Journal articles: 'Active tectonique'

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Yelles-Chaouche, AbdelKrim, Azzedine Boudiaf, Hamou Djellit, and Rabah Bracene. "La tectonique active de la région nord-algérienne." Comptes Rendus Geoscience 338, no. 1-2 (January 2006): 126–39. http://dx.doi.org/10.1016/j.crte.2005.11.002.

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Winter, Thierry, and Alain Lavenu. "Tectonique active en Équateur : ébauche d’une nouvelle interprétation géodynamique." Bulletin de l’Institut français d’études andines 18, no. 1 (1989): 95–115. http://dx.doi.org/10.3406/bifea.1989.988.

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Van Vliet-Lanoë, Brigitte, Michel Laurent, Michel Everaerts, Jean-Louis Mansy, and Geoffrey Manby. "Évolution néogène et quaternaire de la Somme, une flexuration tectonique active." Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science 331, no. 2 (July 2000): 151–58. http://dx.doi.org/10.1016/s1251-8050(00)01392-6.

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Peulvast, Jean-Pierre. "Géomorphologie et tectonique active : premiers enseignements de la traversée Kashgar-Khunjerab (Kunlun, Karakorum, Pamir)." Annales de Géographie 101, no. 566 (1992): 433–71. http://dx.doi.org/10.3406/geo.1992.21102.

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Lécuyer, Frédéric, Olivier Bellier, Alain Gourgaud, and Pierre M. Vincent. "Tectonique active du Nord-Est de Sulawesi(Indonésie) et contrôle structural de la caldeira de Tondano." Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science 325, no. 8 (October 1997): 607–13. http://dx.doi.org/10.1016/s1251-8050(97)89462-1.

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Arthaud, François, Jean-Claude Grillot, and Michel Raunet. "La tectonique cassante à Madagascar: son incidence sur la géomorphologie et sur les écoulements." Canadian Journal of Earth Sciences 27, no. 10 (October 1, 1990): 1394–407. http://dx.doi.org/10.1139/e90-149.

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In Madagascar, evidence of a rift neotectonics oriented north–south is shown and analyzed on microtectonic, kilometric, and regional scales. This phase, reported for the first time, influences significantly the water flow patterns and the following modern processes: directional control of the hydrographic system; local changes in base water levels; development of zones of active erosion and sedimentation; opening and (or) reopening of drainage fractures in karstic systems; typological diversification of some depressions (lowland floodings); hydraulic transfer between surface and subsurface controlled by preferential major axes of underground water drainage. [Journal Translation]

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Grillot, J. C., and M. Schoeller. "Exemple d'approche pluridisciplinaire dans la caractérisation d'eaux thermales carbo-gazeuses." Revue des sciences de l'eau 2, no. 2 (April 12, 2005): 211–28. http://dx.doi.org/10.7202/705029ar.

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Une approche pluridisciplinaire est menée à propos d'eaux souterraines carbo-gazeuses : au niveau des relations entre tectonique active et hydrothermalisme; sur les origines des composants aqueux et gazeux (CO2) par analyse de compositions isotopiques (2H, 18O, 3H et 13C) et mises en équation des équilibres carboniques. Trois exemples sont traités dans te Sud-Est de la France : le premier en région de socle métamorphique (émergence thermale chaude); les deux autres en domaine de couverture carbonatée épaisse (source karstique littorale froide et aquifère karstique peu profond). La complémentarité des informations acquises permet de préciser d'une part, le rôle de certaines directions fissurales dans les cheminements souterrains par rapport au contexte sismotectonique régional; d'autre part, la genèse des eaux et leur âge relatif; enfin l'origine du CO2 qui peut se révéler mixte (biogénique-mantellique) ou infracrustal. Se dégage de la sorte une méthodologie d'étude de ces eaux particulières qui mérite d'être plus largement développée.

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Carozza, Jean-Michel, and Stéphane Baize. "L'escarpement de faille de la Têt est-il le résultat de la tectonique active Plio-Pléistocène ou d'une exhumation Pléistocène ?" Comptes Rendus Geoscience 336, no. 3 (March 2004): 217–26. http://dx.doi.org/10.1016/j.crte.2003.10.026.

