Pub Date : 2024-05-07DOI: 10.5194/egusphere-2024-1263
Alan Chen, Xuanhua Chen
Abstract. The Bohai Sea in eastern China is located in the back-arc extensional regime due to westward subduction of the Pacific Plate underneath the Eurasian Plate. It is one of the regions with frequent earthquakes. Previous recognition of the origin of the Bohai Sea was limited by the understanding of back-arc extensional mode perpendicular to the subduction zone in eastern Asian continental margin. In this paper, a new model for the genesis of the Bohai Sea is proposed, based on the construction of major fault system and investigation of several main boundaries enclosing the Bohai Sea. Through field investigation and analyses of tectonic landforms and boundary faults on the northwest coast of the Bohai Sea and eastern and western margins of the Liaodong Peninsula, and geological correlation of the Liaodong and Jiaodong Peninsulas and surrounding areas, we revealed a left-lateral strike-slip fault between the northwest coast of the Liaodong Bay and western margin of the Liaodong Peninsula, and proposed a right-lateral strike-slip fault between the eastern margin of the Liaodong Peninsula and northwestern margin of the Jiaodong Peninsula. This mode of movement may have been resulted from the NE stretching which is parallel to the subduction zone in northwestern Pacific margin. Therefore, we suggest that the formation of the Bohai Sea is resulted from the superimposition of the NE extension parallel to the subduction zone on the NW extension perpendicular to the subduction zone. We speculate that the two-direction extension perpendicular and parallel to the subduction zone should be the basic pattern of the back-arc extension with spherical-geometric effect.
{"title":"Origin of the Bohai Sea, North China Craton and implication for bi-directional back-arc extension in East Asia continental margin","authors":"Alan Chen, Xuanhua Chen","doi":"10.5194/egusphere-2024-1263","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1263","url":null,"abstract":"<strong>Abstract.</strong> The Bohai Sea in eastern China is located in the back-arc extensional regime due to westward subduction of the Pacific Plate underneath the Eurasian Plate. It is one of the regions with frequent earthquakes. Previous recognition of the origin of the Bohai Sea was limited by the understanding of back-arc extensional mode perpendicular to the subduction zone in eastern Asian continental margin. In this paper, a new model for the genesis of the Bohai Sea is proposed, based on the construction of major fault system and investigation of several main boundaries enclosing the Bohai Sea. Through field investigation and analyses of tectonic landforms and boundary faults on the northwest coast of the Bohai Sea and eastern and western margins of the Liaodong Peninsula, and geological correlation of the Liaodong and Jiaodong Peninsulas and surrounding areas, we revealed a left-lateral strike-slip fault between the northwest coast of the Liaodong Bay and western margin of the Liaodong Peninsula, and proposed a right-lateral strike-slip fault between the eastern margin of the Liaodong Peninsula and northwestern margin of the Jiaodong Peninsula. This mode of movement may have been resulted from the NE stretching which is parallel to the subduction zone in northwestern Pacific margin. Therefore, we suggest that the formation of the Bohai Sea is resulted from the superimposition of the NE extension parallel to the subduction zone on the NW extension perpendicular to the subduction zone. We speculate that the two-direction extension perpendicular and parallel to the subduction zone should be the basic pattern of the back-arc extension with spherical-geometric effect.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"40 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-05-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140887717","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}
Joaquín Bastías-Silva, David Chew, Fernando Poblete, Paula Castillo, William Guenthner, Anne Grunow, Ian W. D. Dalziel, Airton N. C. Dias, Cristóbal Ramírez de Arellano, Rodrigo Fernandez
Abstract. While thermochronological studies have constrained the landscape evolution of several of the crustal blocks of West and East Antarctica, the tectono-thermal evolution of the Ellsworth Mountains remains relatively poorly constrained. These mountains are among the crustal blocks that comprise West Antarctica and exhibit an exceptionally well-preserved Palaeozoic sedimentary sequence. Despite the seminal contribution of Fitzgerald and Stump (1991), who suggested an Early Cretaceous uplift event for the Ellsworth Mountains, further thermochronological studies are required to improve the current understanding of the landscape evolution of this mountain chain. We present new zircon (U–Th) / He (ZHe) ages, which provide insights into the landscape evolution of the Ellsworth Mountains. The ZHe ages collected from near the base and the top of the sequence suggest that these rocks underwent burial reheating after deposition. A cooling event is recorded during the Jurassic–Early Cretaceous, which we interpret as representing exhumation in response to rock uplift of the Ellsworth Mountains. Moreover, our results show that while ZHe ages at the base of the sequence are fully reset, towards the top ZHe ages are partially reset. Uplift and exhumation of the Ellsworth Mountains during the Jurassic–Early Cretaceous was contemporaneous with the rotation and translation of this crustal block with respect to East Antarctica and possibly the Antarctic Peninsula. Furthermore, this period is characterized by widespread extension associated with the disassembly and breakup of Gondwana, with the Ellsworth Mountains playing a key role in the opening of the far southern Atlantic. Based on these results, we suggest that uplift of the Ellsworth Mountains during the disassembly of Gondwana provides additional evidence for major rearrangement of the crustal blocks between the South American, African, Australian and Antarctic plates. Finally, uplift of the Ellsworth Mountains commenced during the Jurassic, which predates the Early Cretaceous uplift of the Transantarctic Mountains. We suggest that the rift-related exhumation of the Ellsworth Mountains occurred throughout two events: (i) a Jurassic uplift associated with the disassembly of southwestern Gondwana and (ii) an Early Cretaceous uplift related with the separation between Antarctica and Australia, which is also recorded in the Transantarctic Mountains.
