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1
Lermontova, A. S. « STRESS FIELD IN A SHEAR ZONE, AND FORMATION OF THE MAIN FAULT ». Geodynamics & ; Tectonophysics 12, no 3 (17 septembre 2021) : 499–507. http://dx.doi.org/10.5800/gt-2021-12-3-0536.
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Using the analytical approximation method, we calculated stress field parameters for cases with different relative positions of Riedel shears and loads required for shearing. Considering an internal friction angle of 30°, and the distance between adjacent shears exceeding 0.7 of the characteristic shear length, we estimated the Coulomb stress that can lead to fracturing. In the areas between the shears, it is below the shear strength value. This means that if an increase in the external load is lacking, there are no prerequisites for the formation of new fractures that may connect adjacent shears. If the shears are spaced closer to each other (i.e. at distances less than 0.7 of the shear length), the shear strength is exceeded in the areas between them, and new shears can occur there and connect the Riedel shears to each other. Therefore, in observations of a natural system of Riedel shears, it becomes possible to assess whether this system is sufficiently stable in its current status, or, in case of a critical increase in the Coulomb stress in the areas between adjacent shears, the equilibrium can be easily disturbed, and there is a possibility that the main fault forms in the strike-slip zone under study.
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Strahilov, Dian, Plamen Doychev et Ivan Dimitrov. « Ore shoots formation in a sinistral strike-slip setting : an interpreted from the map of the Au-Ag Milin Kamak deposit in the Breznic area, Southwest Bulgaria ». Review of the Bulgarian Geological Society 83, no 3 (décembre 2022) : 131–34. http://dx.doi.org/10.52215/rev.bgs.2022.83.3.131.
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This work presents а structural interpretation of a well-known gold deposit from SW Bulgaria. The interpretation is based on the geological map and structural data, collected during the prospecting. The data indicates that а regional sinistral shearing was responsible for a low rank sinistral shear system, which created ore depositional space by the combined action of shear extension and compression. The two mechanisms opened tension gashes, dilated previously formed Riedel faults and buckled the veins and the faults. The buckling happened, when the structures were rotated anticlockwise in the compressional quadrant of the space between the regional shears thus creating buckling structures. Ore shoots have been formed in the extended domains of the main shear and along the dilated previously formed Riedel shears.
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Dresen, G. « Stress distribution and orientation of Riedel shears ». International Journal of Rock Mechanics and Mining Sciences & ; Geomechanics Abstracts 28, no 6 (novembre 1991) : A332. http://dx.doi.org/10.1016/0148-9062(91)91140-m.
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Dresen, G. « Stress distribution and the orientation of Riedel shears ». Tectonophysics 188, no 3-4 (mars 1991) : 239–47. http://dx.doi.org/10.1016/0040-1951(91)90458-5.
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Tsui, Po C., David M. Cruden et Stanley Thomson. « Mesofabric, microfabric, and submicrofabric of ice-thrust bedrock, Highvale mine, Wabamun Lake area, Alberta ». Canadian Journal of Earth Sciences 25, no 9 (1 septembre 1988) : 1420–31. http://dx.doi.org/10.1139/e88-136.
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The fabric of the ice-thrust argillaceous bedrock from a shear zone was studied in hand specimens, under a polarizing microscope and a scanning electron microscope. The fabric included principal displacement shears, Riedel shears, conjugate sets of particle alignments, cutans, lithorelics, and aggregations which dense cores of randomly oriented groups of clay platelets wrapped by an external layer of oriented clay particles in a turbostatic arrangement. In addition, the bedrock has been disturbed by permafrost, cycles of loading and unloading, and weathering, causing the magnitude of deformation to vary within the ice-thrust shear zone.The fabric of the ice-thrust shear zone is similar to that of shear zones formed by tectonic activity and by laboratory shear tests, suggesting that all these shear zones were formed under conditions of similar kinematic restraint.
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Kavyani-Sadr, Khashayar, Behnam Rahimi, Mohammad Mahdi Khatib et Young-Seog Kim. « Assessment of open spaces related to Riedel-shears dip effect in brittle shear zones ». Journal of Structural Geology 154 (janvier 2022) : 104486. http://dx.doi.org/10.1016/j.jsg.2021.104486.
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Mueller, Matthias, Petri Peltonen, Pasi Eilu, Richard Goldfarb et Eero Hanski. « The Mustajärvi orogenic gold occurrence, Central Lapland Greenstone Belt, Finland : a telluride-dominant mineral system ». Mineralium Deposita 55, no 8 (30 juin 2020) : 1625–46. http://dx.doi.org/10.1007/s00126-020-00990-w.
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Abstract The Mustajärvi gold occurrence lies in the southern part of the Paleoproterozoic Central Lapland Greenstone Belt, in proximity to the first-order transcrustal Venejoki thrust fault system. The gold occurrence is structurally controlled by the second-order Mustajärvi shear zone, which is located at the contact between siliciclastic metasedimentary and mafic to ultramafic metavolcanic rocks. The main mineralization comprises a set of parallel veins and sulfidized rocks that are slightly oblique to the shear zone and are hosted by third-order structures likely representing Riedel R-type shears. The gold-mineralized rock at Mustajärvi is associated with pyrite that is present in 0.15- to 1-m-wide quartz-pyrite-tourmaline veins and in zones of massive pyrite in the host rocks with thicknesses ranging from 1.15 to 2 m. In unweathered rock, hypogene gold is hosted by Au- and Au-Bi-telluride micro-inclusions in pyrite, whereas strong weathering at near surface levels has caused a remobilization of gold, resulting in free gold deposited mainly in the cracks of oxidized pyrite. The geochemistry of both mineralization styles is typical of orogenic gold systems with strong enrichments comprising Au, B, Bi, CO2, Te, and Se; and less consistent anomalous amounts of Ag, As, Sb, and W. Unusual for orogenic gold deposits is the strong enrichment of Ni and Co, which leads to the classification of Mustajärvi as orogenic gold occurrence with atypical metal association.
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Li, Yuqiang, Dun Wang, Shenghui Xu, Lihua Fang, Yifang Cheng, Gang Luo, Bing Yan, Enescu Bogdan et Jim Mori. « Thrust and Conjugate Strike‐Slip Faults in the 17 June 2018 MJMA 6.1 (Mw 5.5) Osaka, Japan, Earthquake Sequence ». Seismological Research Letters 90, no 6 (18 septembre 2019) : 2132–41. http://dx.doi.org/10.1785/0220190122.
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ABSTRACT The 17 June 2018 MJMA 6.1 (Mw 5.5) Osaka earthquake exhibits a large non–double‐couple component (∼26%), and its aftershock sequence shows a complicated spatial pattern. To better understand the ruptured faults, we relocate the earthquake sequence using P and S arrival times and waveform cross correlations and calculate the focal mechanisms of all MJMA≥2.5 (Mw≥2.3) earthquakes within three months after the mainshock using P‐wave first‐motion polarities and S/P amplitude ratios. Relocated aftershocks image several faults, the northeast‐striking strike‐slip fault, the north‐northwest‐striking reverse fault, and at least two small northwest‐striking features. P‐wave first motions of the mainshock indicate nearly a pure thrust mechanism. We deduce that the earthquake sequence started from a north‐northwest‐striking reverse fault and propagated to a northeast‐striking strike‐slip fault. The aligned strike‐slip aftershocks occurring in the vicinity of the northeast‐striking strike‐slip fault delineates the growth of several newly formed or reactivated northwest‐striking Riedel shears that are conjugated to the northeast‐striking strike‐slip fault.
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TUTKUN, Z., et S. PAVLIDES. « Small scale contractional-extensional structures and morphotectonics along the fault traces of Izmit-Cocaeli (Turkey) 1999 earthquake ». Bulletin of the Geological Society of Greece 34, no 1 (1 janvier 2001) : 345. http://dx.doi.org/10.12681/bgsg.17033.
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The Mw=7.4 Izmit (Kocaeli) earthquake of August 17, 1999 (Turkey) ruptured 100 km at least surface faults on land along the northwestern branch of the North Anatolian Fault Zone (NAFZ). Although the preexisting structures of NAFZ has been divided into segments, showing stepover and pull apart geometry, the earthquake ruptures are generally linear, E-W striking (N80°-100°), right-lateral. In small scale and on the recent sediments they show very typical strike-slip displacements (2 to 5m), pop-ups and pressure ridges (N 40- 70°), Ρ (N80°), R (N100-1100) and R' (~N350°) Riedel shears, extensional cracks (N115°-135°), restraining and releasing bends and small pull apart structures. In the epicentral area (Gölcük-Tepetarla) the seismic ruptures did not follow any known or previously mapped fault, but the morphology and the Digital Elevation Model (DEM) show typical and recognizable paleo-earthquake features. That is elongated valleys, shutter ridges, high angle slopes, scarplets, stream offset; while trenching tectonostratigraphy indicate palaeo sag-ponds (clayly deposits) and palaeo liquefaction (C14 dating-Holocene-historical deposits 200 to 11,000 yr. BP).
