Pub Date : 2024-06-19DOI: 10.1134/s0016852124700043
I. U. Atabekov, Yu. M. Sadykov, J. K. Mamarakhimov
Abstract—
The geodynamic features of the Fergana intermontane depression are the presence of rifting during regional meridional compression and the discrepancy between the location of earthquake sources and boundaries of inhomogeneities in crustal layers. The first feature is solved using the ideas of multistage plate tectonics, which also makes it possible to assess the oil and gas content of the basin. However, existing hypothetical tectonic schemes are not supported by mathematical calculations. To clarify these features, we have developed a mathematical model of the stress–strain state with respect to one of the cross sections of the crust in the Fergana depression, which has a zonally inhomogeneous density structure. The results of the mathematical model show that the presence of blocks with different densities creates displacements under the impact of horizontal compressive stresses. It is also shown that the isolines of maximum tangential stresses are located close to the boundaries of inhomogeneous zones, which indicates large errors in determining earthquake hypocenters.
{"title":"Layered Tectonics and Mathematical Modeling of the Geodynamic Setting of the Fergana Depression (Uzbekistan)","authors":"I. U. Atabekov, Yu. M. Sadykov, J. K. Mamarakhimov","doi":"10.1134/s0016852124700043","DOIUrl":"https://doi.org/10.1134/s0016852124700043","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">\u0000<b>Abstract</b>—</h3><p>The geodynamic features of the Fergana intermontane depression are the presence of rifting during regional meridional compression and the discrepancy between the location of earthquake sources and boundaries of inhomogeneities in crustal layers. The first feature is solved using the ideas of multistage plate tectonics, which also makes it possible to assess the oil and gas content of the basin. However, existing hypothetical tectonic schemes are not supported by mathematical calculations. To clarify these features, we have developed a mathematical model of the stress–strain state with respect to one of the cross sections of the crust in the Fergana depression, which has a zonally inhomogeneous density structure. The results of the mathematical model show that the presence of blocks with different densities creates displacements under the impact of horizontal compressive stresses. It is also shown that the isolines of maximum tangential stresses are located close to the boundaries of inhomogeneous zones, which indicates large errors in determining earthquake hypocenters.</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"16 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141521560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-19DOI: 10.1134/s001685212470002x
S. Yu. Sokolov, V. G. Trifonov
Abstract
Analysis of the upper mantle plumes spatial distribution in the inner part of the Sunda arc shows a number of plume bodies interrupting the stagnant slab framed from the south by the sinking slab of the Sunda arc. Possible mechanisms resulting in this structure of the mantle are (i) W-E-trending toroidal mantle flow through a gap in a flat slab and (ii) rollback capable of forming a gap in a flat slab and launching upper mantle plumes in it without deep (>1000 km) roots. The space above the top of the slab consists of local hot mantle bodies, which are considered secondary plumes and often form local rift segments. The 3D visualization of velocity variations δVp in the Tibet and Central Asia region demonstrates structural patterns similar to those in the Sunda arc area. One can observe a region of subhorizontal slab fragments and a gap, which is recorded by plume anomalies of deep and secondary origin. The motion vectors of the rock mass along the fault planes of the Sunda arc, detected from seismic events, are directed outward from its center of curvature, in which secondary upper mantle plumes are concentrated. This indicates the development of thrust processes at the arc front unassociated with the subducting plate. The arc thrusting is accompanied by a small number of displacements along antithetic thrust faults. The displacement azimuths along the Himalayas are fan-shaped, oriented toward Hindustan. This shows that the main indicator of tectonic activity (seismic events) has a direction of rock mass displacement to the south from the extensional back-arc basin within Tibet with the development of thrust deformations during movements along the detachment planes. Two directions of seismic movements are distinguished in the Himalayan arc, as well as in the Sunda arc. The first direction follows the Indian Plate subduction model. The second direction includes variable azimuth rock mass movements along the thrust planes onto the Indian Plate.