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Boutib, Lahcen, Fetheddine Melki, and Fouad Zargouni. "Tectonique synsedimentaire d'age cretace superieur en Tunisie nord orientale; blocs bascules et reorganisation des aires de subsidence." Bulletin de la Société Géologique de France 171, no. 4 (July 1, 2000): 431–40. http://dx.doi.org/10.2113/171.4.431.

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Abstract Structural analysis of late Cretaceous sequences from the northeastern Tunisian Atlas, led to conclude on an active basin floor instability. Regional tectonics resulted in tilted blocks with a subsidence reorganization, since the Campanian time. These structural movements are controlled both by N140 and N100-120 trending faults. The Turonian-Coniacian and Santonian sequences display lateral thickness and facies variation, due to tectonic activity at that time. During Campanian-Maastrichtian, a reorganization of the main subsidence areas occurred, the early Senonian basins, have been sealed and closed and new half graben basins developed on area which constituted previously palaeohigh structures. These syndepositional deformations are characterized by frequent slumps, synsedimentary tilting materials, sealed normal faults and progressive low angle unconformities. These tilted blocks combined to a subsidence axis migration were induced by a NE-SW trending extensional regime. This extension which affects the Tunisian margin during the Upper Cretaceous, is related to the Tethyan and Mesogean rifting phase which resulted from the combined movements of the African and European plates.

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Jolet, P. "La plate-forme carbonatée du Turonien inférieur à moyen de Provence (S.E. France) : mise en évidence d'une tectonique active en distension." Géologie Méditerranéenne 24, no. 3 (1997): 207–23. http://dx.doi.org/10.3406/geolm.1997.1608.

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11

Bousquet, Jean-Claude, and Gianni Lanzafame. "Nouvelle interpretation des fractures des eruptions laterales de l'Etna; consequences pour son cadre tectonique." Bulletin de la Société Géologique de France 172, no. 4 (July 1, 2001): 455–67. http://dx.doi.org/10.2113/172.4.455.

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Abstract Mt Etna is cut by numerous fractures (fissures and faults) of very different origin and orientation. They have been used to define the activity and the tectonic setting of the volcano. After a discussion of the proposed tectonic models for Etna, an examination of the fractures, which are linked to the high flank eruptions, was carried out based on the geological and geophysical studies of the recent eruptions (1983, 1989, 1991-93). All of these surface breaks are of strictly volcanic origin; they open and advance very slowly, in relation to the propagation of the dyke, as well as its width and depth from the volcano surface. If the dyke summit is not too far from the surface (about 200-300 m), fissures and normal faults, arranged in a graben, appear. When the dyke intersects the slope of the volcano, a flank eruption follows. Therefore, these fractures do not have a tectonic or volcano-tectonic origin: they do not cut the entire volcanic edifice, and thus cannot be used to define the rift-zones nor to characterise the tectonic regime controlling the functioning of Etna. They give information on the dyke orientation on the slopes of the volcanic edifice and cannot be used as significative markers of extension [Frazzetta and Villari, 1981; Kieffer 1983a and b; Monaco et al., 1997]. The simultaneous opening of radial fractures, according to various azimuths, is frequent and clearly indicates that, in these cases, the regional stress field is not implicated. But high on Etna, the concentration of flank eruptions, on the eastern side, and the orientation change of the fractures (fig. 6), when they travel away from the summit, have been repeatedly indicated. The repetition of flank eruptions and the azimuth changes can be explained, simply, by the closeness of the Valle del Bove [Murray, 1994], which induces a decrease of the confinement pressure. The dyke emplacements of the summit eruptions cause an eastward displacement of the higher part of Etna. Marine geophysical data indicate that this volcano is, however, not the site of a large scale lateral spreading to the Ionian sea. Consequently, an eastward detachment is present only on the superior part of the volcano (figs. 1B and 7C). In fact, an up to 100 m high and oversteepened east-facing scarp, between the towns of Vena and Presa, extends towards the south for some kilometers [Lanzafame et al., 2000]. It is made up of volcanic rocks affected by strong brecciation. Inverse faults are found in front of the scarp. The base of this one is found at the level of the pre-Etnean clays, which would have helped the displacement of the volcanics. The studies on the tectonic setting in which Etna is located has called the attention of numerous researchers. From the earliest studies, the presence of numerous normal faults has supported the idea that this volcano, as many others, is active in an extensional regime. The most recent geological and geophysical data show a more complex situation. Deep under Etna (more than 10 km), a compressive field (sigma 1 N-S) is present according to focal mechanisms [Cardaci et al.; 1990; Ferrucci et al., 1993; Cocina et al., 1997]. More superficially, instead, extension is usual. The importance of the weight of the volcanic edifice, in the spatial (horizontal and vertical) modification of the compressive stress field, must still be clarified. It is very clear, in any case, that Etna cannot be explained by an extensional regime or kinematics in extension [Monaco et al., 1997] using normal faults, which form during the flank eruptions.