{"title":"Uplift and denudation history of the Ellsworth Mountains: insights from low-temperature thermochronology","authors":"Joaquín Bastías-Silva, David Chew, Fernando Poblete, Paula Castillo, William Guenthner, Anne Grunow, Ian W. D. Dalziel, Airton N. C. Dias, Cristóbal Ramírez de Arellano, Rodrigo Fernandez","doi":"10.5194/se-15-555-2024","DOIUrl":"https://doi.org/10.5194/se-15-555-2024","url":null,"abstract":"Abstract. While thermochronological studies have constrained the landscape evolution of several of the crustal blocks of West and East Antarctica, the tectono-thermal evolution of the Ellsworth Mountains remains relatively poorly constrained. These mountains are among the crustal blocks that comprise West Antarctica and exhibit an exceptionally well-preserved Palaeozoic sedimentary sequence. Despite the seminal contribution of Fitzgerald and Stump (1991), who suggested an Early Cretaceous uplift event for the Ellsworth Mountains, further thermochronological studies are required to improve the current understanding of the landscape evolution of this mountain chain. We present new zircon (U–Th) / He (ZHe) ages, which provide insights into the landscape evolution of the Ellsworth Mountains. The ZHe ages collected from near the base and the top of the sequence suggest that these rocks underwent burial reheating after deposition. A cooling event is recorded during the Jurassic–Early Cretaceous, which we interpret as representing exhumation in response to rock uplift of the Ellsworth Mountains. Moreover, our results show that while ZHe ages at the base of the sequence are fully reset, towards the top ZHe ages are partially reset. Uplift and exhumation of the Ellsworth Mountains during the Jurassic–Early Cretaceous was contemporaneous with the rotation and translation of this crustal block with respect to East Antarctica and possibly the Antarctic Peninsula. Furthermore, this period is characterized by widespread extension associated with the disassembly and breakup of Gondwana, with the Ellsworth Mountains playing a key role in the opening of the far southern Atlantic. Based on these results, we suggest that uplift of the Ellsworth Mountains during the disassembly of Gondwana provides additional evidence for major rearrangement of the crustal blocks between the South American, African, Australian and Antarctic plates. Finally, uplift of the Ellsworth Mountains commenced during the Jurassic, which predates the Early Cretaceous uplift of the Transantarctic Mountains. We suggest that the rift-related exhumation of the Ellsworth Mountains occurred throughout two events: (i) a Jurassic uplift associated with the disassembly of southwestern Gondwana and (ii) an Early Cretaceous uplift related with the separation between Antarctica and Australia, which is also recorded in the Transantarctic Mountains.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"69 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140839588","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 : 2024-04-29DOI: 10.5194/egusphere-2024-1135
Emanuele Scaramuzzo, Franz A. Livio, Maria Giuditta Fellin, Colin Maden
Abstract. We delve into the transition between the Paleozoic Variscan cycle and the Meso-Cenozoic Alpine supercontinent cycle, both of which have played a pivotal role in shaping the central European-Mediterranean plate’s architecture. Our focus is on the European western Southern Alps (Varese Area, N Italy), where we documented the tectonic events occurred during this transition. Two main scenarios have been proposed so far for this transition: i) a single, long-lasting, Permo-Triassic rifting event, culminating in the opening of the Alpine Tethys, or ii) multiple, distinct rifting events, preceding the onset of the Alpine cycle. By means of a tectono-stratigraphic and thermochronological approach, we recognized a first early Permian rifting stage associated with magmatic activity, followed during the early-middle Permian by transpressive tectonics and regional-scale erosion that signal the end of the first cycle of crustal rifting. During the Middle Triassic, a second event initiated, which, we propose, marks the onset of the Alpine Tethys opening. This event could represent the stretching phase, which predates the well documented Upper Triassic crustal-thinning phase. Based on our findings, we propose that the Middle Triassic stretching phase represents the first stage of the Alpine Tethys rifting, thereby rejecting the hypothesis of a continuous Permo-Triassic long-lasting phase of extension.