{"title":"Arc Tectonic Elements and Upper Mantle Structure of Central and Southeast Asia: Seismic Tomography and Seismicity Data","authors":"S. Yu. Sokolov, V. G. Trifonov","doi":"10.1134/s001685212470002x","DOIUrl":"https://doi.org/10.1134/s001685212470002x","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Analysis of the upper mantle plumes spatial distribution in the inner part of the Sunda arc shows a number of plume bodies interrupting the stagnant slab framed from the south by the sinking slab of the Sunda arc. Possible mechanisms resulting in this structure of the mantle are (i) W-E-trending toroidal mantle flow through a gap in a flat slab and (ii) rollback capable of forming a gap in a flat slab and launching upper mantle plumes in it without deep (>1000 km) roots. The space above the top of the slab consists of local hot mantle bodies, which are considered secondary plumes and often form local rift segments. The 3D visualization of velocity variations δ<i>V</i><sub>p</sub> in the Tibet and Central Asia region demonstrates structural patterns similar to those in the Sunda arc area. One can observe a region of subhorizontal slab fragments and a gap, which is recorded by plume anomalies of deep and secondary origin. The motion vectors of the rock mass along the fault planes of the Sunda arc, detected from seismic events, are directed outward from its center of curvature, in which secondary upper mantle plumes are concentrated. This indicates the development of thrust processes at the arc front unassociated with the subducting plate. The arc thrusting is accompanied by a small number of displacements along antithetic thrust faults. The displacement azimuths along the Himalayas are fan-shaped, oriented toward Hindustan. This shows that the main indicator of tectonic activity (seismic events) has a direction of rock mass displacement to the south from the extensional back-arc basin within Tibet with the development of thrust deformations during movements along the detachment planes. Two directions of seismic movements are distinguished in the Himalayan arc, as well as in the Sunda arc. The first direction follows the Indian Plate subduction model. The second direction includes variable azimuth rock mass movements along the thrust planes onto the Indian Plate.</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"53 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141521546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-19DOI: 10.1134/s0016852124700031
A. E. Rybalko, V. A. Shcherbakov, M. Yu. Tokarev, A. A. Kudinov, P. Yu. Belyaev, T. Yu. Repkina, N. E. Zaretskaya, Ya. E. Terekhina, V. V. Ivanova, V. I. Slichenkov
Abstract
The article presents the results of a study of modern geodynamic movements in bottom structures of the White Sea (Baltic Shield). Based on expeditionary work in the White Sea, data were obtained on the formation of the seabed relief and thickness of unconsolidated sediments under the influence of modern seismotectonic events and geodynamic movements, as well as long-term neotectonic processes. It is shown that the Kandalaksha Bay depression is a modern graben developing along faults activated in the Quaternary. Graben development continues to the northwest, where a new Quaternary structure is being formed. Signs of modern geodynamic movements have been identified. The authors demonstrate the role of disjunctive tectonics in the formation of slopes and tectonic structures transverse to the strike of the bay, morphologically represented by relief ridges cutting the Sredny Ludy rise in Kandalaksha Bay. The influence of modern geodynamic processes on the distribution of thicknesses of Quaternary sediments of various genesis and the mosaic distribution of modern bottom sediments has been established. The influence of gravitational processes involved in the formation of underwater landslides, leading to the appearance of abnormally thick layers of the unconsolidated sedimentary cover, has been studied.
