Journal of Structural Geology最新文献

{"title":"Revisiting surface ruptures of the 1955 Zheduotang earthquake (Mw 7.1) in eastern tibet: kinematic implications on the southern Xianshuihe fault zone","authors":"Guangchun Xu ,&nbsp;Junjie Ren ,&nbsp;Yufa Liu ,&nbsp;Chao Ma ,&nbsp;Yaning Yi ,&nbsp;Yanwu Lv ,&nbsp;Xiwei Xu","doi":"10.1016/j.jsg.2025.105540","DOIUrl":"10.1016/j.jsg.2025.105540","url":null,"abstract":"<div><div>Surface ruptures associated with large historical earthquakes provide essential insights into earthquake magnitudes and the kinematics of their seismogenic faults. In 1955, a major earthquake struck Zheduotang Village, Kangding City, producing surface ruptures along the Zheduotang fault, a segment of the southern Xianshuihe fault zone. The magnitude of this event remains a topic of debate, with estimates ranging from M6.6 to M7.5, primarily due to discrepancies in the interpretation of its associated surface ruptures. This study synthesizes previous research on the surface ruptures of the 1955 Zheduotang earthquake and presents new field data, including high-resolution unmanned aerial vehicle (UAV)-based topographic surveys, trenching, and lichenometry in the epicentral region. Analysis of surface rupture freshness, faulting event chronology from trenching, and lichen size measurements collectively support a ∼55 km-long surface rupture zone, corresponding to a moment magnitude (M_w) of ∼7.1 for the 1955 earthquake. Offset glacial landform analysis reveals a late Quaternary left-lateral slip rate of ∼2.5–3.0 mm/yr in the southern segment of the Zheduotang fault, which is lower than the previously documented ∼4 mm/yr in the northern segment. Deformed landforms and surface ruptures indicate that the fault trends NNW and exhibits predominantly left-lateral strike-slip motion in its northern segment, while the southern segment trends NW and includes a notable normal faulting component. Our findings suggest that the Zheduotang fault defines the southwestern boundary of the Bamei-Kangding releasing stepover zone within the southern Xianshuihe left-lateral strike-slip fault zone. These results enhance the understanding of seismic hazards and the tectonic kinematics along the eastern boundary of the Tibetan Plateau.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105540"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144906887","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}

{"title":"Structural and stratigraphic control on fluid flow in the Mt. Conero anticline, Italy: An analog for offshore resource reservoirs in fold-and-thrust belts","authors":"Luca Smeraglia ,&nbsp;Luca Aldega ,&nbsp;Stefano M. Bernasconi ,&nbsp;Andrea Billi ,&nbsp;Sabina Bigi ,&nbsp;Eduardo di Marcantonio ,&nbsp;Andrea Fiorini ,&nbsp;Andrew Kylander-Clark ,&nbsp;Eugenio Carminati","doi":"10.1016/j.jsg.2025.105502","DOIUrl":"10.1016/j.jsg.2025.105502","url":null,"abstract":"<div><div>We investigate the structural control on paleofluid flow in the Mt. Conero anticline, Italy, located in the frontal part of the Apennines fold-and-thrust belt. This anticline can be considered as an exhumed analog for buried anticlines in the Adriatic offshore, currently exploited for hydrocarbons and potential geothermal reservoirs or CO₂ storage sites in the future. By integrating field structural analyses, stable and clumped isotope geochemistry of carbonates, and U-Pb geochronology, we demonstrate that the structural evolution of the Mt. Conero anticline in a carbonate-siliciclastic succession is marked by: (1) pre-orogenic normal faulting and veining during foreland flexure, (2) layer-parallel shortening during early contraction, with the development of <em>en-echelon</em> bed-perpendicular conjugate veins and stylolites, (3) syn-folding thrusting and strike-slip faulting, and (4) transtensional faulting during fold exhumation and extensional collapse. Fluid circulation took place in a closed system, predominantly involving formation water, such as marine pore water trapped during diagenesis. Effective sealing by clay-rich formations overlying the fractured, permeable carbonates, coupled with low displacement strike-slip faults and thrusts, prevented the ingress of meteoric fluids and/or the upward migration of deep (hydrothermal) fluids. Limited mixing between formation and meteoric waters in a semi-closed system was observed during fold exhumation and extensional collapse. Our results show that folds in the frontal part of offshore fold-and-thrust belts are likely to retain fluids trapped during diagenesis due to the preservation of sealing layers. This suggests that such anticlines can preserve hydrocarbon reservoirs and are excellent candidates for CO₂ storage due to their low leakage potential, offering also good storage capacity for geothermal fluids. These results may represent a benchmark for offshore anticlines in the frontal part of other offshore fold-and-thrust belts, particularly those with carbonate anticlines overlain by clay-rich sealing layers.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105502"},"PeriodicalIF":2.6,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144687535","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}

