Pub 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":"2025-07-22","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}
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":"2025-07-21","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 : 2025-07-21DOI: 10.1016/j.jsg.2025.105515
Shijie Liu , Hengxing Lan , C. Derek Martin , Langping Li , Han Bao
As two fundamental fracture types in rock engineering, tension and shear fractures are commonly considered to operate under different stress conditions. However, abundant recent research shows that the microscale heterogeneity of rocks leads to the possibility of microscale tensile and shear fracturing under any stress state. In particular, localised stress concentrations and tensile fractures caused by mineral heterogeneity under compressive stress have been widely studied. However, the heterogeneity-induced processes involved in the shear fracture under direct tension conditions remain ambiguous. In this study, a micro-direct tensile test was used to comprehensively reveal the process and mechanism by which mineral heterogeneity leads to shear fracture in the gneiss of the eastern Himalayas under direct tension. Microscopic observation of the failure process under direct tension, normalised crack initiation and propagation stress, and transverse strain dilation caused by shear behaviour indicate that gneiss with an exceptional anisotropy angle may exhibit more pronounced shear sliding during progressive tensile failure processes. Micro shear sliding significantly increased the strength of the gneiss and changed its tensile strain, elastic modulus, and progressive failure process, which were determined using a direct tension test. Depending on the degree of frictional sliding, the tensile failure mode of gneiss can be divided into three modes: tensile, hybrid, and shear. Mineral heterogeneity influences the pattern of crack propagation through potential fracture planes, altering the crack propagation stress, significantly affecting the mobilisation of frictional strength, and resulting in a progressive transition between the three modes. The observation of shear sliding under direct tension caused by heterogeneity emphasises the importance of mineral-scale heterogeneity in evaluating the tensile strength of anisotropic rocks.
{"title":"Mineral heterogeneity dominates the tensile failure mode of Eastern Himalayan Gneiss","authors":"Shijie Liu , Hengxing Lan , C. Derek Martin , Langping Li , Han Bao","doi":"10.1016/j.jsg.2025.105515","DOIUrl":"10.1016/j.jsg.2025.105515","url":null,"abstract":"<div><div>As two fundamental fracture types in rock engineering, tension and shear fractures are commonly considered to operate under different stress conditions. However, abundant recent research shows that the microscale heterogeneity of rocks leads to the possibility of microscale tensile and shear fracturing under any stress state. In particular, localised stress concentrations and tensile fractures caused by mineral heterogeneity under compressive stress have been widely studied. However, the heterogeneity-induced processes involved in the shear fracture under direct tension conditions remain ambiguous. In this study, a micro-direct tensile test was used to comprehensively reveal the process and mechanism by which mineral heterogeneity leads to shear fracture in the gneiss of the eastern Himalayas under direct tension. Microscopic observation of the failure process under direct tension, normalised crack initiation and propagation stress, and transverse strain dilation caused by shear behaviour indicate that gneiss with an exceptional anisotropy angle may exhibit more pronounced shear sliding during progressive tensile failure processes. Micro shear sliding significantly increased the strength of the gneiss and changed its tensile strain, elastic modulus, and progressive failure process, which were determined using a direct tension test. Depending on the degree of frictional sliding, the tensile failure mode of gneiss can be divided into three modes: tensile, hybrid, and shear. Mineral heterogeneity influences the pattern of crack propagation through potential fracture planes, altering the crack propagation stress, significantly affecting the mobilisation of frictional strength, and resulting in a progressive transition between the three modes. The observation of shear sliding under direct tension caused by heterogeneity emphasises the importance of mineral-scale heterogeneity in evaluating the tensile strength of anisotropic rocks.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105515"},"PeriodicalIF":2.6,"publicationDate":"2025-07-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144696806","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 : 2025-07-19DOI: 10.1016/j.jsg.2025.105512
Henrique C. Joncew , Ginaldo A.C. Campanha , Melina C.B. Esteves , Frederico M. Faleiros , Leonardo E. Lagoeiro , Klaus Wemmer , Ruy A.C. Vasconcelos , Bruno V. Ribeiro , Mathias Hueck
