Maxime Jamet, Gregory Ballas, Roger Soliva, Olivier Gerbeaud, Thierry Lefebvre, Christine Leredde, Didier Loggia
Abstract. This study delves into the characterisation of a heterogenous reservoir, the Tchirezrine II sandstone unit in northern Niger. The characterisation is crucial for potential uranium in situ recovery (ISR) in a naturally fractured and faulted context. Employing a multifaceted approach, including well log data, optical borehole imagery, and hydrogeological tests, alongside satellite-based lineament analysis, this study provides a comprehensive understanding of the structures and their impact on fluid flow. Lineament analysis reveals scale-dependent patterns, consistent with spatially homogeneous joint networks restricted to mechanical units, as well as nearly scale-invariant patterns, better corresponding to spatially heterogeneous fault networks. Various deformation structures are detected from borehole imagery, including extensional fractures, cataclastic deformation bands, and brecciated–cataclastic fault cores. Based on well log data, the Tchirezrine II reservoir displays heterogeneous porosity and permeability related to its fluvial context. These data differ from the traditional porosity–permeability relationship obtained in a sandstone reservoir matrix but are instead consistent with Nelson's classification, emphasising the impact of deformation structures on such petrophysical properties. Hydrological tests have been implemented into a zone of E–W-trending deformation structures, revealing a strong permeability anisotropy. This strong E–W anisotropy is consistent with the presence of the observed E–W structures, i.e. with a draining behaviour of extensional open fractures and a sealing behaviour of both cataclastic bands and fault rocks. Considering implications for ISR mining, this study allows the discussion of the interplay between fractures, faults, and fluid flow properties. It suggests that a well pattern perpendicular to the main permeability orientation can attenuate channelled flow, thus improving the contact of the leach solution with the mineralised matrix. These results provide an integrated approach and a multi-scale characterisation of naturally fractured reservoir (NFR) properties in sandstone, offering a basis for the optimisation of NFR production such as ISR development.
摘要本研究深入探讨了尼日尔北部 Tchirezrine II 砂岩单元这一异质储层的特征。该储层的特征描述对于在天然断裂和断层背景下进行潜在的铀原位采收（ISR）至关重要。这项研究采用了多方面的方法，包括测井数据、井眼光学成像和水文地质测试，以及基于卫星的线状分析，全面了解了这些结构及其对流体流动的影响。线状分析揭示了与尺度相关的模式，与局限于力学单元的空间均质联合网络相一致，同时也揭示了几乎与尺度无关的模式，更符合空间异质断层网络。从井眼图像中探测到了各种变形结构，包括延伸断裂、巨碎变形带和角砾岩-巨碎屑断层岩心。根据测井数据，Tchirezrine II 储层显示出与其河流背景相关的异质性孔隙度和渗透率。这些数据不同于在砂岩储层基质中获得的传统孔隙度-渗透率关系，而是与纳尔逊分类法一致，强调了变形结构对此类岩石物理特性的影响。在 E-W 向变形结构区进行了水文测验，揭示了强烈的渗透率各向异性。这种强烈的 E-W 向各向异性与观测到的 E-W 结构的存在是一致的，即与延伸性开放断裂的排水行为以及岩屑带和断层岩的密封行为是一致的。考虑到对 ISR 采矿的影响，这项研究有助于讨论断裂、断层和流体流动特性之间的相互作用。研究表明，垂直于主要渗透方向的井型可以减弱导流，从而改善浸出液与矿化基质的接触。这些结果提供了一种综合方法和砂岩天然裂缝储层（NFR）特性的多尺度表征，为天然裂缝储层生产的优化（如 ISR 开发）提供了基础。
{"title":"Naturally fractured reservoir characterisation in heterogeneous sandstones: insight for uranium in situ recovery (Imouraren, Niger)","authors":"Maxime Jamet, Gregory Ballas, Roger Soliva, Olivier Gerbeaud, Thierry Lefebvre, Christine Leredde, Didier Loggia","doi":"10.5194/se-15-895-2024","DOIUrl":"https://doi.org/10.5194/se-15-895-2024","url":null,"abstract":"Abstract. This study delves into the characterisation of a heterogenous reservoir, the Tchirezrine II sandstone unit in northern Niger. The characterisation is crucial for potential uranium in situ recovery (ISR) in a naturally fractured and faulted context. Employing a multifaceted approach, including well log data, optical borehole imagery, and hydrogeological tests, alongside satellite-based lineament analysis, this study provides a comprehensive understanding of the structures and their impact on fluid flow. Lineament analysis reveals scale-dependent patterns, consistent with spatially homogeneous joint networks restricted to mechanical units, as well as nearly scale-invariant patterns, better corresponding to spatially heterogeneous fault networks. Various deformation structures are detected from borehole imagery, including extensional fractures, cataclastic deformation bands, and brecciated–cataclastic fault cores. Based on well log data, the Tchirezrine II reservoir displays heterogeneous porosity and permeability related to its fluvial context. These data differ from the traditional porosity–permeability relationship obtained in a sandstone reservoir matrix but are instead consistent with Nelson's classification, emphasising the impact of deformation structures on such petrophysical properties. Hydrological tests have been implemented into a zone of E–W-trending deformation structures, revealing a strong permeability anisotropy. This strong E–W anisotropy is consistent with the presence of the observed E–W structures, i.e. with a draining behaviour of extensional open fractures and a sealing behaviour of both cataclastic bands and fault rocks. Considering implications for ISR mining, this study allows the discussion of the interplay between fractures, faults, and fluid flow properties. It suggests that a well pattern perpendicular to the main permeability orientation can attenuate channelled flow, thus improving the contact of the leach solution with the mineralised matrix. These results provide an integrated approach and a multi-scale characterisation of naturally fractured reservoir (NFR) properties in sandstone, offering a basis for the optimisation of NFR production such as ISR development.