{"title":"Simultaneous determination of deviatoric stress tensors from polyphase calcite twin data: improvement and application","authors":"Yehua Shan ,&nbsp;Jian Zheng","doi":"10.1016/j.jsg.2025.105534","DOIUrl":"10.1016/j.jsg.2025.105534","url":null,"abstract":"<div><div>It is a challenge to obtain the meaningful solution of deviatoric stress tensors from polyphase calcite twin data measured in multi-deformed rocks. Our paper advances current approaches that simultaneously determine stresses from polyphase twin data. Key refinements include the selection of the dimensionless stress space, the estimation of the dimensionless critical resolved shear stress (<span><math><mrow><msub><mover><mi>τ</mi><mo>‾</mo></mover><mi>c</mi></msub></mrow></math></span>), the definition of the stress criterion including <span><math><mrow><msub><mover><mi>τ</mi><mo>‾</mo></mover><mi>c</mi></msub></mrow></math></span>, and the exclusion or inclusion of incompatible untwinned planes (IU). The improved simultaneous-determination method (ISDM) is applied to three series of two–three-phase IU-free synthetic datasets generated under imposed stresses. Stress results demonstrate that the ISDM is accurate in principal stress direction, stress ratio, and <span><math><mrow><msub><mover><mi>τ</mi><mo>‾</mo></mover><mi>c</mi></msub></mrow></math></span>, although the ISDM including IU is a little more accurate than the ISDM excluding IU. For two-phase equally-sized synthetic datasets, the ISDM excluding IU is generally more accurate than existing similar methods. Applying both the ISDM and an existing similar method to a natural dataset reveals that the ISDM excluding IU yields the most reasonable stress solution.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105534"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144852671","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}

{"title":"General transpression and transtension","authors":"Carlos Fernández ,&nbsp;Manuel Díaz Azpiroz ,&nbsp;Jorge Alonso-Henar","doi":"10.1016/j.jsg.2025.105537","DOIUrl":"10.1016/j.jsg.2025.105537","url":null,"abstract":"<div><div>In this work, a triclinic transpression and transtension model is presented in which the coaxial part of the flow is general, including both constriction and flattening as well as pure shear. The results show that, for both transtension and transpression, the different combinations of the variables that control the model allow obtaining finite strain ellipsoids in all fields of the deformation diagram, including prolate and oblate ellipsoids. It is mainly the <em>ζ</em> angle between the simple-shearing direction and the extrusion (transpression) or sinking (transtension) direction, together with the value of the vorticity, and the characteristics of the coaxial part of the flow, which controls the shape of the finite strain ellipsoid in each case. The orientations of the principal axes (<em>X</em>, <em>Y</em>, <em>Z</em>) of the finite strain ellipsoids show a wide variation, also dependent on <em>ζ</em>. The model has been applied to natural examples, improving the knowledge of their kinematic evolution and tectonic interpretation.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105537"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144867379","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}

