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Academic literature on the topic 'Shortening and vergence'
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Journal articles on the topic "Shortening and vergence"
1
Greenhalgh, Scott R., John H. McBride, John M. Bartley, R. William Keach, Brooks B. Britt, and Bart J. Kowallis. "Along-strike variability of thrust fault vergence." Interpretation 3, no. 3 (2015): SX1—SX12. http://dx.doi.org/10.1190/int-2014-0182.1.
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The 3D kinematic evolution of thrust systems, in which vergence changes along strike, is poorly understood. This study uses 3D seismic data from Big Piney-LaBarge field, Wyoming, to examine the geometry and kinematics of two faults at the leading edge of the Hogsback thrust sheet, the frontal thrust of the Late Cretaceous Sevier fold-thrust belt. These thrusts lie along strike of each another and share an east-vergent detachment within the Cretaceous Baxter Shale. The two thrusts verge in opposite directions: The southern thrust verges eastward forming a frontal ramp consistent with major thrusts of the Sevier belt, whereas the northern thrust verges westward to form a type 1 triangle zone with the Hogsback thrust. The thrusts have strike lengths of 5 km (3.1 mi) and 8 km (5.0 mi), respectively, and they are separated by a transfer zone of less than 0.5 km (0.3 mi) wide. Strata in the transfer zone appear to be relatively undeformed, but reflections are less coherent here, which suggests small offsets unresolved by the seismic survey. Retrodeformable cross sections and a structure contour map on the Cretaceous Mesaverde Group indicate that shortening varies along strike, with a pronounced minimum at the transfer zone and greater shortening across the northern, west-vergent thrust (610 m [2000 ft]) than across the southern, east-vergent thrust (230 m [755 ft]). Mapping of these thrusts suggests that they propagated laterally toward each other to form a type 1 antithetic fault linkage in the transfer zone. Spatial patterns expressed in seismic attributes in and near the detachment horizon, which include waveform classification and spectral decomposition, suggest that stratigraphic variations may have pinned the detachment, thus localizing the transfer zone. Thickness variations in the thrust sheet also may have influenced the thrust geometry. Our study provides an analog for analysis of similar complex contractional belts around the world.
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Vasconcelos, Bruno Rodrigo, Amarildo Salina Ruiz, and João Batista de Matos. "Polyphase deformation and metamorphism of the Cuiabá group in the Poconé region (MT), Paraguay Fold and Thrust Belt: kinematic and tectonic implications." Brazilian Journal of Geology 45, no. 1 (2015): 51–63. http://dx.doi.org/10.1590/23174889201500010004.
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Several deformation models have been proposed for the Paraguay Belt, which primarily differ in the number of phases of deformation, direction of vergence and tectonic style. Structural features presented in this work indicate that the tectonics was dominated by low dip thrust sheets in an initial phase, followed by two progressive deformation phases. The first phase of deformation is characterized by a slate cleavage and axial plane of isoclinal recumbent folds with a NE axial direction, with a recrystallization of the minerals in the greenschist facies associated with horizontal shear zones with a top-to-the-SE sense of movement. The second stage shows vergence towards the NW, characterized by crenulation cleavage axial plane to F2 open folds over S0 and S1, locally associated with reverse faults. The third phase of deformation is characterized by subvertical faults and fractures with a NW direction showing sinistral movement, which are commonly filled by quartz veins. The collection of tectonic structures and metamorphic paragenesis described indicate that the most intense deformation at the deeper crustal level, greenschistfacies, occurred during F1, which accommodated significant crustal shortening through isoclinal recumbent folds and shear zones with low dip angles and hangwall movement to the SE, in a thin-skinned tectonic regime. The F2 deformation phase was less intense and had a brittle to ductile behavior that accommodated a slight shortening through normal open subvertical folds, and reverse faults developed in shallower crustal level, with vergence towards the Amazonian Craton. The third phase was less pervasive, and the shortening was accommodated by relief subvertical sinistral faults.
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Gracia-Marroquín, Diego, Mariano Cerca, Dora Carreón-Freyre, and Bernardino Barrientos-García. "Analogue model of gravity driven deformation in the salt tectonics zone of northeastern Mexico." Revista Mexicana de Ciencias Geológicas 35, no. 3 (2018): 277–90. http://dx.doi.org/10.22201/cgeo.20072902e.2018.3.739.