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Herbst, Paul, Franz Neubauer et Martin PJ Schöpfer. « The development of brittle structures in an alpine valley glacier : Pasterzenkees, Austria, 1887–1997 ». Journal of Glaciology 52, no 176 (2006) : 128–36. http://dx.doi.org/10.3189/172756506781828872.
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AbstractBrittle structures exposed in the ablation area of Pasterzenkees, Austria, were interpreted using aerial photographs and maps covering a period of 100 years. The most common structural features observed in aerial photographs are: (1) normal faults, which are particularly well developed along the lateral margins of the glacier and at the terminus; (2) large-scale tension gashes and Riedel shears that develop along the northeastern lateral margin of the glacier and between ice-flow units; (3) thrust faults, which develop at the terminus and cross-cut the full width of the glacier; and (4) band ogives. Longitudinal and transverse topographic profiles are available for the period covered in this study, and ice-flow velocity data are available from 1927. These data provide a means for interpreting the variations of observed structures in terms of ice-flow velocity. Thrust faults predominantly develop during periods of glacier retreat, when the glacier snout becomes an obstacle. Normal faults typically develop in areas of high glacier surface relief and are interpreted as gravity collapse structures. The orientation of sub-vertical, wide open crevasses along the lateral margin of Pasterzenkees varied. These variations are interpreted as reflecting changes of the flow regime and indicate a transition from simple shearing to transtension during a period of ice-flow deceleration.
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Armitage, Timothy B., Lee M. Watts, Robert E. Holdsworth et Robin A. Strachan. « Late Carboniferous dextral transpressional reactivation of the crustal-scale Walls Boundary Fault, Shetland : the role of pre-existing structures and lithological heterogeneities ». Journal of the Geological Society 178, no 1 (25 septembre 2020) : jgs2020–078. http://dx.doi.org/10.1144/jgs2020-078.
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The Walls Boundary Fault in Shetland, Scotland, formed during the Ordovician–Devonian Caledonian orogeny and underwent dextral reactivation in the Late Carboniferous. In a well-exposed section at Ollaberry, westerly verging, gently plunging regional folds in the Neoproterozoic Queyfirth Group on the western side of the Walls Boundary Fault are overprinted by faults and steeply plunging Z-shaped brittle–ductile folds that indicate contemporaneous right-lateral and top-to-the-west reverse displacement. East of the Walls Boundary Fault, the Early Silurian Graven granodiorite complex exhibits fault-parallel fractures with Riedel, P and conjugate shears indicating north–south-striking dextral deformation and an additional contemporaneous component of east–west shortening. In the Queyfirth Group, the structures are arranged in geometrically and kinematically distinct fault-bounded domains that are interpreted to result from two superimposed tectonic events, the youngest of which displays evidence for bulk dextral transpressional strain partitioning into end-member wrench and contractional strain domains. During dextral transpressional deformation, strain was focused into pelite horizons and favourably aligned pre-existing structures, leaving relicts of older deformation in more competent lithologies. This study highlights the importance of pre-existing structures and lithological heterogeneity during reactivation and suggests the development of a regional transpressional tectonic environment during the Late Carboniferous on the Shetland Platform.
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Bhatt, S. C., et Vinod K. Singh. « Neoarchean crustal shear zones and implications of shear indicators in tectonic evolution of Bundelkhand craton, central India ». Journal of Geoscience, Engineering, Environment, and Technology 4, no 2-2 (25 juillet 2019) : 11. http://dx.doi.org/10.25299/jgeet.2019.4.2-2.2125.
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The gneisses and granitoids emplaced along E-W sub-vertical crustal shear zones are represented as important tectonic units in Bundelkhand craton of central India. The tonalite-trondhjemite-granodiorite (TTG) gneisses (3.5-3.2 Ga; oldest unit), and streaky to mafic gneisses structurally deformed in D 1 deformation. The metabasic, felsic, banded iron formation and metasedimentaries of greenstone complex exposed in central part, have characteristics of three sets of folding (F 1 -F 3 ). These gneisses associated with migmatite, amphibolite, quartzite, and schist were evolved in D 2 compressive phase, which are not occurring in northern part of craton. The K-rich Neoarchean granitoids (2.6-2.49 Ga) were intruded as granitic complex (D 3 magmatic phase) and the E-W strike-slip Raksa-Garhmau shear zone reported as important tectonic unit, were evolved in asyn-to post-tectonic D 3 phase. The dolerite dykes (ca. 2.0 Ga) were emplaced along NW-SE fractures in extension setting during D 4 magmatic event. The NE-SW riedel shears occupied by giant quartz veins (reefs) evolved in Paleoproterozoic during D 5 endogenic activity.
The relationship between macro and microstructural fabrics has been documented within mylonitic foliation, stretching lineation, S-C planes and rotated fabrics, reflect mesoscopic shear indicators, as noted in three types of mylonitic rocks. i) The rotated porphyroclasts of quartz, feldspars and asymmetric pressure shadows showing strong undulose extinction, deformation lamellae, and dynamic recrystallization are characteristic features of protomylonite where altered orthoclase and kinked plagioclase are noticed. ii) Mylonite, a distinct mylonitic foliation represented by parallel orientation of elongated quartz and feldspar with flakes of mica. iii) The ground matrix of recrystallized quartz with few protoliths of quartz and feldspar are observed, important features of ultramylonite. The asymmetric microstructures viz. σa and σb mantled porphyroclasts, othermicrostructures show progressively deformed by crystal plastic (non-coaxial) strain softening under low to moderate temperature conditions. The sinistral top- to- SW sense of shear movement was dominant. The microfractures/ microfaults, kinking and pull apart structures observed in K- feldspars and are indicative of overprinting of brittle deformation on ductile shearing.
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Rhéaume, P., et K. Schrijver. « Structural analysis of Bic fault, a thrust-related strike-slip fault of the external domain of the Taconic Orogen, Appalachians, Quebec, and metallogenic implications ». Canadian Journal of Earth Sciences 28, no 5 (1 mai 1991) : 788–99. http://dx.doi.org/10.1139/e91-068.
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The Bic fault is exposed along the shoreline of the St. Lawrence River, 21 km southwest of Rimouski, for 210 m at Cap à l'Orignal and for 100 m at Cap Enragé. The fault brings in contact two major thrust sheets, the Des Seigneuries and the Des Iles, Cambrian lithologies of the former overlying Ordovician rocks of the latter. In the Taconic Orogen, such contacts are normally thrust faults, but the Bic fault is a dextral strike-slip fault, striking east–west and dipping southward. A study of a narrow zone straddling the fault and an adjacent part of the Des Seigneuries thrust sheet has led to the recognition of four successive stages of deformation, all compatible with a northeast–southwest-trending strain ellipsoid. The two first stages are most important: stage 1 brought about regional folding and faulting, whereas stage 2 was characterized by the development of various structural elements (C–S fabrics, stretching lineation, Riedel shears, and kink bands) exclusive to the fault zone. We infer that (i) in the study area, the Bic fault constituted a lateral ramp along which the Des Seigneuries thrust sheet slid horizontally westward; and (ii) emplacement of Ba–Pb–Zn deposits took place slightly after this movement, probably during regional uplift of the orogen in Late Ordovician to Early Silurian time. The latter hypothesis tends to be corroborated by model lead ages of galena in two deposits.
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Carpentier, S. F. A., A. G. Green, R. Langridge, S. Boschetti, J. Doetsch, A. N. Abächerli, H. Horstmeyer et M. Finnemore. « Flower structures and Riedel shears at a step over zone along the Alpine Fault (New Zealand) inferred from 2-D and 3-D GPR images ». Journal of Geophysical Research : Solid Earth 117, B2 (février 2012) : n/a. http://dx.doi.org/10.1029/2011jb008749.
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Scharf, Andreas, Frank Mattern et Sawsan S. Al-Sadi. « Kinematics of Post-obduction Deformation of the Tertiary Ridge at Al-Khod Village (Muscat, Oman) ». Sultan Qaboos University Journal for Science [SQUJS] 21, no 1 (1 novembre 2016) : 26. http://dx.doi.org/10.24200/squjs.vol21iss1pp26-40.
