Pub Date : 2024-07-03DOI: 10.5194/egusphere-2024-1906
Anthony Adwan, Bertrand Maillot, Pauline Souloumiac, Christophe Barnes, Christophe Nussbaum, Meinert Rahn, Thomas Van Stiphout
Abstract.This study employs numerical simulations based on the Limit Analysis (LA) method to calculate the stress distribution in a kilometric-scale model developed over a basal detachment, featuring the lateral termination of a generic fault under compression. We conduct 2500 2D and 500 3D simulations, varying basement and fault friction angles, to analyze and classify the results into clusters representing similar failure patterns to understand the stress fields. Automatic fault detection methods are employed to identify the number and positions of fault lines in 2D and fault surfaces in 3D. Clustering approaches are utilized to group the models based on the detected failure patterns. For the 2D models, the analysis reveals three primary clusters and five transitional ones, qualitatively consistent with the critical Coulomb wedge theory and the influence of inherited structural and geometric aspects over rupture localization. In the 3D models, four different clusters portray the lateral prolongation of the inherited fault. High stress magnitudes are detected between the compressive boundary and the activated or created faults, and at the root of the inherited active fault. Tension zones appear near the outcropping surface relief while stress decreases with depth at the footwall of the created back-thrusts. A statistical, cluster-based stress field analysis indicates that for a given cluster, the stress field mainly conserves the same orientations, while the magnitude varies with changes in friction angles and compressive field intensity, except in failure zones where variations are sparse. Small parametric variations could lead to significantly different stress fields, while larger deviations might result in similar configurations. The comparison between 2D and 3D models shows the importance of lateral stresses and their influence on rupture patterns, distinguishing between 3D analysis and 2D cross-sections. Lastly, despite using small-scale models, stress field variations over a span of a couple of kilometers are quite large.
{"title":"Understanding the stress field at the lateral termination of a thrust fold using generic geomechanical models and clustering methods","authors":"Anthony Adwan, Bertrand Maillot, Pauline Souloumiac, Christophe Barnes, Christophe Nussbaum, Meinert Rahn, Thomas Van Stiphout","doi":"10.5194/egusphere-2024-1906","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1906","url":null,"abstract":"<strong>Abstract.</strong> <span>This study employs numerical simulations based on the Limit Analysis (LA) method to calculate the stress distribution in a </span><span>kilometric</span><span>-scale model developed over a basal detachment, featuring the lateral termination of a generic fault under compression. We conduct 2500 </span><span>2D</span><span> and 500 </span><span>3D</span><span> simulations, varying basement and fault friction angles, to analyze and classify the results into clusters representing similar failure patterns to understand the stress fields. Automatic fault detection methods are employed to identify the number and positions of fault lines in </span><span>2D</span><span> and fault surfaces in </span><span>3D</span><span>. Clustering approaches are utilized to group the models based on the detected failure patterns. For the </span><span>2D</span><span> models, the analysis reveals three primary clusters and five transitional ones, qualitatively consistent with the critical Coulomb wedge theory and the influence of inherited structural and geometric aspects over rupture localization. In the </span><span>3D</span><span> models, four different clusters portray the lateral prolongation of the inherited fault. High stress magnitudes are detected between the </span><span>compressive</span><span> boundary and the activated or created faults, and at the root of the inherited active fault. Tension zones appear near the outcropping surface relief while stress decreases with depth at the </span><span>footwall</span><span> of the created back-thrusts. A statistical, cluster-based stress field analysis indicates that for a given cluster, the stress field mainly conserves the same orientations, while the magnitude varies with changes in friction angles and </span><span>compressive</span><span> field intensity, except in failure zones where variations are sparse. Small parametric variations could lead to significantly different stress fields, while larger deviations might result in similar configurations. The comparison between </span><span>2D</span><span> and </span><span>3D</span><span> models shows the importance of lateral stresses and their influence on rupture patterns, distinguishing between </span><span>3D</span><span> analysis and </span><span>2D</span><span> cross-sections. Lastly, despite using small-scale models, stress field variations over a span of a couple of kilometers are quite large.</span>","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"22 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141524212","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Geochemical mapping is a fundamental tool for elucidating the distribution and behaviour of economically significant elements and providing valuable insights into geological processes. Nevertheless, the quantification of uncertainty associated with geochemical mapping has only recently become a subject of widespread concern. This study presents a procedure that primarily consists of the determination of homogeneous clusters, the recognition of elemental associations for each cluster, and the identification of geochemical anomalies, with the aim of accounting for the uncertainty of elemental association in geochemical mapping. To illustrate and validate the procedure, a case study was conducted wherein geochemical stream-sediment samples from the northwestern region of the province of Sichuan, China, were processed to map anomalies associated with disseminated gold mineralization. The results indicate that (1) the representativeness of elemental association for the underlying geological process is an important source of uncertainty for geochemical mapping; (2) the procedure presented here is effective in addressing the uncertainty of elemental associations in geochemical mapping; and (3) the study area can be classified into two clusters, each characterized by unique elemental associations that align well with the distribution of Paleozoic and Triassic lithological units, respectively. Furthermore, the region still holds great potential for the discovery of gold deposits, particularly in areas proximal to known mineralization sites.
