The upper-crustal extensional structures developed in the Himalayan orogen record deep dynamics, that have played significant roles in the Himalayan tectonic evolution. This study presents new detailed field investigations, microstructures, quartz [c] axis crystallographic preferred orientation (CPO) patterns, kinematic vorticity, deformation temperatures, zircon U-Pb, and mica 40Ar/39Ar geochronology data of the two sets of intersecting extensional structures in the Cona area of the eastern Himalayan orogen. The results suggest that the Cona Detachment (CD) is mainly in simple shear deformation and the ductile deformation temperature ranges from 280 °C to 517 °C. It was active between 19 and 16 Ma, and ceased at 15 Ma. However, the Cona Rift (CR) is mainly in pure shear deformation and its top-down-to-the-E ductile deformation is recorded at temperatures from 500 °C to 608 °C. It initiated at ∼16 Ma, and ceased activity before 10 Ma. During the transition from N-S to E-W extension, the change in dynamic mechanism led to coupled fluid injection and crustal heating. This study indicates that the N-S and E-W extensional structures in the Cona area exhibited overlapping deformation histories during 16–15 Ma.
{"title":"Structural and geochronological studies of the Cona detachment and Cona Rift: Implications for the Miocene evolution of the Cona region","authors":"Zhuo Tang , Hanwen Dong , Rongze Fei , Linghao Zhao , Li'e Gao , Yaying Wang , Lilong Yan , Lingsen Zeng","doi":"10.1016/j.jsg.2025.105562","DOIUrl":"10.1016/j.jsg.2025.105562","url":null,"abstract":"<div><div>The upper-crustal extensional structures developed in the Himalayan orogen record deep dynamics, that have played significant roles in the Himalayan tectonic evolution. This study presents new detailed field investigations, microstructures, quartz [c] axis crystallographic preferred orientation (CPO) patterns, kinematic vorticity, deformation temperatures, zircon U-Pb, and mica <sup>40</sup>Ar/<sup>39</sup>Ar geochronology data of the two sets of intersecting extensional structures in the Cona area of the eastern Himalayan orogen. The results suggest that the Cona Detachment (CD) is mainly in simple shear deformation and the ductile deformation temperature ranges from 280 °C to 517 °C. It was active between 19 and 16 Ma, and ceased at 15 Ma. However, the Cona Rift (CR) is mainly in pure shear deformation and its top-down-to-the-E ductile deformation is recorded at temperatures from 500 °C to 608 °C. It initiated at ∼16 Ma, and ceased activity before 10 Ma. During the transition from N-S to E-W extension, the change in dynamic mechanism led to coupled fluid injection and crustal heating. This study indicates that the N-S and E-W extensional structures in the Cona area exhibited overlapping deformation histories during 16–15 Ma.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"201 ","pages":"Article 105562"},"PeriodicalIF":2.9,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145361647","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 : 2025-12-01Epub Date: 2025-09-12DOI: 10.1016/j.jsg.2025.105551
Michele Perozzo , Niccolò Menegoni , Laura Crispini , Laura Federico , Silvio Seno , Matteo Maino
Predictive models for the origin and distribution of tectonic fractures in regions with multiple and heterogeneous deformation events are still considered as characterized by a high degree of uncertainty. In fact, it is known that fracture networks development is dependent by many factors, such as composition, diagenesis, structural position, fold bending and changes in the tectonic stress history. However, several studies noted that the high-curvature regions of large folds often show a good correlation between the measured and theoretical geometry of the fracture sets. This paper presents a field- and digital outcrop model-based structural investigation of refolded km-scale sheath fold (Caprazoppa fold) and associated fractures host in a metamorphic carbonate sequence (Ligurian Briançonnais, Western Alps) that experienced multiple regional deformation phases. The orientation of the fracture sets along the 3D fold structure are broadly consistent with the network theoretically expected as due by the main sheath fold curvature. The subsequent, less intense ductile phase produced significant change of the structural patterns only in the schistose lithologies, whereas the more competent rocks mostly recycled the early foliations and fracture sets. Even the post-metamorphic brittle faulting/fracturing selectively reactivated the pre-existing fractures favorably oriented. We infer that, when strain is high, the strongly curved sheath folds exert a major control in the development of the fracture network, the geometry of which is preserved through the subsequent ductile/brittle deformation stages.