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Structural investigations in post-obductional Paleocene to Eocene limestones of the Tertiary Ridge reveal a ~1 km long WNW-ESE striking strike-slip fault system within the ridge, consisting of two main sub-parallel, strike-slip faults. Considering the geometry of the Harding Strain Ellipse, the orientation of structures between the two strike-slip faults (e.g., Riedel shears, folds, reverse faults) point to left-lateral motion. The abundance of large-scale folds (up to 100 m in wave length and amplitude) between the two strike-slip faults led us to the interpretation of transpressive conditions in a first approximation. Moreover, the Tertiary Ridge of the study area consists of three distinct structural domains. The faults of Domain A and C are oriented WNW-ESE, but the trend of the faults in the central Domain B differs by ~10°. The left-lateral strike-slip fault system exists only in Domain B. We propose that the direction of greatest stress during Miocene plate convergence (sigma 1) was oriented 032°/212°. Considering the trend of the strike-slip zone and the orientation of sigma 1, the left-lateral motion must have been transpressive. Sigma 1 is perpendicularly oriented to the domains A and C. Prior to the Miocene D2 compressional event the study area was affected by a D1 extensional event, related to the opening of the Red Sea and the Gulf of Aden or to gravity-driven normal faulting. The D2 compressional/transpressional structures of the Miocene are reactivating the D1 structures of the Oligocene.
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Hasan, Md Nahidul, Sally Potter-McIntyre et Steve Tedesco. « Wrench faulting and trap breaching : A case study of the Kizler North Field, Lyon County, Kansas, USA ». Midcontinent Geoscience 2 (13 mai 2021) : 1–14. http://dx.doi.org/10.17161/mg.v2i.15532.
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The Kizler North Field in northwest Lyon County, Kansas, is a producing field with structures associated with both uplift of the Ancestral Rockies (Pennsylvanian to early Permian) and reactivation of structures along the Proterozoic midcontinent rift system (MRS), which contributed to the current complex and poorly understood play mechanisms. The Lower Paleozoic dolomitic Simpson Group, Viola Limestone, and “Hunton Group” are the reservoir units within the field. These units have significant vuggy porosity, which is excellent for field potential; however, in places, the reservoir is inhibited by high water saturation. The seismic data show that two late-stage wrench fault events reactivated existing faults. The observed wrench faults exhibit secondary P, R’, and R Riedel shears, which likely resulted from Central Kansas uplift-MRS wrenching. The latest stage event breached reservoir caprock units during post-Mississippian to pre-Desmoinesian time and allowed for hydrocarbon migration out of the reservoirs. Future exploration models of the Kizler North and analog fields should be based on four play concepts: 1) four-way closure with wrench-fault-related traps, 2) structural highs in the Simpson Group and Viola Limestone, 3) thick “Hunton Group,” and 4) presence of a wrench fault adjacent to the well location that generates subtle closure but not directly beneath it, which causes migration out of reservoirs. In settings where complex structural styles are overprinted, particular attention should be paid to the timing of events that may cause breaches of seals in some structures but not others. Mapping the precise location and vertical throw of the reactivated wrench faults using high-resolution seismic data can help reduce the drilling risk in analog systems.
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Bellot, Jean-Philippe, Jean-Yves Roig et Antonin Genna. « The Hospital coal basin (Massif Central, France) : relay on the left-lateral strike-slip Argentat fault in relation to the Variscan postorogenic extension ». Bulletin de la Société Géologique de France 176, no 2 (1 mars 2005) : 151–59. http://dx.doi.org/10.2113/176.2.151.
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Abstract Structural and microstructural analyses of the Argentat fault, combined with sedimentological and structural analyses of the associated Hospital basin allow us to discuss the tectonic control of coal basins by crustal-scale faults during the late Palaeozoic evolution of the Variscan lithosphere in the French Massif Central. The brittle Argentat fault zone consists of first- and second-order strike-slip faults, with dominant NNW-sinistral faults, NNE-dextral or sinistral faults and secondary ENE-dextral faults. Several experimental and theoretical models explain the observed fault patterns, like en echelon faults, A-type secondary faults, conjugate faults and Riedel shears. Strike-slip faulting is responsible for folding of the metamorphic formations characterized by N-S to NE-SW-trending axis. The regional-scale geometry of brittle faults and associated folds corresponds to a positive flower structure centered on the brittle Argentat fault, combined to a negative flower structure centered on the coal basin. Using tectonic inversion software, we show that these structures result from a left-lateral movement of the brittle Argentat fault in relation to a tectonic regime intermediate between extension and strike-slip, with a horizontal NE-SW to NNE-SSW-trending maximum stretching axis. Detailed map and cross-sections, and sedimentological interpretations of the late Stephanian Hospital basin show the occurrence of intra-basin syn-sedimentary strike-slip faults and progressive overlaying, indicating that sedimentation occurs during left-lateral strike-slip faulting and folding of basement along the Argentat fault. These data are consistent with a model of N-S to NE-SW-trending postorogenic extension proposed to account for the late Carboniferous evolution of the Variscan lithosphere. They also point out the complexity and the variety of structures developed along a regional brittle strike-slip fault zone and the necessity to take into account all the structures and the resulting geometry of the basement in order to better constrain the tectonic setting of intra-continental deposits.
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Davis, George H., Alexander P. Bump, Pilar E. Garcı́a et Stephen G. Ahlgren. « Conjugate Riedel deformation band shear zones ». Journal of Structural Geology 22, no 2 (février 2000) : 169–90. http://dx.doi.org/10.1016/s0191-8141(99)00140-6.
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Hooke, Roger LeB, Veijo Allan Pohjola, Peter Jansson et Jack Kohler. « Intra-seasonal changes in deformation profiles revealed by borehole studies, Storglaciären, Sweden ». Journal of Glaciology 38, no 130 (1992) : 348–58. http://dx.doi.org/10.3189/s0022143000002239.
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AbstractIn 1985, 1987 and 1988, we measured deformation of boreholes in the ablation zone of Storglaciären. A different hole was used each year. Deformation profiles were determined for four consecutive time periods between mid-July and early September. All three holes were in an area where the glacier lies in an overdeepened part of the bed, up-glacier from a riegel. The first hole was approximately on the glacier center line while the others were midway between the center line and one or the other margin. Despite large standard errors, variations in the deformation profiles during the melt season are broadly consistent with other data. We thus believe that they are real, and that they reflect changes in the stress field resulting from changes in drag at the bed. A decrease in drag early in the melt season, coupled with convergence of the bed contours towards the riegel, is believed to be responsible for a previously documented increase in vertical velocity just up glacier from the riegal at this time of year. Also noteworthy, but perhaps problematical, was an abrupt transverse shear of at a depth of ~25 m near the center of the glacier in July 1985. The shear took place in the zone in which cold ice near the surface gives way to temperate ice deeper in the glacier.
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Hooke, Roger LeB, Veijo Allan Pohjola, Peter Jansson et Jack Kohler. « Intra-seasonal changes in deformation profiles revealed by borehole studies, Storglaciären, Sweden ». Journal of Glaciology 38, no 130 (1992) : 348–58. http://dx.doi.org/10.1017/s0022143000002239.
Texte intégralRésumé :
AbstractIn 1985, 1987 and 1988, we measured deformation of boreholes in the ablation zone of Storglaciären. A different hole was used each year. Deformation profiles were determined for four consecutive time periods between mid-July and early September. All three holes were in an area where the glacier lies in an overdeepened part of the bed, up-glacier from a riegel. The first hole was approximately on the glacier center line while the others were midway between the center line and one or the other margin. Despite large standard errors, variations in the deformation profiles during the melt season are broadly consistent with other data. We thus believe that they are real, and that they reflect changes in the stress field resulting from changes in drag at the bed. A decrease in drag early in the melt season, coupled with convergence of the bed contours towards the riegel, is believed to be responsible for a previously documented increase in vertical velocity just up glacier from the riegal at this time of year. Also noteworthy, but perhaps problematical, was an abrupt transverse shear ofat a depth of ~25 m near the center of the glacier in July 1985. The shear took place in the zone in which cold ice near the surface gives way to temperate ice deeper in the glacier.
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Rajlich, Petr. « Riedel shear : a mechanism for crenulation cleavage ». Earth-Science Reviews 34, no 3 (juin 1993) : 167–95. http://dx.doi.org/10.1016/0012-8252(93)90033-4.
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Csontos, László, István Dunkl, Gábor Vakarcs et Abid H. Abbaso. « Transversal folding in Himalaya foothill ranges ». Földtani Közlöny 149, no 3 (29 septembre 2019) : 255. http://dx.doi.org/10.23928/foldt.kozl.2019.149.3.255.