{"title":"Mapping geochemical anomalies by accounting for the uncertainty of mineralization-related elemental associations","authors":"Jian Wang, Renguang Zuo, Qinghai Liu","doi":"10.5194/se-15-731-2024","DOIUrl":"https://doi.org/10.5194/se-15-731-2024","url":null,"abstract":"Abstract. Geochemical mapping is a fundamental tool for elucidating the distribution and behaviour of economically significant elements and providing valuable insights into geological processes. Nevertheless, the quantification of uncertainty associated with geochemical mapping has only recently become a subject of widespread concern. This study presents a procedure that primarily consists of the determination of homogeneous clusters, the recognition of elemental associations for each cluster, and the identification of geochemical anomalies, with the aim of accounting for the uncertainty of elemental association in geochemical mapping. To illustrate and validate the procedure, a case study was conducted wherein geochemical stream-sediment samples from the northwestern region of the province of Sichuan, China, were processed to map anomalies associated with disseminated gold mineralization. The results indicate that (1) the representativeness of elemental association for the underlying geological process is an important source of uncertainty for geochemical mapping; (2) the procedure presented here is effective in addressing the uncertainty of elemental associations in geochemical mapping; and (3) the study area can be classified into two clusters, each characterized by unique elemental associations that align well with the distribution of Paleozoic and Triassic lithological units, respectively. Furthermore, the region still holds great potential for the discovery of gold deposits, particularly in areas proximal to known mineralization sites.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"92 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508878","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-06-26DOI: 10.5194/egusphere-2024-1145
Renyu Zeng, Hui Su, Mark B. Allen, Haiyan Shi, Houfa Dua, Chenguang Zhange, Jie Yan
Abstract.In the Paleozoic, the Alxa Block was situated between the Central Asian Orogenic Belt and the North Qilian Orogenic Belt, and experienced intense magmatic activity. Thus, the Alxa Block is an important area for understanding the tectonic framework and evolution of these two orogenic belts. However, there has long been debate regarding the tectonic affinity and tectonic evolution of the Longshoushan, located in southwestern margin of the Alxa Block, during the Paleozoic. In this study, we present zircon U-Pb ages, whole-rock major and trace elements, and Hf isotopic data for the granitoids from the east of the Longshoushan to investigate these issues. Bulk-rock analyses show that these granitoids are weakly peraluminous, with high SiO2 and K2O, but low MgO, TFe2O3 and P2O5. They are also characterized by enrichment in LREE and LILE, depletion in HREE and HFSE, and a large range of variation in εHf(t) values (monzogranite: -0.37 to -16.28; K-feldspar granite: 3.53 to -7.74). These geochemical features indicate that these granitoids are highly fractionated I-type granite, which were formed by crust and mantle-derived magma mixing. LA-ICP-MS zircon U-Pb dating constrains that the monzogranite and K-feldspar granite were formed at 440.8 ± 2.1 Ma and 439.4 ± 2.0 Ma, respectively. Combining these results with previous chronological data, the geochronology framework of Paleozoic magmatic events in the Longshoushan is consistent with the North Qilian Orogenic Belt to the south, but significantly differs from other parts of the Alxa Block and the Central Asian Orogenic Belt to the north. This result indicates that the Longshoushan was primarily influenced by the North Qilian Orogenic Belt during the Early Paleozoic. Integrated with previous studies, a three-stage tectonic model is proposed of Early Paleozoic accretion and arc magmatism leading to collision in the Longshoushan. (1) 460–445 Ma: Arc magmatism on an active continental margin with the northward subduction of the North Qilian back-arc basins (NQ bab). (2) 445–435 Ma: Magmatic rocks, dominated by I-type granites, were formed in a continent-continent collision setting. Significant crustal thickening is interpreted to result from compressional stress and/or magmatic additions. (3) 435–410 Ma: The development of abundant A-type granites and mafic dikes in response to intraplate extension, supported by a change in trace element chemistry indicating crustal thinning at this stage. This sequence of events and their timings is similar to other parts of the Central China Orogenic Belt, and requires either a coincidence of several oceanic plates closing at the same time, or an along-strike repetition of the same system.