{"title":"Quantitative characterization of fracture network in large sheath-fold: field and UAV-based digital outcrop model analysis (Ligurian Alps, Italy)","authors":"Michele Perozzo , Niccolò Menegoni , Laura Crispini , Laura Federico , Silvio Seno , Matteo Maino","doi":"10.1016/j.jsg.2025.105551","DOIUrl":"10.1016/j.jsg.2025.105551","url":null,"abstract":"<div><div>Predictive models for the origin and distribution of tectonic fractures in regions with multiple and heterogeneous deformation events are still considered as characterized by a high degree of uncertainty. In fact, it is known that fracture networks development is dependent by many factors, such as composition, diagenesis, structural position, fold bending and changes in the tectonic stress history. However, several studies noted that the high-curvature regions of large folds often show a good correlation between the measured and theoretical geometry of the fracture sets. This paper presents a field- and digital outcrop model-based structural investigation of refolded km-scale sheath fold (Caprazoppa fold) and associated fractures host in a metamorphic carbonate sequence (Ligurian Briançonnais, Western Alps) that experienced multiple regional deformation phases. The orientation of the fracture sets along the 3D fold structure are broadly consistent with the network theoretically expected as due by the main sheath fold curvature. The subsequent, less intense ductile phase produced significant change of the structural patterns only in the schistose lithologies, whereas the more competent rocks mostly recycled the early foliations and fracture sets. Even the post-metamorphic brittle faulting/fracturing selectively reactivated the pre-existing fractures favorably oriented. We infer that, when strain is high, the strongly curved sheath folds exert a major control in the development of the fracture network, the geometry of which is preserved through the subsequent ductile/brittle deformation stages.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"201 ","pages":"Article 105551"},"PeriodicalIF":2.9,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145060287","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 : 2025-12-01Epub Date: 2025-08-19DOI: 10.1016/j.jsg.2025.105533
F. Porta, L.R. Berio, C. Cavozzi, F. Balsamo
Prediction of sub-seismic fault properties is a key factor to mitigate the uncertainties in reservoir modeling. The present study focuses on the geometry and origin of the NE-trending sub-seismic faults in Monte Capanne pluton (Elba Island, Italy), characterized by transtensive kinematics and developed in an interacting sector between two regional-scale faults. A detailed analysis of the fracture network (digitized fractures >10,000) was conducted along and across the NE-trending faults using Digital Outcrop Model (DOM). This dataset was further integrated with field mapping at a 1:200 scale of four representative sectors. Overall, our multiscale mapping identifies three different fault-related fracture sets: (i) NE-SW-trending fractures, (ii) E-W-trending fractures, and (iii) NNW-SSE-trending fractures. Statistical analysis of fracture orientation and length in DOM reveals a heterogeneous spatial distribution of deformation in the outcrop, showing an increase in fracture density and intensity (P10 and P21), and connectivity (connections per branch CB) towards the northeastern region of the outcrop, where NE-trending faults are closely spaced. A comparison between DOM-based and DOM-integrated datasets reveals that the former tends to underestimate small-scale fractures due to pixel-resolution limit (truncation effect), leading to an underestimation of across-fault damage zone width and internal fracture density and intensity. However, the proportion of connected nodes (X, Y) and connectivity (CB) from the DOM-based dataset is consistent with topological parameters from the DOM-integrated dataset. This study highlights the necessity of a multiscale approach for fracture network characterization in sub-seismic faults, combining DOM with field mapping to develop reliable templates for reservoir analysis.
亚地震断层性质预测是降低储层建模不确定性的关键因素。本文研究了意大利厄尔巴岛Monte Capanne岩体北东向次地震断裂的几何形态和成因，该次地震断裂具有横向运动学特征，发育于两条区域尺度断裂之间的相互作用板块。利用数字露头模型（DOM）对北东向断裂进行了详细的裂缝网络（数字化裂缝>； 10000条）分析。该数据集进一步与四个代表性部门的1:200比例尺的实地测绘相结合。总的来说，我们的多尺度映射确定了三种不同的断层相关裂缝组：(i) ne - sw走向裂缝，（ii） e - w走向裂缝，（iii） nnw - se走向裂缝。DOM中裂缝方向和长度的统计分析表明，露头变形的空间分布不均匀，裂缝密度和强度（P10和P21）增加，连通性（每分支CB的连接）向露头东北地区靠拢，ne向断裂密集分布。基于dom的数据集与集成dom的数据集的对比表明，由于像素分辨率的限制（截断效应），前者往往低估了小尺度裂缝，从而低估了断层间损伤带宽度、内部裂缝密度和强度。然而，基于dom的数据集的连接节点（X， Y）和连通性（CB）的比例与dom集成数据集的拓扑参数一致。该研究强调了亚地震断层裂缝网络表征的多尺度方法的必要性，将DOM与现场测绘相结合，为储层分析开发可靠的模板。