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The Himalayan foreland in N Pakistan, dissected by Main Frontal Thrust (MFT) and Main Boundary Thrust (MBT) contains spectacular salients and syntaxes. The lateral (N-S) boundaries between these salients and syntaxes around Kalabagh city and east-southeast of Islamabad were believed to host deep-seated lateral ramps with strike slip movements. However, seismic data in these two sectors suggest that there are N-S trending folds and locally east- or west-vergent thrusts that affect the Paleozoic-Paleogene cover of the Indian shield, as well as the Miocene-Pliocene molasse sediments. The proposed lateral ramps cannot be followed on the seismic and on maps either; instead, both maps and seismic data suggest folding, often on a regional scale of harder Paleo-Mesozoic-Paleogene and softer Oligo-Miocene-Pilo-Pleistocene cover. The NE corner of Surghar range is proposed to be formed of relaying thrust sheets with emergent heads composed of Paleozoic-Paleogene and its slightly detached Miocene molasse. These relaying imbricates are taken in a southward flexure generated by a major right lateral shear of a wide zone, where transpressive Riedel shears, en echelon anticlines and southwards flexed earlier thrust faults are the main elements (but a single, through-going Kalabagh fault is missing). The generation of mapped N-S trending folds and east-vergent thrusts preceded the formation of the wide shear zone and southwards flexing.Hazara syntaxis is interpreted as a major antiform that re-folded MBT and Panjal thrust around Oligo-Miocene molasse, itself forming an antiform (BOSSART ET AL. 1988). In our model we propose that the west-vergent Balakot thrust and deeper blind thrusts are in the core of this antiform. In the southern continuation we propose that folds in Miocene molasse continue from eastern Potwar region to western Kashmir and there appears no major break. These structures are also re-folded in a major antiform with N-S axial trend. Map analysis also suggests that N-S trending folds bending earlier main thrusts are occurring in a wide area south of the Indus-Tsangpo suture.Several independent geological and geophysical observations including mapping, seismic analysis, earlier measurements of strain axes and of paleomagnetic declinations suggest that the salients and syntaxes may have been much more linear in the past (although a total linearity is not realistic). It is proposed that the present-day undulating pattern may have been generated by N-S trending folds due to general (and episodic) E-W shortening. If the main fault zones were more linear, the relay pattern along their segments suggests a left lateral shear component along MBT and a mixed, locally left, locally right lateral component along MFT. Earlier (ZEITLER 1985) and now provided low temperature thermochronological ages strongly suggest a rather general episode of E-W shortening between 4-5 Ma for the whole northern Indian margin. However, there should have been original transversal dome formation as early as Oligocene (DIPIETRO ET AL. 2008). It is also clear that longer N-S shortening and shorter E-W shortening episodes should alternate eventually in a very short time frame, since earthquake focal mechanisms (LISA AND KHWAJA 2004, BURG ET AL. 2005) suggest the coexistence of E-W compression and NW-SE compression in Potwar.There are several potential explanations for generating E-W shortening and related structures in a general N-S shortening regime. Possibilities range from fault terminations of thrust faults at high angles in a particular zone (TREOLAR ET AL. 1992) to en echelon folding along a major right lateral E-W fault zone. However, we speculate that E-W shortening could be much more general, suggesting a mechanism that affects the whole of Indian plate. Possibly the best explanation is given by analogue models (REPLUMAZ ET AL. 2012) proposing major, slightly convergent confining boundaries. If applied to the northwards advance of India, the northwards converging boundaries generate secondary E-W shortening and east-or west-vergent orogens parallel to these boundaries.
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Lavallée, Yan, Takahiro Miwa, James D. Ashworth, Paul A. Wallace, Jackie E. Kendrick, Rebecca Coats, Anthony Lamur et al. « Transient conduit permeability controlled by a shift between compactant shear and dilatant rupture at Unzen volcano (Japan) ». Solid Earth 13, no 5 (10 mai 2022) : 875–900. http://dx.doi.org/10.5194/se-13-875-2022.
Texte intégralRésumé :
Abstract. The permeability of magma in volcanic conduits controls the fluid flow and pore pressure development that regulates gas emissions and the style of volcanic eruptions. The architecture of the permeable porous structure is subject to changes as magma deforms and outgasses during ascent. Here, we present a high-resolution study of the permeability distribution across two conduit shear zones (marginal and central) developed in the dacitic spine that extruded towards the closing stages of the 1991–1995 eruption at Unzen volcano, Japan. The marginal shear zone is approximately 3.2 m wide and exhibits a 2 m wide, moderate shear zone with porosity and permeability similar to the conduit core, transitioning into a ∼ 1 m wide, highly sheared region with relatively low porosity and permeability, as well as an outer 20 cm wide cataclastic fault zone. The low-porosity, highly sheared rock further exhibits an anisotropic permeability network, with slightly higher permeability along the shear plane (parallel to the conduit margin), and is locally overprinted by oblique dilational Riedel fractures. The central shear zone is defined by a 3 m long by ∼ 9 cm wide fracture ending bluntly and bordered by a 15–40 cm wide damage zone with permeability enhanced by ∼ 3 orders of magnitude; directional permeability and resultant anisotropy could not be measured from this exposure. We interpret the permeability and porosity of the marginal shear zone to reflect the evolution of compactional (i.e. ductile) shear during ascent up to the point of rupture, which was estimated by Umakoshi et al. (2008) at ∼ 500 m depth. At this point the compactional shear zone would have been locally overprinted by brittle rupture, promoting the development of a shear fault and dilational Riedel fractures during repeating phases of increased magma ascent rate, enhancing anisotropic permeability that channels fluid flow into and along the conduit margin. In contrast, we interpret the central shear zone as a shallow, late-stage dilational structure, which partially tore the core of the spine, leaving a slight permanent displacement. We explore constraints from monitored seismicity and stick-slip behaviour to evaluate the rheological controls, which accompanied the shift from compactional toward dilational shear as magma approached the surface, and discuss their importance in controlling the permeability development of magma evolving from overall ductile to increasingly brittle behaviour during ascent and eruption.
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Henri, Razananirina, et Rakotondrazafy Raymond. « Airborne Magnetic Survey and Remote Sensing Applied to Structural Study in Vohilava Area Madagascar ». International Journal of Geography and Geology 11, no 2 (13 octobre 2022) : 43–61. http://dx.doi.org/10.18488/10.v11i2.3165.
Texte intégralRésumé :
Mananjary district is known for its gold production. To better understand the gold mineralization distribution, a regional structural study was undertaken using airborne geophysics and remote sensing (RS). Magnetometry data, Landsat Operational Land Imager (OLI) 8 satellite-image and DEM (Digital Elevation Model) have been processed and interpreted. Signals associated with deep structures are weak and dominated by strong signals from surficial magnetic sources. To overcome this problem, local-phase based filters were used. A deep knowledge of each filter allows to use it separately or in combination with other filters. RS is a powerful tool for a regional study. Color composite technique and DEM analysis were helpful to bring out faults and structures. The combination of magnetometry and RS allows geologists to efficiently delineate prospective zones. The study has unveiled a dextral strike-slip fault (SSF) over 240km and associated faults, folds, flower structure and pull-apart basins within the Mananjary gold district. Moreover, the SSF structurally controlled the spatial distribution of Vohilava-Nosivolo and Maha groups. R Riedel shear faults appear as North North East – South South West faults. R’ Riedel shear faults occur in the north of the study area with East North East -West South West orientation. Tectonic block rotation occurred between Ampasinambo and Soavina. P’ shear faults striking West North West – East South East occur in Vohilava. Some folds are associated with the SSF as well. Vohilava positive flower structure which used to be a syncline and its antiform equivalent are SSF footprints. The latter was active since Mesoarchean.
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Casas, Nathalie, Guilhem Mollon et Ali Daouadji. « Shear bands in dense fault gouge ». EPJ Web of Conferences 249 (2021) : 11006. http://dx.doi.org/10.1051/epjconf/202124911006.
Texte intégralRésumé :
Earthquakes happen with frictional sliding, by releasing all the stresses accumulated in the prestressed surrounding medium. The geological fault gouge, coming from the wear of previous slips, acts on friction stability and plays a key role in this sudden energy release. A large part of slip mechanisms are influenced, if not controlled, by the characteristics and environment of this tribological “third body”. A 2D granular fault (mm scale) is implemented with Discrete Element Modelling (DEM). A displacement-driven model with dry contact is studied to observe kinematics and properties of the slipping zone. Increasing the length of the granular media increases the slip needed to weaken the friction from friction peak to steadystate. Low-angle Riedel shear bands are mostly observed. Their number increases with the inter-particle friction coefficient, which also influences shear bands formation in their orientation angle (higher friction leads to higher angle with the main slip direction).
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Misra, Santanu, Nibir Mandal et Chandan Chakraborty. « Formation of Riedel shear fractures in granular materials : Findings from analogue shear experiments and theoretical analyses ». Tectonophysics 471, no 3-4 (juin 2009) : 253–59. http://dx.doi.org/10.1016/j.tecto.2009.02.017.