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12

Lagabrielle, Yves. "La dorsale est-Pacifique entre 10° et 20° S. Alternance du volcanisme et de la tectonique le long de la zone active axiale." Géomorphologie : relief, processus, environnement 11, no. 2 (July 1, 2005): 105–20. http://dx.doi.org/10.4000/geomorphologie.281.

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13

Chorowicz, J., A. Emran, and E. M. Alem. "Tectonique et venues volcaniques en contexte de collision, exemple du massif néogène du Siroua (Atlas Marocain) : effets combinés d'une transformante et de la suture panafricaine." Canadian Journal of Earth Sciences 38, no. 3 (March 1, 2001): 411–25. http://dx.doi.org/10.1139/e00-074.

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The Late Miocene Early Pliocene Siroua strato-volcano is made of particular hyperalkaline rocks. It lies between the High-Atlas and the Anti-Atlas, in a collisional zone related to the continental subduction of the African plate under the Moroccan Meseta. Our field observations and analyses of SPOT, Landsat-MSS, and DEM (digital elevation model) imagery have permitted mapping of faults, joints, and volcanic edifices. The elongate shape of volcanoes and linear clusters of adjacent edifices, together with their relationships with faults, show that magma ascent was favored by tectonic crustal scale open fractures, essentially tension fractures, tail-cracks, and open faults. These fractures, together with other nonvolcanic, narrow, NNE-striking troughs, provide valuable information on the regional deformation since the Late Miocene. The shorteningextension type strain, which is responsible for the open fractures, is situated near the Azdem transform, a zone of active faults striking NNE, parallel to the convergence trend. The transform links two segments of the "Accident Sud-Atlasique," which constitute the border between the Moroccan Meseta and the African plate. The magma seems to originate from the lithospheric mantle, but asthenospheric material had previously migrated upward along the Panafrican suture zone. This mixed magma finally was transferred to the surface as a result of the onset of the open fractures prior to fault motions. The Siroua volcanic activity results from the conjunction of (1) a Panafrican suture zone and (2) a zone of open fractures due to "strike-slip" strain near a local transform inside the area of collision.

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Tricart, Pierre, Stephane Schwartz, Christian Sue, Gerard Poupeau, and Jean-Marc Lardeaux. "La denudation tectonique de la zone ultradauphinoise et l'inversion du front brianconnais au sud-est du Pelvoux (Alpes occidentales); une dynamique miocene a actuelle." Bulletin de la Société Géologique de France 172, no. 1 (January 1, 2001): 49–58. http://dx.doi.org/10.2113/172.1.49.

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Abstract In the western Alps, to the southeast of the Pelvoux massif (Champsaur-Embrunais-Brianconnais-Queyras transect), the Brianconnais zone consists of the southern tip of the Zone Houillere and small nappes of Mesozoic sediments, emplaced during the Eocene in HP-LT metamorphic conditions. During the Oligocene this tectonic pile was thrusted onto a late Eocene to early Oligocene flexural basin, deformed in low grade metamorphic conditions and belonging to the Ultradauphine zone. This major thrust, called here CBF [Chevauchement Brianconnais Frontal: Tricart 1986] represents the boundary between the external and the internal zones of the western Alps. It contains thin tectonic lenses of Subbrianconnais origin, so that the Brianconnais Front and the Penninic Front almost merge. Late Alpine extension. - We have recently discovered that the CBF was subsequently reactivated as an extensional detachment. This major negative inversion is associated with widespread extension in the internal (Brianconnais and Piemont) zones, resulting in multiscale normal faulting. Current field work in the Queyras area shows that this brittle multitrend extension is a continuation of the ductile extension that accompanied the exhumation of blue-schist bearing metamorphic units. Along the same transect, the external (Ultradauphine) zone was not affected by late-Alpine extension. This is still the present situation: to the east of the aseismic Pelvoux massif, the CBF bounds the Brianconnais seismic arc, the activity of which may be the continuation of the late-Alpine extension. At the scale of the western Alpine arc, active extensional-transtensional tectonics dominate in the internal zones while compressional uplift affects the external zone. In this contrasted stress field, the thrust-fault zone between internal and external arcs plays a major role of decoupling that can be demonstrated in several sites between the area analysed here and the Central Alps, including along the Ecors profile. Contribution of thermochronology. - In this paper, we compare apatite fission track (FT) ages from both sides of the inverted CBF to the southeast of the Pelvoux massif. In the hangingwall of the CBF, two ages were obtained from magmatic intrusions within the Zone houillere, close to Briancon. They are compared to recently published ages from the Champsaur Sandstones unit in the footwall of the CBF, along the same transect.