{"title":"Multiscale characterization of fracture network in sub-seismic faults (Monte Capanne Pluton, Elba Island, Italy)","authors":"F. Porta, L.R. Berio, C. Cavozzi, F. Balsamo","doi":"10.1016/j.jsg.2025.105533","DOIUrl":"10.1016/j.jsg.2025.105533","url":null,"abstract":"<div><div>Prediction of sub-seismic fault properties is a key factor to mitigate the uncertainties in reservoir modeling. The present study focuses on the geometry and origin of the NE-trending sub-seismic faults in Monte Capanne pluton (Elba Island, Italy), characterized by transtensive kinematics and developed in an interacting sector between two regional-scale faults. A detailed analysis of the fracture network (digitized fractures >10,000) was conducted along and across the NE-trending faults using Digital Outcrop Model (DOM). This dataset was further integrated with field mapping at a 1:200 scale of four representative sectors. Overall, our multiscale mapping identifies three different fault-related fracture sets: (i) NE-SW-trending fractures, (ii) E-W-trending fractures, and (iii) NNW-SSE-trending fractures. Statistical analysis of fracture orientation and length in DOM reveals a heterogeneous spatial distribution of deformation in the outcrop, showing an increase in fracture density and intensity (P<sub>10</sub> and P<sub>21</sub>), and connectivity (connections per branch C<sub>B</sub>) towards the northeastern region of the outcrop, where NE-trending faults are closely spaced. A comparison between DOM-based and DOM-integrated datasets reveals that the former tends to underestimate small-scale fractures due to pixel-resolution limit (truncation effect), leading to an underestimation of across-fault damage zone width and internal fracture density and intensity. However, the proportion of connected nodes (X, Y) and connectivity (C<sub>B</sub>) from the DOM-based dataset is consistent with topological parameters from the DOM-integrated dataset. This study highlights the necessity of a multiscale approach for fracture network characterization in sub-seismic faults, combining DOM with field mapping to develop reliable templates for reservoir analysis.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"201 ","pages":"Article 105533"},"PeriodicalIF":2.9,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144934255","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 : 2025-12-01Epub Date: 2025-09-11DOI: 10.1016/j.jsg.2025.105543
Ana Paula Burgoa Tanaka , Philippe Renard , Jefter Natan de Moraes Caldeira , Celia Trunz
Graph theory has emerged as a promising method for analyzing fracture networks and complementing traditional geometrical descriptions. It emphasizes the network’s topological aspects, highlighting the importance that fractures have in enhancing permeability and influencing flow anisotropy. However, integrating different structural geology analyses in a single framework remains a challenge. We propose a graph-based fracture network analysis combining geometry, topology, kinematics, age relationships, and geomechanics to identify the most important connections within a network. We apply it to the karstic aquifer system of Tsanfleuron, in the Western Helvetic Alps domain, where fractures play a crucial role in groundwater circulation and karstification. We acquired new structural data from a high-resolution digital elevation model (DEM), a 3D point cloud digital outcrop model (DOM), fieldwork, and one scanline. We interpreted and measured lineaments in 1:2.500 (DEM) and measured attitudes (DOM). Verification was done in the field, adding more measurements and the kinematics. The fracture network was transformed into a graph, and measurements were stored as attributes. Four main subvertical fracture sets were identified in chronological order, for the study site: E-W (85°), NE-SW (57°), N-S (176°), and NW-SE (117°). Censored fractures were identified to unbiased length, and abutting relationships were defined for pairs of sets to define age relationships. The E-W and NE-SW are the most persistent and longer fractures through all the site. The N-S set is localized in the central area, and the set NW-SE superimposes the others. The displacement is mostly dextral for the NE-SW and E-W faults, and sinistral for the N-S and NW-SE sets. Paleo tensor analysis results in NW-SE directed maximum compression. Fractures are opened and often enlarged by dissolution. Connectivity is moderate in terms of percolation. Betweenness and percolation centralities highlight the preferential water flow towards NE, ENE, and E.