To reconstruct the tectonic evolution of a foreland fold-and-thrust belt, a multi-method approach was carried out involving field-based structural observations, strain quantification, analyses of quartz crystallographic textures, fluid inclusions and illite crystallinity (IC), and in situ muscovite Rb-Sr dating and K-Ar dating of fine fractions of white mica. The studied area encompasses the Southern Espinhaço Front in Serra do Cipó, Brazil, marking the boundary between the Foreland Domain (FLD) of the São Francisco Craton (west) and the Fold-and-Thrust Domain (FTD) of the Araçuaí-West Congo Orogen (east). In this area, the Mesoproterozoic Espinhaço Supergroup was thrust over the Ediacaran-Cambrian Bambuí Group during the Brasiliano-Pan-African orogeny. All structural features indicate west-verging tectonics, with oblate strain ellipsoids, suggesting flattening strain and volume loss. Quartz crystallographic textures indicate primarily rhomb <a> dislocation glide for the larger granulometric fractions (>100 μm), with finer grains experiencing dissolution-precipitation creep. Primary, aqueous fluid inclusions hosted in syn-tectonic veins indicate local intra-basinal fluid circulation. Deformation conditions ranges were 300–410 °C and 1.7–6.0 kbar in the FLD, and 385–450 °C and 2.8–8.0 kbar in the FTD. Rb-Sr muscovite dating suggests a metamorphic peak at 549 ± 17 Ma. K-Ar ages for <2 μm mica were 510–496 Ma in the FLD and 476–456 Ma in the FTD, and <0.2 μm mica dated at 432.6 ± 7.5 Ma. These results indicate progressive crustal wedge thickening under a critical taper model, driving deformation and basal detachment propagation into the foreland accompanied by exhumation.
{"title":"Pressure-temperature-time deformation of an Ediacaran-Cambrian foreland fold-and-thrust belt: the Southern Espinhaço Front, Araçuaí Orogen","authors":"Henrique C. Joncew , Ginaldo A.C. Campanha , Melina C.B. Esteves , Frederico M. Faleiros , Leonardo E. Lagoeiro , Klaus Wemmer , Ruy A.C. Vasconcelos , Bruno V. Ribeiro , Mathias Hueck","doi":"10.1016/j.jsg.2025.105512","DOIUrl":"10.1016/j.jsg.2025.105512","url":null,"abstract":"<div><div>To reconstruct the tectonic evolution of a foreland fold-and-thrust belt, a multi-method approach was carried out involving field-based structural observations, strain quantification, analyses of quartz crystallographic textures, fluid inclusions and illite crystallinity (IC), and in situ muscovite Rb-Sr dating and K-Ar dating of fine fractions of white mica. The studied area encompasses the Southern Espinhaço Front in Serra do Cipó, Brazil, marking the boundary between the Foreland Domain (FLD) of the São Francisco Craton (west) and the Fold-and-Thrust Domain (FTD) of the Araçuaí-West Congo Orogen (east). In this area, the Mesoproterozoic Espinhaço Supergroup was thrust over the Ediacaran-Cambrian Bambuí Group during the Brasiliano-Pan-African orogeny. All structural features indicate west-verging tectonics, with oblate strain ellipsoids, suggesting flattening strain and volume loss. Quartz crystallographic textures indicate primarily rhomb <a> dislocation glide for the larger granulometric fractions (>100 μm), with finer grains experiencing dissolution-precipitation creep. Primary, aqueous fluid inclusions hosted in syn-tectonic veins indicate local intra-basinal fluid circulation. Deformation conditions ranges were 300–410 °C and 1.7–6.0 kbar in the FLD, and 385–450 °C and 2.8–8.0 kbar in the FTD. Rb-Sr muscovite dating suggests a metamorphic peak at 549 ± 17 Ma. K-Ar ages for <2 μm mica were 510–496 Ma in the FLD and 476–456 Ma in the FTD, and <0.2 μm mica dated at 432.6 ± 7.5 Ma. These results indicate progressive crustal wedge thickening under a critical taper model, driving deformation and basal detachment propagation into the foreland accompanied by exhumation.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105512"},"PeriodicalIF":2.9,"publicationDate":"2025-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144750593","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 : 2025-07-18DOI: 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":"2025-07-18","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 : 2025-07-17DOI: 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":"2025-07-17","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 : 2025-07-16DOI: 10.1016/j.jsg.2025.105509
Yunwen Guan , Qichao Wang , Renhai Pu , Sujie Yan , Shuo Chen , Siyu Su
High-resolution 3D seismic reflection data and coherence attribute analysis reveal a complex network of small-scale strike-slip faults (0.2–20 km in length) within the Xunyi area of the southern Ordos Basin at burial depths of 0.4–3.5 km. These structures exhibit a multi-phase evolution history characterized by distinct deformation patterns across different stratigraphic intervals.