{"title":"Transpressional tectonics during the Variscan-Alpine cycle transition: supporting a multi-rifting model, evidence from the European western Southern Alps","authors":"Emanuele Scaramuzzo, Franz A. Livio, Maria Giuditta Fellin, Colin Maden","doi":"10.5194/egusphere-2024-1135","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1135","url":null,"abstract":"<strong>Abstract.</strong> We delve into the transition between the Paleozoic Variscan cycle and the Meso-Cenozoic Alpine supercontinent cycle, both of which have played a pivotal role in shaping the central European-Mediterranean plate’s architecture. Our focus is on the European western Southern Alps (Varese Area, N Italy), where we documented the tectonic events occurred during this transition. Two main scenarios have been proposed so far for this transition: i) a single, long-lasting, Permo-Triassic rifting event, culminating in the opening of the Alpine Tethys, or ii) multiple, distinct rifting events, preceding the onset of the Alpine cycle. By means of a tectono-stratigraphic and thermochronological approach, we recognized a first early Permian rifting stage associated with magmatic activity, followed during the early-middle Permian by transpressive tectonics and regional-scale erosion that signal the end of the first cycle of crustal rifting. During the Middle Triassic, a second event initiated, which, we propose, marks the onset of the Alpine Tethys opening. This event could represent the stretching phase, which predates the well documented Upper Triassic crustal-thinning phase. Based on our findings, we propose that the Middle Triassic stretching phase represents the first stage of the Alpine Tethys rifting, thereby rejecting the hypothesis of a continuous Permo-Triassic long-lasting phase of extension.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"42 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140808781","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 : 2024-04-26DOI: 10.5194/egusphere-2024-866
Jaroslav Klokocnik, Vaclav Cilek, Jan Kostelecky, Ales Bezdek
Abstract. More advanced data (gravity field model EIGEN 6C4 with GOCE gradiometry data instead of EGM2008) and more sophisticated method (using a set of the gravity aspects instead of the gravity anomalies and the radial second derivative of the disturbing potential only) enable a deeper study of various geological features, here the impact craters Chicxulub and Popigai. We confirm our results from 2010, extend them, and offer more complicated models, namely by means of the gravity strike angles. Both craters are double or multiple craters. The probable impactor direction is from NE for Chicxulub and SE-NW for Popigai. The both crater formations seem to be associated with impact induced tectonics that triggered development of impact grabens.
摘要更先进的数据（重力场模型 EIGEN 6C4 与全球海洋观测卫星梯度测量数据，而不是 EGM2008）和更复杂的方法（使用一组重力方面，而不是仅使用重力异常和扰动势的径向二阶导数）使我们能够更深入地研究各种地质特征，这里指的是撞击坑 Chicxulub 和 Popigai。我们确认了 2010 年的研究结果，并对其进行了扩展，通过重力撞击角提供了更为复杂的模型。这两个陨石坑都是双重或多重陨石坑。奇克苏卢布的撞击方向可能是东北方向，波皮盖的撞击方向可能是东南-西北方向。这两个陨石坑的形成似乎都与撞击引起的构造有关，撞击引发了地堑的发育。
{"title":"Popigai and Chicxulub craters: multiple impacts and their associated grabens","authors":"Jaroslav Klokocnik, Vaclav Cilek, Jan Kostelecky, Ales Bezdek","doi":"10.5194/egusphere-2024-866","DOIUrl":"https://doi.org/10.5194/egusphere-2024-866","url":null,"abstract":"<strong>Abstract.</strong> More advanced data (gravity field model EIGEN 6C4 with GOCE gradiometry data instead of EGM2008) and more sophisticated method (using a set of the gravity aspects instead of the gravity anomalies and the radial second derivative of the disturbing potential only) enable a deeper study of various geological features, here the impact craters Chicxulub and Popigai. We confirm our results from 2010, extend them, and offer more complicated models, namely by means of the gravity strike angles. Both craters are double or multiple craters. The probable impactor direction is from NE for Chicxulub and SE-NW for Popigai. The both crater formations seem to be associated with impact induced tectonics that triggered development of impact grabens.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"41 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140804240","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. The scattered seismic waves of fractured porous rock are strongly affected by the wave-induced fluid pressure diffusion effects between the compliant fractures and the stiffer embedding background. To include these poroelastic effects in seismic modeling, we develop a numerical scheme for discretely distributed large-scale fractures embedded in fluid-saturated porous rock. Using Coates and Schoenberg's local-effective-medium theory and Barbosa's dynamic linear slip model characterized by complex-valued and frequency-dependent fracture compliances, we derive the effective viscoelastic compliances in each spatial discretized cell by superimposing the compliances of the background and the fractures. The effective governing equations for fractured porous rocks are viscoelastic anisotropic and numerically solved by the mixed-grid-stencil frequency-domain finite-difference method. The main advantage of our proposed modeling scheme over poroelastic modeling schemes is that the fractured domain can be modeled using a viscoelastic solid, while the rest of the domain can be modeled using an elastic solid. We have tested the modeling scheme in a single fracture model, a fractured model, and a modified Marmousi model. The good consistency between the scattered waves off a single horizontal fracture calculated using our proposed scheme and the poroelastic modeling validates that our modeling scheme can properly capture the fluid pressure diffusion (FPD) effects. In the case of a set of aligned fractures, the scattered waves from the top and bottom of the fractured reservoir are strongly influenced by the FPD effects, and the reflected waves from the underlying formation can retain the relevant attenuation and dispersion information. The proposed numerical modeling scheme can also be used to improve migration quality and the estimation of fracture mechanical characteristics in inversion.