{"title":"Graph-based fracture network analysis to integrate structural geology properties and identify preferential flow pathways in the aquifer system of Tsanfleuron, Swiss Alps","authors":"Ana Paula Burgoa Tanaka , Philippe Renard , Jefter Natan de Moraes Caldeira , Celia Trunz","doi":"10.1016/j.jsg.2025.105543","DOIUrl":"10.1016/j.jsg.2025.105543","url":null,"abstract":"<div><div>Graph theory has emerged as a promising method for analyzing fracture networks and complementing traditional geometrical descriptions. It emphasizes the network’s topological aspects, highlighting the importance that fractures have in enhancing permeability and influencing flow anisotropy. However, integrating different structural geology analyses in a single framework remains a challenge. We propose a graph-based fracture network analysis combining geometry, topology, kinematics, age relationships, and geomechanics to identify the most important connections within a network. We apply it to the karstic aquifer system of Tsanfleuron, in the Western Helvetic Alps domain, where fractures play a crucial role in groundwater circulation and karstification. We acquired new structural data from a high-resolution digital elevation model (DEM), a 3D point cloud digital outcrop model (DOM), fieldwork, and one scanline. We interpreted and measured lineaments in 1:2.500 (DEM) and measured attitudes (DOM). Verification was done in the field, adding more measurements and the kinematics. The fracture network was transformed into a graph, and measurements were stored as attributes. Four main subvertical fracture sets were identified in chronological order, for the study site: E-W (85°), NE-SW (57°), N-S (176°), and NW-SE (117°). Censored fractures were identified to unbiased length, and abutting relationships were defined for pairs of sets to define age relationships. The E-W and NE-SW are the most persistent and longer fractures through all the site. The N-S set is localized in the central area, and the set NW-SE superimposes the others. The displacement is mostly dextral for the NE-SW and E-W faults, and sinistral for the N-S and NW-SE sets. Paleo tensor analysis results in NW-SE directed maximum compression. Fractures are opened and often enlarged by dissolution. Connectivity is moderate in terms of percolation. Betweenness and percolation centralities highlight the preferential water flow towards NE, ENE, and E.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"201 ","pages":"Article 105543"},"PeriodicalIF":2.9,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145050130","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 : 2025-12-01Epub Date: 2025-09-23DOI: 10.1016/j.jsg.2025.105559
Marco Voltolini , Luca Smeraglia , Andrea Billi , Eugenio Carminati , Flavio Cognigni , Marco Rossi , Michele Zucali
Fault zones in carbonate rocks exhibit distinct microstructural fabrics that develop different microstructures with increasing deformation, going from the outer zone towards the fault core. These fabrics can be effectively characterized using X-ray micro-computed tomography (XRμCT), a powerful imaging technique that supports a wide range of analyses, from morphometric measurements (e.g., pore size distribution, fractures orientation) to digital rock physics (i.e., virtual experiments on 3D volumes). However, the need for an automated, user-independent tool to classify these microstructures is crucial for large-scale studies. Furthermore, a fully quantitative classification of fault rock fabrics provides valuable insights into the extent and nature of deformation within these rocks. In this study, we present a deep learning-based supervised neural network designed to automate the classification of fault rock microstructures. This system offers rapid, quantitative, and scalable analysis of XRμCT data, facilitating the identification and classification of fabrics of brittle fault limestone rocks with high precision. The network was trained and validated on purpose collected datasets representing specific fabrics, then it was successfully used on different limestone fault rocks collected from the same area or obtained from the literature. The results show that the software can reliably classify fault rock fabrics affected by brittle deformation into three primary categories, each representing a distinct stage of deformation: fractured limestone, breccia, and cataclasite. The network assigns identification probabilities to each image, which can then be visualized in a ternary diagram for intuitive comparison and interpretation. This classification system streamlines fabric analysis and provides a quantitative measure of the degree of deformation within the rock. This automated classification tool paves the way for advanced studies on the anisotropic properties of fault rocks, enabling high-throughput analysis and enhancing our understanding of fault zone mechanics.
{"title":"Decoding microstructures of fault carbonate rocks with X-ray microtomography: A deep learning approach to fabric classification and analysis","authors":"Marco Voltolini , Luca Smeraglia , Andrea Billi , Eugenio Carminati , Flavio Cognigni , Marco Rossi , Michele Zucali","doi":"10.1016/j.jsg.2025.105559","DOIUrl":"10.1016/j.jsg.2025.105559","url":null,"abstract":"<div><div>Fault zones in carbonate rocks exhibit distinct microstructural fabrics that develop different microstructures with increasing deformation, going from the outer zone towards the fault core. These fabrics can be effectively characterized using X-ray micro-computed tomography (XRμCT), a powerful imaging technique that supports a wide range of analyses, from morphometric measurements (e.g., pore size distribution, fractures orientation) to digital rock physics (i.e., virtual experiments on 3D volumes). However, the need for an automated, user-independent tool to classify these microstructures is crucial for large-scale studies. Furthermore, a fully quantitative classification of fault rock fabrics provides valuable insights into the extent and nature of deformation within these rocks. In this study, we present a deep learning-based supervised neural network designed to automate the classification of fault rock microstructures. This system offers rapid, quantitative, and scalable analysis of XRμCT data, facilitating the identification and classification of fabrics of brittle fault limestone rocks with high precision. The network was trained and validated on purpose collected datasets representing specific fabrics, then it was successfully used on different limestone fault rocks collected from the same area or obtained from the literature. The results show that the software can reliably classify fault rock fabrics affected by brittle deformation into three primary categories, each representing a distinct stage of deformation: fractured limestone, breccia, and cataclasite. The network assigns identification probabilities to each image, which can then be visualized in a ternary diagram for intuitive comparison and interpretation. This classification system streamlines fabric analysis and provides a quantitative measure of the degree of deformation within the rock. This automated classification tool paves the way for advanced studies on the anisotropic properties of fault rocks, enabling high-throughput analysis and enhancing our understanding of fault zone mechanics.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"201 ","pages":"Article 105559"},"PeriodicalIF":2.9,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145227243","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 : 2025-12-01Epub Date: 2025-07-17DOI: 10.1016/j.jsg.2025.105510
Andrew J.M. Evans , Natalie J.C. Farrell , David A. Neave , Margaret E. Hartley , David Healy , John P. Waters , Tara R. McElhinney , Joshua J. Shea , Nico Bigaroni , Simon A. Hunt
Fracture systems within low-permeability crystalline granitic rocks are critical pathways for fluid flow within these bodies. Constraining the sequence of mineralisation in fracture sets is key to effectively determining the mineral potential and exploitability of rare and critical metals within granite bodies. This study presents the results of a field fracture analysis at the greisen-bearing, lithium-rich Cligga Head granite—a satellite granitic body of the Cornubian Batholith in southwest England. Field mapping of the well-exposed granite body, younging tables and scanning electron microscopy (SEM) are used to develop a temporal model for the evolution of fractures in the Cligga Head granite. Seven fracture sets with varying mineral infill were identified. These fractures exhibit a sequence of cross-cutting relationships that broadly correspond to regional lineament trends — associated with the Variscan Orogeny. As high-quality granite exposure in the region is limited, detailed fracture analysis of satellite granite bodies like Cligga Head provides valuable context for regional critical mineral exploration.