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Carozza, Jean-Michel, and Bernard Delcaillau. "Réponse des bassins versants à l'activité tectonique : l'exemple de la terminaison orientale de la chaîne pyrénéenne. Approche morphotectonique / Drainage basins response to active tectonics: example from Eastern Pyrenees. Morphotectonic approach." Géomorphologie : relief, processus, environnement 6, no. 1 (2000): 45–60. http://dx.doi.org/10.3406/morfo.2000.1042.

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Touret, Jacques. "Présentation du Point sur… de Bernard Déruelle, Ismaïla Ngounouno et Daniel Demaiffe, La « ligne chaude du Cameroun » (LChC) : l’unique exemple sur Terre d’une entité magmato-tectonique alcaline intraplaque active en domaines océanique et continental." Comptes Rendus Geoscience 339, no. 9 (August 2007): 587–88. http://dx.doi.org/10.1016/j.crte.2007.08.004.

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Farki, Khadija, Ghalem Zahour, Youssef Zerhouni, and Hamid Wafa. "Contribution to the Understanding of the Sedimentary and Tectono-Volcanic Evolution of Triassic and Liassic Series of Oued N’Fifikh (Coast Meseta, Morocco)." Annales de la Société Géologique du Nord, no. 19 (December 1, 2012): 145–56. http://dx.doi.org/10.54563/asgn.1479.

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La série géologique de l’Oued N’Fifikh (région de Mohammedia, Maroc) est constituée d’un socle cambro-ordovicien gréso-micacé et d’une couverture méso-cénozoïque. Cette dernière débute par des terrains triasiques constitués successivement, de la base vers le sommet, par un ensemble silto-gréso-conglomératique (20m), des argilites inférieures (40m), et des coulés basaltiques (50m). Sur cette formation, se déposent des argilites supérieures évaporitiques (60m) d’âge liasique. Cette série est coiffée par des calcaires du Néogène. L’étude tectono-volcanologique associée à une étude sédimentologique permet de proposer un modèle d’ouverture de ce bassin sous forme d’un hémi-graben. Ce dernier, axé sur l’Oued N’Fifikh, s’intègre dans une dynamique distensive liée au rifting atlantique. La sédimentation et le volcanisme ont été guidés par des failles actives volcano-tectoniques héritées du socle hercynien. Celles-ci ont été réactivées lors de la distension triasico-liasique avant de rejouer pendant la compression atlasique.

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Siame, Lionel L., Regis Braucher, Didier L. Bourles, Olivier Bellier, and Michel Sebrier. "Datation de surfaces geomorphologiques reperes par le 10 Be produit in-situ; implications tectoniques et climatiques." Bulletin de la Société Géologique de France 172, no. 2 (March 1, 2001): 223–36. http://dx.doi.org/10.2113/172.2.223.

