Pub Date : 2026-03-01Epub Date: 2026-01-16DOI: 10.1016/j.jsg.2026.105628
Simone Vezzoni , Diego Pieruccioni , Giancarlo Molli , Andrea Dini , Cristian Biagioni
Research on the ore-forming event(s) and their relationships with the Apennine deformation and metamorphism of the Alpi Apuane ore district (NW Tuscany, Italy) was abandoned with the closure of mining activities. The discovery of a remarkable thallium (Tl) anomaly associated with the pyrite ± baryte ± Fe-oxides ores has renewed scientific interest in this ore district during the last fifteen years. This work provides a detailed field and underground geological-structural investigation of one of these orebodies (previously exploited at the Buca della Vena mine), performed from cartographic to micro-scales, and integrated with available drill-log data, providing new insights into ore-forming events and late remobilisation during metamorphic processes. Our investigation suggests that the current ore settings were acquired during successive geological events related to a Permian hydrothermal-magmatic phase, and more recent Apennine-related deformations. The Permian hydrothermal activity related to the post-Variscan magmatic cycle produced the proto-ore associated with tourmalinisation and hydrothermal alteration halo in the Palaeozoic host-rock. The proto-ore was then partially exhumed, undergoing supergene alteration and minor syn-sedimentary Fe-oxide mineralisation during the upper Norian-Hettangian. Finally, the earlier hydrothermal and syn-sedimentary ores and the host rocks were involved in the Apennine orogenesis, suffering recrystallisation and partial remobilisation, acquiring their current mineralogical, textural, and structural settings.
随着采矿活动的停止，对意大利西北部托斯卡纳Alpi Apuane矿区的成矿事件及其与亚平宁变形变质作用关系的研究被放弃。在过去的15年中，与黄铁矿±重晶石±氧化铁矿石相关的铊（Tl）异常的发现重新引起了科学界的兴趣。这项工作对其中一个矿体（以前在Buca della Vena矿开采）进行了详细的现场和地下地质结构调查，从制图到微观尺度进行了研究，并与现有的钻井测井数据相结合，为变质过程中的成矿事件和晚期再活化提供了新的见解。我们的研究表明，目前的矿石背景是在与二叠纪热液-岩浆期相关的连续地质事件中获得的，以及最近与亚平宁岛相关的变形。与后瓦里斯坎岩浆旋回相关的二叠纪热液活动在古生代寄主岩中产生了与电气石化和热液蚀变晕相关的原矿石。原矿石部分出土，在上诺里安—鹤唐期经历了表生蚀变和少量同沉积铁氧化物矿化。最后，亚平宁造山过程中早期热液和同沉积矿石及寄主岩经历了重结晶和部分再活化作用，形成了现今的矿物学、构造和构造环境。
{"title":"Origin, metamorphic remobilisation and structural control of the Buca della Vena orebody (Alpi Apuane, Italy)","authors":"Simone Vezzoni , Diego Pieruccioni , Giancarlo Molli , Andrea Dini , Cristian Biagioni","doi":"10.1016/j.jsg.2026.105628","DOIUrl":"10.1016/j.jsg.2026.105628","url":null,"abstract":"<div><div>Research on the ore-forming event(s) and their relationships with the Apennine deformation and metamorphism of the Alpi Apuane ore district (NW Tuscany, Italy) was abandoned with the closure of mining activities. The discovery of a remarkable thallium (Tl) anomaly associated with the pyrite ± baryte ± Fe-oxides ores has renewed scientific interest in this ore district during the last fifteen years. This work provides a detailed field and underground geological-structural investigation of one of these orebodies (previously exploited at the Buca della Vena mine), performed from cartographic to micro-scales, and integrated with available drill-log data, providing new insights into ore-forming events and late remobilisation during metamorphic processes. Our investigation suggests that the current ore settings were acquired during successive geological events related to a Permian hydrothermal-magmatic phase, and more recent Apennine-related deformations. The Permian hydrothermal activity related to the post-Variscan magmatic cycle produced the proto-ore associated with tourmalinisation and hydrothermal alteration halo in the Palaeozoic host-rock. The proto-ore was then partially exhumed, undergoing supergene alteration and minor syn-sedimentary Fe-oxide mineralisation during the upper Norian-Hettangian. Finally, the earlier hydrothermal and syn-sedimentary ores and the host rocks were involved in the Apennine orogenesis, suffering recrystallisation and partial remobilisation, acquiring their current mineralogical, textural, and structural settings.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"204 ","pages":"Article 105628"},"PeriodicalIF":2.9,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146022944","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}
Connectivity of two-dimensional fault networks documented with connecting nodes and branches shows spatial variation of Cenozoic fault networks in the Zhu I Depression, Pearl River Mouth Basin, South China Sea. Our data indicate that the fault network topology of the basement and syn-rift sequence is dominated by isolated nodes (I-nodes ≈ 80 %) and partly connecting branches (I–C branches ≈ 40 %). The connecting nodes and branches are primarily located at the depocentres and lateral surroundings of border faults of the half-grabens and grabens within the Zhu I Depression. In the post-rift fault networks, there is an increase in the proportion of isolated nodes (I-nodes ≈ 85 %) with the isolated branches (I–I branches ≈ 45 %) replacing partly connecting branches as the dominant branch type. The fault connections are concentrated in the locations of fault splays and relay-breaching along right-stepping en echelon fault sets. Due to the basin-scale sampling area with varying connectivity, the average number of connections per branch of the basement and syn-rift fault networks, both of which have undergone multi-phase extension, is close to that of the post-rift fault network, which has undergone single-phase extension. The location and size of the sampling area hinder the discrimination of the origins of fault networks through topological parameters. Intensified post-rift faulting that occurred at ∼16 Ma has led to an extra increase in the connectivity of the fault network at the upper post-rift sequence.