Structural analysis identifies four distinct tectonic episodes: (1) initial development of NE and NW-trending fault systems during the Caledonian movement (Cambrian-Ordovician), (2) limited reactivation during the Hercynian event (Carboniferous-Permian), (3) formation of NWW to E-W-trending sinistral strike-slip faults during the Indosinian event (Early-Middle Triassic), and (4) right-lateral transpressional reactivation during the Yanshanian event (Late Jurassic-Early Cretaceous).
Mohr space analysis reveals that the angular relationship between fault orientation and regional stress fields fundamentally controls three distinct patterns of structural inheritance: (1) The XY1 fault maintains continuous activity through all tectonic phases due to its optimal N72-86°E orientation relative to successive stress fields; (2) The XY2-4 faults exhibit early termination after the Caledonian period despite their basement-cutting nature, attributed to their unfavorable orientation under subsequent stress regimes; (3) The Mesozoic faults (W1-4) initiated independently during the Indosinian period with N64-86°E strikes, displaying 33–44° counterclockwise rotation from pre-existing Paleozoic structures.
Detailed fault growth analysis reveals an early stress interaction mechanism where approaching fault segments develop secondary faults and displacement patterns before geometric overlap occurs. This observation challenges the traditional four-stage fault linkage model that assumes significant interaction only after substantial fault overlap, suggesting more complex stress field interactions during early fault development.
This integrated study provides critical insights into intraplate deformation processes within cratonic basins, demonstrating how the orientation of pre-existing structures relative to evolving regional stress fields fundamentally controls fault reactivation patterns in multi-phase tectonic settings.
{"title":"Analysis of middle to deep-depth strike-slip faults in the southern Ordos Basin, China: A case study of the Xunyi area","authors":"Yunwen Guan , Qichao Wang , Renhai Pu , Sujie Yan , Shuo Chen , Siyu Su","doi":"10.1016/j.jsg.2025.105509","DOIUrl":"10.1016/j.jsg.2025.105509","url":null,"abstract":"<div><div>High-resolution 3D seismic reflection data and coherence attribute analysis reveal a complex network of small-scale strike-slip faults (0.2–20 km in length) within the Xunyi area of the southern Ordos Basin at burial depths of 0.4–3.5 km. These structures exhibit a multi-phase evolution history characterized by distinct deformation patterns across different stratigraphic intervals.</div><div>Structural analysis identifies four distinct tectonic episodes: (1) initial development of NE and NW-trending fault systems during the Caledonian movement (Cambrian-Ordovician), (2) limited reactivation during the Hercynian event (Carboniferous-Permian), (3) formation of NWW to E-W-trending sinistral strike-slip faults during the Indosinian event (Early-Middle Triassic), and (4) right-lateral transpressional reactivation during the Yanshanian event (Late Jurassic-Early Cretaceous).</div><div>Mohr space analysis reveals that the angular relationship between fault orientation and regional stress fields fundamentally controls three distinct patterns of structural inheritance: (1) The XY1 fault maintains continuous activity through all tectonic phases due to its optimal N72-86°E orientation relative to successive stress fields; (2) The XY2-4 faults exhibit early termination after the Caledonian period despite their basement-cutting nature, attributed to their unfavorable orientation under subsequent stress regimes; (3) The Mesozoic faults (W1-4) initiated independently during the Indosinian period with N64-86°E strikes, displaying 33–44° counterclockwise rotation from pre-existing Paleozoic structures.</div><div>Detailed fault growth analysis reveals an early stress interaction mechanism where approaching fault segments develop secondary faults and displacement patterns before geometric overlap occurs. This observation challenges the traditional four-stage fault linkage model that assumes significant interaction only after substantial fault overlap, suggesting more complex stress field interactions during early fault development.</div><div>This integrated study provides critical insights into intraplate deformation processes within cratonic basins, demonstrating how the orientation of pre-existing structures relative to evolving regional stress fields fundamentally controls fault reactivation patterns in multi-phase tectonic settings.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"199 ","pages":"Article 105509"},"PeriodicalIF":2.6,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144655257","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 : 2025-07-16DOI: 10.1016/j.jsg.2025.105507