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Abstract The evolution of continental landforms is mainly modulated by the impact of climatic and tectonic processes. Because of their distinctive morphology and the periodicity of their deposition, climatically induced landforms such as alluvial fans or terraces are well suited to infer rates of tectonic and continental climatic processes. Within tectonically active regions, an important step consists in dating displaced geomorphic features to calculate slip rates on active faults. Dating is probably the most critical tool because it is generally much more simpler to measure deformation resulting from tectonic activity than it is to accurately date when that deformation occurred. Recent advances in analytical chemistry and nuclear physics (accelerator mass spectrometry) now allow quantitative abundance measurements of the extremely rare isotopes produced by the interaction of cosmic rays with surface rocks and soils, the so-called in situ-produced cosmogenic nuclides ( 3 He, 10 Be, 21 Ne, 26 Al, 36 Cl), and allow to directly date the duration that a landform has been exposed to cosmic rays at the Earth's surface [Lal, 1991; Nishiizumi et al., 1993; Cerling and Craig, 1994; Clark et al., 1995]. In fact, the abundance of these cosmonuclides is proportional to landscape stability and, under favorable circumstances, their abundance within surface rocks can be used as a proxy for erosion rate or exposure age. These cosmonuclides thus provide geomorphologists with the opportunity to constrain rates of landscape evolution. This paper presents a new approach that combines cosmic ray exposure (CRE) dating using in situ-produced 10 Be and geomorphic as well as structural analyses. This approach has been applied on two active strike-slip and reverse faults located in the Andean foreland of western Argentina. These two case studies illustrate how CRE dating using in situ-produced 10 Be is particularly well suited for geomorphic studies that aim to estimate the respective control of climate and tectonics on morphogenesis.

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Terrier, Monique Cécile, Anne Bialkowski, Claude Prepetit, Yves-Fritz Joseph, Didier Bertil, and Marcello De Michele. "Utilisation des images Pléiades dans le cadr du microzonage sismique de Port-au-Prince (Haïti) : application à l'étude géologique." Revue Française de Photogrammétrie et de Télédétection, no. 209 (January 29, 2015): 59–64. http://dx.doi.org/10.52638/rfpt.2015.105.

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Le 12 janvier 2010, la capitale d'Haïti, Port-au-Prince, a subit un des plus violents séismes qu'elle ait connu au cours de ces derniers siècles. Soutenue par le PNUD et l'Etat haïtien (LNBTP et BME), une étude de microzonage sismique sur Port-au-Prince a alors été engagée. La connaissance géologique locale et les données topographiques constituent des préalables essentiels dans le processus de réalisation d'un microzonage sismique. Dans ce cadre, les images Pléiades et le MNT (dérivé de ces images PLEIADES et calculé par le SERTIT/CNES dans le cadre du projet KalHaiti) ont été utilisés pour l'étude géologique et l'analyse morphologique de la région de Port-au-Prince. L'étude lithostratigraphique montre un substratum marno-calcaire d'âge miocène à pliocène, caractéristique de dépôts en milieu profond à sublittoral. Ces dépôts sont entrecoupés de dépôts détritiques d'origine tectonique liée au jeu des failles bordières sud de la plaine de Port-au-Prince. La carte des failles actives réalisée est directement intégrée à la carte du microzonage sismique. Les résultats géologiques ont constitué des éléments essentiels pour l'évaluation des aléas mouvements de terrain (effets induits) et des effets de site lithologiques et topographiques du microzonage sismique.

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Rasskazov, S. V., I. A. Aslamov, S. V. Snopkov, V. I. Archipenko, A. M. Ilyasova, and E. P. Chebykin. "Real-time monitoring of oxidation-reduction potential in groundwater from the Kultuk area in late 2023 – early 2024: comparison of electric effects with earthquakes in the central Baikal Rift System." Geology and Environment 4, no. 1 (2024): 42–60. http://dx.doi.org/10.26516/2541-9641.2024.1.42.

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The results of real-time observations of the oxidation-reduction potential (ORP) in groundwater from two wells in the Kultuk area from December 2023 to March 2024 are presented. Variations of this parameter show reorganizations, accompanied by short episodes of single earthquakes and longer intervals of earthquake series in the central part of the Baikal Rift System. A change from low to high ORP values accompanies the general transition from strong to weak earthquakes. The uneven variations in ORP of the monitoring stations are suggested to associate with piezoelectric effects that arise when seismic waves act on quartz of the ordered tectonite structures in different active structures of the South Baikal basin: in its marginal Obruchev fault and in the axial Kultuk tectonic step.

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Pelletier, B., J. F. Stephan, R. Blanchet, C. Muller, and H. N. Hu. "L'emergence d'une zone de collision active a la pointe sud de Taiwan (peninsule d'Hengchun); tectoniques superposees et mise en evidence d'une obduction miocene moyen." Bulletin de la Société Géologique de France I, no. 2 (March 1, 1985): 161–71. http://dx.doi.org/10.2113/gssgfbull.i.2.161.