{"title":"Spatial variation in topological characteristics of fault networks in rift basins: Zhu I Depression, Pearl River Mouth Basin, South China Sea","authors":"Guangrong Peng , Meng Zhang , Xiangtao Zhang , Hongbo Li , Zhe Wu , Chenxi Ma , Faru Liang , Zhiping Wu","doi":"10.1016/j.jsg.2026.105632","DOIUrl":"10.1016/j.jsg.2026.105632","url":null,"abstract":"<div><div>Connectivity of two-dimensional fault networks documented with connecting nodes and branches shows spatial variation of Cenozoic fault networks in the Zhu I Depression, Pearl River Mouth Basin, South China Sea. Our data indicate that the fault network topology of the basement and syn-rift sequence is dominated by isolated nodes (I-nodes ≈ 80 %) and partly connecting branches (I–C branches ≈ 40 %). The connecting nodes and branches are primarily located at the depocentres and lateral surroundings of border faults of the half-grabens and grabens within the Zhu I Depression. In the post-rift fault networks, there is an increase in the proportion of isolated nodes (I-nodes ≈ 85 %) with the isolated branches (I–I branches ≈ 45 %) replacing partly connecting branches as the dominant branch type. The fault connections are concentrated in the locations of fault splays and relay-breaching along right-stepping en echelon fault sets. Due to the basin-scale sampling area with varying connectivity, the average number of connections per branch of the basement and syn-rift fault networks, both of which have undergone multi-phase extension, is close to that of the post-rift fault network, which has undergone single-phase extension. The location and size of the sampling area hinder the discrimination of the origins of fault networks through topological parameters. Intensified post-rift faulting that occurred at ∼16 Ma has led to an extra increase in the connectivity of the fault network at the upper post-rift sequence.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"204 ","pages":"Article 105632"},"PeriodicalIF":2.9,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146078201","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 : 2026-03-01Epub Date: 2025-12-17DOI: 10.1016/j.jsg.2025.105610
Adrien Damon , Roger Soliva , Jean Busson , Christopher Wibberley , Céline Fliedner , Frédéric Bourgeois , Frédéric Ego
We propose a model of the permeability behavior of clayrocks based on a review of plastic deformation observed in the field and permeability measurements in reactivation tests of fractures and faults. Firstly, we classify structures observed in the field according to their deformation mode and propose a model of clayrock deformation relative to usual mechanical concepts described in the literature. Secondly, we evidence controls on clayrock fracture/fault permeability by the stress conditions of the reactivated structures, the amount of shear displacement along them, and the mechanical properties of the clayrock. Finally, we formulate our model based on similarities in the concepts of clayrock deformation and the experimental evolution of clayrock fracture/fault permeability. This model links quantitative data on permeability evolution to deformation mechanisms, defining the permeability behavior of clayrocks, which was lacking in the literature until now. We highlight the dependence of this behavior on the stress and shear conditions, and demonstrate that the ratio of effective normal stress () to the Unconfined Compressive Strength (UCS) of the clayrock can be used to describe this behavior. This model can be used in the assessment of clayrock formation sealing capacity in the context of geological storage. Particularly, the use of the UCS has the advantage of integrating important geological parameters in this assessment, such as the clay content or consolidation history. According to this model, we recommend to preserve a level larger than 0.5 in order to avoid a significant permeability increasing behavior associated with reactivation.