{"title":"Seismic wave modeling of fluid-saturated fractured porous rock: including fluid pressure diffusion effects of discretely distributed large-scale fractures","authors":"Yingkai Qi, Xuehua Chen, Qingwei Zhao, Xin Luo, Chunqiang Feng","doi":"10.5194/se-15-535-2024","DOIUrl":"https://doi.org/10.5194/se-15-535-2024","url":null,"abstract":"Abstract. The scattered seismic waves of fractured porous rock are strongly affected by the wave-induced fluid pressure diffusion effects between the compliant fractures and the stiffer embedding background. To include these poroelastic effects in seismic modeling, we develop a numerical scheme for discretely distributed large-scale fractures embedded in fluid-saturated porous rock. Using Coates and Schoenberg's local-effective-medium theory and Barbosa's dynamic linear slip model characterized by complex-valued and frequency-dependent fracture compliances, we derive the effective viscoelastic compliances in each spatial discretized cell by superimposing the compliances of the background and the fractures. The effective governing equations for fractured porous rocks are viscoelastic anisotropic and numerically solved by the mixed-grid-stencil frequency-domain finite-difference method. The main advantage of our proposed modeling scheme over poroelastic modeling schemes is that the fractured domain can be modeled using a viscoelastic solid, while the rest of the domain can be modeled using an elastic solid. We have tested the modeling scheme in a single fracture model, a fractured model, and a modified Marmousi model. The good consistency between the scattered waves off a single horizontal fracture calculated using our proposed scheme and the poroelastic modeling validates that our modeling scheme can properly capture the fluid pressure diffusion (FPD) effects. In the case of a set of aligned fractures, the scattered waves from the top and bottom of the fractured reservoir are strongly influenced by the FPD effects, and the reflected waves from the underlying formation can retain the relevant attenuation and dispersion information. The proposed numerical modeling scheme can also be used to improve migration quality and the estimation of fracture mechanical characteristics in inversion.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"5 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140636961","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 : 2024-04-22DOI: 10.5194/egusphere-2024-1077
Pramit Chatterjee, Arnab Roy, Nibir Mandal
Abstract. Understanding the underlying mechanisms of strain localization in Earth’s lithosphere is crucial to explain the mechanics of tectonic plate boundaries and various failure-assisted geophysical phenomena, such as earthquakes. Geological observations suggest that ductile shear zones are the most important lithospheric structures of intense shear localization, sharing a major part of tectonic deformations. Despite extensive studies in the past several decades, the factors governing how they accommodate the bulk shear, whether by distributed homogeneous strain (i.e., development of S tectonic foliation normal to the principal shortening strain axis) or by localized shearing (formation of shear-parallel C bands) remain largely unexplored. This article aims to address this gap in knowledge, providing observational evidences of varying S and C development in ductile shear zones from two geological terrains of Eastern India. The field observations are complemented with 2D-viscoplastic numerical simulations within a strain-softening rheological framework to constrain the factors controlling the two competing shear-accommodation mechanisms: homogeneously distributed strain accumulation versus shear band formation. The model based analysis recognizes the bulk shear rate (γb), the bulk viscosity (ηv) and the initial cohesion (Ci) of a shear zone as the most critical factors to determine the dominance of one mechanism over the other. For a given Ci, low γb and ηv facilitate the formation of S foliation (uniformly distributed strain), which transforms to C-dominated shear-accommodation mechanism with increasing ηv. However, increasing γb, facilitates shear accommodation in a combination of the two mechanisms leading to CS- structures. The article finally discusses the conditions in which ductile shear zones can enormously intensify localized shear rates to produce rapid slip events, such as frictional melting and seismic activities.
摘要了解地球岩石圈应变局部化的基本机制对于解释构造板块边界力学和地震等各种破坏作用地球物理现象至关重要。地质观测表明，韧性剪切带是岩石圈中最重要的强剪切局部化结构，分担了构造变形的主要部分。尽管在过去几十年中进行了广泛的研究，但无论是通过分布式均质应变（即与主缩短应变轴线平行的 S 构造褶皱的发展），还是通过局部剪切（剪切平行 C 带的形成），控制它们如何容纳大量剪切的因素在很大程度上仍未得到探讨。本文旨在填补这一知识空白，提供印度东部两个地质地形的韧性剪切带中不同 S 和 C 发展的观测证据。野外观测结果与应变软化流变学框架内的二维粘弹性数值模拟结果相辅相成，以确定控制两种相互竞争的剪切容纳机制的因素：均匀分布的应变累积与剪切带的形成。基于模型的分析认为，剪切带的体积剪切速率 (γb)、体积粘度 (ηv) 和初始内聚力 (Ci) 是决定一种机制优于另一种机制的最关键因素。对于给定的 Ci，低 γb 和 ηv 有利于形成 S 型褶皱（均匀分布的应变），随着 ηv 的增加，S 型褶皱会转变为 C 型为主的剪切容纳机制。文章最后讨论了韧性剪切带在何种条件下可以极大地增强局部剪切速率，从而产生快速滑移事件，如摩擦熔化和地震活动。
{"title":"Localized shear versus distributed strain accumulation as shear-accommodation mechanisms in ductile shear zones: Constraining their dictating factors","authors":"Pramit Chatterjee, Arnab Roy, Nibir Mandal","doi":"10.5194/egusphere-2024-1077","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1077","url":null,"abstract":"<strong>Abstract.</strong> Understanding the underlying mechanisms of strain localization in Earth’s lithosphere is crucial to explain the mechanics of tectonic plate boundaries and various failure-assisted geophysical phenomena, such as earthquakes. Geological observations suggest that ductile shear zones are the most important lithospheric structures of intense shear localization, sharing a major part of tectonic deformations. Despite extensive studies in the past several decades, the factors governing how they accommodate the bulk shear, whether by distributed homogeneous strain (i.e., development of S tectonic foliation normal to the principal shortening strain axis) or by localized shearing (formation of shear-parallel C bands) remain largely unexplored. This article aims to address this gap in knowledge, providing observational evidences of varying S and C development in ductile shear zones from two geological terrains of Eastern India. The field observations are complemented with 2D-viscoplastic numerical simulations within a strain-softening rheological framework to constrain the factors controlling the two competing shear-accommodation mechanisms: homogeneously distributed strain accumulation versus shear band formation. The model based analysis recognizes the bulk shear rate (<em>γ<sub>b</sub></em>), the bulk viscosity (<em>η<sub>v</sub></em>) and the initial cohesion (<em>C<sub>i</sub></em>) of a shear zone as the most critical factors to determine the dominance of one mechanism over the other. For a given <em>C<sub>i</sub></em>, low <em>γ<sub>b</sub></em> and <em>η<sub>v</sub></em> facilitate the formation of S foliation (uniformly distributed strain), which transforms to C-dominated shear-accommodation mechanism with increasing <em>η<sub>v</sub></em>. However, increasing <em>γ<sub>b</sub></em>, facilitates shear accommodation in a combination of the two mechanisms leading to CS- structures. The article finally discusses the conditions in which ductile shear zones can enormously intensify localized shear rates to produce rapid slip events, such as frictional melting and seismic activities.