly into a dynamic strain adjustment, which appears quasi-synchronously between different measurement points, and, finally, an earthquake is generated.","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":"78050106","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-2020-11-2-0482
A. Kirdyashkin, A. Kirdyashkin, V. Distanov, I. Gladkov
The study is focused on thermochemical mantle plumes with intermediate thermal power (1.15 < Ka < 1.9). Previously we have shown that these plumes are diamondiferous. Based on the laboratory modeling data, the flow structure of a melt in a plume conduit is represented. A plume melts out and ascends from the core – mantle boundary to the bottom of the continental lithosphere. The plume roof moves upwards in the lithosphere because of melting of the lithospheric matter at the plume roof and due to the effect of superlithostatic pressure on the roof, which causes motion in the lithosphere block above the plume roof. The latter manifests itself by uplifting of the ground surface above the plume. As the plume ascends through the lithosphere, the elevation of the surface increases until the plume ascends to critical level xкр, where an eruption conduit is formed. In our model, plume ascent velocity uпл is the rate of melting at the plume roof. Values of uпл and the ascent velocity of a spherical plume roof due to superlithostatic pressure U are calculated. Relationships are found between these velocities and the plume roof depth. The dependence of the velocity of the surface’s rise on the dynamic viscosity of the lithosphere block above the plume is obtained. A relationship is determined between the maximum surface elevation and the lithosphere viscosity. The elevation values are determined for different times and different lithosphere viscosities.The results of laboratory modeling of flow structure at the plume conduit/eruption conduit interface are presented. The flow was photographed (1) in the plane passing through the axes of the plume conduit and the eruption conduit; and (2) in case of the line-focus beam perpendicular to the axial plane. The photographs were used for measuring the flow velocities in the plume conduit and the eruption conduit. Corresponding Reynolds numbers and flow regimes are determined. The relation of dynamic pressure in the eruption conduit to that in the plume conduit is found for intermediate-power plumes. The melt flow velocity in the eruption conduit depends on superlithostatic pressure on the plume roof, plume diameter and kinematic viscosity of the melt. Its values are determined for different kinematic viscosities of melt.
研究重点为热化学地幔柱，热功率为中等(1.15 < Ka < 1.9)。之前我们已经证明这些羽流是钻石状的。在实验室模拟数据的基础上，描述了羽流管道中熔体的流动结构。地幔柱融化并从核心-地幔边界上升到大陆岩石圈的底部。地幔柱顶板在岩石圈内向上移动，主要是由于地幔柱顶板处岩石圈物质的熔融作用和地幔顶处的超静岩压力作用，使得地幔柱顶板上方的岩石圈块体发生运动。后者表现为地幔柱上方地表的抬升。当火山柱上升穿过岩石圈时，地表的高度增加，直到火山柱上升到临界水平xкр，在那里形成了一个喷发通道。在我们的模型中，烟羽上升速度uпл是烟羽顶部的融化速度。计算了uпл值和超静岩压力U作用下的球形羽顶上升速度。发现了这些速度与羽顶深度之间的关系。得到了地幔柱上方岩石圈块体的动态黏度与地表上升速度的关系。确定了最大地表高度与岩石圈粘度之间的关系。根据不同的时间和不同的岩石圈粘度，确定了海拔高度值。本文介绍了羽流管道/喷发管道界面流动结构的室内模拟结果。(1)在穿过羽流导管和喷发导管轴线的平面上对气流进行了拍摄;(2)垂直于轴向面的线聚焦光束。这些照片被用于测量羽流管道和喷发管道中的流速。确定了相应的雷诺数和流型。在中等强度的羽流中，发现了喷发导管内动压力与羽流导管内动压力的关系。熔体在喷发管道中的流动速度取决于羽顶的超静岩压力、羽管直径和熔体的运动粘度。它的值取决于熔体的不同运动粘度。
{"title":"GEODYNAMIC PROCESSES DURING ASCENT OF A PLUME WITH INTERMEDIATE THERMAL POWER THROUGH THE CONTINENTAL LITHOSPHERE AND DURING ITS ERUPTION ON THE SURFACE","authors":"A. Kirdyashkin, A. Kirdyashkin, V. Distanov, I. Gladkov","doi":"10.5800/gt-2020-11-2-0482","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0482","url":null,"abstract":"The study is focused on thermochemical mantle plumes with intermediate thermal power (1.15 < Ka < 1.9). Previously we have shown that these plumes are diamondiferous. Based on the laboratory modeling data, the flow structure of a melt in a plume conduit is represented. A plume melts out and ascends from the core – mantle boundary to the bottom of the continental lithosphere. The plume roof moves upwards in the lithosphere because of melting of the lithospheric matter at the plume roof and due to the effect of superlithostatic pressure on the roof, which causes motion in the lithosphere block above the plume roof. The latter manifests itself by uplifting of the ground surface above the plume. As the plume ascends through the lithosphere, the elevation of the surface increases until the plume ascends to critical level xкр, where an eruption conduit is formed. In our model, plume ascent velocity uпл is the rate of melting at the plume roof. Values of uпл and the ascent velocity of a spherical plume roof due to superlithostatic pressure U are calculated. Relationships are found between these velocities and the plume roof depth. The dependence of the velocity of the surface’s rise on the dynamic viscosity of the lithosphere block above the plume is obtained. A relationship is determined between the maximum surface elevation and the lithosphere viscosity. The elevation values are determined for different times and different lithosphere viscosities.The results of laboratory modeling of flow structure at the plume conduit/eruption conduit interface are presented. The flow was photographed (1) in the plane passing through the axes of the plume conduit and the eruption conduit; and (2) in case of the line-focus beam perpendicular to the axial plane. The photographs were used for measuring the flow velocities in the plume conduit and the eruption conduit. Corresponding Reynolds numbers and flow regimes are determined. The relation of dynamic pressure in the eruption conduit to that in the plume conduit is found for intermediate-power plumes. The melt flow velocity in the eruption conduit depends on superlithostatic pressure on the plume roof, plume diameter and kinematic viscosity of the melt. Its values are determined for different kinematic viscosities of melt.","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":"86579285","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-2020-11-2-0481