{"title":"Clayrock deformation and permeability: insights from natural observations and experimental tests","authors":"Adrien Damon , Roger Soliva , Jean Busson , Christopher Wibberley , Céline Fliedner , Frédéric Bourgeois , Frédéric Ego","doi":"10.1016/j.jsg.2025.105610","DOIUrl":"10.1016/j.jsg.2025.105610","url":null,"abstract":"<div><div>We propose a model of the permeability behavior of clayrocks based on a review of plastic deformation observed in the field and permeability measurements in reactivation tests of fractures and faults. Firstly, we classify structures observed in the field according to their deformation mode and propose a model of clayrock deformation relative to usual mechanical concepts described in the literature. Secondly, we evidence controls on clayrock fracture/fault permeability by the stress conditions of the reactivated structures, the amount of shear displacement along them, and the mechanical properties of the clayrock. Finally, we formulate our model based on similarities in the concepts of clayrock deformation and the experimental evolution of clayrock fracture/fault permeability. This model links quantitative data on permeability evolution to deformation mechanisms, defining the permeability behavior of clayrocks, which was lacking in the literature until now. We highlight the dependence of this behavior on the stress and shear conditions, and demonstrate that the ratio of effective normal stress (<span><math><mrow><msubsup><mi>σ</mi><mi>n</mi><mo>′</mo></msubsup></mrow></math></span>) to the Unconfined Compressive Strength (UCS) of the clayrock can be used to describe this behavior. This model can be used in the assessment of clayrock formation sealing capacity in the context of geological storage. Particularly, the use of the UCS has the advantage of integrating important geological parameters in this assessment, such as the clay content or consolidation history. According to this model, we recommend to preserve a <span><math><mrow><msubsup><mi>σ</mi><mi>n</mi><mo>′</mo></msubsup><mo>/</mo><mi>U</mi><mi>C</mi><mi>S</mi></mrow></math></span> level larger than 0.5 in order to avoid a significant permeability increasing behavior associated with reactivation.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"204 ","pages":"Article 105610"},"PeriodicalIF":2.9,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145771939","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 : 2026-03-01Epub Date: 2025-12-18DOI: 10.1016/j.jsg.2025.105605
Lirong Dou , Xinshun Zhang , Chuanbo Shen , Yebo Du , Li Wang , Xiang Ge , Huahua Gao , Yu Yang
Investigating the deformation evolution of rifting, strike-slip faulting, and positive inversion within the Central African Shear Zone (CASZ) is crucial for understanding regional tectonic evolution, dynamic processes, and improving the exploration of hydrocarbon-rich basins. To better understand the deformation evolution of the CASZ, three brittle/ductile analog models with different block angles were tested. The results indicate that under NE–SW extensional stress: (1) rifting intensity in the CASZ decreases progressively from west to east, with the Doba Basin experiencing the strongest rifting, followed by the Doseo Basin, and the weakest rifting occurring in the Salamat Basin; (2) significant strike-slip deformation is concentrated primarily in the Doseo Basin, followed by the Salamat Basin, with minimal strike-slip deformation in the Doba Basin; and (3) strong positive inversion occurs near boundary regions of the CASZ—predominantly along the basin boundaries in the Doba Basin, whereas in the Doseo and Salamat Basins, it is more pronounced in the central depression areas.
{"title":"Deformation evolution of the rifting and positive inversion in the Central African Shear Zone: Insights from Analogue Modelling","authors":"Lirong Dou , Xinshun Zhang , Chuanbo Shen , Yebo Du , Li Wang , Xiang Ge , Huahua Gao , Yu Yang","doi":"10.1016/j.jsg.2025.105605","DOIUrl":"10.1016/j.jsg.2025.105605","url":null,"abstract":"<div><div>Investigating the deformation evolution of rifting, strike-slip faulting, and positive inversion within the Central African Shear Zone (CASZ) is crucial for understanding regional tectonic evolution, dynamic processes, and improving the exploration of hydrocarbon-rich basins. To better understand the deformation evolution of the CASZ, three brittle/ductile analog models with different block angles were tested. The results indicate that under NE–SW extensional stress: (1) rifting intensity in the CASZ decreases progressively from west to east, with the Doba Basin experiencing the strongest rifting, followed by the Doseo Basin, and the weakest rifting occurring in the Salamat Basin; (2) significant strike-slip deformation is concentrated primarily in the Doseo Basin, followed by the Salamat Basin, with minimal strike-slip deformation in the Doba Basin; and (3) strong positive inversion occurs near boundary regions of the CASZ—predominantly along the basin boundaries in the Doba Basin, whereas in the Doseo and Salamat Basins, it is more pronounced in the central depression areas.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"204 ","pages":"Article 105605"},"PeriodicalIF":2.9,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145841637","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 : 2026-03-01Epub Date: 2025-12-26DOI: 10.1016/j.jsg.2025.105611
Aurora E. Rosenberger , Sean P. Long , Nolan Blackford , Johannes Haemmerli , Kyle P. Larson , Brianna Dowler , Scott Jess
Several metamorphic core complexes exhibit structural asymmetry in their exhumed footwalls, with ductile strain, crystallographic preferred orientation (CPO) intensity, and/or mean kinematic vorticity (Wm) increasing in the direction of detachment fault displacement. Here, we investigate the Northern Snake Range metamorphic core complex in Nevada, to explore the processes that are the most influential for generating transport-parallel strain gradients in detachment fault footwalls. Eocene-Oligocene tectonic strain (Rs), lineation-parallel extension, and foliation-normal thinning in the Northern Snake Range increase eastward from 1.5–1.6 to 240–820, 25–30 % to 1400–2400 %, and 15–21 % to 93–95 %, respectively (assuming no volume change). CPO intensity parameters (cylindricity and JPF index) increase eastward from 0.45 to 0.90–0.95 and 1.40 to 2.64–6.40, respectively, and average Wm increases eastward from 0.26–0.40 (72–82 % pure shear) to 0.77–0.83 (56–63 % simple shear). Restoration of a strain model supported by a range-wide cross-section defines 17.9 km (470 %) of Eocene-Oligocene ductile extension. Published footwall cooling histories demonstrate an eastward progression of exhumation-related cooling, driven by unroofing via top-down-to-ESE displacement on the master detachment. This progressive unroofing resulted in an eastward increase in the residence time of quartz-rich footwall rocks at temperatures above ∼300 °C (and thus a longer ductile strain history on the eastern side of the range), which we interpret was a 1st-order factor for generating the eastward increases in strain, CPO intensity, and Wm. The Northern Snake Range is an excellent case study that demonstrates the potential for generation of pronounced transport-parallel structural asymmetry in metamorphic core complexes that are exhumed by high-displacement detachment faults.