{"title":"Petrogenesis of Early Paleozoic I-type granitoids in the Longshoushan and implications for the tectonic affinity and evolution of the southwestern Alxa Block","authors":"Renyu Zeng, Hui Su, Mark B. Allen, Haiyan Shi, Houfa Dua, Chenguang Zhange, Jie Yan","doi":"10.5194/egusphere-2024-1145","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1145","url":null,"abstract":"<strong>Abstract.</strong> <span><span>In the Paleozoic, the Alxa Block was situated between the Central Asian Orogenic Belt and the North Qilian Orogenic Belt, and experienced intense magmatic activity. Thus, the Alxa Block is an important area for understanding the tectonic framework and evolution of these two orogenic belts. However, there has long been debate regarding the tectonic affinity and tectonic evolution of the Longshoushan, located in southwestern margin of the Alxa Block, during the Paleozoic. In this study, we present zircon U-Pb ages, whole-rock major and trace elements, and Hf isotopic data for the granitoids from the east of the Longshoushan to investigate these issues. Bulk-rock analyses show that these granitoids are weakly peraluminous, with high SiO</span><sub>2</sub><span> and K</span><sub>2</sub><span>O, but low MgO, TFe</span><sub>2</sub><span>O</span><sub>3</sub><span> and P</span><sub>2</sub><span>O</span><sub>5</sub><span>. They are also characterized by enrichment in LREE and LILE, depletion in HREE and HFSE, and a large range of variation in εHf(t) values (monzogranite: -0.37 to -16.28; K-feldspar granite: 3.53 to -7.74). These geochemical features indicate that these granitoids are highly fractionated I-type granite, which were formed by crust and mantle-derived magma mixing. LA-ICP-MS zircon U-Pb dating constrains that the monzogranite and K-feldspar granite were formed at 440.8 ± 2.1 Ma and 439.4 ± 2.0 Ma, respectively. Combining these results with previous chronological data, the geochronology framework of Paleozoic magmatic events in the Longshoushan is consistent with the North Qilian Orogenic Belt to the south, but significantly differs from other parts of the Alxa Block and the Central Asian Orogenic Belt to the north. This result indicates that the Longshoushan was primarily influenced by the North Qilian Orogenic Belt during the Early Paleozoic. Integrated with previous studies, a three-stage tectonic model is proposed of Early Paleozoic accretion and arc magmatism leading to collision in the Longshoushan. (1) 460–445 Ma: Arc magmatism on an active continental margin with the northward subduction of the North Qilian back-arc basins (NQ bab). (2) 445–435 Ma: Magmatic rocks, dominated by I-type granites, were formed in a continent-continent collision setting. Significant crustal thickening is interpreted to result from compressional stress and/or magmatic additions. (3) 435–410 Ma: The development of abundant A-type granites and mafic dikes in response to intraplate extension, supported by a change in trace element chemistry indicating crustal thinning at this stage. This sequence of events and their timings is similar to other parts of the Central China Orogenic Belt, and requires either a coincidence of several oceanic plates closing at the same time, or an along-strike repetition of the same system.</span></span>","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"73 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Extension tectonics responsible for intracratonic rift basin formation are often the consequences of active or passive tectonic regimes. The present work puts forth a plume-related rifting mechanism for the creation and evolution of two Proterozoic sedimentary basins outlining the Bundelkhand Craton, namely the Bijawar and Vindhyan basins. Using global gravity data, a regional-scale study is performed over the region encompassing the southern boundary of the Bundelkhand Craton consisting of the Bijawar Basin, Vindhyan Basin, and Deccan basalt outcrops. The gravity highs in the central part of the complete Bouguer anomaly and the upward-continued regional anomaly, derived from global gravity grid data, suggest that the Vindhyan sedimentary basin overlies a deeper high-density crustal source. The deepest interface as obtained from the radially averaged power spectrum analysis is observed to occur at a depth of ∼30.3 km, indicating that the sources responsible for the observed gravity signatures occur at larger depths. The 3D inversion of complete Bouguer anomaly data based on Parker–Oldenburg's algorithm revealed the Moho depth of ∼32 km below the Vindhyan Basin, i.e., south of the craton. The 2D crustal models along two selected profiles showcase a thick underplated layer with a maximum thickness of ∼12 km beneath the southern part of the Bundelkhand Craton. The inferred large E–W-trending underplating and deciphered shallower Moho beneath the regions south of the exposed Bundelkhand Craton point to crustal thinning compensated for magmatic emplacement due to a Paleoproterozoic plume activity below the craton margin.