{"title":"Influence of Modern Geodynamic Processes on the Formation of the Coastal Relief and Seabed of the White Sea","authors":"A. E. Rybalko, V. A. Shcherbakov, M. Yu. Tokarev, A. A. Kudinov, P. Yu. Belyaev, T. Yu. Repkina, N. E. Zaretskaya, Ya. E. Terekhina, V. V. Ivanova, V. I. Slichenkov","doi":"10.1134/s0016852124700031","DOIUrl":"https://doi.org/10.1134/s0016852124700031","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The article presents the results of a study of modern geodynamic movements in bottom structures of the White Sea (Baltic Shield). Based on expeditionary work in the White Sea, data were obtained on the formation of the seabed relief and thickness of unconsolidated sediments under the influence of modern seismotectonic events and geodynamic movements, as well as long-term neotectonic processes. It is shown that the Kandalaksha Bay depression is a modern graben developing along faults activated in the Quaternary. Graben development continues to the northwest, where a new Quaternary structure is being formed. Signs of modern geodynamic movements have been identified. The authors demonstrate the role of disjunctive tectonics in the formation of slopes and tectonic structures transverse to the strike of the bay, morphologically represented by relief ridges cutting the Sredny Ludy rise in Kandalaksha Bay. The influence of modern geodynamic processes on the distribution of thicknesses of Quaternary sediments of various genesis and the mosaic distribution of modern bottom sediments has been established. The influence of gravitational processes involved in the formation of underwater landslides, leading to the appearance of abnormally thick layers of the unconsolidated sedimentary cover, has been studied.</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"203 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141521547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-19DOI: 10.1134/s0016852124700018
D. V. Kovalenko, V. V. Yarmolyuk, A. M. Kozlovsky
Abstract—
The article summarizes paleomagnetic data for Tuva, Mongolia, and Eastern China, which showed that in the central part of the Central Asian Fold Belt, areas with different paleomagnetic characteristics are distinguished. These are areas located north of the Mongol–Okhotsk mobile belt, the western and eastern parts of Southern Mongolia, and Eastern China. The areas located north of the Mongol–Okhotsk mobile belt were part of the structure of the Siberian continent from the Ordovician and experienced movement similar to the Siberian continent. The regions of the western part of Southern Mongolia have been part of the structure of the Siberian continent since the Late Carboniferous. The geological complexes of the eastern part of Southern Mongolia and blocks of Eastern China in the Middle Paleozoic and Early Mesozoic were located in a latitudinal interval close to the North China block and experienced similar latitudinal movements and rotations. The large difference between the paleolatitudes of coeval strata in western and eastern Mongolia and Eastern China south of the Mongol–Okhotsk mobile belt suggests the existence of a tectonic boundary that separated blocks formed at paleolatitudes along the 107° E meridian, close to Siberia and North China. To the west of the 107° E meridian, the paleolatitudes of the formation of Late Carboniferous–Permian strata are close to the paleolatitudes of Siberia, and east of the meridian, to the paleolatitudes of North China. The width of the Mongol–Okhotsk Ocean in the Late Paleozoic–Early Mesozoic was 30°–40° E (~3000–4000 km). The southern limit of the Mongol–Okhotsk Ocean was segmented and consisted of terranes of various genesis and structure. The closure of segments of the Mongol–Okhotsk Ocean occurred as a result of collision of terranes with the Siberian continent from the Late Carboniferous (in the west) to the Jurassic (in the east).