{"title":"Investigating the generation of transport-parallel gradients in ductile strain and kinematic vorticity in the footwalls of metamorphic core complexes: Insights from the Northern Snake Range, Nevada, USA","authors":"Aurora E. Rosenberger , Sean P. Long , Nolan Blackford , Johannes Haemmerli , Kyle P. Larson , Brianna Dowler , Scott Jess","doi":"10.1016/j.jsg.2025.105611","DOIUrl":"10.1016/j.jsg.2025.105611","url":null,"abstract":"<div><div>Several metamorphic core complexes exhibit structural asymmetry in their exhumed footwalls, with ductile strain, crystallographic preferred orientation (CPO) intensity, and/or mean kinematic vorticity (W<sub>m</sub>) increasing in the direction of detachment fault displacement. Here, we investigate the Northern Snake Range metamorphic core complex in Nevada, to explore the processes that are the most influential for generating transport-parallel strain gradients in detachment fault footwalls. Eocene-Oligocene tectonic strain (Rs), lineation-parallel extension, and foliation-normal thinning in the Northern Snake Range increase eastward from 1.5–1.6 to 240–820, 25–30 % to 1400–2400 %, and 15–21 % to 93–95 %, respectively (assuming no volume change). CPO intensity parameters (cylindricity and J<sub>PF</sub> index) increase eastward from 0.45 to 0.90–0.95 and 1.40 to 2.64–6.40, respectively, and average W<sub>m</sub> increases eastward from 0.26–0.40 (72–82 % pure shear) to 0.77–0.83 (56–63 % simple shear). Restoration of a strain model supported by a range-wide cross-section defines 17.9 km (470 %) of Eocene-Oligocene ductile extension. Published footwall cooling histories demonstrate an eastward progression of exhumation-related cooling, driven by unroofing via top-down-to-ESE displacement on the master detachment. This progressive unroofing resulted in an eastward increase in the residence time of quartz-rich footwall rocks at temperatures above ∼300 °C (and thus a longer ductile strain history on the eastern side of the range), which we interpret was a 1st-order factor for generating the eastward increases in strain, CPO intensity, and W<sub>m</sub>. The Northern Snake Range is an excellent case study that demonstrates the potential for generation of pronounced transport-parallel structural asymmetry in metamorphic core complexes that are exhumed by high-displacement detachment faults.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"204 ","pages":"Article 105611"},"PeriodicalIF":2.9,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145885797","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 : 2026-03-01Epub Date: 2026-01-21DOI: 10.1016/j.jsg.2026.105627
Wei Lv, Xing Liu
Under conditions of data scarcity, traditional methods often struggle to construct reliable geological models. To maximize the utilization of information from limited data, this paper presents an implicit modeling method for shallow bedrock based on Generalized Radial Basis Function (GRBF) interpolation. Grounded in GRBF theory, the method extracts outcrop line data and geological attitude information from topographic and geological maps. These are then transformed into multiple interpolation constraints, including point, gradient, and tangential constraints, which are subsequently incorporated into a GRBF linear system to solve for the geological interfaces. The resulting surfaces are then processed according to established topological relationships and geological rules, forming solid models for visualization. Uncertainty is inherent in both the data and the process of three-dimensional (3D) modeling. As attitude information provides only an approximation of the normal vector, its associated uncertainty is significant. Therefore, this study primarily focuses on the uncertainty of attitude. A von Mises–Fisher (vMF) probability distribution model is defined for the normal vectors, and an ensemble of possible geological scenarios is generated through Monte Carlo sampling. This ensemble is used to construct multiple geological models, and the information entropy metric is then employed to quantitatively evaluate their quality and assess overall model uncertainty. The final uncertainty models provide effective decision support for engineering exploration, resource development, and disaster prevention and mitigation.