J.K. Ammu, Kathakali Bhattacharyya
We decipher the progressive stages of fracture formation and examine the competing effects of proximity to a thrust, lithology, and bed thickness on fracture abundance, orientation, mode, and length. We address this study in the interfoliated quartzite-phyllite sequence of the leading-edge (∼3.4 km) of the Ramgarh thrust (RT) sheet, the roof thrust of the lower Lesser Himalayan duplex in the Darjeeling Himalaya. Only ∼30 % of the total studied fractures (n = 884) preserve slickenlines and plumose structures. Due to favorable orientations relative to the vertical outcrop bearing, small displacement faults (shear fractures) (n = 236; ∼27 % of total fractures) with slickenlines are better exposed than opening-mode (n = 32; ∼4 %) with plumose structures. Further structural analyses reveal coexisting shear (∼59 %) and opening-mode (∼41 %) fractures. Through crosscutting, fold test, and intensity distribution, we establish fracturing initiated with low-angle, shear fractures during early layer parallel shortening. High-angle, shear, and opening-mode fractures formed post-folding. Fracture density fluctuates with perpendicular distance from the footwall contact due to variation in lithology and bed thickness. Fracture density most strongly depends on lithology (quartzitefractures > phyllitefractures), followed by bed thickness (thin bedsfractures > thick bedsfractures) and distance from the RT. Fracture mode and orientation, with respect to bedding, are similar across lithologies, only intensity differs. High-angle and Riedel shear fractures are localized proximal to the RT. Shear vs opening-mode proportions remain unchanged with increasing distance from the RT. Litho-boundaries and early-formed fractures constrain fracture lengths (ntraces = 10,758), irrespective of their mode and orientation. Fracture networks show more evolved length distributions close to the RT.
{"title":"Unraveling progressive stages of formation and examining relative roles of proximity to fault, mechanical stratigraphy on fracturing in the leading-edge of thrust sheets: Insights from Ramgarh thrust, Darjeeling Himalaya","authors":"J.K. Ammu, Kathakali Bhattacharyya","doi":"10.1016/j.jsg.2025.105507","DOIUrl":"10.1016/j.jsg.2025.105507","url":null,"abstract":"<div><div>We decipher the progressive stages of fracture formation and examine the competing effects of proximity to a thrust, lithology, and bed thickness on fracture abundance, orientation, mode, and length. We address this study in the interfoliated quartzite-phyllite sequence of the leading-edge (∼3.4 km) of the Ramgarh thrust (RT) sheet, the roof thrust of the lower Lesser Himalayan duplex in the Darjeeling Himalaya. Only ∼30 % of the total studied fractures (n = 884) preserve slickenlines and plumose structures. Due to favorable orientations relative to the vertical outcrop bearing, small displacement faults (shear fractures) (n = 236; ∼27 % of total fractures) with slickenlines are better exposed than opening-mode (n = 32; ∼4 %) with plumose structures. Further structural analyses reveal coexisting shear (∼59 %) and opening-mode (∼41 %) fractures. Through crosscutting, fold test, and intensity distribution, we establish fracturing initiated with low-angle, shear fractures during early layer parallel shortening. High-angle, shear, and opening-mode fractures formed post-folding. Fracture density fluctuates with perpendicular distance from the footwall contact due to variation in lithology and bed thickness. Fracture density most strongly depends on lithology (quartzite<sub>fractures</sub> > phyllite<sub>fractures</sub>), followed by bed thickness (thin beds<sub>fractures</sub> > thick beds<sub>fractures</sub>) and distance from the RT. Fracture mode and orientation, with respect to bedding, are similar across lithologies, only intensity differs. High-angle and Riedel shear fractures are localized proximal to the RT. Shear vs opening-mode proportions remain unchanged with increasing distance from the RT. Litho-boundaries and early-formed fractures constrain fracture lengths (n<sub>traces</sub> = 10,758), irrespective of their mode and orientation. Fracture networks show more evolved length distributions close to the RT.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105507"},"PeriodicalIF":2.6,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144687524","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 : 2025-07-15DOI: 10.1016/j.jsg.2025.105508