S. K. Pavlov, K. Chudnenko, A. Khromov
Physicochemical interactions in the water – porphyrite system in conditions of formation of nitrogen-rich hot springs were studied using computer simulation. Compositions of model solutions during such interactions are determined by a combined influence of the compositions of primary and secondary rock minerals. In the investigated interaction range, the solution actively processes large quantities of the primary rock in favor of secondary minerals, while dissolved components are accumulated in small amounts in the solution itself, and therefore the salinity is low. The intervals of the formation of hydrosilicate, bicarbonate and sulfate sodium solutions are clearly distinguished in the process of irreversible hydrolytic transformation of porphyrite. In a certain range of interactions, the compositions of the model solutions are well comparable with the compositions of natural high-fluoride hot springs. Nitrogen-rich hot springs are strongly influenced by meteogenic factors detectable by detailed and/or sufficiently long-term observations. In deep and surface conditions, the model solutions and natural hot springs considerably differ in composition. Differences are hardly noticeable in the behavior of cations, fluorine, chlorine, and sulfates, but are strongly manifested in changes in the quantities of carbon and silicon compounds and transformations of their forms. These transformations explain the hitherto incomprehensibly different ratios of hydrocarbonate and carbonate ions and hydrosilicate ions and silicic acid both in different hydrothermal sources and in different analyses of hot springs in nature. The development of thermal waters in crystalline rocks is related to two types of heterogeneities that are typical for the development of geological bodies. The first heterogeneity is the disturbed continuity of rocks in fault zones of various orders, due to which groundwater can penetrate into these structures. The uneven distribution of anionic elements in space is another heterogeneity predetermining the groundwater composition and, in particular, accumulation of fluorine, which is confirmed by the results of geological studies, as well as the study of the formation of high-fluoride groundwaters (including thermal water) in various geological structures.
{"title":"MODELING THE FORMATION OF FLUORIDE NITROGEN-RICH HOT SPRINGS IN THE WATER – CRYSTALLINE ROCK SYSTEM","authors":"S. K. Pavlov, K. Chudnenko, A. Khromov","doi":"10.5800/gt-2020-11-2-0481","DOIUrl":"https://doi.org/10.5800/gt-2020-11-2-0481","url":null,"abstract":"Physicochemical interactions in the water – porphyrite system in conditions of formation of nitrogen-rich hot springs were studied using computer simulation. Compositions of model solutions during such interactions are determined by a combined influence of the compositions of primary and secondary rock minerals. In the investigated interaction range, the solution actively processes large quantities of the primary rock in favor of secondary minerals, while dissolved components are accumulated in small amounts in the solution itself, and therefore the salinity is low. The intervals of the formation of hydrosilicate, bicarbonate and sulfate sodium solutions are clearly distinguished in the process of irreversible hydrolytic transformation of porphyrite. In a certain range of interactions, the compositions of the model solutions are well comparable with the compositions of natural high-fluoride hot springs. Nitrogen-rich hot springs are strongly influenced by meteogenic factors detectable by detailed and/or sufficiently long-term observations. In deep and surface conditions, the model solutions and natural hot springs considerably differ in composition. Differences are hardly noticeable in the behavior of cations, fluorine, chlorine, and sulfates, but are strongly manifested in changes in the quantities of carbon and silicon compounds and transformations of their forms. These transformations explain the hitherto incomprehensibly different ratios of hydrocarbonate and carbonate ions and hydrosilicate ions and silicic acid both in different hydrothermal sources and in different analyses of hot springs in nature. The development of thermal waters in crystalline rocks is related to two types of heterogeneities that are typical for the development of geological bodies. The first heterogeneity is the disturbed continuity of rocks in fault zones of various orders, due to which groundwater can penetrate into these structures. The uneven distribution of anionic elements in space is another heterogeneity predetermining the groundwater composition and, in particular, accumulation of fluorine, which is confirmed by the results of geological studies, as well as the study of the formation of high-fluoride groundwaters (including thermal water) in various geological structures.","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":"82171787","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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