{"title":"Three-dimensional bedrock implicit modeling and uncertainty quantification from sparse geological map data","authors":"Wei Lv, Xing Liu","doi":"10.1016/j.jsg.2026.105627","DOIUrl":"10.1016/j.jsg.2026.105627","url":null,"abstract":"<div><div>Under conditions of data scarcity, traditional methods often struggle to construct reliable geological models. To maximize the utilization of information from limited data, this paper presents an implicit modeling method for shallow bedrock based on Generalized Radial Basis Function (GRBF) interpolation. Grounded in GRBF theory, the method extracts outcrop line data and geological attitude information from topographic and geological maps. These are then transformed into multiple interpolation constraints, including point, gradient, and tangential constraints, which are subsequently incorporated into a GRBF linear system to solve for the geological interfaces. The resulting surfaces are then processed according to established topological relationships and geological rules, forming solid models for visualization. Uncertainty is inherent in both the data and the process of three-dimensional (3D) modeling. As attitude information provides only an approximation of the normal vector, its associated uncertainty is significant. Therefore, this study primarily focuses on the uncertainty of attitude. A von Mises–Fisher (vMF) probability distribution model is defined for the normal vectors, and an ensemble of possible geological scenarios is generated through Monte Carlo sampling. This ensemble is used to construct multiple geological models, and the information entropy metric is then employed to quantitatively evaluate their quality and assess overall model uncertainty. The final uncertainty models provide effective decision support for engineering exploration, resource development, and disaster prevention and mitigation.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"204 ","pages":"Article 105627"},"PeriodicalIF":2.9,"publicationDate":"2026-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146022943","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 : 2026-02-01Epub Date: 2025-11-12DOI: 10.1016/j.jsg.2025.105584
Eloi González-Esvertit , Josep Maria Casas , Àngels Canals , Paul D. Bons , Kevin Konrad , Maria-Gema Llorens , Gabriel Serrano-López , Claudia Prieto-Torrell , Joyce Neilson , Diego Domínguez-Carretero , Aratz Beranoaguirre , Axel Gerdes , Enrique Gomez-Rivas
The age of the mylonite belts in the basement rocks of the Pyrenees is a subject of debate in the structural geology and petrology communities because of its potential implication on the regional tectonothermal history and on the tectonic evolution of SW Europe. Here we address when and how mylonitisation took place in two key areas of the Eastern Pyrenees, where shear zones are associated with Giant Quartz Veins (GQVs). We conducted zircon U-Pb and muscovite 40Ar/39Ar dating coupled with structural, textural, and crystallographic preferred orientation (CPO) analyses of mylonites from the Cap de Creus and Canigó Massifs. U-Pb zircon dating of a dacite porphyry dyke crosscut by GQVs and mylonitic bands yields a maximum shear zone and GQV formation age of ca. 292 ± 3 Ma. 40Ar/39Ar analyses of muscovite within mylonitised GQVs yield initial crystallisation ages between ca. 164 and 188 Ma, as well as younger recrystallisation ages of ca. 110–118 Ma. A qualitative assessment of the GQV history is inferred from step-heating spectra of muscovite and quartz CPOs. The results indicate that GQV formation and mylonitisation were coupled, coeval, and long-lasting processes that took place from early Jurassic to early Cretaceous times. A comparative evaluation of quartz CPOs reveals inconsistencies regarding the strain distribution, quartz slip systems activity, and deformation temperatures depending on the deformed rock type. Quartz mylonites have stronger CPOs dominated by basal <a>, prism <a>, or prism <c> slip systems, whilst phyllonites and granite mylonites show weaker fabrics mostly dominated by mixed <a> slip. This apparently suggests higher deformation temperatures in quartz mylonites than those inferred from more reliable proxies, such as mineral assemblages, brittle behaviour of K-feldspar, and fluid inclusion data. We suggest that the water-weakening effect caused by coeval formation and deformation of GQVs enabled easier dislocation glide and creep, allowing strain localisation and transitions between slip systems at lower temperatures than commonly inferred due to enhanced ductility. U-Pb zircon dating further suggests the existence of an early Carboniferous (ca. 332 ± 4 Ma; Visean) magmatic episode in the Pyrenees, in agreement with a cyclic, rather than a progressive, geodynamic history of the region during Variscan times. The present work challenges classical interpretations stating that Pyrenean mylonite belts developed during the retrograde stages of the Variscan Orogeny, highlighting that the structural evolution of this region during Mesozoic times deserves further investigation. Results have implications for interpreting deformation localisation mechanisms and conditions in crustal rocks, for the formation mechanisms of GQVs in worldwide orogenic belts, and for the tectonothermal history of the Pyrenees since late-Variscan times.