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Bhowmick, Sreyashi, et Tridib Kumar Mondal. « Control of pre-existing fabric in fracture formation, reactivation and vein emplacement under variable fluid pressure conditions : an example from Archean greenstone belt, India ». Solid Earth 11, no 4 (8 juillet 2020) : 1227–46. http://dx.doi.org/10.5194/se-11-1227-2020.
Texte intégralRésumé :
Abstract. Most of the upper crustal fluid flows are strongly influenced by the pre-existing fractures/foliations in the rocks under a certain state of tectonic stress and fluid pressure condition. In the present study, we analyzed a wide range of crosscutting fractures that are filled with quartz veins of variable orientations and thicknesses, from the gold-bearing massive metabasalts (supracrustals) of the Chitradurga Schist Belt adjacent to the Chitradurga Shear Zone (CSZ), Western Dharwar Craton, southern India. The study involves the following steps: (1) analyzing the internal magnetic fabric, using anisotropy of magnetic susceptibility (AMS) studies, and determining strength of the host metabasalts, (2) quantifying the fluid pressure condition through lower hemisphere equal area projection of pole to veins by determining the driving pressure ratio (R′), stress ratio (ϕ), and susceptibility to fracturing, and (3) deciphering the paleostress condition using fault-slip analysis. We interpret the NNW–SSE to NW–SE (mean 337/69∘ NE) oriented magnetic fabric in the rocks of the region as having developed during regional D1/D2 deformation on account of NE–SW shortening. However, D3 deformation manifested by NW–SE to E–W shortening led to the sinistral movement along CSZ. As a consequence of this sinistral shearing, fractures with prominent orientations formed riedel shear components, with CSZ as the shear boundary. Subsequently, all the pre-existing fabrics along with the riedel shear components were reactivated and vein emplacement took place through episodic fluid pressure fluctuation from high to low Pf at shallow depth (∼ 2.4 km). However, NNW–SSE orientations were prone to reactivate under both high- and low-Pf conditions, thereby attaining maximum vein thickness along these orientations. The deduced paleostress from fault-slip analysis along with the kinematics of the fractures and veins are in good agreement with previously estimated regional tectonics. Thus, integrating multiple domains of studies helps in the logical interpretation of fluid flow conditions and vein emplacement mechanisms in the study area that has not been ventured before.
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Katz, Yoram, Ram Weinberger et Atilla Aydin. « Geometry and kinematic evolution of Riedel shear structures, Capitol Reef National Park, Utah ». Journal of Structural Geology 26, no 3 (mars 2004) : 491–501. http://dx.doi.org/10.1016/j.jsg.2003.08.003.
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Little, T. A., P. Morris, M. P. Hill, J. Kearse, R. J. Van Dissen, J. Manousakis, D. Zekkos et A. Howell. « Coseismic deformation of the ground during large-slip strike-slip ruptures : Finite evolution of “mole tracks” ». Geosphere 17, no 4 (14 mai 2021) : 1170–92. http://dx.doi.org/10.1130/ges02336.1.
Texte intégralRésumé :
Abstract To evaluate ground deformation resulting from large (~10 m) coseismic strike-slip displacements, we focus on deformation of the Kekerengu fault during the November 2016 Mw 7.8 Kaikōura earthquake in New Zealand. Combining post-earthquake field observations with analysis of high-resolution aerial photography and topographic models, we describe the structural geology and geomorphology of the rupture zone. During the earthquake, fissured pressure bulges (“mole tracks”) initiated at stepovers between synthetic Riedel (R) faults. As slip accumulated, near-surface “rafts” of cohesive clay-rich sediment, bounded by R faults and capped by grassy turf, rotated about a vertical axis and were internally shortened, thus amplifying the bulges. The bulges are flanked by low-angle contractional faults that emplace the shortened mass of detached sediment outward over less-deformed ground. As slip accrued, turf rafts fragmented into blocks bounded by short secondary fractures striking at a high angle to the main fault trace that we interpret to have originated as antithetic Riedel (R′) faults. Eventually these blocks were dispersed into strongly sheared earth and variably rotated. Along the fault, clockwise rotation of these turf rafts within the rupture zone averaged ~20°–30°, accommodating a finite shear strain of 1.0–1.5 and a distributed strike slip of ~3–4 m. On strike-slip parts of the fault, internal shortening of the rafts averaged 1–2 m parallel to the R faults and ~1 m perpendicular to the main fault trace. Driven by distortional rotation, this contraction of the rafts exceeds the magnitude of fault heave. Turf rafts on slightly transtensional segments of the fault were also bulged and shortened—relationships that can be explained by a kinematic model involving “deformable slats.” In a paleoseismic trench cut perpendicular the fault, one would observe fissures, low-angle thrusts, and steeply dipping strike-slip faults—some cross-cutting one another—yet all may have formed during a single earthquake featuring a large strike-slip displacement.
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Ahlgren, S. G. « The nucleation and evolution of Riedel shear zones as deformation bands in porous sandstone ». Journal of Structural Geology 23, no 8 (août 2001) : 1203–14. http://dx.doi.org/10.1016/s0191-8141(00)00183-8.
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Coelho, Sara, Cees Passchier et Fernando Marques. « Riedel-shear control on the development of pennant veins : Field example and analogue modelling ». Journal of Structural Geology 28, no 9 (septembre 2006) : 1658–69. http://dx.doi.org/10.1016/j.jsg.2006.05.009.
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Wang, Haifu, Jianguang Xiao, Yuanfeng Zheng et Qingbo Yu. « Failure and Ejection Behavior of Concrete Materials under Internal Blast ». Shock and Vibration 2016 (2016) : 1–7. http://dx.doi.org/10.1155/2016/8409532.
Texte intégralRésumé :
In order to investigate the failure and ejection behavior of concrete materials under internal blast, the default Riedel-Hiermaier-Thoma (RHT) concrete model in AUTODYN and a meshfree processor called SPH are employed in this numerical simulation. It is shown that the failure mechanisms are significantly different in these damaged zones. Crushed zone is caused by shear failure while fractured zone is induced by tensile failure, and spalled zone is formed by a combination of shear and tensile failure. In addition, the ejection velocity distribution of the fragmented concrete mass on free surface is examined. The results indicate that the ejection velocity declines monotonously with the increase of the distance to symmetry axis of computational model. On the wall of the prefabricated borehole, two types of fragmented concrete mass are analyzed, and bottom initiation is recommended to eject the fragmented concrete mass effectively. Moreover, an algorithm of average ejection speed is developed to effectively estimate the drill capacity of high velocity, energetic (HE) projectiles. At last, the validity of numerical simulation is verified by physical experiments.
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Atmaoui, Nassima, Nina Kukowski, Bernhard Stöckhert et Diethard König. « Initiation and development of pull-apart basins with Riedel shear mechanism : insights from scaled clay experiments ». International Journal of Earth Sciences 95, no 2 (14 octobre 2005) : 225–38. http://dx.doi.org/10.1007/s00531-005-0030-1.
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Kirkwood, Donna, et Michel Malo. « Across-strike geometry of the Grand Pabos fault zone : evidence for Devonian dextral transpression in the Quebec Appalachians ». Canadian Journal of Earth Sciences 30, no 7 (1 juillet 1993) : 1363–73. http://dx.doi.org/10.1139/e93-117.
Texte intégralRésumé :
The principal faults of southeastern Gaspé Peninsula in Quebec consist of a central high-strain zone that is characterized by mainly ductile deformation structures and bordered by low-strain zones each dominated by brittle deformation structures. The overall geometry of shear fractures within the low-strain zones is quite similar to the expected geometry of Riedel shear fractures. The brittle structures overprint the dominant C–S-type fabric of the high-strain zone, which implies that brittle deformation outlasted ductile deformation. The asymmetry of local micro- to meso-scale deformation features along the fault zones reflects the non-coaxiality of the shear. Other features described within the fault zone (stylolitic cleavage, shear bands, and reverse faults) are evidence for a component of shortening perpendicular or oblique to the fault zone. The geometry of the Grand Pabos fault zone (GPFZ), a major fault of southern Gaspé, indicates that deeper seated fault rocks (high-strain zone) have been brought up to higher crustal levels and are presently in contact with brittlely deformed fault rocks (low-strain zone). The proposed model for the evolution of the GPFZ involves Early to Late Devonian, dextral, transcurrent movement accompanied by relatively minor amounts of vertical slip within a dextral transpressive regime. The main pulse of the Acadian orogeny in Gaspé is restricted to the Devonian and therefore occurred later than elsewhere in the Canadian Appalachians.