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"354 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141781968","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. On 20 April 2013, Lushan experienced an earthquake with a magnitude of 7.0. In seismic assessments, borehole strainmeters, recognized for their remarkable sensitivity and inherent reliability in tracking crustal deformation, are extensively employed. However, traditional data-processing methods encounter challenges when handling massive dataset-s. This study proposes using a Graph WaveNet graph neural network to analyze borehole strain data from multiple stations near the earthquake epicenter and establishes a node graph structure using data from four stations near the Lushan epicenter, covering the years 2010–2013. After excluding the potential effects of pressure, temperature, and rainfall, we statistically analyzed the pre-earthquake anomalies. Focusing on the Guza, Xiaomiao, and Luzhou stations, which are the closest to the epicenter, the fitting results revealed two acceleration events of anomalous accumulation that occurred before the earthquake. Occurring approximately 4 months before the earthquake event, the first acceleration event indicated the pre-release of energy from a weak fault section. Conversely, the acceleration event observed a few days before the earthquake indicated a strong fault section that reached an unstable state with accumulating strain. We tentatively infer that these two anomalous cumulative accelerations may be related to the preparation phase for a large earthquake. This study highlights the considerable potential of graph neural networks in conducting multistation studies of pre-earthquake anomalies.
{"title":"Extraction of pre-earthquake anomalies from borehole strain data using Graph WaveNet: a case study of the 2013 Lushan earthquake in China","authors":"Chenyang Li, Yu Duan, Ying Han, Zining Yu, Chengquan Chi, Dewang Zhang","doi":"10.5194/se-15-877-2024","DOIUrl":"https://doi.org/10.5194/se-15-877-2024","url":null,"abstract":"Abstract. On 20 April 2013, Lushan experienced an earthquake with a magnitude of 7.0. In seismic assessments, borehole strainmeters, recognized for their remarkable sensitivity and inherent reliability in tracking crustal deformation, are extensively employed. However, traditional data-processing methods encounter challenges when handling massive dataset-s. This study proposes using a Graph WaveNet graph neural network to analyze borehole strain data from multiple stations near the earthquake epicenter and establishes a node graph structure using data from four stations near the Lushan epicenter, covering the years 2010–2013. After excluding the potential effects of pressure, temperature, and rainfall, we statistically analyzed the pre-earthquake anomalies. Focusing on the Guza, Xiaomiao, and Luzhou stations, which are the closest to the epicenter, the fitting results revealed two acceleration events of anomalous accumulation that occurred before the earthquake. Occurring approximately 4 months before the earthquake event, the first acceleration event indicated the pre-release of energy from a weak fault section. Conversely, the acceleration event observed a few days before the earthquake indicated a strong fault section that reached an unstable state with accumulating strain. We tentatively infer that these two anomalous cumulative accelerations may be related to the preparation phase for a large earthquake. This study highlights the considerable potential of graph neural networks in conducting multistation studies of pre-earthquake anomalies.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"22 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141745843","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}
Erik van der Wiel, Cedric Thieulot, Douwe J. J. van Hinsbergen
Abstract. Geodynamic models of mantle convection provide a powerful tool to obtain insights into the structure and composition of the Earth's mantle that resulted from a long history of differentiating and mixing. Comparing such models with geophysical and geochemical observations is challenging, as these datasets often sample entirely different temporal and spatial scales. Here, we explore the use of configurational entropy, based on tracer and compositional distribution on a global and local scale. We show means to calculate configurational entropy in a 2D annulus and find that these calculations may be used to quantitatively compare long-term geodynamic models with each other. The entropy may be used to analyse, with a single measure, the mixed state of the mantle as a whole and may also be useful to compare numerical models with local anomalies in the mantle that may be inferred from seismological or geochemical observations.