{"title":"Fracture analysis of the lithium-bearing Cligga Head granite: Impacts on critical mineral mobilisation and fluid flow","authors":"Andrew J.M. Evans , Natalie J.C. Farrell , David A. Neave , Margaret E. Hartley , David Healy , John P. Waters , Tara R. McElhinney , Joshua J. Shea , Nico Bigaroni , Simon A. Hunt","doi":"10.1016/j.jsg.2025.105510","DOIUrl":"10.1016/j.jsg.2025.105510","url":null,"abstract":"<div><div>Fracture systems within low-permeability crystalline granitic rocks are critical pathways for fluid flow within these bodies. Constraining the sequence of mineralisation in fracture sets is key to effectively determining the mineral potential and exploitability of rare and critical metals within granite bodies. This study presents the results of a field fracture analysis at the greisen-bearing, lithium-rich Cligga Head granite—a satellite granitic body of the Cornubian Batholith in southwest England. Field mapping of the well-exposed granite body, younging tables and scanning electron microscopy (SEM) are used to develop a temporal model for the evolution of fractures in the Cligga Head granite. Seven fracture sets with varying mineral infill were identified. These fractures exhibit a sequence of cross-cutting relationships that broadly correspond to regional lineament trends — associated with the Variscan Orogeny. As high-quality granite exposure in the region is limited, detailed fracture analysis of satellite granite bodies like Cligga Head provides valuable context for regional critical mineral exploration.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"201 ","pages":"Article 105510"},"PeriodicalIF":2.9,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145332741","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 : 2025-12-01Epub Date: 2025-09-20DOI: 10.1016/j.jsg.2025.105557
Nandini Choudhury , Suman Guha , Mark D. Lindsay , Atin Kumar Mitra
Curved shear zones are common in orogenic systems, yet the role of boundary curvature in governing strain localization remains underexplored. Using the Singhbhum Shear Zone (SSZ) in eastern India as a natural analogue, we develop an integrated approach combining analytical Couette flow theory, physical analogue modelling with Newtonian viscous Polydimethylsiloxane (PDMS), and finite element simulations. The results consistently reveal a non-monotonic velocity profile with a neutral radius where flow reverses direction, creating distinct zones of localized shear. Strain markers in the experiment deform most intensely near the inner arc and progressively less outward, mirroring field evidence from the SSZ, where high-strain mylonites and strong non-cylindrical folds transition into overprinting crenulations and open folds. This convergence between model predictions and field observations demonstrates that the boundary curvature alone, absent of mechanical or lithological heterogeneity can explain strain partitioning, flow reversal, and fold overprinting in a ductile regime. The study provides a transferable kinematic framework for interpreting curved tectonic interfaces and underscores the often-underestimated role of geometry in shaping deformation. (Words: 168)
{"title":"Boundary curvature as a first-order control on strain localization in arcuate shear zone: Insights from field observations, analogue and numerical modelling","authors":"Nandini Choudhury , Suman Guha , Mark D. Lindsay , Atin Kumar Mitra","doi":"10.1016/j.jsg.2025.105557","DOIUrl":"10.1016/j.jsg.2025.105557","url":null,"abstract":"<div><div>Curved shear zones are common in orogenic systems, yet the role of boundary curvature in governing strain localization remains underexplored. Using the Singhbhum Shear Zone (SSZ) in eastern India as a natural analogue, we develop an integrated approach combining analytical Couette flow theory, physical analogue modelling with Newtonian viscous Polydimethylsiloxane (PDMS), and finite element simulations. The results consistently reveal a non-monotonic velocity profile with a neutral radius where flow reverses direction, creating distinct zones of localized shear. Strain markers in the experiment deform most intensely near the inner arc and progressively less outward, mirroring field evidence from the SSZ, where high-strain mylonites and strong non-cylindrical folds transition into overprinting crenulations and open folds. This convergence between model predictions and field observations demonstrates that the boundary curvature alone, absent of mechanical or lithological heterogeneity can explain strain partitioning, flow reversal, and fold overprinting in a ductile regime. The study provides a transferable kinematic framework for interpreting curved tectonic interfaces and underscores the often-underestimated role of geometry in shaping deformation. (Words: 168)</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"201 ","pages":"Article 105557"},"PeriodicalIF":2.9,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145158675","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}