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NODA, Toshihiro, Shotaro YAMADA, Tomohiro TOYODA et Akira ASAOKA. « EFFECTS OF INITIAL IMPERFECTION ON THE RIEDEL SHEAR BANDS IN SURFACE GROUND DUE TO STRIKE-SLIP FAULT ». Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM)) 71, no 2 (2015) : I_463—I_474. http://dx.doi.org/10.2208/jscejam.71.i_463.
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Rao, Gang, Aiming Lin, Bing Yan, Dong Jia, Xiaojun Wu et Zhikun Ren. « Co-seismic Riedel shear structures produced by the 2010 Mw 6.9 Yushu earthquake, central Tibetan Plateau, China ». Tectonophysics 507, no 1-4 (juillet 2011) : 86–94. http://dx.doi.org/10.1016/j.tecto.2011.05.011.
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Wołosiewicz, Bartosz. « Morphotectonic control of the Białka drainage basin (Central Carpathians) : Insights from DEM and morphometric analysis. » Contemporary Trends in Geoscience 5, no 1 (1 juin 2016) : 61–82. http://dx.doi.org/10.1515/ctg-2016-0005.
Texte intégralRésumé :
Abstract The Białka river valley is directly related to a deep NNW-SSE oriented fault zone. According to the results of previous morphometric analyses, the Białka drainage basin is one of the most tectonically active zones in the Central Carpathians. It is also located within an area of high seismic activity. In this study Digital Elevation Model (DEM) based, morphometric analyses were used to investigate the morphotectonic conditions of the watershed. The results reveal the relationships between the main tectonic feature and the landforms within the research area. The lineaments, as obtained from the classified aspect map, seem to coincide with the orientation of the main structures as well as the trends revealed by the theoretical Riedel-Skempton shear model. Base-level and isolong maps support the conclusion that the Białka and Biały Dunajec fault zones exert a strong influence on the morphology of the adjacent area.
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Rodríguez-Escudero, Emilio, José J. Martínez-Díaz, Jorge L. Giner-Robles, Meaza Tsige et Jaime Cuevas-Rodríguez. « Pulverized quartz clasts in gouge of the Alhama de Murcia fault (Spain) : Evidence for coseismic clast pulverization in a matrix deformed by frictional sliding ». Geology 48, no 3 (9 janvier 2020) : 283–87. http://dx.doi.org/10.1130/g47007.1.
Texte intégralRésumé :
Abstract The fault gouge of the Alhama de Murcia fault (southeast Spain) shows a texture that resembles a mylonite, including a prominent foliation, S-C fabric, and isoclinal folds. It also embeds a large number of isolated pulverized quartz clasts (PQCs). Structural analysis indicates that the gouge fabric was mainly developed by slow frictional sliding along phyllosilicate-lined Riedel shear bands during continued shearing. In contrast, the PQCs show tensile fracture network features that are typically reported in seismically pulverized rocks found along seismogenic faults. This suggests that quartz-clast pulverization was due to a transient dilatational mechanism rather than shearing. We propose that the PQCs are the result of a rapid confined stress drop related to transient tensile stresses during coseismic ruptures that interrupt creep faulting along the gouge zone. The present study suggests that there is probably a large amount of evidence for paleoseismicity in fault rocks that is currently overlooked.
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Huyghe, Pascale, Albert Galy et Jean Louis Mugnier. « Micro-structures, mineralogy and geochemistry of clay size fraction (< ; 2 µm) of thrust zones of western Nepal Siwaliks (Karnali area) ». Journal of Nepal Geological Society 18 (1 décembre 1998) : 239–48. http://dx.doi.org/10.3126/jngs.v18i0.32257.
Texte intégralRésumé :
Shear zones of the Main Dun Thrust (MDT) of the Siwaliks of western Nepal have been investigated in order to specify the deformation mechanisms and mineral transformations. The Riedel fractures and cleavage are developed. They are responsible for the scaly fabric of the fault zones and generate a "tectonic mixture" of both the Upper and Lower Siwaliks at the footwall and hangingwall of the MDT. Grain-size analysis of samples from the shear zones indicates a strong cataclastic deformation. Clay mineralogy varies significantly within the shear zone. However, the smectites abundance is higher in the shear zone than in the Upper and Lower Siwaliks and may exceed 40% of the <2 µm clay fraction.
The isotopic oxygen composition of clay fractions in the shear zone gives δ18O of smectites that implies neoformation. The temperature of smectite neoformation is 40 to 60°C higher than pedogenic smectites present in the borders. δD of fluid inclusion of calcite associated to deformation show values consistent with water similar to the actual surface water and δ18O of mineral implies temperature of crystallisation around 50°C. These low temperatures are in good agreement with the precipitation of smectites and kaolinites. Fluids sampled in hot springs of the Siwaliks of western Nepal have a meteoric origin with respect to the stable isotopes but are enriched in Na and depleted in K. The chemistry suggests the partial dissolution of feldspar and neoformation of smectites induced by fluid circulation.
It is presumed that shearing and crushing take place during seismic slip increasing the exchanging mineral surfaces whereas mineralogical reactions occur during interseismic periods.
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KOCKS, H., R. A. STRACHAN, J. A. EVANS et M. FOWLER. « Contrasting magma emplacement mechanisms within the Rogart igneous complex, NW Scotland, record the switch from regional contraction to strike-slip during the Caledonian orogeny ». Geological Magazine 151, no 5 (16 décembre 2013) : 899–915. http://dx.doi.org/10.1017/s0016756813000940.
Texte intégralRésumé :
AbstractThe Rogart igneous complex is unique within the northern Scottish Caledonides because it comprises an apparent continuum of magma types that records a progressive change in emplacement mechanisms related to large-scale tectonic controls. Syn-D2 leucogranites and late-D2 quartz monzodiorites were emplaced during crustal thickening and focused within the broad zone of ductile deformation associated with the Naver Thrust. In contrast, emplacement of the post-D2 composite central pluton was controlled by development of a steeply dipping dextral shear zone along the Loch Shin Line, interpreted as an anti-Riedel shear within the Great Glen Fault system. The mantle-derived nature of the late-to-post-D2 melts implies that the Naver Thrust and the Loch Shin Line were both crustal-scale structures along which magmas were channelled during deformation. A U–Pb zircon age of 425±1.5 Ma for the outer component of the central pluton provides an upper limit on regional deformation and metamorphism within host Moine rocks. These findings are consistent with the view that a fundamental change in tectonic regime occurred in the Scottish Caledonides at c. 425 Ma, corresponding to the switch from regional thrusting that resulted from the collision of Baltica and Laurentia, to the development of the orogen-parallel Great Glen Fault system.
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Asaoka, Akira, Yoshihiro Sawada et Shotaro Yamada. « Riedel shear band formation with flower structures that develop at the surface ground on a strike slip fault ». Japanese Geotechnical Society Special Publication 2, no 20 (2016) : 751–54. http://dx.doi.org/10.3208/jgssp.jpn-121.
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Xu, S. S., A. F. Nieto-Samaniego et S. A. Alaniz-Álvarez. « Emplacement of pyroclastic dykes in Riedel shear fractures : An example from the Sierra de San Miguelito, central Mexico ». Journal of Volcanology and Geothermal Research 250 (janvier 2013) : 1–8. http://dx.doi.org/10.1016/j.jvolgeores.2012.10.010.
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Oha, Ifeanyi A., Ikenna A. Okonkwo et Silas S. Dada. « Wrench Tectonism and Intracontinental Basin Sedimentation : A Case Study of the Moku Sub-Basin, Upper Benue Trough, Nigeria ». Journal of Geography and Geology 12, no 1 (30 avril 2020) : 65. http://dx.doi.org/10.5539/jgg.v12n1p65.
Texte intégralRésumé :
The Upper Benue trough of Nigeria consists of basins and horsts characterized by numerous structural features. Detailed study of one of the basins revealed sets of “centimetric”, riedel type “en-echelon” NE-SW trending strike slip faults contained in a number of brittle and ductile shear zones characterizing the basement/sediment boundary. Structural analysis suggests that the Moku sub-basin has been pulled apart along a releasing bend in between NE – SW strike slip faults and that three principal axes of stress were acting on the sub-basin during its formation. The maximum stress (1) with orientation 34/304 was responsible for the fault overlap (basin length), whereas the minimum stress (σ_3) with orientation 18/201 controlled the fault separation (basin width). These suggest a qualitative model showing the Moku sub-basin as a separate basin, which must have coalesced with adjacent sub-basins. Deposition of Bima sediments in the basin was closely controlled by tectonism. The immature B1 sediments are restricted mostly to the faulted margin of the basin. The more matured B2 and B3 sediments are distributed around the less disturbed areas.