{"title":"Magmatic underplating associated with Proterozoic basin formation: insights from gravity study over the southern margin of the Bundelkhand Craton, India","authors":"Ananya Parthapradip Mukherjee, Animesh Mandal","doi":"10.5194/se-15-711-2024","DOIUrl":"https://doi.org/10.5194/se-15-711-2024","url":null,"abstract":"Abstract. Extension tectonics responsible for intracratonic rift basin formation are often the consequences of active or passive tectonic regimes. The present work puts forth a plume-related rifting mechanism for the creation and evolution of two Proterozoic sedimentary basins outlining the Bundelkhand Craton, namely the Bijawar and Vindhyan basins. Using global gravity data, a regional-scale study is performed over the region encompassing the southern boundary of the Bundelkhand Craton consisting of the Bijawar Basin, Vindhyan Basin, and Deccan basalt outcrops. The gravity highs in the central part of the complete Bouguer anomaly and the upward-continued regional anomaly, derived from global gravity grid data, suggest that the Vindhyan sedimentary basin overlies a deeper high-density crustal source. The deepest interface as obtained from the radially averaged power spectrum analysis is observed to occur at a depth of ∼30.3 km, indicating that the sources responsible for the observed gravity signatures occur at larger depths. The 3D inversion of complete Bouguer anomaly data based on Parker–Oldenburg's algorithm revealed the Moho depth of ∼32 km below the Vindhyan Basin, i.e., south of the craton. The 2D crustal models along two selected profiles showcase a thick underplated layer with a maximum thickness of ∼12 km beneath the southern part of the Bundelkhand Craton. The inferred large E–W-trending underplating and deciphered shallower Moho beneath the regions south of the exposed Bundelkhand Craton point to crustal thinning compensated for magmatic emplacement due to a Paleoproterozoic plume activity below the craton margin.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"124 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Magma-poor rifted margins, and their corresponding potential zones of exhumed serpentinized mantle, represent a unique class of tectonic boundaries with enormous promise for advancing the energy transition, such as with hydrogen production and carbon sequestration and in the search for critical minerals. In this study, a synthesis of the results from seismic refraction and wide-angle reflection (RWAR) profiling and resulting velocity models across the continent–ocean transitions of the southern North Atlantic Ocean is presented. The models are assessed and compared to understand characteristic basement types and upper mantle behaviour across the region and between conjugate margin pairs and to calibrate how their continent–ocean transition zones (COTZs) are defined. Ultimately, this work highlights the variable nature of continent–ocean transition zones, even within the magma-poor rifted margin end-member case, and points to avenues for future research to fill the knowledge gaps that will accelerate the energy transition.