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"7 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140636977","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 : 2024-04-17DOI: 10.5194/egusphere-2024-1109
Moritz O. Ziegler, Robin Seithel, Thomas Niederhuber, Oliver Heidbach, Thomas Kohl, Birgit Müller, Mojtaba Rajabi, Karsten Reiter, Luisa Röckel
Abstract. Even though the crustal stress state is primarily driven by gravitational volume forces and plate tectonics, interpretations of borehole breakout observations show occasionally abrupt rotations of horizontal stress orientation of up to 90° when faults are crossed. This indicates the influence of faults on the local stress state, which parameter control the degree of rotation. Herein, we investigate the phenomenon of principal stress rotation at a fault by means of a 2D generic numerical model. We parametrised the fault as a rock stiffness contrast and investigate systematically the full model parameter space in terms of the ratio of the applied principal stresses, the rock stiffness contrast, as well as the angle between fault strike and orientation of the principal stress axis. General findings are that the stress rotation is negatively correlated with the ratio of principal stresses. A small angle between the far field stress orientation and the fault facilitates stress rotation. A high contrast in rock stiffness further increases the stress rotation angle. Faults striking perpendicular to the maximum principal stress orientation experience no rotation at all. However, faults oriented parallel to the maximum principal stress orientation experience either no rotation or a 90° rotation, dependent on the ratio of principal stresses and the rock stiffness contrast. A comparison with observations from various boreholes worldwide shows that in general, the findings are well in agreement, even though the dip angle proves to have an influence on the stress rotation, in particular for shallow dipping faults.
{"title":"The effect of stiffness contrasts at faults on stress orientation","authors":"Moritz O. Ziegler, Robin Seithel, Thomas Niederhuber, Oliver Heidbach, Thomas Kohl, Birgit Müller, Mojtaba Rajabi, Karsten Reiter, Luisa Röckel","doi":"10.5194/egusphere-2024-1109","DOIUrl":"https://doi.org/10.5194/egusphere-2024-1109","url":null,"abstract":"<strong>Abstract.</strong> Even though the crustal stress state is primarily driven by gravitational volume forces and plate tectonics, interpretations of borehole breakout observations show occasionally abrupt rotations of horizontal stress orientation of up to 90° when faults are crossed. This indicates the influence of faults on the local stress state, which parameter control the degree of rotation. Herein, we investigate the phenomenon of principal stress rotation at a fault by means of a 2D generic numerical model. We parametrised the fault as a rock stiffness contrast and investigate systematically the full model parameter space in terms of the ratio of the applied principal stresses, the rock stiffness contrast, as well as the angle between fault strike and orientation of the principal stress axis. General findings are that the stress rotation is negatively correlated with the ratio of principal stresses. A small angle between the far field stress orientation and the fault facilitates stress rotation. A high contrast in rock stiffness further increases the stress rotation angle. Faults striking perpendicular to the maximum principal stress orientation experience no rotation at all. However, faults oriented parallel to the maximum principal stress orientation experience either no rotation or a 90° rotation, dependent on the ratio of principal stresses and the rock stiffness contrast. A comparison with observations from various boreholes worldwide shows that in general, the findings are well in agreement, even though the dip angle proves to have an influence on the stress rotation, in particular for shallow dipping faults.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"49 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140612579","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}
Judith Freienstein, Wolfgang Szwillus, Agnes Wansing, Jörg Ebbing
Abstract. Geothermal heat flow is an important boundary condition for ice sheets, affecting, for example, basal melt rates, but for ice-covered regions, we only have sparse heat flow observations with partly high uncertainty of up to 30 m W m−2. In this study, we first investigate the agreement between such pointwise heat flow observations and solid Earth models, applying a 1D steady-state approach to perform a statistical analysis for the entire Arctic region. We find that most of the continental heat flow observations have a high reliability and agreement to solid Earth models, except a few data points, such as, for example, the NGRIP (North Greenland Ice Core Project) point in central Greenland. For further testing, we perform a conditional simulation with focus on Greenland in which the local characteristics of heat flow structures can be considered. Simple kriging shows that including or excluding the less reliable NGRIP point has a large influence on the surrounding heat flow. The geostatistical analysis with the conditional simulation supports the assumption that NGRIP might not only be problematic for representing a regional feature but likely is an outlier. Basal melt estimates show that such a local spot of high heat flow results in local high basal melt rates but leads to less variation than existing geophysical models.