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Lu, Yulong, Xingqiang Li, Yang Liu et Jiahao Leng. « The Establishment of Ore-Controlling Fracture System of Baoginshan Gold Mine Based on Fracture-Tectonic Analysis ». Mobile Information Systems 2021 (1 décembre 2021) : 1–9. http://dx.doi.org/10.1155/2021/5887680.
Texte intégralRésumé :
The Baoginshan quartz vein type gold mine in the Baimashan-Longshan-Ziyunshan gold belt is the object of study, and the nature of the fracture structure and its ore-controlling effect are studied through surface and pit investigation, and the nature of the ore-controlling structure system and combination pattern of the Baoginshan gold mine is established. The F7 and F9 fractures in the near-east-west (EW) direction are the main fractures, which tend to the north and control the spreading of the ore zone; the northwest (NW) direction secondary tension fracture, with a dominant yield of 221°∠63°, is a T-type fracture in the Riedel shear mode and is the ore-holding structure of the vein-like ore body; the northeast-east (NEE) direction secondary shear fracture, with a dominant yield of 343°∠53°, is a P-type fracture and the combination of the two controls the specific positioning of the ore body. The characteristics and nature of the fracture structures in the whole ore zone, as well as their combination patterns, indicate that the overall ore-controlling fracture system of Baoginshan is a right-going tensional shear fracture zone composed of NW-oriented (T-type) and NEE-oriented (P-type) secondary fractures with F7 and F9 fractures as boundary fractures. The directions of the principal stresses are σ1≈158°∠40°, σ2≈288°∠38°, and σ3≈42°∠28°, respectively. In the next step of the prospecting process, based on increasing the spacing of prospecting pits (to 40m), in-pit drilling is deployed in the upper and lower discs of the NEE secondary fracture along with the tendency and strike for literacy, which can significantly improve the efficiency and effectiveness of prospecting and greatly reduce the cost of prospecting.
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Lin, Aiming, et Masayuki Nishikawa. « Riedel shear structures in the co-seismic surface rupture zone produced by the 2001 Mw 7.8 Kunlun earthquake, northern Tibetan Plateau ». Journal of Structural Geology 33, no 9 (septembre 2011) : 1302–11. http://dx.doi.org/10.1016/j.jsg.2011.07.003.
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Sobczyk, Artur, et Jacek Szczygieł. « Paleostress reconstruction of faults recorded in the Niedźwiedzia Cave (Sudetes) : insights into Alpine intraplate tectonic of NE Bohemian Massif ». International Journal of Earth Sciences 110, no 3 (18 février 2021) : 833–47. http://dx.doi.org/10.1007/s00531-021-01994-1.
Texte intégralRésumé :
AbstractBrittle structures identified within the largest karstic cave of the Sudetes (the Niedźwiedzia Cave) were studied to reconstruct the paleostress driving post-Variscan tectonic activity in the NE Bohemian Massif. Individual fault population datasets, including local strike and dip of fault planes, striations, and Riedel shear, enabled us to discuss the orientation of the principal stresses tensor. The (meso) fault-slip data analysis performed both with Dihedra and an inverse method revealed two possible main opposing compressional regimes: (1) NE–SW compression with the formation of strike-slip (transpressional) faults and (2) WNW–ESE horizontal compression related to fault-block tectonics. The (older) NE-SW compression was most probably associated with the Late Cretaceous–Paleogene pan-regional basin inversion throughout Central Europe, as a reaction to ongoing African-Iberian-European convergence. Second WNW–ESE compression was active as of the Middle Miocene, at the latest, and might represent the Neogene–Quaternary tectonic regime of the NE Bohemian Massif. Exposed fault plane surfaces in a dissolution-collapse marble cave system provided insights into the Meso-Cenozoic tectonic history of the Earth’s uppermost crust in Central Europe, and were also identified as important guiding structures controlling the origin of the Niedźwiedzia Cave and the evolution of subsequent karstic conduits during the Late Cenozoic.
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Jiang, Shuai, Weifeng Wang, Aizhu Zhang et Weiwei Zhou. « Genetic Mechanism and Evolution of the Covert Fault Zone and Its Oil-Controlling Mode in Qikou Sag, Eastern China ». Energies 12, no 1 (29 décembre 2018) : 98. http://dx.doi.org/10.3390/en12010098.
Texte intégralRésumé :
Covert fault zone is an important type of geological phenomenon that is closely related to hydrocarbon formation and distribution but has often been overlooked because it lacks obvious fault displacement and fault plane. To meet this challenge, a novel cognitive framework is proposed in this study, in which criteria for identifying the existence of covert fault zone are developed based on the regional tectonic backgrounds and geophysical data. The Riedel shear model is then utilized to analyze the genetic mechanism of the covert fault zone. The Mohr-Coulomb theory is also introduced to conduct a structural physical simulation to interpret the evolution process of the covert fault zone. Information about the genetic mechanism and evolution of the covert fault zone is finally combined to determine the oil-controlling mode. The study site is Qikou Sag in Eastern China. It is found that the covert fault zone in Qikou Sag meets four recognition criteria and is generated by the stress transferred from the strike-slip activity of the basement fault. Moreover, it can be concluded that the covert fault zone in Qikou Sag contains five evolution stages and controls the reservoir mainly via three aspects, that is, sedimentary sand, subtle traps and oil accumulation mode.
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Gonzaga, Francisco De Assis da Silveira, Marx Prestes Barbosa et Paulo Roberto Megna Francisco. « Estudo de Campo Integrado com Imagem Landsat para Indicar Áreas Favoráveis a Captação de Águas Subterrâneas (Field Study with Integrated Landsat Image to Indicate a Favorable Areas Underground Water) ». Revista Brasileira de Geografia Física 5, no 5 (5 janvier 2013) : 1145. http://dx.doi.org/10.26848/rbgf.v5i5.232789.
Texte intégralRésumé :
Este trabalho objetivou o mapeamento de áreas potencialmente favoráveis à pesquisa de água subterrânea para o município de Parari, utilizando técnicas de geoprocessamento. Para a análise de fraturamento foi utilizada a banda 4 em papel fotográfico da imagem TM/Landsat-5 e fotografias aéreas que permitiram identificar as principais direções das estruturas lineares: NS±15º, EW±15º, NNE15º, NNW±15º, NE±15º, NW±15º, N60E±15º e N60W±15º. Os dados obtidos das imagens e medidos nos afloramentos foram submetidos ao tratamento estatístico proposto por Aliyev (1980), que permitiu o estudo regional dos eventos da tectônica rúptil. A partir da utilização do modelo de Riedel (1929), com as modificações de Sadowski (1983), definiu-se 2 sistemas de cisalhamento, dextral e sinistral. O Mapa Integrado contempla os dados obtidos como também o posicionamento das áreas com maior potencialidade à pesquisa de água subterrânea. No mapa estão indicadas áreas favoráveis à pesquisa de água subterrânea, relacionando cruzamento de estruturas abertas, com base na proposta de Sampaio (1987). As direções estruturais que mais se adequaram ao modelo, consequentemente mais propícias à prospecção de água subterrânea foram NS±15º, EW±15º, NE±15º, N60E±15º e N60W±15º.Palavras-chave: geologia, geoprocessamento, semiárido Field Study with Integrated Landsat Image to Indicate a Favorable Areas Underground Water ABSTRACTThis study aimed at mapping the potentially favorable to the survey of underground water for the city of Parari, using geoprocessing techniques. For the analysis of fracturing was used band 4 on photographic paper image TM/Landsat-5 and aerial photographs that have identified the main directions of linear structures: NS ± 15 º, EW ± 15, NNE15 º NNW ± 15, NE ± 15 º , NW ± 15, ± 15 ° N60E and N60W ± 15 °. Data from the images and measured in outcrops were subjected to statistical treatment proposed by Aliyev (1980), which allowed the study of regional tectonic events brittle. From this model of Riedel (1929) with modifications Sadowski (1983) have defined two systems shear dextral and sinistral. The integrated map includes data obtained as well as the positioning of the areas with greatest potential for groundwater research. On the map are indicated favorable areas for groundwater research, cross-linking open structures, based on the proposal of Sampaio (1987). The structural directions that best conformed to the model, thus more conducive to prospecting for groundwater were ± 15 ° NS, EW ± 15, ± 15 ° NE, N60E and N60W ± 15 ° ± 15 °.Keywords: geology, geoprocessing, semiarid
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H., Findlay R. « Geometry, kinematics and regional significance of faulting and related lamprophyric intrusion in the mineralised zone at the Pu Sam Cap complex, Northwest Vietnam ». VIETNAM JOURNAL OF EARTH SCIENCES 40, no 4 (18 septembre 2018) : 320–40. http://dx.doi.org/10.15625/0866-7187/40/4/13102.