{"title":"Quantifying mantle mixing through configurational entropy","authors":"Erik van der Wiel, Cedric Thieulot, Douwe J. J. van Hinsbergen","doi":"10.5194/se-15-861-2024","DOIUrl":"https://doi.org/10.5194/se-15-861-2024","url":null,"abstract":"Abstract. Geodynamic models of mantle convection provide a powerful tool to obtain insights into the structure and composition of the Earth's mantle that resulted from a long history of differentiating and mixing. Comparing such models with geophysical and geochemical observations is challenging, as these datasets often sample entirely different temporal and spatial scales. Here, we explore the use of configurational entropy, based on tracer and compositional distribution on a global and local scale. We show means to calculate configurational entropy in a 2D annulus and find that these calculations may be used to quantitatively compare long-term geodynamic models with each other. The entropy may be used to analyse, with a single measure, the mixed state of the mantle as a whole and may also be useful to compare numerical models with local anomalies in the mantle that may be inferred from seismological or geochemical observations.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"81 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141738110","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 : 2024-07-15DOI: 10.5194/egusphere-2024-2034
Jon Engström, Kathryn Cutts, Stijn Glorie, Esa Heilimo, Ester M. Jolis, Radoslaw M. Michallik
Abstract. The Southern Finland granites and associated migmatitic rocks have a complex metamorphic history, being affected by multiple events during the ca. 1.88–1.79 Ga Svecofennian orogeny. In this study, the prolonged tectonic evolution of migmatites and associated rocks in SW Finland has been studied using the new in situ Lu-Hf method. Results reveal detailed temporal constraints for the tectonic evolution that can be linked to major events in adjacent tectonic blocks in both Finland and Sweden during the Svecofennian orogeny. The metamorphic peak at the Olkiluoto site occurred at 1834 ± 7 Ma based on in situ Lu-Hf dating of garnet. The P-T path for the rocks indicates a prograde evolution, with peak P-T conditions of 3–5 kbar and approximately 700 °C. The metamorphic constraints and age presented in this paper enhance our understanding of the geological and tectonic evolution in SW Finland, coupling the Olkiluoto site to the Häme metamorphic and tectonic belt in Finland and highlighting tectonic and metamorphic similarities with the Ljusdal Block of Sweden.
摘要芬兰南部花岗岩及相关的岩浆岩具有复杂的变质历史，在约 1.88-1.79 Ga 的斯维科芬尼造山运动期间受到多次影响。1.88-1.79 Ga Svecofennian造山运动期间的多次事件的影响。在这项研究中，采用新的原位Lu-Hf方法研究了芬兰西南部伟晶岩及相关岩石的长期构造演化。研究结果揭示了构造演化的详细时间约束条件，这些约束条件可与斯维科芬尼造山运动期间芬兰和瑞典相邻构造区块发生的重大事件联系起来。根据石榴石的原位Lu-Hf年代测定，Olkiluoto地点的变质高峰出现在1834 ± 7 Ma。岩石的P-T轨迹表明其为顺行演化，峰值P-T条件为3-5千巴和约700 °C。本文提出的变质约束条件和年龄加深了我们对芬兰西南部地质和构造演化的理解，将奥尔基卢奥托遗址与芬兰的海梅变质构造带联系起来，并突出了与瑞典柳斯达尔区块在构造和变质方面的相似性。
{"title":"Insights into the tectonic evolution of the Svecofennian orogeny based on in situ Lu-Hf dating of garnet from Olkiluoto, SW Finland","authors":"Jon Engström, Kathryn Cutts, Stijn Glorie, Esa Heilimo, Ester M. Jolis, Radoslaw M. Michallik","doi":"10.5194/egusphere-2024-2034","DOIUrl":"https://doi.org/10.5194/egusphere-2024-2034","url":null,"abstract":"<strong>Abstract.</strong> The Southern Finland granites and associated migmatitic rocks have a complex metamorphic history, being affected by multiple events during the ca. 1.88–1.79 Ga Svecofennian orogeny. In this study, the prolonged tectonic evolution of migmatites and associated rocks in SW Finland has been studied using the new <em>in situ</em> Lu-Hf method. Results reveal detailed temporal constraints for the tectonic evolution that can be linked to major events in adjacent tectonic blocks in both Finland and Sweden during the Svecofennian orogeny. The metamorphic peak at the Olkiluoto site occurred at 1834 ± 7 Ma based on <em>in situ</em> Lu-Hf dating of garnet. The P-T path for the rocks indicates a prograde evolution, with peak P-T conditions of 3–5 kbar and approximately 700 °C. The metamorphic constraints and age presented in this paper enhance our understanding of the geological and tectonic evolution in SW Finland, coupling the Olkiluoto site to the Häme metamorphic and tectonic belt in Finland and highlighting tectonic and metamorphic similarities with the Ljusdal Block of Sweden.