{"title":"Intracontinental deformation and paleo-stress fields of the lower yangtze region during the late Mesozoic: implications for the tectonic evolution of South China","authors":"Beihang Zhang ,&nbsp;Jin Zhang ,&nbsp;Heng Zhao ,&nbsp;Jie Hui ,&nbsp;Yaqi Yang ,&nbsp;Yiping Zhang ,&nbsp;Alimu Adina ,&nbsp;Hai Jiang","doi":"10.1016/j.jsg.2025.105532","DOIUrl":"10.1016/j.jsg.2025.105532","url":null,"abstract":"<div><div>The late Mesozoic intracontinental deformation in South China preserves rich insights into continental evolution, with close link to subduction and collision processes along the eastern margin of the Eurasian Plate. The Lower Yangtze Region, located in the northeastern part of South China, underwent complex intracontinental deformation during the late Mesozoic, making it a key area for understanding the tectonic evolution of East Asia. Through detailed field investigation of representative outcrops and structural analysis of fault-slip data from the regional faults, this study reconstructs the late Mesozoic deformation sequence and paleo-stress fields in the Lower Yangtze Region. Our new data, combined with published results, suggest that the Lower Yangtze Region experienced a three-stage tectonic evolution from the Late Jurassic to early Late Cretaceous, characterized by alternating contractional and extensional tectonic events. The first stage, contractional deformation from the Late Jurassic to early Early Cretaceous, was controlled by NW-SE contractional stress, generating sinistral strike-slip motion along the Tan-Lu Fault, the dextral strike-slip motion along the Chuhe Fault and Yangtze River Fault, and top-to-west thrusting of the Maoshan Fault. This contractional deformation is interpreted as being related to the westward low-angle subduction of the Paleo-Pacific Plate beneath the Eurasian Plate. The second stage is NW-SE extension during the Early Cretaceous, associated with a series of high-angle normal faults, which is correlated with the rollback of the Paleo-Pacific Plate. The third stage is another episode of contractional deformation that resulted in a tectonic inversion controlled by nearly N-S contraction during late Early Cretaceous to early Late Cretaceous. This contraction led to the sinistral strike-slip motion of the regional faults and was associated with a set of conjugate strike-slip faults. The oblique collision between the Okhotomorsk Block and the Eurasian Plate serves as the geodynamic driver for this contraction event. Comparative structural analysis reveals distinct deformation patterns between the Lower Yangtze Region and other areas of South China during the Late Jurassic to early Early Cretaceous. Under the same NW-SE contraction, the Lower Yangtze Region exhibited predominant strike-slip motion along the major faults, whereas other areas of South China developed NNE-SSW-striking thrust-and-fold deformation. This disparity is possibly caused by the unique tectonic position and pre-existing basement faults of the Lower Yangtze Region. Due to the obstruction of the rigid craton (i.e., the North China Craton), the crustal materials underwent lateral extrusion towards the northeast along the pre-existing faults, accommodating the continuous contraction that occurred during the Late Jurassic to early Early Cretaceous.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105532"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144840643","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}

{"title":"An optimization approach to algebraic Rf/ϕ strain analysis","authors":"Yehua Shan","doi":"10.1016/j.jsg.2025.105535","DOIUrl":"10.1016/j.jsg.2025.105535","url":null,"abstract":"<div><div>In algebraic <em>R</em>_<em>f</em>/<em>ϕ</em> strain analysis, there is a lack of the uncertainty of strain caused by, as common in measured post-strain objects, the violation of the assumption of the independence between the major-axis directions and axial ratios of pre-strain objects. A new <em>R</em>_<em>f</em>/<em>ϕ</em> strain method is developed to reduce this uncertainty. The method minimizes the sum of the <em>K</em>-th power of the negative determinant of the tensor difference between each post-strain object and the unknown strain. The method for <span><math><mrow><mi>K</mi><mo>=</mo><mn>1</mn></mrow></math></span> yields an analytical solution of strain, equivalent to existing algebraic estimators of strain. Both synthetic datasets and real examples are used to validate the method for varying <em>K</em> values of 1–10. The strain results illustrate that the method decreases in standard error and tends to increase in accuracy with an increasing <em>K</em>. The variation of the estimated strain with <em>K</em> is helpful to appraise the violation of the independence assumption.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105535"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144895001","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}