{"title":"Magma-poor continent–ocean transition zones of the southern North Atlantic: a wide-angle seismic synthesis of a new frontier","authors":"J. Kim Welford","doi":"10.5194/se-15-683-2024","DOIUrl":"https://doi.org/10.5194/se-15-683-2024","url":null,"abstract":"Abstract. Magma-poor rifted margins, and their corresponding potential zones of exhumed serpentinized mantle, represent a unique class of tectonic boundaries with enormous promise for advancing the energy transition, such as with hydrogen production and carbon sequestration and in the search for critical minerals. In this study, a synthesis of the results from seismic refraction and wide-angle reflection (RWAR) profiling and resulting velocity models across the continent–ocean transitions of the southern North Atlantic Ocean is presented. The models are assessed and compared to understand characteristic basement types and upper mantle behaviour across the region and between conjugate margin pairs and to calibrate how their continent–ocean transition zones (COTZs) are defined. Ultimately, this work highlights the variable nature of continent–ocean transition zones, even within the magma-poor rifted margin end-member case, and points to avenues for future research to fill the knowledge gaps that will accelerate the energy transition.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"10 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141508881","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mathews George Gilbert, Parakkal Unnikrishnan, Munukutla Radhakrishna
Abstract. Previous geophysical investigations of the western continental margin of India (WCMI) confirm the two-phase breakup history of the margin with the first breakup taking place between India and Madagascar that created the Mascarene Basin in the Late Cretaceous and the second breakup event in Early Paleocene with Seychelles separating from India. Despite numerous geoscientific studies along the WCMI, the opening of the Laccadive basin, situated along the southern part of the margin, remains poorly constrained. In this study, we evaluate the multi-channel seismic reflection and gravity anomalies at the margin to identify the early rift signatures in conjunction with the magnetic anomaly identifications in the Mascarene Basin. The analysis led to the identification of two trends of extensional structures, a NNW–SSE-oriented structure over the Laccadive Ridge north of Tellicherry Arch, interpreted to result from ENE–WSW extension, and a SSW–NNE-oriented structure in the Laccadive basin region towards the south, interpreted to result from NW–SE extension. Previous plate reconstruction models of the Mascarene Basin using marine magnetic lineations suggest that the ENE–WSW extension observed over the Laccadive Ridge could be related to the India–Madagascar separation. We associate the pattern of sediment deposition and the presence of a Paleocene trap volcanics, linked with the NW–SE grabens observed in the Laccadive basin region, to the extension between the Laccadive Ridge and the western coast of India after the separation of Madagascar from India. We further propose that the anticlockwise rotation of India and the passage of the Réunion plume have facilitated the opening of the Laccadive basin.
{"title":"Cretaceous–Paleocene extension at the southwestern continental margin of India and opening of the Laccadive basin: constraints from geophysical data","authors":"Mathews George Gilbert, Parakkal Unnikrishnan, Munukutla Radhakrishna","doi":"10.5194/se-15-671-2024","DOIUrl":"https://doi.org/10.5194/se-15-671-2024","url":null,"abstract":"Abstract. Previous geophysical investigations of the western continental margin of India (WCMI) confirm the two-phase breakup history of the margin with the first breakup taking place between India and Madagascar that created the Mascarene Basin in the Late Cretaceous and the second breakup event in Early Paleocene with Seychelles separating from India. Despite numerous geoscientific studies along the WCMI, the opening of the Laccadive basin, situated along the southern part of the margin, remains poorly constrained. In this study, we evaluate the multi-channel seismic reflection and gravity anomalies at the margin to identify the early rift signatures in conjunction with the magnetic anomaly identifications in the Mascarene Basin. The analysis led to the identification of two trends of extensional structures, a NNW–SSE-oriented structure over the Laccadive Ridge north of Tellicherry Arch, interpreted to result from ENE–WSW extension, and a SSW–NNE-oriented structure in the Laccadive basin region towards the south, interpreted to result from NW–SE extension. Previous plate reconstruction models of the Mascarene Basin using marine magnetic lineations suggest that the ENE–WSW extension observed over the Laccadive Ridge could be related to the India–Madagascar separation. We associate the pattern of sediment deposition and the presence of a Paleocene trap volcanics, linked with the NW–SE grabens observed in the Laccadive basin region, to the extension between the Laccadive Ridge and the western coast of India after the separation of Madagascar from India. We further propose that the anticlockwise rotation of India and the passage of the Réunion plume have facilitated the opening of the Laccadive basin.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"10 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141529837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-06-13DOI: 10.5194/egusphere-2024-1668
Cedric Thieulot, Wolfgang Bangerth
Abstract. Many geodynamical models are formulated in terms of the Stokes equations that are then coupled to other equations. For the numerical solution of the Stokes equations, geodynamics codes over the past decades have used essentially every finite element that has ever been proposed for the solution of this equation, on both triangular/tetrahedral ("simplex") and quadrilaterals/hexahedral ("hypercube") meshes. However, in many and perhaps most cases, the specific choice of element does not seem to have been the result of careful benchmarking efforts, but based on implementation efficiency or the implementers' background. In a first part of this paper (Thieulot & Bangerth, 2022), we have provided a comprehensive comparison of the accuracy and efficiency of the most widely used hypercube elements for the Stokes equations. We have done so using a number of benchmarks that illustrate "typical" geodynamic situations, specifically taking into account spatially variable viscosities. Our findings there showed that only Taylor-Hood-type elements with either continuous (Q2 × Q1) or discontinuous (Q2 × P-1) pressure are able to adequately and efficiently approximate the solution of the Stokes equations. In this, the second part of this work, we extend the comparison to simplex meshes. In particular, we compare triangular Taylor-Hood elements against the MINI element and one often referred to as the "Crouzeix-Raviart" element. We compare these choices against the accuracy obtained on hypercube Taylor-Hood elements with approximately the same computational cost. Our results show that, like on hypercubes, the Taylor-Hood element is substantially more accurate and efficient than the other choices. Our results also indicate that hypercube meshes yield slightly more accurate results than simplex meshes, but that the difference is relatively small and likely unimportant given that hypercube meshes often lead to slightly denser (and consequently more expensive) matrices.