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"65 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141720157","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. Monitoring changes in regional terrestrial water storage (TWS) and groundwater storage (GWS) is important for effectively managing water resources. Here, we investigate the TWS and GWS changes in the Yangtze River Delta using the GRACE/GRACE-FO mascon solutions, GLDAS NOAH models and in situ groundwater level changes from monitoring wells over the period of April 2002 to December 2022. The results show that the regional mean TWS change rate of the entire Yangtze River Delta is 0.62±0.10 mm/year, at 0.47±0.07 mm/year for the GWS component and 0.15±0.08 mm/year for the other components, which includes soil moisture, snow water and surface water change derived from the GLDAS NOAH models. At the basin scale, significant positive trends existed in water storage in Shanghai and Zhejiang Provinces; however, relatively small negative trends existed in Jiangsu and Anhui Provinces, which was confirmed by the spatial distributions of areas with linear trends. After comparing the estimated GWS change with the in situ groundwater level change from thirteen monitoring wells, we concluded that the groundwater levels in Shanghai and Zhejiang Provinces slightly recovered over the last 20 years and that this trend will continue in the coming years, mainly due to the sustainable water resource management policies of the local governments.
{"title":"Regional Terrestrial Water Storage Changes in the Yangtze River Delta over the Recent 20 years","authors":"Fengwei Wang, Jianhua Geng, Yunzhong Shen, Yanlin Wen, Tengfei Feng","doi":"10.5194/egusphere-2024-1406","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1406","url":null,"abstract":"<strong>Abstract.</strong> Monitoring changes in regional terrestrial water storage (TWS) and groundwater storage (GWS) is important for effectively managing water resources. Here, we investigate the TWS and GWS changes in the Yangtze River Delta using the GRACE/GRACE-FO mascon solutions, GLDAS NOAH models and in situ groundwater level changes from monitoring wells over the period of April 2002 to December 2022. The results show that the regional mean TWS change rate of the entire Yangtze River Delta is 0.62±0.10 mm/year, at 0.47±0.07 mm/year for the GWS component and 0.15±0.08 mm/year for the other components, which includes soil moisture, snow water and surface water change derived from the GLDAS NOAH models. At the basin scale, significant positive trends existed in water storage in Shanghai and Zhejiang Provinces; however, relatively small negative trends existed in Jiangsu and Anhui Provinces, which was confirmed by the spatial distributions of areas with linear trends. After comparing the estimated GWS change with the in situ groundwater level change from thirteen monitoring wells, we concluded that the groundwater levels in Shanghai and Zhejiang Provinces slightly recovered over the last 20 years and that this trend will continue in the coming years, mainly due to the sustainable water resource management policies of the local governments.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"36 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141586415","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}
Ran Issachar, Peter Haas, Nico Augustin, Jörg Ebbing
Abstract. The causal relationship between the activity of mantle plumes and continental break-up is still elusive. The Afro-Arabian rift system offers an opportunity to examine these relationships, in which an ongoing continental break-up intersects a large Cenozoic plume-related flood basalt series. In the Afar region, the Gulf of Aden, the Red Sea, and the Main Ethiopian Rift form an R-R-R triple junction within plume-related flood basalt series. We provide an up-to-date synthesis of the available geophysical and geological data from this region. We map the rift architecture in the intersection region by applying the difference in Gaussians to the topography and the bathymetry and interpreting vertical gravity gradients and Bouguer anomalies. With the aid of these methods we review the spatiotemporal constraints in the evolution of the different features of the plume–rift system. Our results show rough and irregular morphologies of the Gulf of Aden and the Red Sea arms in contrast to the symmetric, continuous, and smooth Main Ethiopian Rift. The triple junction formed by the northeastward propagation of the Main Ethiopian Rift and developed simultaneously with the abandonment of the tectonic connection between the Red Sea and the Gulf of Aden through Bab al Mandab Strait. The triple junction was the last feature to develop in the plume–rift system and marked a tectonic reorganization. By this time, all rift arms were sufficiently evolved and the break-up between Africa and Arabia was already accomplished. We argue that the classical active and passive rifting mechanisms cannot simply explain the progressive development of the Afro-Arabian rift. Instead, we propose a plume-induced plate rotation, which includes an interaction between active and passive mechanisms. In this tectonic scenario, the arrival of the Afar plume provided a push force that promoted the rotation of Arabia around a nearby pole located to the northwest of the plate boundary, enabling the rifting and, ultimately, the break-up of Arabia from Africa.