{"title":"Pore space properties and permeability of solution surfaces in Mesozoic shallow-water carbonates, southern Apennines, Italy","authors":"C. Manniello ,&nbsp;V. La Bruna ,&nbsp;E. Michie ,&nbsp;R.E.B. Araùjo ,&nbsp;F.H.R. Bezerra ,&nbsp;D. Faulkner ,&nbsp;M. Allen ,&nbsp;X.M. Morais ,&nbsp;G. Prosser ,&nbsp;F. Agosta","doi":"10.1016/j.jsg.2025.105520","DOIUrl":"10.1016/j.jsg.2025.105520","url":null,"abstract":"<div><div>Focusing on the Mesozoic and Eocene carbonate samples from the Viggiano Mt. and Raparo Mt., Southern Apennines of Italy, we examine the role of solution surfaces on the present-day porosity and permeability. Carbonate lithofacies include mudstones, packstones, grainstones, and rudstones and gas-porosimetry measurements show effective porosity up to 5 %. The value is mainly due to the secondary porosity localized along microfractures and within the rough bed-parallel and rough bed-oblique solution surfaces, contrary to what was found in the smooth bed-parallel ones, showing that roughness can control pore localization. NMR (Nuclear Magnetic Resonance) results indicate that the former group of solution surfaces include vugs characterized by subspherical to tubular shapes (pore throat r &lt; 3 μm), and low aspect ratios (r &lt; 2), forming pores with low sensitivity to compression. The microfractures form capillary porosity (r ≈ 1 μm) and are characterized by high aspect ratios (r &gt; 2), typical of pores with high sensitivity to compression. Permeability measurements at room pressure reveal that samples with visible microfractures are characterized by values up 2 order magnitude greater than of those with only visible solution surfaces, showing that the pore connectivity is controlled by opening-mode, sub-mm scale microfractures. At confining pressures greater than 25 MPa, both fracture- and stylolite dominated samples show similar values of permeability, indicating that at depths larger than ca. 1 km, the rough stylolite localize effective porosity that may enhance the along-solution surface fluid flow in carbonates.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105520"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144810158","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}

{"title":"Structural architecture, tectonic stacking and extensional reactivation of nappe contacts in the southern Middle Tuscan Ridge, Inner Northern Apennines orogenic belt (Italy)","authors":"Andrea Brogi ,&nbsp;Enrico Capezzuoli ,&nbsp;Amalia Spina ,&nbsp;Martina Zucchi ,&nbsp;Chiara Montemagni ,&nbsp;Federico Lucci","doi":"10.1016/j.jsg.2025.105541","DOIUrl":"10.1016/j.jsg.2025.105541","url":null,"abstract":"<div><div>Interpreting tectonic stacking patterns and the nature of contacts between tectonic units is a major challenge in orogenic belts, particularly when mafic rock slices are embedded within the tectonic stack. These occurrences raise fundamental questions about their origin and the tectonic processes responsible for their emplacement. Such complexities, which characterize several orogenic belts worldwide, are especially prominent in the inner Northern Apennines orogenic belt (Italy). This belt is characterized by abrupt metamorphic discontinuities, local omissions of portions of the tectonic stack, significant stratigraphic gaps within individual tectonic units and contains discontinuous mafic bodies within the nappe pile. These features point to a polyphase tectonic evolution, which over the last decades has led to a range of hypotheses concerning the Neogene evolution of the inner Northern Apennines. Testing these models requires integrated structural, petrological, and stratigraphic investigations. This study presents structural, kinematic and stratigraphic data on detailed field mapping in the southern Middle Tuscan Ridge (southern Tuscany), a key area within the inner Northern Apennines. Our results document a polyphase extensional evolution characterised by the sequential development of normal faults during post-orogenic deformation (∼19–20 Ma). Based on this evidence, we propose an updated tectonic model that integrates the geometry, timing, and evolution of extensional structures in this part of the chain. The model refines the regional tectonic framework and provides a basis for further investigation into the metamorphic evolution, the chronology of tectonic events, and the origin of mafic bodies within continental units. On a broader scale, it offers a reference for interpreting post-collisional extensional settings in other orogenic belts worldwide.</div></div>","PeriodicalId":50035,"journal":{"name":"Journal of Structural Geology","volume":"200 ","pages":"Article 105541"},"PeriodicalIF":2.9,"publicationDate":"2025-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144917418","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}

{"title":"Pressure-temperature-time deformation of an Ediacaran-Cambrian foreland fold-and-thrust belt: the Southern Espinhaço Front, Araçuaí Orogen","authors":"Henrique C. Joncew ,&nbsp;Ginaldo A.C. Campanha ,&nbsp;Melina C.B. Esteves ,&nbsp;Frederico M. Faleiros ,&nbsp;Leonardo E. Lagoeiro ,&nbsp;Klaus Wemmer ,&nbsp;Ruy A.C. Vasconcelos ,&nbsp;Bruno V. Ribeiro ,&nbsp;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 &lt;a&gt; dislocation glide for the larger granulometric fractions (&gt;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 &lt;2 μm mica were 510–496 Ma in the FLD and 476–456 Ma in the FTD, and &lt;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":"2025-11-01","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}

{"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,&nbsp;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_fractures &gt; phyllite_fractures), followed by bed thickness (thin beds_fractures &gt; thick beds_fractures) 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_traces = 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":"2025-11-01","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}