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In the deep seated gravity-driven deformation systems of the Gulf of Mexico contemporaneous extension and contraction of the overburden is favored by mechanical decoupling from the basement along thick salt sequences (up to 4 km). The updip extension is located inland, on the continental shelf of northeast Mexico, and is characterized by extensional listric faults and roll-overs; the downdip shortening zone is located at the deep waters and is characterized by a fold and thrust belt detached above the salt layer. Two physical experiments are used to discuss some aspects of these gravity-driven systems. The experimental setup includes a motor-driven experimental table, an inclined brittle basement (1°), a silicone layer simulating the salt sequences, and sand layers simulating the pre-kinematic Jurassic-Cretaceous strata before Laramide shortening. Deformation resulted in further tilting of the basement (3° to 4°). After the onset of deformation, thin sand layers were added at regular time intervals simulating the syntectonic sedimentation. The experiments reproduced the geometry of the deformation at the frontal ramp characterized by a seaward vergent thrust and its associated deformed region (the Perdido fold belt). The fold and thrust belt localization was favored by the change in basement inclination (a built-in slope change). Key elements interpreted in one available section of the area were reproduced in the model: a) the presence of an antithethic roll-over in the extensional zone and, b) the basinward vergence of folds and thrusts observed in the downdip shortening zone in the mexican Perdido fold belt.
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Carboni, Filippo, Francesco Brozzetti, Francesco Mirabella, et al. "Geological and geophysical study of a thin-skinned tectonic wedge formed during an early collisional stage: the Trasimeno Tectonic Wedge (Northern Apennines, Italy)." Geological Magazine 157, no. 2 (2019): 213–32. http://dx.doi.org/10.1017/s001675681900061x.
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AbstractThe presence of a set of well-known turbidite successions, deposited in progressively E-migrating foredeep basins and subsequently piled up with east vergence, makes the Northern Apennines of Italy paradigmatic of the evolution of deepwater fold-and-thrust belts. This study focuses on the early Apenninic collisional stage, early Miocene in age, which led to the accretion of the turbidites of the Trasimeno Tectonic Wedge (TTW), in the central part of the Northern Apennines. Based on the interpretation of previously unpublished seismic reflection profiles with new surface geology data and tectonic balancing, we present a detailed tectonic reconstruction of the TTW. In the study area, the TTW is characterized by a W-dipping shaly basal décollement located at a depth of 1–5 km. The tectonic wedge is c. 5 km thick at its central-western part and tapers progressively eastwards to c. 1 km. The total shortening, balanced along a 33 km long cross-section, is c. 60 km, including 20 km (40%) of internal imbrication, c. 23 km of horizontal ENE-wards translation along the basal décollement and c. 17 km of passive translation caused by the later shortening of footwall units. Deformation balancing, constrained through upper Aquitanian – upper Burdigalian (c. 21–16 Ma) biostratigraphy, provides an average shortening rate of c. 8.6 mm a–1. Internal shortening of the TTW shows an average shortening rate of c. 4 mm a–1 for this period.
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van Kooten, Willemijn Sarah Maria Theresia, Hugo Ortner, Ernst Willingshofer, Dimitrios Sokoutis, Alfred Gruber, and Thomas Sausgruber. "Fold localization at pre-existing normal faults: field observations and analogue modelling of the Achental structure, Northern Calcareous Alps, Austria." Solid Earth 15, no. 1 (2024): 91–120. http://dx.doi.org/10.5194/se-15-91-2024.
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Abstract. Within the Northern Calcareous Alps (NCA) fold-and-thrust belt of the Eastern Alps, multiple pre-shortening deformation phases have contributed to the structural grain that controlled localization of deformation at later stages. In particular, Jurassic rifting and opening of the Alpine Tethys led to the formation of extensional basins at the northern margin of the Apulian plate. Subsequent Cretaceous shortening within the Northern Calcareous Alps produced the enigmatic Achental structure, which forms a sigmoidal transition zone between two E–W-striking major synclines. One of the major complexities of the Achental structure is that all structural elements are oblique to the Cretaceous direction of shortening. Its sigmoidal form was, therefore, proposed to be a result of forced folding at the boundaries of the Jurassic Achental basin. This study analyses the structural evolution of the Achental structure through integrating field observations with crustal-scale physical analogue modelling to elucidate the influence of pre-existing crustal heterogeneities on oblique basin inversion. From brittle–ductile models that include a weak basal décollement, we infer that oblique shortening of pre-existing extensional faults can lead to the localization of deformation at the pre-existing structure and predicts thrust and fold structures that are consistent with field observations. Consequently, the Achental low-angle thrust and sigmoidal fold train was able to localize at the former Jurassic basin margin, with a vergence opposite to the controlling normal fault, creating the characteristic sigmoidal morphology during a single phase of NW-directed shortening.