{"title":"Rift and plume: a discussion on active and passive rifting mechanisms in the Afro-Arabian rift based on synthesis of geophysical data","authors":"Ran Issachar, Peter Haas, Nico Augustin, Jörg Ebbing","doi":"10.5194/se-15-807-2024","DOIUrl":"https://doi.org/10.5194/se-15-807-2024","url":null,"abstract":"Abstract. The causal relationship between the activity of mantle plumes and continental break-up is still elusive. The Afro-Arabian rift system offers an opportunity to examine these relationships, in which an ongoing continental break-up intersects a large Cenozoic plume-related flood basalt series. In the Afar region, the Gulf of Aden, the Red Sea, and the Main Ethiopian Rift form an R-R-R triple junction within plume-related flood basalt series. We provide an up-to-date synthesis of the available geophysical and geological data from this region. We map the rift architecture in the intersection region by applying the difference in Gaussians to the topography and the bathymetry and interpreting vertical gravity gradients and Bouguer anomalies. With the aid of these methods we review the spatiotemporal constraints in the evolution of the different features of the plume–rift system. Our results show rough and irregular morphologies of the Gulf of Aden and the Red Sea arms in contrast to the symmetric, continuous, and smooth Main Ethiopian Rift. The triple junction formed by the northeastward propagation of the Main Ethiopian Rift and developed simultaneously with the abandonment of the tectonic connection between the Red Sea and the Gulf of Aden through Bab al Mandab Strait. The triple junction was the last feature to develop in the plume–rift system and marked a tectonic reorganization. By this time, all rift arms were sufficiently evolved and the break-up between Africa and Arabia was already accomplished. We argue that the classical active and passive rifting mechanisms cannot simply explain the progressive development of the Afro-Arabian rift. Instead, we propose a plume-induced plate rotation, which includes an interaction between active and passive mechanisms. In this tectonic scenario, the arrival of the Afar plume provided a push force that promoted the rotation of Arabia around a nearby pole located to the northwest of the plate boundary, enabling the rifting and, ultimately, the break-up of Arabia from Africa.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"78 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141568391","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}
Onyedika Anthony Igbokwe, Jithender J. Timothy, Ashwani Kumar, Xiao Yan, Mathias Mueller, Alessandro Verdecchia, Günther Meschke, Adrian Immenhauser
Abstract. Changing stress regimes control fracture network geometry and influence porosity and permeability in carbonate reservoirs. Using outcrop data analysis and a displacement-based linear elastic finite-element method, we investigate the impact of stress regime change on fracture network permeability. The model is based on fracture networks, specifically fracture substructures. The Latemar, predominantly affected by subsidence deformation and Alpine compression, is taken as an outcrop analogue for an isolated (Mesozoic) carbonate buildup with fracture-dominated permeability. We apply a novel strategy involving two compressive boundary loading conditions constrained by the study area's NW–SE and N–S stress directions. Stress-dependent heterogeneous apertures and effective permeability were computed in the 2D domain by (i) using the local stress state within the fracture substructure and (ii) running a single-phase flow analysis considering the fracture apertures in each fracture substructure. Our results show that the impact of the modelled far-field stresses at (i) subsidence deformation from the NW–SE and (ii) Alpine deformation from N–S increased the overall fracture aperture and permeability. In each case, increasing permeability is associated with open fractures parallel to the orientation of the loading stages and with fracture densities. The anisotropy of permeability is increased by the density and connectedness of the fracture network and affected by shear dilation. The two far-field stresses simultaneously acting within the selected fracture substructure at a different magnitude and orientation do not necessarily cancel each other out in the mechanical deformation modelling. These stresses affect the overall aperture and permeability distributions and the flow patterns. These effects – potentially ignored in simpler stress-dependent permeability – can result in significant inaccuracies in permeability estimation.