{"title":"On the choice of finite element for applications in geodynamics. Part II: A comparison of simplex and hypercube elements","authors":"Cedric Thieulot, Wolfgang Bangerth","doi":"10.5194/egusphere-2024-1668","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1668","url":null,"abstract":"<strong>Abstract.</strong> Many geodynamical models are formulated in terms of the Stokes equations that are then coupled to other equations. For the numerical solution of the Stokes equations, geodynamics codes over the past decades have used essentially every finite element that has ever been proposed for the solution of this equation, on both triangular/tetrahedral (\"simplex\") and quadrilaterals/hexahedral (\"hypercube\") meshes. However, in many and perhaps most cases, the specific choice of element does not seem to have been the result of careful benchmarking efforts, but based on implementation efficiency or the implementers' background. In a first part of this paper (Thieulot & Bangerth, 2022), we have provided a comprehensive comparison of the accuracy and efficiency of the most widely used hypercube elements for the Stokes equations. We have done so using a number of benchmarks that illustrate \"typical\" geodynamic situations, specifically taking into account spatially variable viscosities. Our findings there showed that only Taylor-Hood-type elements with either continuous (<em>Q</em><sub>2</sub> × <em>Q</em><sub>1</sub>) or discontinuous (<em>Q</em><sub>2 </sub>× <em>P</em><sub>-1</sub>) pressure are able to adequately and efficiently approximate the solution of the Stokes equations. In this, the second part of this work, we extend the comparison to simplex meshes. In particular, we compare triangular Taylor-Hood elements against the MINI element and one often referred to as the \"Crouzeix-Raviart\" element. We compare these choices against the accuracy obtained on hypercube Taylor-Hood elements with approximately the same computational cost. Our results show that, like on hypercubes, the Taylor-Hood element is substantially more accurate and efficient than the other choices. Our results also indicate that hypercube meshes yield slightly more accurate results than simplex meshes, but that the difference is relatively small and likely unimportant given that hypercube meshes often lead to slightly denser (and consequently more expensive) matrices.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"15 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141524213","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-06-10DOI: 10.5194/egusphere-2024-1670
Hong-Xiang Wu, Han-Lin Chen, Andrew V. Zuza, Yildirim Dilek, Du-Wei Qiu, Qi-Ye Lu, Feng-Qi Zhang, Xiao-Gan Cheng, Xiu-Bin Lin
Abstract. The Tethyan Orogenic Belt records a long-lived geological cycle involving subduction and collision along the southern margin of the Eurasian continent. The West Kunlun Mountains, located at the junction between the Tibetan and Western Asian Tethyan realm, records multiple orogenic events from the Paleozoic to the Cenozoic that shape the northwestern Tibetan Plateau. However, deciphering the complex Mesozoic contractional and extensional tectonics to interpret the broader Tethyan geodynamics remains challenging. To address the tectonic transition following the early Cimmerian (Late Triassic) collision, this study investigates the newly identified Jurassic sedimentary strata and volcanic rocks in the West Kunlun Mountains. Zircon geochronological results of basalts and sandstones reveal that this ~ 2.5-km-thick package was deposited at ca. 178 Ma, rather than the previously reported Neoproterozoic age. The alkaline basalts at the top of the formation exhibit chemical compositions similar to oceanic island basalts, consistent with the intracontinental extension environment revealed by the upward-fining sedimentary pattern. Provenance analysis, integrating conglomerate clast lithologies with detrital zircons, suggests a substantial contribution from adjacent basement sources, likely influenced by the normal faulting during initial rift stage. These findings indicate that the West Kunlun Mountains rapidly transitioned into an extensional setting after suturing with Cimmerian terranes. The regional structure, stratigraphy and magmatism suggest that this Early - Middle Jurassic basin was subsequently inverted during the Late Jurassic and earliest Cretaceous. We propose that the Mesozoic deformational history in the West Kunlun Mountains was related to the northward subduction of the Neo-Tethys Ocean, as it transitioned from southward retreat to northward flat-slab advancement. Comparing with the entire strike-length of the Eurasian Tethyan orogen, we find that the subduction mode varied from the west to the east, reflecting the broad geodynamic changes to, or initial conditions of, the Neo-Tethyan system.