Understanding how strain is localized and concentrated in the mid-crust is critical to geological research. Investigating the microstructure and texture of quartzo-feldspathic mylonites is essential in this context. The Patos shear zone (PSZ), stretching ∼600 km long and responsible for the deformation of the paleoproterozoic basement in the Borborema Province under varying temperature conditions, is a significant shear zone for exploration. Combining techniques, including optical and scanning electron microscopy and Electron Backscatter Diffraction (EBSD) our research focused on quartzo-feldspathic mylonites to comprehend the solid-state processes responsible for strain localization within the Patos shear zone. As materials undergo uplift and deformation transition from a submagmatic to a solid-state flow, strain is concentrated within increasingly narrow zones. Our results demonstrated that after melt solidification, biotite-rich layers at temperatures exceeding 650 °C become weaker domains that accommodate strain through dislocation creep in feldspar, biotite and to a lesser extent in quartz, with the activation of prism-[c] slip system. During late reactivation, under upper greenschist/lower amphibolite facies, dislocation creep, strain-induced myrmekitization, solution-precipitation mechanisms are the dominant mechanisms for grain-size reduction in feldspar, with the resulting fine-grained matrix deforming via dislocation-accommodated and fluid-assisted grain boundary sliding (GBS). Quartz undergoes recrystallization as it transitions from grain boundary migration to subgrain rotation, with the activation of prism-<a> slip system. At temperatures below 450 °C, in the southern Patos shear zone, quartz ribbons experience bulging recrystallization with the activation of prism-<a> and rhomb<a> slip systems. Feldspar porphyroclasts undergo fracturing, myrmekitization and dissolution-precipitation creep. Rock rheology is controlled by fine-grained polyphase aggregates deforming via Dislocation-accommodated GBS. Finally, our study highlights the role of discontinuities during low-temperature deformation, such as the contact between rheologically contrasting layers and transgranular fractures, which serve as a precursor that led to shear zones nucleation in the northern block of the Patos shear zone.
{"title":"Strain localization in quartzo-feldspathic mylonites from Patos shear zone revealed by EBSD data","authors":"Matheus Alves da Silva , Leonardo Lagoeiro , Carolina Cavalcante , Paola Ferreira Barbosa","doi":"10.1016/j.jsg.2025.105514","DOIUrl":"10.1016/j.jsg.2025.105514","url":null,"abstract":"<div><div>Understanding how strain is localized and concentrated in the mid-crust is critical to geological research. Investigating the microstructure and texture of quartzo-feldspathic mylonites is essential in this context. The Patos shear zone (PSZ), stretching ∼600 km long and responsible for the deformation of the paleoproterozoic basement in the Borborema Province under varying temperature conditions, is a significant shear zone for exploration. Combining techniques, including optical and scanning electron microscopy and Electron Backscatter Diffraction (EBSD) our research focused on quartzo-feldspathic mylonites to comprehend the solid-state processes responsible for strain localization within the Patos shear zone. As materials undergo uplift and deformation transition from a submagmatic to a solid-state flow, strain is concentrated within increasingly narrow zones. Our results demonstrated that after melt solidification, biotite-rich layers at temperatures exceeding 650 °C become weaker domains that accommodate strain through dislocation creep in feldspar, biotite and to a lesser extent in quartz, with the activation of prism-[c] slip system. During late reactivation, under upper greenschist/lower amphibolite facies, dislocation creep, strain-induced myrmekitization, solution-precipitation mechanisms are the dominant mechanisms for grain-size reduction in feldspar, with the resulting fine-grained matrix deforming via dislocation-accommodated and fluid-assisted grain boundary sliding (GBS). Quartz undergoes recrystallization as it transitions from grain boundary migration to subgrain rotation, with the activation of prism-<a> slip system. At temperatures below 450 °C, in the southern Patos shear zone, quartz ribbons experience bulging recrystallization with the activation of prism-<a> and rhomb<a> slip systems. Feldspar porphyroclasts undergo fracturing, myrmekitization and dissolution-precipitation creep. Rock rheology is controlled by fine-grained polyphase aggregates deforming via Dislocation-accommodated GBS. Finally, our study highlights the role of discontinuities during low-temperature deformation, such as the contact between rheologically contrasting layers and transgranular fractures, which serve as a precursor that led to shear zones nucleation in the northern block of the Patos shear zone.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105514"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144723563","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 : 2025-11-01Epub Date: 2025-07-18DOI: 10.1016/j.jsg.2025.105511