{"title":"Impact of stress regime change on the permeability of a naturally fractured carbonate buildup (Latemar, the Dolomites, northern Italy)","authors":"Onyedika Anthony Igbokwe, Jithender J. Timothy, Ashwani Kumar, Xiao Yan, Mathias Mueller, Alessandro Verdecchia, Günther Meschke, Adrian Immenhauser","doi":"10.5194/se-15-763-2024","DOIUrl":"https://doi.org/10.5194/se-15-763-2024","url":null,"abstract":"Abstract. Changing stress regimes control fracture network geometry and influence porosity and permeability in carbonate reservoirs. Using outcrop data analysis and a displacement-based linear elastic finite-element method, we investigate the impact of stress regime change on fracture network permeability. The model is based on fracture networks, specifically fracture substructures. The Latemar, predominantly affected by subsidence deformation and Alpine compression, is taken as an outcrop analogue for an isolated (Mesozoic) carbonate buildup with fracture-dominated permeability. We apply a novel strategy involving two compressive boundary loading conditions constrained by the study area's NW–SE and N–S stress directions. Stress-dependent heterogeneous apertures and effective permeability were computed in the 2D domain by (i) using the local stress state within the fracture substructure and (ii) running a single-phase flow analysis considering the fracture apertures in each fracture substructure. Our results show that the impact of the modelled far-field stresses at (i) subsidence deformation from the NW–SE and (ii) Alpine deformation from N–S increased the overall fracture aperture and permeability. In each case, increasing permeability is associated with open fractures parallel to the orientation of the loading stages and with fracture densities. The anisotropy of permeability is increased by the density and connectedness of the fracture network and affected by shear dilation. The two far-field stresses simultaneously acting within the selected fracture substructure at a different magnitude and orientation do not necessarily cancel each other out in the mechanical deformation modelling. These stresses affect the overall aperture and permeability distributions and the flow patterns. These effects – potentially ignored in simpler stress-dependent permeability – can result in significant inaccuracies in permeability estimation.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"9 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141568390","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}
Renxian Xie, Lin Chen, Jason P. Morgan, Yongshun John Chen
Abstract. Continents are formed by the amalgamation of numerous micro-terranes and island arcs, so they have spatially varying lithosphere strengths. The crème brûlée (CB) model and the jelly sandwich (JS) model have been commonly used to describe continental lithosphere strength–depth variations. Depending on the strength of the continental lower crust, the CB and JS models can be further subdivided into two subclasses in which the I subclass (CB-I and JS-I) and II subclass (CB-II and JS-II), respectively, have a strong or weak lower crust. During the continental collision, lithosphere deformation is the byproduct of the comprehensive interaction of multiple terranes. Here we used 2-D thermomechanical numerical models that contain three continental terranes to systematically explore the effects of terranes with various strengths on continental deformation and studied the effects of different rheological assumptions on terrane deformation. We found four types of lithosphere deformation patterns: collision, subduction, thickening and delamination, and replacement. These simulation patterns are seen in observed deformation patterns and structures in East Asia, suggesting they are likely to be naturally occurring modes of intracontinental orogenesis.
摘要大陆是由众多微地壳和岛弧合并而成的，因此它们的岩石圈强度在空间上各不相同。奶油布丁（CB）模型和果冻三明治（JS）模型常用来描述大陆岩石圈强度-深度变化。根据大陆下地壳强度的不同，CB 和 JS 模型可进一步细分为两个亚类，其中 I 亚类（CB-I 和 JS-I）和 II 亚类（CB-II 和 JS-II）分别具有强或弱的下地壳。在大陆碰撞过程中，岩石圈变形是多地块综合作用的副产品。在此，我们利用包含三块大陆岩石圈的二维热力学数值模型，系统地探讨了不同强度的岩石圈对大陆变形的影响，并研究了不同流变学假设对岩石圈变形的影响。我们发现了四种岩石圈变形模式：碰撞、俯冲、增厚和分层以及置换。这些模拟模式在东亚观测到的变形模式和结构中都可以看到，表明它们很可能是自然发生的大陆内部造山模式。