{"title":"Paleomagnetism of Phanerozoic Strata of the Central Part of the Central Asian Fold Belt","authors":"D. V. Kovalenko, V. V. Yarmolyuk, A. M. Kozlovsky","doi":"10.1134/s0016852124700018","DOIUrl":"https://doi.org/10.1134/s0016852124700018","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">\u0000<b>Abstract</b>—</h3><p>The article summarizes paleomagnetic data for Tuva, Mongolia, and Eastern China, which showed that in the central part of the Central Asian Fold Belt, areas with different paleomagnetic characteristics are distinguished. These are areas located north of the Mongol–Okhotsk mobile belt, the western and eastern parts of Southern Mongolia, and Eastern China. The areas located north of the Mongol–Okhotsk mobile belt were part of the structure of the Siberian continent from the Ordovician and experienced movement similar to the Siberian continent. The regions of the western part of Southern Mongolia have been part of the structure of the Siberian continent since the Late Carboniferous. The geological complexes of the eastern part of Southern Mongolia and blocks of Eastern China in the Middle Paleozoic and Early Mesozoic were located in a latitudinal interval close to the North China block and experienced similar latitudinal movements and rotations. The large difference between the paleolatitudes of coeval strata in western and eastern Mongolia and Eastern China south of the Mongol–Okhotsk mobile belt suggests the existence of a tectonic boundary that separated blocks formed at paleolatitudes along the 107° E meridian, close to Siberia and North China. To the west of the 107° E meridian, the paleolatitudes of the formation of Late Carboniferous–Permian strata are close to the paleolatitudes of Siberia, and east of the meridian, to the paleolatitudes of North China. The width of the Mongol–Okhotsk Ocean in the Late Paleozoic–Early Mesozoic was 30°–40° E (~3000–4000 km). The southern limit of the Mongol–Okhotsk Ocean was segmented and consisted of terranes of various genesis and structure. The closure of segments of the Mongol–Okhotsk Ocean occurred as a result of collision of terranes with the Siberian continent from the Late Carboniferous (in the west) to the Jurassic (in the east).</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"58 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141506542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-18DOI: 10.1134/s0016852124700092
Sh. Mirahmadi, A. Sadidkhouy, Gh. Javan-Doloei, N. Mohammadi
Abstract
The study investigates the variation of shear wave anisotropy among the crustal structure of the Zagros and Central Iran. We used the waveforms of 327 tele-seismic earthquakes with magnitude greater than 5.0 (Mb) at epicentral distances between 30° and 90°, recorded by 22 broadband seismic stations in the study area. The radial and transverse components of the receiver functions in the frequency band from 0.05 to 0.5 Hz were calculated using the earthquakes recorded at each station. Considering t0 as arrival time of the Ps-converted phase on radial receiver functions in the isotropic case, we estimate the effective arrival time for the overlapping phases of the split shear waves as a function of back azimuth. Then we determined the seismic anisotropy parameters of the shear waves (φ, δt). The results show that the average splitting time in the study area varies from 0.24 to 0.65 s, which is a good constraint on the seismic anisotropy compared to the range of crustal seismic anisotropy. Analysis of the fast direction of motion shows that φ changes parallel to the direction of the surface structures and agrees with measurements of the velocity vector GPS that the deformation is rooted in shallower, brittle structures of the crust and active fault zones throughout the environment.
{"title":"Crustal Seismic Anisotropy Beneath the Zagros and Central Iran","authors":"Sh. Mirahmadi, A. Sadidkhouy, Gh. Javan-Doloei, N. Mohammadi","doi":"10.1134/s0016852124700092","DOIUrl":"https://doi.org/10.1134/s0016852124700092","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The study investigates the variation of shear wave anisotropy among the crustal structure of the Zagros and Central Iran. We used the waveforms of 327 tele-seismic earthquakes with magnitude greater than 5.0 (<i>M</i>b) at epicentral distances between 30° and 90°, recorded by 22 broadband seismic stations in the study area. The radial and transverse components of the receiver functions in the frequency band from 0.05 to 0.5 Hz were calculated using the earthquakes recorded at each station. Considering <i>t</i><sub>0</sub> as arrival time of the Ps-converted phase on radial receiver functions in the isotropic case, we estimate the effective arrival time for the overlapping phases of the split shear waves as a function of back azimuth. Then we determined the seismic anisotropy parameters of the shear waves (φ, δ<i>t</i>). The results show that the average splitting time in the study area varies from 0.24 to 0.65 s, which is a good constraint on the seismic anisotropy compared to the range of crustal seismic anisotropy. Analysis of the fast direction of motion shows that φ changes parallel to the direction of the surface structures and agrees with measurements of the velocity vector GPS that the deformation is rooted in shallower, brittle structures of the crust and active fault zones throughout the environment.</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"98 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140626023","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-18DOI: 10.1134/s0016852124700055