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McLoon, Linda K., Han na Park, Jong-Hee Kim, Fatima Pedrosa-Domellöf, and LaDora V. Thompson. "A continuum of myofibers in adult rabbit extraocular muscle: force, shortening velocity, and patterns of myosin heavy chain colocalization." Journal of Applied Physiology 111, no. 4 (2011): 1178–89. http://dx.doi.org/10.1152/japplphysiol.00368.2011.
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Extraocular muscle (EOM) myofibers do not fit the traditional fiber typing classifications normally used in noncranial skeletal muscle, in part, due to the complexity of their individual myofibers. With single skinned myofibers isolated from rectus muscles of normal adult rabbits, force and shortening velocity were determined for 220 fibers. Each fiber was examined for myosin heavy chain (MyHC) isoform composition by densitometric analysis of electrophoresis gels. Rectus muscle serial sections were examined for coexpression of eight MyHC isoforms. A continuum was seen in single myofiber shortening velocities as well as force generation, both in absolute force (g) and specific tension (kN/m2). Shortening velocity correlated with MyHCIIB, IIA, and I content, the more abundant MyHC isoforms expressed within individual myofibers. Importantly, single fibers with similar or identical shortening velocities expressed significantly different ratios of MyHC isoforms. The vast majority of myofibers in both the orbital and global layers expressed more than one MyHC isoform, with up to six isoforms in single fiber segments. MyHC expression varied significantly and unpredictably along the length of single myofibers. Thus EOM myofibers represent a continuum in their histological and physiological characteristics. This continuum would facilitate fine motor control of eye position, speed, and direction of movement in all positions of gaze and with all types of eye movements—from slow vergence movements to fast saccades. To fully understand how the brain controls eye position and movements, it is critical that this significant EOM myofiber heterogeneity be integrated into hypotheses of oculomotor control.
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Wu, Jonny, Ken McClay, and Jose de Vera. "Growth of triangle zone fold-thrusts within the NW Borneo deep-water fold belt, offshore Sabah, southern South China Sea." Geosphere 16, no. 1 (2019): 329–56. http://dx.doi.org/10.1130/ges02106.1.
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Abstract The NW Borneo deep-water fold-and-thrust belt, offshore Sabah, southern South China Sea, contains a structurally complex region of three to four seafloor ridges outboard of the shelf-slope break. Previous studies have suggested the seafloor ridges formed either above shale diapirs produced by mass movement of overpressured shales (i.e., mobile shale) or above an imbricate fold-and-thrust array. Here, we performed tectonostratigraphic analyses on a petroleum industry three-dimensional (3-D) seismic volume that imaged the full growth stratal record. We show fold growth history, deformation styles, along-strike structural variabilities, and synkinematic sedimentation during triangle zone–style fold growth. Nine seismic horizons within growth strata were mapped and correlated to petroleum industry seismostratigraphy. Synkinematic sedimentation interactions with growing folds and near-surface strains were analyzed from seismic attribute maps. We interpret that the seafloor structures were formed by imbricate thrusts above multiple detachments. We estimate ∼8 km minimum shortening since the late Miocene ca. 10 Ma. The folds show oversteepened fold forelimbs, back-rotated backlimbs, and forward-vergent (NW to NNW) “blind” thrust ramps that terminate within the growth strata. Fold cores show evidence of internal shear. Immature folds show detachment fold geometries, whereas mature folds show forelimb break thrusts, type I triangle zones, and rotated forward-vergent roof thrusts. Thrust linkages spaced ∼10 km apart were exploited as thrust top synkinematic sedimentation pathways; the linkages also partition near-surface strains. Our comprehensive, three-dimensional documentation of triangle zone fold growth and sedimentation in a deep-water fold belt highlights internal shear, multiple detachments, and opposite thrust vergence; mobile shales are not required to explain the deformation.
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Pinet, Nicolas, Sébastien Castonguay, and Alain Tremblay. "Thrusting and back thrusting in the Taconian internal zone, southern Quebec Appalachians." Canadian Journal of Earth Sciences 33, no. 9 (1996): 1283–93. http://dx.doi.org/10.1139/e96-097.