{"title":"Hydrolytic weakening controls Jurassic to early Cretaceous mylonitisation in the basement of the Pyrenees","authors":"Eloi González-Esvertit , Josep Maria Casas , Àngels Canals , Paul D. Bons , Kevin Konrad , Maria-Gema Llorens , Gabriel Serrano-López , Claudia Prieto-Torrell , Joyce Neilson , Diego Domínguez-Carretero , Aratz Beranoaguirre , Axel Gerdes , Enrique Gomez-Rivas","doi":"10.1016/j.jsg.2025.105584","DOIUrl":"10.1016/j.jsg.2025.105584","url":null,"abstract":"<div><div>The age of the mylonite belts in the basement rocks of the Pyrenees is a subject of debate in the structural geology and petrology communities because of its potential implication on the regional tectonothermal history and on the tectonic evolution of SW Europe. Here we address when and how mylonitisation took place in two key areas of the Eastern Pyrenees, where shear zones are associated with Giant Quartz Veins (GQVs). We conducted zircon U-Pb and muscovite <sup>40</sup>Ar/<sup>39</sup>Ar dating coupled with structural, textural, and crystallographic preferred orientation (CPO) analyses of mylonites from the Cap de Creus and Canigó Massifs. U-Pb zircon dating of a dacite porphyry dyke crosscut by GQVs and mylonitic bands yields a maximum shear zone and GQV formation age of ca. 292 ± 3 Ma. <sup>40</sup>Ar/<sup>39</sup>Ar analyses of muscovite within mylonitised GQVs yield initial crystallisation ages between ca. 164 and 188 Ma, as well as younger recrystallisation ages of ca. 110–118 Ma. A qualitative assessment of the GQV history is inferred from step-heating spectra of muscovite and quartz CPOs. The results indicate that GQV formation and mylonitisation were coupled, coeval, and long-lasting processes that took place from early Jurassic to early Cretaceous times. A comparative evaluation of quartz CPOs reveals inconsistencies regarding the strain distribution, quartz slip systems activity, and deformation temperatures depending on the deformed rock type. Quartz mylonites have stronger CPOs dominated by basal <a>, prism <a>, or prism <c> slip systems, whilst phyllonites and granite mylonites show weaker fabrics mostly dominated by mixed <a> slip. This apparently suggests higher deformation temperatures in quartz mylonites than those inferred from more reliable proxies, such as mineral assemblages, brittle behaviour of K-feldspar, and fluid inclusion data. We suggest that the water-weakening effect caused by coeval formation and deformation of GQVs enabled easier dislocation glide and creep, allowing strain localisation and transitions between slip systems at lower temperatures than commonly inferred due to enhanced ductility. U-Pb zircon dating further suggests the existence of an early Carboniferous (ca. 332 ± 4 Ma; Visean) magmatic episode in the Pyrenees, in agreement with a cyclic, rather than a progressive, geodynamic history of the region during Variscan times. The present work challenges classical interpretations stating that Pyrenean mylonite belts developed during the retrograde stages of the Variscan Orogeny, highlighting that the structural evolution of this region during Mesozoic times deserves further investigation. Results have implications for interpreting deformation localisation mechanisms and conditions in crustal rocks, for the formation mechanisms of GQVs in worldwide orogenic belts, and for the tectonothermal history of the Pyrenees since late-Variscan times.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"203 ","pages":"Article 105584"},"PeriodicalIF":2.9,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145693865","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 : 2026-02-01Epub Date: 2025-12-09DOI: 10.1016/j.jsg.2025.105608
Shaohua Yang , Haibing Li , Jiawei Pan , Yaolin Shi
While the initiation mechanisms, patterns, and effects of subduction involving an old oceanic plate beneath a younger plate (old-beneath-young subduction) are well established, the dynamics of young-beneath-old subduction, such as that observed at the Manila Trench in East Asia, remain poorly understood. The influence of key parameters, including oceanic plate age and convergence rate, on the geometry of young-beneath-old subduction, and how these factors differ from those in old-beneath-young subduction, has yet to be fully explored. Furthermore, the role of young-beneath-old subduction in modulating subduction-related volcanism, exemplified by the double volcanic arc between Taiwan and Luzon, is not well characterized. In this study, we present ocean-ocean subduction numerical models to investigate these issues. Our results reveal that when the overriding plate is older or the subducting plate is younger, the subduction angle is smaller. Additionally, for a constant age difference between the plates, younger subducting plates are associated with shallower subduction angles. Faster convergence rates tend to promote low-angle subduction. These findings provide new insights into the formation of the Taiwan-Luzon double volcanic arc. We propose that the initial low-velocity convergence between the Philippine and South China Sea plates caused high-angle subduction, leading to the formation of the West Volcanic Chain (WVC). Subsequently, the acceleration of the Philippine Plate in the north-westward direction resulted in a decrease in subduction angle, halting WVC activity and facilitating the formation of the East Volcanic Chain (EVC). Latitudinal lithospheric age gradients drive WVC-EVC divergence through differential subduction angles, inducing contrasting mantle wedge dynamics and volcanic chain spacing.