R. Azizi, N. Mahmoudi, S. Gaieb, H. Mnasri, Y. Houla, Ch. Mezni
Abstract
Based on the field observations and tectono-sedimentary analysis, we suggest reconstruction of the geological evolution from case study of Northern Tunisia since the Eocene age. The reconstruction of the structural architecture of this region can be aided by knowing the spatiotemporal occurrence and the deformation of the Oligo‒Early Miocene deposits. In the research area, two depositional basin types that coexisted but in different tectonic settings were seen in the reconstruction of Oligo‒Early Miocene successions. In Northern Tunisia, the Late Eocene shortening episode led to a thin-skinned deformation that produced irregular basement topography. During the Oligo‒Early Miocene subduction process, the earliest lithofacies of the Maghrebian Numidian flysch deposited in deep marine offshore environment. Synchronously in the onshore, the second lithofacies of Fortuna were deposited in NW-trending extensional structures after a rifting episode that characterized north-eastern Tunisia (ante-nappes). During the Middle Miocene, the curving fore-arc of subduction between Africa and the Mesomediterranean Microplate dominated northern Tunisia. As a result, the Numidian basin was raised, resulting in thrust sheets in northwestern part of Tunisia, while the extensional structures supporting the Fortuna succession were closed and created push-up structures following transpressional deformation along the NW‒SE boundary faults. Continental collision has occurred in northern Tunisia since the Late Miocene, resulting in shortening structures, some elevated areas, and sedimentary gaps encompassing a substantial portion of the study area.
{"title":"Structural Reconstruction of the Oligo–Early Miocene Basins of the Eastern Segment of Maghrebian Belt (Northern Tunisia): Influence of Subduction of the Fore-Arc Curvature","authors":"R. Azizi, N. Mahmoudi, S. Gaieb, H. Mnasri, Y. Houla, Ch. Mezni","doi":"10.1134/s0016852124700055","DOIUrl":"https://doi.org/10.1134/s0016852124700055","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Based on the field observations and tectono-sedimentary analysis, we suggest reconstruction of the geological evolution from case study of Northern Tunisia since the Eocene age. The reconstruction of the structural architecture of this region can be aided by knowing the spatiotemporal occurrence and the deformation of the Oligo‒Early Miocene deposits. In the research area, two depositional basin types that coexisted but in different tectonic settings were seen in the reconstruction of Oligo‒Early Miocene successions. In Northern Tunisia, the Late Eocene shortening episode led to a thin-skinned deformation that produced irregular basement topography. During the Oligo‒Early Miocene subduction process, the earliest lithofacies of the Maghrebian Numidian flysch deposited in deep marine offshore environment. Synchronously in the onshore, the second lithofacies of Fortuna were deposited in NW-trending extensional structures after a rifting episode that characterized north-eastern Tunisia (ante-nappes). During the Middle Miocene, the curving fore-arc of subduction between Africa and the Mesomediterranean Microplate dominated northern Tunisia. As a result, the Numidian basin was raised, resulting in thrust sheets in northwestern part of Tunisia, while the extensional structures supporting the Fortuna succession were closed and created push-up structures following transpressional deformation along the NW‒SE boundary faults. Continental collision has occurred in northern Tunisia since the Late Miocene, resulting in shortening structures, some elevated areas, and sedimentary gaps encompassing a substantial portion of the study area.</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"94 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140626045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-18DOI: 10.1134/s0016852124700080
P. Das, S. S. Acharyya, T. K. Mondal, V. Thirukumaran
Abstract
We investigate how a highly elliptical and mechanically rigid clast embedded in an infinite rock mass respond to the far-field stresses. The numerical analysis is carried out on elliptical clasts with aspect ratios ranging from 13.5 to 58.5, oriented at a right angle to the maximum far-field stress. A 2D plane strain model has been adopted to decipher the states of stress inside elliptical clasts. We argue that the tensile stress within the clasts gets enhanced and develops systematic mode-I (tensile) fractures within it as the far-field stress increases. We conclude that the intra-clast tensile stress decreases with increasing clast ellipticity, i.e., tensile fractures develop more easily within clasts with higher aspect ratios (~>20) while a higher far field tensile stress is required to fracture clasts with lower aspect ratios. We also interpret that stress enhancement is independent of the clast area and inter-focii distance of the clast, whilst the aspect ratio of the clast is found to be crucial for the development of tensile fractures within the elliptical clast for a constant material property.