摘要。地热热流是冰盖的一个重要边界条件，会影响基底融化率等，但对于冰盖地区，我们只有稀疏的热流观测数据，且部分数据的不确定性高达 30 m W m-2。在本研究中，我们首先研究了这些点状热流观测数据与固体地球模型之间的一致性，采用一维稳态方法对整个北极地区进行了统计分析。我们发现，除了格陵兰岛中部的 NGRIP（北格陵兰冰芯项目）点等少数几个数据点外，大多数大陆热流观测数据与固体地球模型具有很高的可靠性和一致性。为了进一步测试，我们以格陵兰岛为重点进行了条件模拟，其中可以考虑热流结构的局部特征。简单的克里金分析表明，包括或不包括可靠性较低的 NGRIP 点对周围的热流有很大影响。利用条件模拟进行的地质统计分析支持这样的假设，即 NGRIP 不仅在代表区域特征方面存在问题，而且很可能是一个离群点。基底熔融估算表明，这种局部高热流点会导致局部高基底熔融率，但导致的变化比现有地球物理模型要小。
{"title":"Statistical appraisal of geothermal heat flow observations in the Arctic","authors":"Judith Freienstein, Wolfgang Szwillus, Agnes Wansing, Jörg Ebbing","doi":"10.5194/se-15-513-2024","DOIUrl":"https://doi.org/10.5194/se-15-513-2024","url":null,"abstract":"Abstract. Geothermal heat flow is an important boundary condition for ice sheets, affecting, for example, basal melt rates, but for ice-covered regions, we only have sparse heat flow observations with partly high uncertainty of up to 30 m W m−2. In this study, we first investigate the agreement between such pointwise heat flow observations and solid Earth models, applying a 1D steady-state approach to perform a statistical analysis for the entire Arctic region. We find that most of the continental heat flow observations have a high reliability and agreement to solid Earth models, except a few data points, such as, for example, the NGRIP (North Greenland Ice Core Project) point in central Greenland. For further testing, we perform a conditional simulation with focus on Greenland in which the local characteristics of heat flow structures can be considered. Simple kriging shows that including or excluding the less reliable NGRIP point has a large influence on the surrounding heat flow. The geostatistical analysis with the conditional simulation supports the assumption that NGRIP might not only be problematic for representing a regional feature but likely is an outlier. Basal melt estimates show that such a local spot of high heat flow results in local high basal melt rates but leads to less variation than existing geophysical models.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"26 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600168","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}
Roberto Emanuele Rizzo, Damien Freitas, James Gilgannon, Sohan Seth, Ian B. Butler, Gina Elizabeth McGill, Florian Fusseis
Abstract. X-ray computed tomography has established itself as a crucial tool in the analysis of rock materials, providing the ability to visualise intricate 3D microstructures and capture quantitative information about internal phenomena such as structural damage, mineral reactions, and fluid–rock interactions. The efficacy of this tool, however, depends significantly on the precision of image segmentation, a process that has seen varied results across different methodologies, ranging from simple histogram thresholding to more complex machine learning and deep-learning strategies. The irregularity in these segmentation outcomes raises concerns about the reproducibility of the results, a challenge that we aim to address in this work. In our study, we employ the mass balance of a metamorphic reaction as an internal standard to verify segmentation accuracy and shed light on the advantages of deep-learning approaches, particularly their capacity to efficiently process expansive datasets. Our methodology utilises deep learning to achieve accurate segmentation of time-resolved volumetric images of the gypsum dehydration reaction, a process that traditional segmentation techniques have struggled with due to poor contrast between reactants and products. We utilise a 2D U-net architecture for segmentation and introduce machine-learning-obtained labelled data (specifically, from random forest classification) as an innovative solution to the limitations of training data obtained from imaging. The deep-learning algorithm we developed has demonstrated remarkable resilience, consistently segmenting volume phases across all experiments. Furthermore, our trained neural network exhibits impressively short run times on a standard workstation equipped with a graphic processing unit (GPU). To evaluate the precision of our workflow, we compared the theoretical and measured molar evolution of gypsum to bassanite during dehydration. The errors between the predicted and segmented volumes in all time series experiments fell within the 2 % confidence intervals of the theoretical curves, affirming the accuracy of our methodology. We also compared the results obtained by the proposed method with standard segmentation methods and found a significant improvement in precision and accuracy of segmented volumes. This makes the segmented computed tomography images suited for extracting quantitative data, such as variations in mineral growth rate and pore size during the reaction. In this work, we introduce a distinctive approach by using an internal standard to validate the accuracy of a segmentation model, demonstrating its potential as a robust and reliable method for image segmentation in this field. This ability to measure the volumetric evolution during a reaction with precision paves the way for advanced modelling and verification of the physical properties of rock materials, particularly those involved in tectono-metamorphic processes. Our work underscores the promise of d
摘要。X 射线计算机断层扫描已成为分析岩石材料的重要工具，它能够将复杂的三维微观结构可视化，并捕捉结构损伤、矿物反应和流体-岩石相互作用等内部现象的定量信息。然而，这一工具的功效在很大程度上取决于图像分割的精确度，这一过程在不同的方法中结果各异，从简单的直方图阈值法到更复杂的机器学习和深度学习策略，不一而足。这些分割结果的不规则性引发了人们对结果可重复性的担忧，而这正是我们在这项工作中要解决的难题。在我们的研究中，我们采用了变质反应的质量平衡作为内部标准来验证分割的准确性，并阐明了深度学习方法的优势，尤其是其高效处理庞大数据集的能力。我们的方法利用深度学习实现了对石膏脱水反应的时间分辨体积图像的精确分割，由于反应物和产物之间的对比度较低，传统的分割技术在这一过程中困难重重。我们利用二维 U 型网架构进行分割，并引入机器学习获得的标记数据（特别是从随机森林分类中获得），作为解决从成像中获得的训练数据局限性的创新方案。我们开发的深度学习算法表现出了非凡的适应能力，在所有实验中都能持续分割体积相位。此外，我们训练的神经网络在配备图形处理器（GPU）的标准工作站上的运行时间非常短，令人印象深刻。为了评估我们工作流程的精确性，我们比较了脱水过程中石膏到重晶石的摩尔演化的理论值和测量值。在所有时间序列实验中，预测体积和分段体积之间的误差都在理论曲线的 2% 置信区间内，这肯定了我们方法的准确性。我们还将建议方法与标准分割方法的结果进行了比较，发现分割体积的精确度和准确性有了显著提高。这使得分割后的计算机断层扫描图像适用于提取定量数据，如反应过程中矿物生长速度和孔隙大小的变化。在这项工作中，我们引入了一种与众不同的方法，即使用内部标准来验证分割模型的准确性，从而证明其作为该领域图像分割的稳健可靠方法的潜力。这种精确测量反应过程中体积演变的能力为岩石材料物理性质的高级建模和验证铺平了道路，尤其是那些涉及构造-变质过程的岩石材料。我们的工作强调了深度学习方法在提高地球科学研究质量和可重复性方面的前景。