Manuel Bullejos , Manuel Martín-Martín
Interactive 3D HTML models and visualizations of geological structures derived from classic surface geological information have been developed, for the first time, in a Python environment, using the key case of the tectonic Mula sheets in the Betic Cordillera (southern Spain). These models were performed through several steps: a geological 2D sketch map, creating equispaced geological cross-sections, 3D topography, a complete 3D model, and detailed 3D block diagrams. The result of the extrapolation of the equispaced geological cross-sections and their integration with the geological map into a 3D geological model shows the thrust-faulted and contractionally folded structure of the entire area, which affects the Cretaceous to Lower Miocene succession. The faults (strike-slip and normal) present in the tectonic thrust sheets are also represented. Three detailed 3D HTML blocks of illustrative regions within the modeled area were also created. For the 3D modeling, Bézier curves/surfaces as well as linear interpolation were used, as geological (stratigraphic and tectonic) contacts and surfaces between different stratigraphic units can be expressed geometrically with these tools. Compared to commercial alternatives, our software offers three key advantages: free user-friendly solutions, browser-compatible 3D models, and open-source software. The 3D visualization of stratigraphic-structural architecture enables predictive interpretations with applications in environmental and economic geology (e.g., groundwater, geotechnical studies, mining research, etc.). Moreover, 3D visualization and modeling provide valuable insights into geological phenomena, benefiting both the scientific community and society at large. Furthermore, advances in interactive 3D visualization bridge the gap between cutting-edge geological research and public understanding, enhancing social awareness.
{"title":"3D modeling and visualization of geological structures with python-implemented Bézier curves/surfaces","authors":"Manuel Bullejos , Manuel Martín-Martín","doi":"10.1016/j.jsg.2025.105508","DOIUrl":"10.1016/j.jsg.2025.105508","url":null,"abstract":"<div><div>Interactive 3D HTML models and visualizations of geological structures derived from classic surface geological information have been developed, for the first time, in a Python environment, using the key case of the tectonic Mula sheets in the Betic Cordillera (southern Spain). These models were performed through several steps: a geological 2D sketch map, creating equispaced geological cross-sections, 3D topography, a complete 3D model, and detailed 3D block diagrams. The result of the extrapolation of the equispaced geological cross-sections and their integration with the geological map into a 3D geological model shows the thrust-faulted and contractionally folded structure of the entire area, which affects the Cretaceous to Lower Miocene succession. The faults (strike-slip and normal) present in the tectonic thrust sheets are also represented. Three detailed 3D HTML blocks of illustrative regions within the modeled area were also created. For the 3D modeling, Bézier curves/surfaces as well as linear interpolation were used, as geological (stratigraphic and tectonic) contacts and surfaces between different stratigraphic units can be expressed geometrically with these tools. Compared to commercial alternatives, our software offers three key advantages: free user-friendly solutions, browser-compatible 3D models, and open-source software. The 3D visualization of stratigraphic-structural architecture enables predictive interpretations with applications in environmental and economic geology (e.g., groundwater, geotechnical studies, mining research, etc.). Moreover, 3D visualization and modeling provide valuable insights into geological phenomena, benefiting both the scientific community and society at large. Furthermore, advances in interactive 3D visualization bridge the gap between cutting-edge geological research and public understanding, enhancing social awareness.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105508"},"PeriodicalIF":2.9,"publicationDate":"2025-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144750591","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 : 2025-07-12DOI: 10.1016/j.jsg.2025.105506