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Cambro-Ordovician continental-margin rocks of the Humber zone of the Quebec Appalachians were mainly deformed during the Taconian orogeny (Middle Ordovician to Early Silurian). Two Taconian deformational events are recorded west of the Sutton–Notre-Dame mountains anticlinorium axis. They are characterized, respectively, by northwest-directed faulting and synmetamorphic folding (D1−2) and by southeastward back-thrusting motion (D3); the latter deformation has previously been poorly documented in the Quebec Appalachians. This duality of structural vergence is probably induced by the progressive tectonic wedging of basement rocks during a nearly constant northwest–southeast Taconian shortening. In correlative higher grade metamorphic rocks of New England, back-thrusting structures (D3) have not been described and are most probably absent because their root zone is located well above the present-day erosional surface of that part of the Appalachian belt.
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Qaisar, Sohail, Sajjad Ahmad, Mukhtiar Ghani, and Tehseen Ullah. "The Regional Extents of Local Thrust Systems in Jabbari and Rupper Town, South East of Hazara Pakistan." Pakistan Journal of Scientific & Industrial Research Series A: Physical Sciences 65, no. 1 (2022): 87–96. http://dx.doi.org/10.52763/pjsir.phys.sci.65.1.2022.87.96.
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Geological traverse between the town of Jabbri and Rupper, southeast Hazara delineates the stratigraphic and structural element of the area presented by high resolution geological map and cross section of the area. Oldest rocks in this section is Precambrian Hazara formation which is disconformably overlain by a Jurassic to Eocene sequence including Samana Suk, Chichali, Lumshiwal, Kawagarh, Hangu, Lockhart, Patala, Margalla-hill-limestone, Chorgali and Kuldana formations. Located in Lesser Himalayas, under the influence of main boundary thrust (MBT), this area developed several thrust systems from north to south including Hazara thrust, Haro thrust, Sangoda thrust, Rupper thrust. The main regional Hazara thrust has Precambrian rock in its hanging wall thrusted over the Jurassic Samna Suk formation. In lower detachment, there are several local thrust systems within Jurassic-Eocene strata.These thrusts trends in NE-SW direction indicating NW-SE compressional regime with the hanging wall Drag folds showing southward vergence. The stereographic plot of mesoscopic scale folds shows at least three folding events and varying plunging directions between the range of 240° and 290°. Most of the folds are plunging towards west and this is yet another indicator of east-west compressional forces. These folds orientations suggest transpressional deformation rather than pure compression. The balanced restore section shows that there is about 2.5 km shortening along 15 km restored section which makes about 16% shortening along the section.
 
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Högdahl, Karin, and Stefan Bergman. "Chapter 5 Paleoproterozoic (1.9–1.8 Ga), syn-orogenic magmatism and sedimentation in the Ljusdal lithotectonic unit, Svecokarelian orogen." Geological Society, London, Memoirs 50, no. 1 (2020): 131–53. http://dx.doi.org/10.1144/m50-2016-30.
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AbstractDuctile shear zones with dextral transpressive deformation separate the Ljusdal lithotectonic unit from the neighbouring units (Bothnia–Skellefteå and Bergslagen) in the 2.0–1.8 Ga Svecokarelian orogen. Sedimentation steered by regional crustal extension at c. 1.86–1.83 Ga was sandwiched between two separate phases of ductile strain with crustal shortening and predominantly high-grade metamorphism with plutonic activity. Metamorphism occurred under low-pressure, medium- to high-temperature conditions that locally reached granulite facies. The earlier shortening event resulted in the accretion of outboard sedimentary and c. 1.89 Ga volcanic rocks (formed in back- or inter-arc basin and volcanic arc settings, respectively) to a continental margin. Fabric development (D1), the earlier phase of low-pressure and variable temperature metamorphism (M1) and the intrusion of a predominantly granitic to granodioritic batholith with rather high εNd values (the Ljusdal batholith) occurred along this active margin at 1.87–1.84 Ga. Thrusting with westerly vergence, regional folding and ductile shearing (D2–3), the later phase of low-pressure and variable temperature metamorphism (M2), and the subsequent minor shear-related intrusion of granite, again with relatively high εNd values, prevailed at 1.83–1.80 Ga. Mineral deposits include epithermal Au–Cu deposits hosted by supracrustal rocks, V–Fe–Ti mineralization in subordinate gabbro and norite bodies inside the Ljusdal batholith, and graphite in metasedimentary rocks.