摘要 我们研究了嵌入无限岩体中的高椭圆形机械刚性岩屑对远场应力的响应。数值分析的对象是长宽比从 13.5 到 58.5 的椭圆形岩屑，其方向与最大远场应力成直角。采用二维平面应变模型来解读椭圆形岩屑内部的应力状态。我们认为，随着远场应力的增加，碎屑内部的拉应力会增强，并在其内部形成系统的 I 型（拉伸）断裂。我们的结论是，碎屑内部的拉应力随着碎屑椭圆度的增加而减小，也就是说，在长宽比（~>20）较高的碎屑内部更容易形成拉断裂，而长宽比较低的碎屑则需要较高的远场拉应力才能断裂。我们还解释说，应力增强与岩屑面积和岩屑间距无关，而在材料性质不变的情况下，岩屑的纵横比对椭圆形岩屑内拉伸断裂的发展至关重要。
{"title":"Evaluating Tensile Fractures in Rigid Clasts with Very High Aspect Ratio","authors":"P. Das, S. S. Acharyya, T. K. Mondal, V. Thirukumaran","doi":"10.1134/s0016852124700080","DOIUrl":"https://doi.org/10.1134/s0016852124700080","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>We investigate how a highly elliptical and mechanically rigid clast embedded in an infinite rock mass respond to the far-field stresses. The numerical analysis is carried out on elliptical clasts with aspect ratios ranging from 13.5 to 58.5, oriented at a right angle to the maximum far-field stress. A 2D plane strain model has been adopted to decipher the states of stress inside elliptical clasts. We argue that the tensile stress within the clasts gets enhanced and develops systematic mode-I (tensile) fractures within it as the far-field stress increases. We conclude that the intra-clast tensile stress decreases with increasing clast ellipticity, i.e., tensile fractures develop more easily within clasts with higher aspect ratios (~>20) while a higher far field tensile stress is required to fracture clasts with lower aspect ratios. We also interpret that stress enhancement is independent of the clast area and inter-focii distance of the clast, whilst the aspect ratio of the clast is found to be crucial for the development of tensile fractures within the elliptical clast for a constant material property.</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"21 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140626143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-18DOI: 10.1134/s0016852124700067
S. Aourari, D. Machane, M. Guemache, H. Haddoum, A. Benhamouche, H. Moulouel, S. Sadrati, N. Sidi Said, D. Ait Benamar
Abstract
The neotectonic processes are crucial for identification of active faults in a seismic unstable area. The Aїn Smara active fault runs along the Middle Rhumel Valley located in Constantine area of Algerian Eastern Tell Atlas mountain chain and it emerges in the south‒western part of the epicentral zone of the earthquake occurred on October 27, 1985 (Mw = 5.8) within a corridor displaying morphological features and deformed Pliocene‒Quaternary layers, which are the consequence of transpressive tectonic regime. In our study the morpho-tectonic and structural research supported by the fieldwork, was performed. The thick fault gouge indicating simple shear deformation, fault breccias and minor faults affecting the Pliocene limestone and Quaternary alluvial terraces, were found. The active fault splits into northern and southern segments. The northern segment corresponds to the El Aria Fault that ruptured during the earthquake in 1985 and the southern segment with the studied Aĭn Smara Fault. Our research showed the significant extent of the active fault and including its parameters for improved seismic hazard assessment of the Constantine area.