{"title":"Alternating Extensional and Contractional Tectonics in the West Kunlun Mountains during Jurassic: Responses to the Neo-Tethyan Geodynamics along the Eurasian Margin","authors":"Hong-Xiang Wu, Han-Lin Chen, Andrew V. Zuza, Yildirim Dilek, Du-Wei Qiu, Qi-Ye Lu, Feng-Qi Zhang, Xiao-Gan Cheng, Xiu-Bin Lin","doi":"10.5194/egusphere-2024-1670","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1670","url":null,"abstract":"<strong>Abstract.</strong> The Tethyan Orogenic Belt records a long-lived geological cycle involving subduction and collision along the southern margin of the Eurasian continent. The West Kunlun Mountains, located at the junction between the Tibetan and Western Asian Tethyan realm, records multiple orogenic events from the Paleozoic to the Cenozoic that shape the northwestern Tibetan Plateau. However, deciphering the complex Mesozoic contractional and extensional tectonics to interpret the broader Tethyan geodynamics remains challenging. To address the tectonic transition following the early Cimmerian (Late Triassic) collision, this study investigates the newly identified Jurassic sedimentary strata and volcanic rocks in the West Kunlun Mountains. Zircon geochronological results of basalts and sandstones reveal that this ~ 2.5-km-thick package was deposited at ca. 178 Ma, rather than the previously reported Neoproterozoic age. The alkaline basalts at the top of the formation exhibit chemical compositions similar to oceanic island basalts, consistent with the intracontinental extension environment revealed by the upward-fining sedimentary pattern. Provenance analysis, integrating conglomerate clast lithologies with detrital zircons, suggests a substantial contribution from adjacent basement sources, likely influenced by the normal faulting during initial rift stage. These findings indicate that the West Kunlun Mountains rapidly transitioned into an extensional setting after suturing with Cimmerian terranes. The regional structure, stratigraphy and magmatism suggest that this Early - Middle Jurassic basin was subsequently inverted during the Late Jurassic and earliest Cretaceous. We propose that the Mesozoic deformational history in the West Kunlun Mountains was related to the northward subduction of the Neo-Tethys Ocean, as it transitioned from southward retreat to northward flat-slab advancement. Comparing with the entire strike-length of the Eurasian Tethyan orogen, we find that the subduction mode varied from the west to the east, reflecting the broad geodynamic changes to, or initial conditions of, the Neo-Tethyan system.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"66 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141529839","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-06-06DOI: 10.5194/egusphere-2024-1602
África Gamisel-Muzás, Ruth Soto, Conxi Ayala, Tania Mochales, Félix Manuel Rubio, Pilar Clariana, Carmen Rey-Moral, Juliana Martín-León
Abstract. The major goal of this work is to provide an insight into the structural anatomy of the Pyrenees based on the magnetic data from the Earth Magnetic Anomaly Grid 2-arc-minute resolution (EMAG2v2). We focused on providing qualitative and semi-quantitative evidence on the magnetic signature of the Pyrenees Mountain Range domains and structures. The integration of reduced to the pole and processed maps, as well as the Bouguer anomaly map with geological data, has proved to be significantly useful in order to shed light on the main anomaly sources. Considering their magnetic response and texture, several anomalies can be linked to buried geological bodies or changes in the magnetic character of the basement. We have estimated their source bodies depth through Euler and power spectrum calculations. We have identified eight magnetic zones with different features and interpreted them in terms of the geological and structural setting of the area. The result is an overall interpretation of the Pyrenees main magnetic domains.