{"title":"Using internal standards in time-resolved X-ray micro-computed tomography to quantify grain-scale developments in solid-state mineral reactions","authors":"Roberto Emanuele Rizzo, Damien Freitas, James Gilgannon, Sohan Seth, Ian B. Butler, Gina Elizabeth McGill, Florian Fusseis","doi":"10.5194/se-15-493-2024","DOIUrl":"https://doi.org/10.5194/se-15-493-2024","url":null,"abstract":"Abstract. X-ray computed tomography has established itself as a crucial tool in the analysis of rock materials, providing the ability to visualise intricate 3D microstructures and capture quantitative information about internal phenomena such as structural damage, mineral reactions, and fluid–rock interactions. The efficacy of this tool, however, depends significantly on the precision of image segmentation, a process that has seen varied results across different methodologies, ranging from simple histogram thresholding to more complex machine learning and deep-learning strategies. The irregularity in these segmentation outcomes raises concerns about the reproducibility of the results, a challenge that we aim to address in this work. In our study, we employ the mass balance of a metamorphic reaction as an internal standard to verify segmentation accuracy and shed light on the advantages of deep-learning approaches, particularly their capacity to efficiently process expansive datasets. Our methodology utilises deep learning to achieve accurate segmentation of time-resolved volumetric images of the gypsum dehydration reaction, a process that traditional segmentation techniques have struggled with due to poor contrast between reactants and products. We utilise a 2D U-net architecture for segmentation and introduce machine-learning-obtained labelled data (specifically, from random forest classification) as an innovative solution to the limitations of training data obtained from imaging. The deep-learning algorithm we developed has demonstrated remarkable resilience, consistently segmenting volume phases across all experiments. Furthermore, our trained neural network exhibits impressively short run times on a standard workstation equipped with a graphic processing unit (GPU). To evaluate the precision of our workflow, we compared the theoretical and measured molar evolution of gypsum to bassanite during dehydration. The errors between the predicted and segmented volumes in all time series experiments fell within the 2 % confidence intervals of the theoretical curves, affirming the accuracy of our methodology. We also compared the results obtained by the proposed method with standard segmentation methods and found a significant improvement in precision and accuracy of segmented volumes. This makes the segmented computed tomography images suited for extracting quantitative data, such as variations in mineral growth rate and pore size during the reaction. In this work, we introduce a distinctive approach by using an internal standard to validate the accuracy of a segmentation model, demonstrating its potential as a robust and reliable method for image segmentation in this field. This ability to measure the volumetric evolution during a reaction with precision paves the way for advanced modelling and verification of the physical properties of rock materials, particularly those involved in tectono-metamorphic processes. Our work underscores the promise of d","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"54 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600169","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. Seismic reflection interpretation at magma-poor rifted margins shows that crustal thinning within the hyper-extended domain occurs by in-sequence oceanward extensional faulting which terminates in a sub-horizontal reflector in the topmost mantle immediately beneath tilted crustal fault blocks. This sub-horizontal reflector is interpreted to be a detachment surface that develops sequentially with oceanward in-sequence crustal faulting. We investigate the geometry and evolution of active and inactive extensional faulting due to flexural isostatic rotation during magma-poor margin hyper-extension using a recursive adaptation of the rolling-hinge model of Buck (1988) and compare modelling results with published seismic interpretation. In the case of progressive in-sequence faulting, we show that sub-horizontal reflectors imaged on published seismic reflection profiles can be generated by the flexural isostatic rotation of faults with initially high-angle geometry. Our modelling supports the hypothesis of Lymer et al. (2019) that the S reflector on the Galician margin is a sub-horizontal detachment generated by the in-sequence incremental addition of the isostatically rotated soles of block-bounding extensional faults. Flexural isostatic rotation produces shallowing of emergent fault angles, fault locking, and the development of new high-angle shortcut fault segments within the hanging wall. This results in the transfer and isostatic rotation of triangular pieces of hanging wall onto exhumed fault footwall, forming extensional allochthons which our modelling predicts are typically limited to a few kilometres in lateral extent and thickness. The initial geometry of basement extensional faults is a long-standing question. Our modelling results show that a sequence of extensional listric or planar faults with otherwise identical tectonic parameters produce very similar seabed bathymetric relief but distinct Moho and allochthon shapes. Our preferred interpretation of our modelling results and seismic observations is that faults are initially planar in geometry but are isostatically rotated and coalesce at depth to form the seismically observed sub-horizontal detachment in the topmost mantle. In-sequence extensional faulting of hyper-extended continental crust results in a smooth bathymetric transition from thinned continental crust to exhumed mantle. In contrast, out-of-sequence faulting results in a transition to exhumed mantle with bathymetric relief.