{"title":"Various lithospheric deformation patterns derived from rheological contrasts between continental terranes: insights from 2-D numerical simulations","authors":"Renxian Xie, Lin Chen, Jason P. Morgan, Yongshun John Chen","doi":"10.5194/se-15-789-2024","DOIUrl":"https://doi.org/10.5194/se-15-789-2024","url":null,"abstract":"Abstract. Continents are formed by the amalgamation of numerous micro-terranes and island arcs, so they have spatially varying lithosphere strengths. The crème brûlée (CB) model and the jelly sandwich (JS) model have been commonly used to describe continental lithosphere strength–depth variations. Depending on the strength of the continental lower crust, the CB and JS models can be further subdivided into two subclasses in which the I subclass (CB-I and JS-I) and II subclass (CB-II and JS-II), respectively, have a strong or weak lower crust. During the continental collision, lithosphere deformation is the byproduct of the comprehensive interaction of multiple terranes. Here we used 2-D thermomechanical numerical models that contain three continental terranes to systematically explore the effects of terranes with various strengths on continental deformation and studied the effects of different rheological assumptions on terrane deformation. We found four types of lithosphere deformation patterns: collision, subduction, thickening and delamination, and replacement. These simulation patterns are seen in observed deformation patterns and structures in East Asia, suggesting they are likely to be naturally occurring modes of intracontinental orogenesis.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"40 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141568394","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. We investigate the upper-crustal structure of the Rukwa–Tanganyika rift zone in East Africa, where the Tanganyika rift interacts with the Rukwa and Mweru-Wantipa rift tips, evidenced by prominent fault scarps and seismicity across the rift interaction zones. We invert earthquake P-wave and S-wave travel times to produce 3D upper-crustal velocity models for the region and perform seismicity cluster analysis to understand strain accommodation in rift interaction zones and at the propagating rift tips. The resulting models reveal the occurrence of anomalously high Vp/Vs (primary-to-secondary wave velocity) ratios in the upper crust beneath the Rukwa and Mweru-Wantipa rift tips – regions with basement exposures and sparse rift sedimentation. We detect distinct earthquake families within the deeper clusters which exhibit a temporal evolution pattern characterized by an upward linear trend that suggests triggering caused by upward fluid migration and creep failure. A spatial transition from proximal tip zones dominated by a thinned crust and through-going crustal and upper-mantle seismicity to distal tip zones with a thick crust and dominantly upper-crustal seismicity indicates an along-axis variation in the controls on rift tip deformation. Overall, the collocation of basement faulting, crustal and upper-mantle seismicity, and high upper-crustal Vp/Vs ratios suggests a mechanically weakened crust at the rift tips, likely accommodated by brittle damage from crustal-bending strain and thermomechanical alteration via ascending fluids (mantle-sourced volatiles and hydrothermal fluids). These findings provide new insights into the physics of the propagation, linkage, and coalescence of continental rift tips – a necessary ingredient for initiating continental-breakup axes.
摘要我们研究了东非鲁夸-坦噶尼喀断裂带的上地壳结构，坦噶尼喀断裂与鲁夸和姆韦鲁-万提帕断裂尖端相互作用，突出的断层疤痕和跨越断裂相互作用区的地震活动证明了这一点。我们反演了地震 P 波和 S 波的传播时间，为该地区建立了三维上地壳速度模型，并进行了地震群分析，以了解裂谷互动区和传播裂谷尖端的应变容纳情况。由此产生的模型揭示了鲁克瓦和姆韦鲁-万蒂帕裂谷顶端--基底暴露和裂谷沉积稀少的区域--下方上地壳出现异常高的 Vp/Vs（一次波速与二次波速）比。我们在较深的地震群中发现了不同的地震家族，这些地震家族的时间演化模式以上升的线性趋势为特征，表明触发地震的原因是流体向上迁移和蠕变破坏。从地壳变薄、贯穿地壳和上地幔地震为主的近端尖区到地壳较厚、上地壳地震为主的远端尖区的空间过渡，表明裂谷端部变形的控制存在沿轴变化。总体而言，基底断裂、地壳和上地幔地震以及上地壳高Vp/Vs比值的搭配表明，裂谷尖端的地壳机械性减弱，很可能是由地壳弯曲应变的脆性破坏和通过上升流体（地幔源挥发物和热液）产生的热机械改变所造成的。这些发现为了解大陆裂谷尖端的传播、联系和凝聚的物理学原理提供了新的视角--这是启动大陆断裂轴的必要因素。
{"title":"Propagating rifts: the roles of crustal damage and ascending mantle fluids","authors":"Folarin Kolawole, Rasheed Ajala","doi":"10.5194/se-15-747-2024","DOIUrl":"https://doi.org/10.5194/se-15-747-2024","url":null,"abstract":"Abstract. We investigate the upper-crustal structure of the Rukwa–Tanganyika rift zone in East Africa, where the Tanganyika rift interacts with the Rukwa and Mweru-Wantipa rift tips, evidenced by prominent fault scarps and seismicity across the rift interaction zones. We invert earthquake P-wave and S-wave travel times to produce 3D upper-crustal velocity models for the region and perform seismicity cluster analysis to understand strain accommodation in rift interaction zones and at the propagating rift tips. The resulting models reveal the occurrence of anomalously high Vp/Vs (primary-to-secondary wave velocity) ratios in the upper crust beneath the Rukwa and Mweru-Wantipa rift tips – regions with basement exposures and sparse rift sedimentation. We detect distinct earthquake families within the deeper clusters which exhibit a temporal evolution pattern characterized by an upward linear trend that suggests triggering caused by upward fluid migration and creep failure. A spatial transition