{"title":"Numerical modeling of young-beneath-old subduction and implications for Taiwan-Luzon double volcanic arc in East Asia","authors":"Shaohua Yang , Haibing Li , Jiawei Pan , Yaolin Shi","doi":"10.1016/j.jsg.2025.105608","DOIUrl":"10.1016/j.jsg.2025.105608","url":null,"abstract":"<div><div>While the initiation mechanisms, patterns, and effects of subduction involving an old oceanic plate beneath a younger plate (old-beneath-young subduction) are well established, the dynamics of young-beneath-old subduction, such as that observed at the Manila Trench in East Asia, remain poorly understood. The influence of key parameters, including oceanic plate age and convergence rate, on the geometry of young-beneath-old subduction, and how these factors differ from those in old-beneath-young subduction, has yet to be fully explored. Furthermore, the role of young-beneath-old subduction in modulating subduction-related volcanism, exemplified by the double volcanic arc between Taiwan and Luzon, is not well characterized. In this study, we present ocean-ocean subduction numerical models to investigate these issues. Our results reveal that when the overriding plate is older or the subducting plate is younger, the subduction angle is smaller. Additionally, for a constant age difference between the plates, younger subducting plates are associated with shallower subduction angles. Faster convergence rates tend to promote low-angle subduction. These findings provide new insights into the formation of the Taiwan-Luzon double volcanic arc. We propose that the initial low-velocity convergence between the Philippine and South China Sea plates caused high-angle subduction, leading to the formation of the West Volcanic Chain (WVC). Subsequently, the acceleration of the Philippine Plate in the north-westward direction resulted in a decrease in subduction angle, halting WVC activity and facilitating the formation of the East Volcanic Chain (EVC). Latitudinal lithospheric age gradients drive WVC-EVC divergence through differential subduction angles, inducing contrasting mantle wedge dynamics and volcanic chain spacing.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"203 ","pages":"Article 105608"},"PeriodicalIF":2.9,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145736862","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 : 2026-02-01Epub Date: 2025-11-05DOI: 10.1016/j.jsg.2025.105569
Abhisek Basa , Behzad Alaei , Anita Torabi
Generation of 3D fault network in conventional seismic interpretation involves creation of structural models by manually tracking the same discontinuity across seismic horizons on several adjacent vertical profiles. This process is often time-consuming, susceptible to human bias and introduces uncertainties in the characterization of fault geometric attributes - such as length, width and throw - that cannot be reliably quantified. In this study, we adopt a data-driven approach and extract the geometric attributes of the individual segments constituting the 3D seismic fault zone architecture in remarkable detail, that provides insights beyond the capabilities of conventional seismic attributes. This is achieved through the application of 3D Deep Learning (DL) Networks trained on 3D synthetic seismic datasets on a seismic survey from the eastern flank of Polhem Subplatform, SW of Norwegian Barents Sea to automatically create probabilistic fault volumes. Detailed extraction of individual fault segments from the fault probability volume allows us to investigate the seismic fault zone architecture at multiple scales. Our results show that the maximum segment length of all the studied faults is present near the upper tips and reduces towards the lower tips. The fault zone widths of individual segments measured on E-W-oriented vertical scanplanes orthogonal to the strike of the dominant fault set mostly vary between 10 and 20m. They exhibit higher values at locations where fault segments link laterally/vertically or interact with antithetic fault sets with similar strike of the dominant westward dipping fault set. Throw estimates and the total accumulated fault zone widths are higher towards the lower tips of the faults. Thus, the application of Deep Learning enables data-driven, high-resolution visualization of the seismic fault zone architecture and facilitates comprehensive extraction of fault geometric attributes, providing a more robust complement to traditional interpretation techniques.