{"title":"Transpressive Tectonics Evidence in the Epicentral Area of the Modern Earthquake in Constantine Area of Algerian Eastern Tell Atlas: New Insights from Rhumel Valley","authors":"S. Aourari, D. Machane, M. Guemache, H. Haddoum, A. Benhamouche, H. Moulouel, S. Sadrati, N. Sidi Said, D. Ait Benamar","doi":"10.1134/s0016852124700067","DOIUrl":"https://doi.org/10.1134/s0016852124700067","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The neotectonic processes are crucial for identification of active faults in a seismic unstable area. The Aїn Smara active fault runs along the Middle Rhumel Valley located in Constantine area of Algerian Eastern Tell Atlas mountain chain and it emerges in the south‒western part of the epicentral zone of the earthquake occurred on October 27, 1985 (<i>M</i><sub>w</sub> = 5.8) within a corridor displaying morphological features and deformed Pliocene‒Quaternary layers, which are the consequence of transpressive tectonic regime. In our study the morpho-tectonic and structural research supported by the fieldwork, was performed. The thick fault gouge indicating simple shear deformation, fault breccias and minor faults affecting the Pliocene limestone and Quaternary alluvial terraces, were found. The active fault splits into northern and southern segments. The northern segment corresponds to the El Aria Fault that ruptured during the earthquake in 1985 and the southern segment with the studied Aĭn Smara Fault. Our research showed the significant extent of the active fault and including its parameters for improved seismic hazard assessment of the Constantine area.</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"45 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140626047","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-04-18DOI: 10.1134/s0016852124700079
M. H. Al-Hashim, O. M. K. Kassem
Abstract
The present work illustrates the structural setting in the Hamadat core complex, which located in the Midyan terrane. It is essential to understand deformational processes and products at different scales, which depend on the calculation of finite strain. To assess the tectonic development and structures in the Hamadat core complex, we use field investigation, finite strain analysis and microstructural examination. The Hamadat core complex employed the Rf/φ and Fry techniques for feldspar and mafic grains with 24 collected samples for gneisses, metavolcano-sedimentary rocks from both the Zaam and Baydah groups, deformed granodiorite for Jar-Salajah intrusion and Qazzaz granite. According to finite-strain data, the various rock units have moderate to high degree of deformation, and the axial ratios for XZ section vary from 1.80 to 4.50 for the Rf/φ technique and from 2.10 to 7.40 for the Fry technique. It concluded that the shortening axes display the subvertical related to the subhorizontal foliation. The strain data have the same main-phase foliation and similar deformation behavior. Finite strain acquired through high pressure metamorphism in this instance suggested that the contacts of nappe developed through the buildup of ductile strains. Also, during thrusting and intrusions throughout the deformation process, a building of brittle to ductile deformation was mostly caused by pure shearing in the study area.
{"title":"Strain Analysis and Microstructural Study of Hamadat Core Complex, Northwestern Arabian Shield, Saudi Arabia","authors":"M. H. Al-Hashim, O. M. K. Kassem","doi":"10.1134/s0016852124700079","DOIUrl":"https://doi.org/10.1134/s0016852124700079","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The present work illustrates the structural setting in the Hamadat core complex, which located in the Midyan terrane. It is essential to understand deformational processes and products at different scales, which depend on the calculation of finite strain. To assess the tectonic development and structures in the Hamadat core complex, we use field investigation, finite strain analysis and microstructural examination. The Hamadat core complex employed the Rf/φ and Fry techniques for feldspar and mafic grains with 24 collected samples for gneisses, metavolcano-sedimentary