摘要。岩浆贫乏的断裂边缘的地震反射解释表明，超延伸域内的地壳减薄是通过向洋的顺序延伸断层发生的，其终点是紧靠倾斜地壳断层块体下方的最上层地幔中的次水平反射面。这个次水平反射镜被解释为一个脱离面，它是随着大洋向序地壳断层的发生而依次形成的。我们利用对 Buck（1988 年）的滚动铰链模型的递归改编，研究了贫岩浆边缘超伸展过程中由于挠性等静定旋转引起的活动和非活动伸展断层的几何形状和演化，并将建模结果与已发表的地震解释结果进行了比较。在渐进式顺层断层的情况下，我们表明，已公布的地震反射剖面上的次水平反射体可能是由最初具有高角度几何形状的断层的挠曲等静定旋转产生的。我们的建模支持 Lymer 等人（2019 年）的假设，即加利西亚边缘的 S 型反射体是由块带状伸展断层的等静力旋转底面的内序增量所产生的次水平剥离。挠性等静力旋转导致出现的断层角度变浅、断层锁定，并在悬壁内形成新的高角度捷径断层段。这导致悬壁的三角形片段转移并等静力旋转到出露的断层底壁上，形成延伸断层，根据我们的建模预测，这些断层的横向范围和厚度通常仅限于几公里。基底延伸断层的初始几何形状是一个长期存在的问题。我们的建模结果表明，在构造参数完全相同的情况下，一连串的延伸性环状或平面断层会产生非常相似的海底水深起伏，但却具有不同的莫霍面和等深线形状。我们对建模结果和地震观测结果的首选解释是，断层在几何形状上最初是平面的，但在深度上发生了等静力旋转和凝聚，从而在最上层地幔形成了地震观测到的次水平剥离。超延伸大陆地壳的顺层延伸断层导致从变薄的大陆地壳到脱壳地幔的平稳水深过渡。与此相反，序外断裂则导致地幔向出露地幔的过渡，并伴有水深起伏。
{"title":"Extensional fault geometry and evolution within rifted margin hyper-extended continental crust leading to mantle exhumation and allochthon formation","authors":"Júlia Gómez-Romeu, Nick Kusznir","doi":"10.5194/se-15-477-2024","DOIUrl":"https://doi.org/10.5194/se-15-477-2024","url":null,"abstract":"Abstract. Seismic reflection interpretation at magma-poor rifted margins shows that crustal thinning within the hyper-extended domain occurs by in-sequence oceanward extensional faulting which terminates in a sub-horizontal reflector in the topmost mantle immediately beneath tilted crustal fault blocks. This sub-horizontal reflector is interpreted to be a detachment surface that develops sequentially with oceanward in-sequence crustal faulting. We investigate the geometry and evolution of active and inactive extensional faulting due to flexural isostatic rotation during magma-poor margin hyper-extension using a recursive adaptation of the rolling-hinge model of Buck (1988) and compare modelling results with published seismic interpretation. In the case of progressive in-sequence faulting, we show that sub-horizontal reflectors imaged on published seismic reflection profiles can be generated by the flexural isostatic rotation of faults with initially high-angle geometry. Our modelling supports the hypothesis of Lymer et al. (2019) that the S reflector on the Galician margin is a sub-horizontal detachment generated by the in-sequence incremental addition of the isostatically rotated soles of block-bounding extensional faults. Flexural isostatic rotation produces shallowing of emergent fault angles, fault locking, and the development of new high-angle shortcut fault segments within the hanging wall. This results in the transfer and isostatic rotation of triangular pieces of hanging wall onto exhumed fault footwall, forming extensional allochthons which our modelling predicts are typically limited to a few kilometres in lateral extent and thickness. The initial geometry of basement extensional faults is a long-standing question. Our modelling results show that a sequence of extensional listric or planar faults with otherwise identical tectonic parameters produce very similar seabed bathymetric relief but distinct Moho and allochthon shapes. Our preferred interpretation of our modelling results and seismic observations is that faults are initially planar in geometry but are isostatically rotated and coalesce at depth to form the seismically observed sub-horizontal detachment in the topmost mantle. In-sequence extensional faulting of hyper-extended continental crust results in a smooth bathymetric transition from thinned continental crust to exhumed mantle. In contrast, out-of-sequence faulting results in a transition to exhumed mantle with bathymetric relief.","PeriodicalId":21912,"journal":{"name":"Solid Earth","volume":"126 1","pages":""},"PeriodicalIF":3.4,"publicationDate":"2024-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140599933","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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