Jae Hoon Kim , Jin-Han Ree
This study investigates seismogenesis in the brittle–plastic transition zone of the Yecheon Shear Zone, South Korea. The NE-to NNE-striking right-lateral shear zone cuts a Mesozoic granitoid pluton in an outcrop that was investigated in this study. We focus on light green layers within granite mylonitic rocks that preserve evidence of seismic slip events and subsequent plastic deformation. Field observations and microstructural analysis reveal a complex history of brittle and plastic deformations. The light green layers, formed by frictional melting during seismic events, contain injection structures, flow textures, and euhedral to subhedral microlites with inclusions. Elevated pore-fluid pressure might have played a crucial role in initiating seismic ruptures in the brittle–plastic transition zone, forming shear band ruptures or R shear planes and implosion breccia in the releasing stepovers in shear band ruptures. We propose a seismogenic model involving fluid pressure buildup, formation of shear band ruptures, rupture propagation into the C foliation, and the formation and subsequent alteration of pseudotachylytes. The fine-grained nature of the altered pseudotachylytes would have promoted strain localization during interseismic periods, leading to their transformation into ultramylonite. These findings improve our understanding of earthquake nucleation processes in the brittle–plastic transition zone and highlight the importance of fluids in inducing seismic events.
{"title":"Seismogenesis in the brittle–plastic transition zone of the Yecheon shear zone, South Korea","authors":"Jae Hoon Kim , Jin-Han Ree","doi":"10.1016/j.jsg.2025.105511","DOIUrl":"10.1016/j.jsg.2025.105511","url":null,"abstract":"<div><div>This study investigates seismogenesis in the brittle–plastic transition zone of the Yecheon Shear Zone, South Korea. The NE-to NNE-striking right-lateral shear zone cuts a Mesozoic granitoid pluton in an outcrop that was investigated in this study. We focus on light green layers within granite mylonitic rocks that preserve evidence of seismic slip events and subsequent plastic deformation. Field observations and microstructural analysis reveal a complex history of brittle and plastic deformations. The light green layers, formed by frictional melting during seismic events, contain injection structures, flow textures, and euhedral to subhedral microlites with inclusions. Elevated pore-fluid pressure might have played a crucial role in initiating seismic ruptures in the brittle–plastic transition zone, forming shear band ruptures or R shear planes and implosion breccia in the releasing stepovers in shear band ruptures. We propose a seismogenic model involving fluid pressure buildup, formation of shear band ruptures, rupture propagation into the <em>C</em> foliation, and the formation and subsequent alteration of pseudotachylytes. The fine-grained nature of the altered pseudotachylytes would have promoted strain localization during interseismic periods, leading to their transformation into ultramylonite. These findings improve our understanding of earthquake nucleation processes in the brittle–plastic transition zone and highlight the importance of fluids in inducing seismic events.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105511"},"PeriodicalIF":2.6,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144679911","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 : 2025-11-01Epub Date: 2025-07-22DOI: 10.1016/j.jsg.2025.105513
Musa Mhlanga, Russell Bailie, Jürgen Reinhardt
<div><div>The Sea Point contact, Cape Town, South Africa exposes the intrusive contact between the ∼540 Ma S-type Peninsula Granite and the ∼560–555 Ma metasedimentary rocks of the Malmesbury Group of the Pan-African Saldania Belt. The western Saldania Belt was subjected to low-grade greenschist facies metamorphism and deformation during the ∼560–540 Ma Saldanian orogeny. The Peninsula Granite intruded as a series of numerous granite sheets which made use of the pre-existing country rock anisotropy in order to propagate. These are the steeply dipping S<sub>0</sub> bedding due to folding during the Saldanian orogeny, and a steeply dipping axial planar S<sub>2</sub> foliation to the F<sub>2</sub> folds developed during the dominant D<sub>2</sub> deformation. Magma overpressure relative to tensile stresses in the country rock and regional NE-SW-orientated compressional stresses allowed intrusion of variably crystal-laden magma along the anisotropies. The granitic sheets are commonly concentrated in the hinge zones of F<sub>2</sub> folds, where structural traps facilitated magma “trapping.” Filter pressing at the tail of the magma-filled hydrofracture caused closing during magma through-flow resulting in the entrapping of magmatic crystals, most notably K-feldspar megacrysts, in the wall rock as well as xenoliths dislodged during magma infiltration and stoping, and possibly magma flow. Magma stresses have brought about the alignment