Eric Salomon , Anna Nele Meckler , Axel Gerdes , Richard Albert , Harald Stollhofen
We present a catalogue of calcite vein types in porous sandstone that have the potential to affect fluid flow properties in a reservoir. Host rock is the Lower Cretaceous aeolian Twyfelfontein Formation, covered by voluminous flood volcanic rock of the Paraná-Etendeka Large Igneous Province in the Huab Basin of NW Namibia. Since the host sandstone lacks carbonate components, these veins document advective fluid flow, where solutes were transported through the fractures from an external source. Crystal growth in veins vary from blocky, to radial, and micritic. Some veins exhibit an intergrowth with kaolinite, or show an initial dolomite and iron oxide precipitation. Deformation stages are evident in a number of veins from breccia to cataclasis and fault-slip slickenfibre generations. Some calcite generations underwent partial dissolution and replacement by chalcedony. U-Pb dating shows a predominant vein formation from 31 Ma to recent, with one outlier at ∼65 Ma. Pore-filling calcite cements of sandstone along veins and in contact with the covering volcanic rock show similar ages. Formation temperatures (16–47 °C) derived from clumped isotope analysis indicate precipitation at shallow burial depths (<1 km). An outlier of 59 °C stems from the vein dated to ∼65 Ma. Carbonate δ13CVPDB shows a trend from −8.3 ‰ to −1.3 ‰ between Oligocene to present and we argue this to be a reflection of the region's climatic shift from warm humid to (semi-)arid conditions in this time. We further discuss, that this shift is responsible for many of the observed vein characteristics.
{"title":"A catalogue of calcite vein types in porous sandstone and their formation conditions (Huab Basin, Namibia)","authors":"Eric Salomon , Anna Nele Meckler , Axel Gerdes , Richard Albert , Harald Stollhofen","doi":"10.1016/j.jsg.2025.105506","DOIUrl":"10.1016/j.jsg.2025.105506","url":null,"abstract":"<div><div>We present a catalogue of calcite vein types in porous sandstone that have the potential to affect fluid flow properties in a reservoir. Host rock is the Lower Cretaceous aeolian Twyfelfontein Formation, covered by voluminous flood volcanic rock of the Paraná-Etendeka Large Igneous Province in the Huab Basin of NW Namibia. Since the host sandstone lacks carbonate components, these veins document advective fluid flow, where solutes were transported through the fractures from an external source. Crystal growth in veins vary from blocky, to radial, and micritic. Some veins exhibit an intergrowth with kaolinite, or show an initial dolomite and iron oxide precipitation. Deformation stages are evident in a number of veins from breccia to cataclasis and fault-slip slickenfibre generations. Some calcite generations underwent partial dissolution and replacement by chalcedony. U-Pb dating shows a predominant vein formation from 31 Ma to recent, with one outlier at ∼65 Ma. Pore-filling calcite cements of sandstone along veins and in contact with the covering volcanic rock show similar ages. Formation temperatures (16–47 °C) derived from clumped isotope analysis indicate precipitation at shallow burial depths (<1 km). An outlier of 59 °C stems from the vein dated to ∼65 Ma. Carbonate δ<sup>13</sup>C<sub>VPDB</sub> shows a trend from −8.3 ‰ to −1.3 ‰ between Oligocene to present and we argue this to be a reflection of the region's climatic shift from warm humid to (semi-)arid conditions in this time. We further discuss, that this shift is responsible for many of the observed vein characteristics.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105506"},"PeriodicalIF":2.6,"publicationDate":"2025-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144713550","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：