{"title":"The structural anatomy of the Pyrenees examined through EMAG2v2 magnetic data","authors":"África Gamisel-Muzás, Ruth Soto, Conxi Ayala, Tania Mochales, Félix Manuel Rubio, Pilar Clariana, Carmen Rey-Moral, Juliana Martín-León","doi":"10.5194/egusphere-2024-1602","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1602","url":null,"abstract":"<strong>Abstract.</strong> The major goal of this work is to provide an insight into the structural anatomy of the Pyrenees based on the magnetic data from the Earth Magnetic Anomaly Grid 2-arc-minute resolution (EMAG2v2). We focused on providing qualitative and semi-quantitative evidence on the magnetic signature of the Pyrenees Mountain Range domains and structures. The integration of reduced to the pole and processed maps, as well as the Bouguer anomaly map with geological data, has proved to be significantly useful in order to shed light on the main anomaly sources. Considering their magnetic response and texture, several anomalies can be linked to buried geological bodies or changes in the magnetic character of the basement. We have estimated their source bodies depth through Euler and power spectrum calculations. We have identified eight magnetic zones with different features and interpreted them in terms of the geological and structural setting of the area. The result is an overall interpretation of the Pyrenees main magnetic domains.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"39 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141546358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 : 2024-06-04DOI: 10.5194/egusphere-2024-1567
Jeffrey M. Rahl, Brendan Moehringer, Kenneth S. Befus, John S. Singleton
Abstract. Laboratory experiments demonstrate that intragranular water exerts an important control on deformation within quartz, causing weakening and promoting plasticity. The role of water on natural quartz deformation, however, remains unclear, as recent studies find an inverse relationship between water content and the magnitude of plastic strain. Furthermore, little work has investigated the effects, if any, of water on the relative activity of various slip systems in quartz. We focus on a naturally-strained quartzite from the Antietam Formation of the Blue Ridge in Virginia, USA. Quartz water content ranges from <50 to >2000 ppm H2O. Water content and crystallographic data were correlated for 968 grains, enabling us to explore the relationship between water content and quartz crystallographic preferred orientation (CPO) patterns. “Dry” (<150 ppm H2O) and “wet” (>500 ppm H2O) subsets show distinct CPOs; c-axes of dry grains define a cross-girdle oriented perpendicular to the extension direction (X), whereas c-axes of wet grains are concentrated along the perimeter of the pole figure. All water content subsets show grains clustered near the direction of maximum shortening (Z), consistent with activity of the basal ˂a˃ slip system. The cross girdle in the driest grains suggests activity of prism ˂a˃ and possibly rhomb ˂a˃, whereas the orientation of the wettest grains implies a contribution from prism ˂c˃ slip. These slip system interpretations are supported by analyses of intragranular misorientations. These results indicate that water content impacts the relative activity of various slip systems in natural quartz, potentially affecting application of the quartz opening angle thermometry.
{"title":"Influence of water on crystallographic preferred orientation patterns in a naturally-deformed quartzite","authors":"Jeffrey M. Rahl, Brendan Moehringer, Kenneth S. Befus, John S. Singleton","doi":"10.5194/egusphere-2024-1567","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1567","url":null,"abstract":"<strong>Abstract.</strong> Laboratory experiments demonstrate that intragranular water exerts an important control on deformation within quartz, causing weakening and promoting plasticity. The role of water on natural quartz deformation, however, remains unclear, as recent studies find an inverse relationship between water content and the magnitude of plastic strain. Furthermore, little work has investigated the effects, if any, of water on the relative activity of various slip systems in quartz. We focus on a naturally-strained quartzite from the Antietam Formation of the Blue Ridge in Virginia, USA. Quartz water content ranges from <50 to >2000 ppm H<sub>2</sub>O. Water content and crystallographic data were correlated for 968 grains, enabling us to explore the relationship between water content and quartz crystallographic preferred orientation (CPO) patterns. “Dry” (<150 ppm H<sub>2</sub>O) and “wet” (>500 ppm H<sub>2</sub>O) subsets show distinct CPOs; c-axes of dry grains define a cross-girdle oriented perpendicular to the extension direction (X), whereas c-axes of wet grains are concentrated along the perimeter of the pole figure. All water content subsets show grains clustered near the direction of maximum shortening (Z), consistent with activity of the basal ˂a˃ slip system. The cross girdle in the driest grains suggests activity of prism ˂a˃ and possibly rhomb ˂a˃, whereas the orientation of the wettest grains implies a contribution from prism ˂c˃ slip. These slip system interpretations are supported by analyses of intragranular misorientations. These results indicate that water content impacts the relative activity of various slip systems in natural quartz, potentially affecting application of the quartz opening angle thermometry.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"26 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141259561","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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