from proximal tip zones dominated by a thinned crust and through-going crustal and upper-mantle seismicity to distal tip zones with a thick crust and dominantly upper-crustal seismicity indicates an along-axis variation in the controls on rift tip deformation. Overall, the collocation of basement faulting, crustal and upper-mantle seismicity, and high upper-crustal Vp/Vs ratios suggests a mechanically weakened crust at the rift tips, likely accommodated by brittle damage from crustal-bending strain and thermomechanical alteration via ascending fluids (mantle-sourced volatiles and hydrothermal fluids). These findings provide new insights into the physics of the propagation, linkage, and coalescence of continental rift tips – a necessary ingredient for initiating continental-breakup axes.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"28 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141546594","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 : 2024-07-04DOI: 10.22541/essoar.171995191.13613873/v1
Simone Masoch, Giorgio Pennacchioni, Michele Fondriest, Rodrigo Gomila, Piero Poli, José Cembrano, Giulio Di Toro
Abstract. Earthquake swarms commonly occur in upper-crustal hydrothermal-magmatic systems and activate mesh-like fault networks. How these networks develop through space and time along seismic faults is poorly constrained in the geological record. Here, we describe a spatially dense array of small-displacement (< 1.5 m) epidote-rich fault-veins within granitoids, occurring at the intersections of subsidiary faults with the exhumed seismogenic Bolfin Fault Zone (Atacama Fault System, Northern Chile). Epidote faulting and veining occurred at 3–7 km depth and 200–300 °C ambient temperature. At distance ≤ 1 cm to fault-veins, the magmatic quartz of the wall-rock shows (i) thin (< 10-µm-thick) interlaced deformation lamellae, and (ii) crosscutting quartz-filled veinlets. The epidote-rich fault-veins (i) include clasts of deformed magmatic quartz, with deformation lamellae and quartz-filled veinlets, and (ii) record cyclic events of extensional-to-hybrid veining and either aseismic or seismic shearing. Deformation of the wall-rock quartz is interpreted to record the large stress perturbations associated with the rupture propagation of small earthquakes. In contrast, dilation and shearing forming the epidote-rich fault-veins are interpreted to record the later development of a mature and hydraulically-connected fault-fracture system. In this latter stage, the fault-fracture system cyclically ruptured due to fluid pressure fluctuations, possibly correlated with swarm-like earthquake sequences.
{"title":"Earthquake swarms frozen in an exhumed hydrothermal system (Bolfin Fault Zone, Chile)","authors":"Simone Masoch, Giorgio Pennacchioni, Michele Fondriest, Rodrigo Gomila, Piero Poli, José Cembrano, Giulio Di Toro","doi":"10.22541/essoar.171995191.13613873/v1","DOIUrl":"https://doi.org/10.22541/essoar.171995191.13613873/v1","url":null,"abstract":"<strong>Abstract.</strong> Earthquake swarms commonly occur in upper-crustal hydrothermal-magmatic systems and activate mesh-like fault networks. How these networks develop through space and time along seismic faults is poorly constrained in the geological record. Here, we describe a spatially dense array of small-displacement (< 1.5 m) epidote-rich fault-veins within granitoids, occurring at the intersections of subsidiary faults with the exhumed seismogenic Bolfin Fault Zone (Atacama Fault System, Northern Chile). Epidote faulting and veining occurred at 3–7 km depth and 200–300 °C ambient temperature. At distance ≤ 1 cm to fault-veins, the magmatic quartz of the wall-rock shows (i) thin (< 10-µm-thick) interlaced deformation lamellae, and (ii) crosscutting quartz-filled veinlets. The epidote-rich fault-veins (i) include clasts of deformed magmatic quartz, with deformation lamellae and quartz-filled veinlets, and (ii) record cyclic events of extensional-to-hybrid veining and either aseismic or seismic shearing. Deformation of the wall-rock quartz is interpreted to record the large stress perturbations associated with the rupture propagation of small earthquakes. In contrast, dilation and shearing forming the epidote-rich fault-veins are interpreted to record the later development of a mature and hydraulically-connected fault-fracture system. In this latter stage, the fault-fracture system cyclically ruptured due to fluid pressure fluctuations, possibly correlated with swarm-like earthquake sequences.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"32 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141546595","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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