Texte intégralRésumé :
The alkali volcanics and intrusive rocks, dated at around 35-33Ma, are cut by mineralised northeast and east trending faults showing predominant evidence for strike-slip. Mineralisation includes haematite-Au-Cu and is accompanied by iron-rich alteration of the volcanic rocks. Detailed assessment of the geometry of the fault system at Pu Sam Cap suggests that the faults formed as a Riedel shear system during left-lateral slip within the Song Hong-Song Chay shear zone and the numerous contemporaneous northwest trending faults to the south; the northeast trending faults are interpreted as dextral “book-end’’ faults between major northwest trending faults enclosing the Pu Sam Cap massif. As mineralisation is hosted within these faults and is also associated with lamprohyric dykes it confirms a thermal event younger than the alkaline volcanics and syenitic intrusives at Pu Sam Cap, suggesting a hidden, young porphyry system. The age of faulting, and thus the maximum age for this young intrusive event, is attributed to the 23-21Ma period of late-stage left-lateral strike-slip motion across northwest Vietnam.ReferencesAnczkiewicz R., Viola G., Muntener O., Thrirlwall M., Quong N.Q., 2007. Structure and shearing conditions in the Day Nui Con Voi massif: implications for the evolution of the Red River Fault. Tectonics 26: TC2002.Cao Shunyun, Liu Junlai, Leis B., Zhao Chunquiang 2010. New zircon U/Pb geochronology of the post-kinematic granitic plutons in Diancang Shan Massif along the Ailao-Shan-Red River Shear Zone and its geological implications. Acta Geologica Sinica (English Edition), 84, 1474-1487.Chung S.-L., Lee T., Lo C., et al., 1997. Intraplate extension prior to continental extrusion along the Ailao Shan-Red River shear zone.Geology, 25, 311-314.Cloos H., 1928. Experimentezurinnern Tektonik. Zentralblatt fur Mineralogie und Palaeontologie, 1928, 609-621.Findlay R.H., Phan Trong Trinh 1997. The structural setting of the Song Ma region, Vietnam, and the Indochina-South China plate boundary problem. Gondwana Research, 1, 11-33.Jolivet L., Beysasac O., Goffe B., Avigad D., Leprevrier C., Maluski H., Ta Trong Thang, 2001. Oligo-Miocene midcrustal subhorizontal shear in Indochina. Tectonics, 20, 46-57.Khuong The Hung 2010. The complex tectonic events and their influence on formation of mineral deposits in northwest Vietnam. Unpublished PhD Thesis, University of Science and Technology, Cracow, 167p.Leloup P.H., N. Arnau, R. Lacassin, J.R. Kienast, T.M. Harrison, P.T. Trinh, A. Replumaz and P. Tapponnier, 2001. New constraints on the structure, thermochronology and timing of the Ailao Shan - Red river shear zone, SE Asia, J. G. R., 106, 6657-6671.Leloup PH.., R. Lacassin, P. Tapponnier, U. Scharer, Zhong Dalai, Liu Xaohan, Zhangshan, Ji Shaocheng and PT.Trinh, 1995. The Ailao Shan - Red river shear zone (Yunnan, China), Tertiary transform boundary of Indochina, Tectonophysics, 251, 3-84. Leprevier C., Maluski H., Nguyen Van Vuong, Roques D., Axente V., Rangin C., 1996. Indosinian NW-trending shear zones within the Truong Son belt, Vietnam: 40Ar-39Ar Triassic ages and Cretaceous to Cenozoic overprints. Tectonophysics, 283, 105-107.Lien-Sheng Zhang, Scharer U. 1999. Age and origin of magmatism along the Cenozoic Red River shear belt, China. Contributions to Mineralogy and Petrology, 134, 67-85.Nagy E.A., Scharer U., Minh N.T., 2000. Oligo-Miocene granitic magmatismin central Vietnam and implications for continental deformation in Indochina. Terra Nova, 12, 67-76.Nguyen Thi Bich Thuy, 2016. Isotop dating U-Pb Zircon of Syenit Formation, Pu Sam Cap. Journal of Geology, A Serie, 356, 30-36. (In Vietnamese).Pei-Long Wang, Ching-Hua Lo, Tung-Yi Lee, Sun-ling Chun, Ching-Yan Lan, Nguyen Trong Yem 1998. Thermochronological evidence for the movement of the Ailo Shan-Red River shear zone, a perspective from Vietnam. Geology, 26, 887-890.Phan Trong Trinh, Nguyen Trong Yem, Herve L.P., Tapponnier P., 1994. Late Cenozoic stress fields in North Vietnam from microtectonic measurements. Proceedings of the International Workshop on Seismotectonics and Seismic Hazard in Southeast Asia. Geological Survey of SR Vietnam, Hanoi, 182-186.Riedel W., 1929. Zur Mechanikgreologischer Brucherscheinungen. Zentralblatt fur Mineralogie und Palaeontologie, Abhandlung B, 354-368.Scharer U., Tapponnier P., Lacassin R., Leloup P.H., Dalai Z., Shaosheng J., 1990. Intraplate tectonics in Asia: a precise age for large-scale Miocene movement along the Ailao Shan-Red River shear zone, China. Earth and Planetary Science Letters, 97, 65-77.Scharer U., Zhang L.S., Tapponnier P., 1994. Duration of strike-slip movements in large shear zones: the Red River belt, China. Earth and Planetary Science Letters, 126, 379-397.Searle M.P., 2006. Role of the Red River Shear zone, Yunnan and Vietnam, in the continental extrusion of SE Asia. Journal of the Geological Society, London, 163, 1025-1036.Searle M.P., Meng-Wan Yeh, Te-Hsien Lin, Sun-Lin Chung, 2010. Structural constraints on the timing of left-lateral shear along the Red River shear zone in the Ailao Shan and Diancang Shan Ranges, Yunnan, SW China. Geosphere, 6, 316-338.Tapponnier P., Lacassin R., Leloup H., Scharer U., Zhong Dalai, Wu Hawei, Liu Ziaohan, Ji Shaocheng, Zhang Lianshang, Zong Jiayou, 1990. The Ailao Shan/ Red River metamorphic belt: Tertiary left-lateral shear between Indochina and south China. Nature, 342, 431-437.Tchalenko J.S., 1970. Similarities between shear zones of different magnitudes. Bulletin of the Geological Society of America, 81, 1625-1640.Viola G., Anczkiewicz R. 2009. Exhumation history of the Red River shear zone in northern Vietnam: new insights from zircon and apatite fission-track analysis. Journal of Asian Earth Sciences, 33, 78-90.Yang Yiseng, Hong Qun, Hu Huan-ting, Hieu Pham Trung, Nguyen Thi Bich Thuy, Chen Fu-kun, 2013. Geochemical characteristics and genesis of the Cenozoic porphyry in the Laizhou area, northwestern Vietnam. Acta Petrologica Sinica, 29(3), 899-911. (In Chinese with English abstract, full English version through Google Translate).
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ROSSELLO, Eduardo A., et Sergio A. LÓPEZ. « TRANSTENSIVE ORIGIN OF THE ENCADENADAS-VALLIMANCA CORRIDOR (BUENOS AIRES, ARGENTINA) : A REVISION AND A NEW PROPOSAL FROM SATELLITE IMAGES ». Geosciences = Geociências 39, no 04 (19 décembre 2020) : 965–76. http://dx.doi.org/10.5016/geociencias.v39i04.15107.
Texte intégralRésumé :
The Encadenadas-Vallimanca Corridor (EVC) corresponds to a morphostructural linear feature defining the northern boundary of the Sierra de la Ventana and Tandil hills in the Buenos Aires province. The scarcity of concluding geological studies has resulted in diverse tectonic and hydrographic interpretations regarding the genesis of the corridor. A new analysis of surface morphology, mainly derived from satellite imagery, led to the identification of a series of gentle and elongated en échelon left-stepping relief features or ridges with cross-sectional asymmetric flanks, having an average length of 20 km and oriented sub-latitudinally at 20° to the ENE strike of the corridor. The arrangement of these ridges reminds a tectonic scenario of right-lateral transcurrent faulting, for which, the limiting parallel faults fulfill the function of synthetic Riedel type shear. Besides, the cross-sectional asymmetry of the ridges suggests extensional normal faulting coherent with a transtensional right-lateral flower structure. Shallow seismicity of Mw 4.0 registered by the year 2016 in the proximities of the lineament could suggest recent fault activity. Also, previous gravity potential field mapping in the area seems to highlight basement anomalies underneath the sedimentary cover, coinciding with the main lineament of the Corridor. Based on all this information, the EVC is considered to be the surface expression of dextral transtensional fault activity.