{"title":"Detailed 3D characterization of fault geometric attributes: Insights from deep learning-based fault imaging in seismic data","authors":"Abhisek Basa , Behzad Alaei , Anita Torabi","doi":"10.1016/j.jsg.2025.105569","DOIUrl":"10.1016/j.jsg.2025.105569","url":null,"abstract":"<div><div>Generation of 3D fault network in conventional seismic interpretation involves creation of structural models by manually tracking the same discontinuity across seismic horizons on several adjacent vertical profiles. This process is often time-consuming, susceptible to human bias and introduces uncertainties in the characterization of fault geometric attributes - such as length, width and throw - that cannot be reliably quantified. In this study, we adopt a data-driven approach and extract the geometric attributes of the individual segments constituting the 3D seismic fault zone architecture in remarkable detail, that provides insights beyond the capabilities of conventional seismic attributes. This is achieved through the application of 3D Deep Learning (DL) Networks trained on 3D synthetic seismic datasets on a seismic survey from the eastern flank of Polhem Subplatform, SW of Norwegian Barents Sea to automatically create probabilistic fault volumes. Detailed extraction of individual fault segments from the fault probability volume allows us to investigate the seismic fault zone architecture at multiple scales. Our results show that the maximum segment length of all the studied faults is present near the upper tips and reduces towards the lower tips. The fault zone widths of individual segments measured on E-W-oriented vertical scanplanes orthogonal to the strike of the dominant fault set mostly vary between 10 and 20m. They exhibit higher values at locations where fault segments link laterally/vertically or interact with antithetic fault sets with similar strike of the dominant westward dipping fault set. Throw estimates and the total accumulated fault zone widths are higher towards the lower tips of the faults. Thus, the application of Deep Learning enables data-driven, high-resolution visualization of the seismic fault zone architecture and facilitates comprehensive extraction of fault geometric attributes, providing a more robust complement to traditional interpretation techniques.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"203 ","pages":"Article 105569"},"PeriodicalIF":2.9,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145532424","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 : 2026-02-01Epub Date: 2025-11-13DOI: 10.1016/j.jsg.2025.105560
Hugues Raimbourg , Benjamin Moris-Muttoni , Romain Augier , Kristijan Rajič , Ismay Vénice Akker , Aurélien Canizarès , Emmanuel Le Trong
Carbonaceous matter is a common component of metasedimentary rocks, mainly deriving from the diagenetic and then metamorphic evolution of the organic matter originally present in the sedimentary protolith. During burial, the maturity of carbonaceous particles increases by rearrangements of the aromatic carbon sheets and expulsion of heteroatoms, mostly as a result of temperature increase. However, additional external factors could enhance the maturity such as the pressure, fluid-rock interactions and/or deformation. In this work we explored the effect of strain at low metamorphic temperatures (in the range ∼200–320 °C) along natural strain gradients of variable scales, in three accretionary or collisional complexes (Shimanto and Kodiak accretionary complexes, Infrahelvetic Flysch Units), using Raman spectra of carbonaceous matter. In these examples, both ductile and brittle zones of localized deformation were observed, in the form of shear and breccia zones, respectively. Carbonaceous particles observed by TEM are ∼50–100 nm in size and are distributed throughout the rocks, enabling automated Raman spectroscopy profiles and maps to be carried out. Irrespective of the deformation process, the intensity ratio between D and G band (R1 ratio) of Raman spectra is systematically increased by up to ∼60 % in high strain zones compared to the least deformed, reference zones. From the comparison with a series of undeformed metamorphic rocks spanning the same temperature range, the R1 increase reflects the progressive organization of the carbonaceous matter towards higher maturity. In mm-scale shear bands, the increase in R1 can be unambiguously ascribed to localized strain, whereas in brecciated domains, localized temperature increase may also have contributed to R1 anomaly.
{"title":"Impact of strain on carbonaceous matter crystallinity: Insights from Raman spectroscopy and microstructural analysis of strain gradients from exhumed accretionary complexes","authors":"Hugues Raimbourg , Benjamin Moris-Muttoni , Romain Augier , Kristijan Rajič , Ismay Vénice Akker , Aurélien Canizarès , Emmanuel Le Trong","doi":"10.1016/j.jsg.2025.105560","DOIUrl":"10.1016/j.jsg.2025.105560","url":null,"abstract":"<div><div>Carbonaceous matter is a common component of metasedimentary rocks, mainly deriving from the diagenetic and then metamorphic evolution of the organic matter originally present in the sedimentary protolith. During burial, the maturity of carbonaceous particles increases by rearrangements of the aromatic carbon sheets and expulsion of heteroatoms, mostly as a result of temperature increase. However, additional external factors could enhance the maturity such as the pressure, fluid-rock interactions and/or deformation. In this work we explored the effect of strain at low metamorphic temperatures (in the range ∼200–320 °C) along natural strain gradients of variable scales, in three accretionary or collisional complexes (Shimanto and Kodiak accretionary complexes, Infrahelvetic Flysch Units), using Raman spectra of carbonaceous matter. In these examples, both ductile and brittle zones of localized deformation were observed, in the form of shear and breccia zones, respectively. Carbonaceous particles observed by TEM are ∼50–100 nm in size and are distributed throughout the rocks, enabling automated Raman spectroscopy profiles and maps to be carried out. Irrespective of the deformation process, the intensity ratio between D and G band (R1 ratio) of Raman spectra is systematically increased by up to ∼60 % in high strain zones compared to the least deformed, reference zones. From the comparison with a series of undeformed metamorphic rocks spanning the same temperature range, the R1 increase reflects the progressive organization of the carbonaceous matter towards higher maturity. In mm-scale shear bands, the increase in R1 can be unambiguously ascribed to localized strain, whereas in brecciated domains, localized temperature increase may also have contributed to R1 anomaly.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"203 ","pages":"Article 105560"},"PeriodicalIF":2.9,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145580011","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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