of K-feldspar megacrysts as well as the long axes of xenoliths parallel to the orientation of granite sheets and wall rock septa in the complex lit-par-lit zone and adjacent to the contact. A degree of assimilation (and possibly partial melting) is evident in the rounded shapes of xenoliths, but, more notably in mixed zones where there are gradational contacts not only between different granite types, reflecting multiple granite pulse intrusion, but also between the granites and wall rock, giving rise to hybrid granites. Xenoliths with remnant S<sub>0</sub> and S<sub>2</sub> were picked up and rotated during magma flow, with some embedded in the wall rock during filter pressing. The timing of granite intrusion relative to deformation is evident from examining contact-metamorphic cordierite porphyroblasts and their inclusions. The variation of inclusion patterns relative to the external foliation indicate that thermal metamorphism and, by implication, magma intrusion, occurred from early D<sub>2</sub>- to late-D<sub>3</sub> deformation with continued flattening of the schist matrix leading to an enveloping of the porphyroblasts by the S<sub>2</sub> foliation. The intrusion thus was accompanied by progressive deformation and tightening of the F<sub>2</sub> folding. Some granites, notably the coarse-grained megacrystic granite, crosscut other granite types and intruded late-to post-tectonic. Magma loading led to the development of a shallowly dipping, widely spaced S<sub>3</sub> crenulation. Subsequent magma injections led t
{"title":"Thermo-mechanical intrusion-wall rock interaction and granite emplacement mechanisms of the Peninsula granite at the Sea Point contact, Cape Town, South Africa","authors":"Musa Mhlanga, Russell Bailie, Jürgen Reinhardt","doi":"10.1016/j.jsg.2025.105513","DOIUrl":"10.1016/j.jsg.2025.105513","url":null,"abstract":"<div><div>The Sea Point contact, Cape Town, South Africa exposes the intrusive contact between the ∼540 Ma S-type Peninsula Granite and the ∼560–555 Ma metasedimentary rocks of the Malmesbury Group of the Pan-African Saldania Belt. The western Saldania Belt was subjected to low-grade greenschist facies metamorphism and deformation during the ∼560–540 Ma Saldanian orogeny. The Peninsula Granite intruded as a series of numerous granite sheets which made use of the pre-existing country rock anisotropy in order to propagate. These are the steeply dipping S<sub>0</sub> bedding due to folding during the Saldanian orogeny, and a steeply dipping axial planar S<sub>2</sub> foliation to the F<sub>2</sub> folds developed during the dominant D<sub>2</sub> deformation. Magma overpressure relative to tensile stresses in the country rock and regional NE-SW-orientated compressional stresses allowed intrusion of variably crystal-laden magma along the anisotropies. The granitic sheets are commonly concentrated in the hinge zones of F<sub>2</sub> folds, where structural traps facilitated magma “trapping.” Filter pressing at the tail of the magma-filled hydrofracture caused closing during magma through-flow resulting in the entrapping of magmatic crystals, most notably K-feldspar megacrysts, in the wall rock as well as xenoliths dislodged during magma infiltration and stoping, and possibly magma flow. Magma stresses have brought about the alignment of K-feldspar megacrysts as well as the long axes of xenoliths parallel to the orientation of granite sheets and wall rock septa in the complex lit-par-lit zone and adjacent to the contact. A degree of assimilation (and possibly partial melting) is evident in the rounded shapes of xenoliths, but, more notably in mixed zones where there are gradational contacts not only between different granite types, reflecting multiple granite pulse intrusion, but also between the granites and wall rock, giving rise to hybrid granites. Xenoliths with remnant S<sub>0</sub> and S<sub>2</sub> were picked up and rotated during magma flow, with some embedded in the wall rock during filter pressing. The timing of granite intrusion relative to deformation is evident from examining contact-metamorphic cordierite porphyroblasts and their inclusions. The variation of inclusion patterns relative to the external foliation indicate that thermal metamorphism and, by implication, magma intrusion, occurred from early D<sub>2</sub>- to late-D<sub>3</sub> deformation with continued flattening of the schist matrix leading to an enveloping of the porphyroblasts by the S<sub>2</sub> foliation. The intrusion thus was accompanied by progressive deformation and tightening of the F<sub>2</sub> folding. Some granites, notably the coarse-grained megacrystic granite, crosscut other granite types and intruded late-to post-tectonic. Magma loading led to the development of a shallowly dipping, widely spaced S<sub>3</sub> crenulation. Subsequent magma injections led t","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105513"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144750592","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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