rocks from both the Zaam and Baydah groups, deformed granodiorite for Jar-Salajah intrusion and Qazzaz granite. According to finite-strain data, the various rock units have moderate to high degree of deformation, and the axial ratios for <i>XZ</i> section vary from 1.80 to 4.50 for the Rf/φ technique and from 2.10 to 7.40 for the Fry technique. It concluded that the shortening axes display the subvertical related to the subhorizontal foliation. The strain data have the same main-phase foliation and similar deformation behavior. Finite strain acquired through high pressure metamorphism in this instance suggested that the contacts of nappe developed through the buildup of ductile strains. Also, during thrusting and intrusions throughout the deformation process, a building of brittle to ductile deformation was mostly caused by pure shearing in the study area.</p>","PeriodicalId":55097,"journal":{"name":"Geotectonics","volume":"10 1","pages":""},"PeriodicalIF":1.1,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140626164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-03-14DOI: 10.1134/s0016852123060080
A. V. Zayonchek, S. Yu. Sokolov, A. V. Soloviev
Abstract
This paper presents the results of a study of the pre-Quaternary tectonics and stratigraphy of the Eurasia Basin (EB) according to the interpretation of the ARC1407A seismic profile and calculations of the theoretical positions of linear magnetic anomalies. The sedimentary sequences are recognized in seismic profiles and their stratigraphic position is similar to that of sedimentary sequences in the western parts of the Nansen and Amundsen basins. The age indexation of sedimentary sequences corresponds to the ACEX drilling results and the main evolution stages of the EB. No previously recognized reference horizon with the age of ~34 Ma, which is related to the termination of spreading in the western part of North Atlantic and amalgamation of the Greenland and North American plates, is recognized, as is supported by our studies in the western parts of the EB. In the western part of the Nansen Basin we identified a reference horizon with the age of 38 Ma for the first time, which was previously traced in the western part of the Amundsen Basin, whose formation is related to the evolution stage of the Eurekan Orogen. A reference horizon with the age of ~26 Ma, which has been traced in the western part of the Amundsen Basin before, is also distinguished in the western part of the Nansen Basin within ARC1407A. This geological boundary is related to the beginning of unstable spreading in the western segment of the EB between the Yermak Plateau and Morris Jessup Rise (Plateau). The end of a long stratigraphic hiatus between 44.4 and 18.2 Ma in the section of ACEX boreholes is clearly correlated with the formation of a sedimentary sequence of ~19.6‒18.3 Ma, which is the age of the beginning of the formation of a deep-water gateway between the North Atlantic and Eurasian sedimentary basins. This event coincides with the main reconstruction stage of movements of the Eurasia and North America plates, which led to a change in the direction of migration of momentary opening poles from the NNW to SSE. It is suggested that the thick sedimentary sequences in the Nansen Basin and the rift valley of the Gakkel Ridge that are observed in seismic section ARC1407A include Late Pliocene–Quaternary (<2.7 Ma) glaciomarine rocks, which compose a significant volume of sediments in the eastern part of the EB and the Gakkel Ridge.
摘要 本文介绍了根据 ARC1407A 地震剖面解释和线性磁异常理论位置计算对欧亚盆地（EB）前第四纪构造和地层研究的结果。地震剖面识别了沉积序列，其地层位置与南森盆地和阿蒙森盆地西部的沉积序列相似。沉积序列的年龄指数与 ACEX 钻井结果和 EB 的主要演化阶段相符。我们在 EB 西部地区的研究证实了这一点，目前尚未发现与北大西洋西部扩张终止以及格陵兰板块和北美板块合并有关的年龄为约 34 Ma 的参考层。在南森盆地西部，我们首次发现了一个年龄为 38 Ma 的参照层，此前我们曾在阿蒙森盆地西部追踪到这一参照层，其形成与厄勒干造山运动的演化阶段有关。在 ARC1407A 内的南森盆地西部也发现了一个年龄约为 26 Ma 的参照层，该参照层曾在阿蒙森盆地西部被追踪到。这一地质界线与叶尔马克高原和莫里斯-杰瑟普隆起（高原）之间的 EB 西段不稳定扩张的开始有关。在 ACEX 钻孔剖面中，44.4-18.2Ma 之间漫长地层间断的结束与 ~19.6-18.3 Ma 沉积序列的形成明显相关，而这正是北大西洋与欧亚沉积盆地之间深水门户开始形成的年代。这一事件与欧亚板块和北美板块运动的主要重建阶段相吻合，这导致了瞬时开口极的迁移方向从西北偏北转向东南偏东。ARC1407A 地震剖面中观察到的南森盆地和加克尔海脊裂谷的厚沉积层序包括晚更新世-第四纪（2.7Ma）冰川岩，这些冰川岩构成了 EB 东部和加克尔海脊的大量沉积物。
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