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Hughes, Cameron A., Micah J. Jessup, Colin A. Shaw, and Dennis L. Newell. "Deformation conditions during syn-convergent extension along the Cordillera Blanca shear zone, Peru." Geosphere 15, no. 4 (June 13, 2019): 1342–67. http://dx.doi.org/10.1130/ges02040.1.

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AbstractStrain localization across the brittle-ductile transition is a fundamental process in accommodating tectonic movement in the mid-crust. The tectonically active Cordillera Blanca shear zone (CBSZ), a ∼200-km-long normal-sense shear zone situated within the footwall of a discrete syn-convergent extensional fault in the Peruvian Andes, is an excellent field laboratory to explore this transition. Field and microscopic observations indicate consistent top-down-to-the-southwest sense of shear and a sequence of tectonites ranging from undeformed granodiorite through mylonite and ultimately fault breccia along the detachment.Using microstructural analysis, two-feldspar and Ti-in-quartz (TitaniQ) thermometry, recrystallized quartz paleopiezometry, and analysis of quartz crystallographic preferred orientations, we evaluate the deformation conditions and mechanisms in quartz and feldspar across the CBSZ. Deformation temperatures derived from asymmetric strain-induced myrmekite in a subset of tectonite samples are 410 ± 30 to 470 ± 36 °C, consistent with TitaniQ temperatures of 450 ± 60 to 490 ± 33 °C and temperatures >400 °C estimated from microstructural criteria. Brittle fabrics overprint ductile fabrics within ∼150 m of the detachment that indicate that deformation continued to lower-temperature (∼280–400 °C) and/or higher-strain-rate conditions prior to the onset of pervasive brittle deformation. Initial deformation occurred via high-temperature fracturing and dissolution-precipitation in feldspar. Continued subsolidus deformation resulted in either layering of mylonites into monophase quartz and fine-grained polyphase domains oriented subparallel to macroscopic foliation or the interconnection of recrystallized quartz networks oriented obliquely to macroscopic foliation. The transition to quartz-controlled rheology occurred at temperatures near ∼500 °C and at a differential stress of ∼16.5 MPa. Deformation within the CBSZ occurred predominantly above ∼400 °C and at stresses up to ∼71.4 MPa prior to the onset of brittle deformation.

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Dey, Alosree, Koushik Sen, and Manish A. Mamtani. "Electron Backscatter Diffraction Study of Ultrahigh-Pressure Tso Morari Eclogites (Trans-Himalayan Collisional Zone): Implications for Strain Regime Transition from Constrictional to Plane Strain during Exhumation." Lithosphere 2022, no. 1 (March 16, 2022). http://dx.doi.org/10.2113/2022/7256746.

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Abstract The Tso Morari Crystalline Complex (TMCC) of trans-Himalaya (eastern Ladakh, India) contains enclaves of ultrahigh-pressure eclogites that underwent deep burial (≥80 km) and subsequent rapid exhumation during continental subduction, collision, and final accretion of the Indian plate with the Eurasian plate. We present an electron backscatter diffraction (EBSD) study of eight eclogite samples to investigate the deformation mechanism and strain regimes active during peak (HP) metamorphism and subsequent postpeak rapid exhumation of the TMCC. Our study shows that the least retrogressed eclogite exhibits strong linear fabric (L tectonite) characterized by omphacite, having [001] axes parallel to and (110) poles perpendicular to lineation. These features concur with constrictional strain during peak (HP) metamorphism. A transitional planolinear fabric (LS tectonite) is shown by other eclogites that show petrographic evidence of omphacite alteration to amphibole and the presence of lower metamorphic grade minerals like actinolite and chlorite. Characteristics of lattice preferred orientation (LPO) of omphacite and quartz, indicated, respectively, by the LS and B indices, also suggest variation in strain regime from pristine eclogites to their altered counterparts. Based on these results, it is suggested that a constrictional strain regime prevailed during peak (HP) metamorphism in the TMCC due to the buoyant rise of TMCC in response to slab break-off and reverse slab pull during and after the deepest continental subduction. This buoyant rise was also facilitated by compression related to the ongoing India-Eurasia collision. This regime evolved later to plane strain that was superimposed on the UHP rocks at a shallower depth. It is plausibly associated with foliation-parallel extension during exhumation at midcrustal depths. A high-temperature prism c-slip in quartz shown by few samples is interpreted to have formed due to a subsequent granulite facies metamorphic overprint on the eclogite during collisional thickening.

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Santos, Gabriel S., Jean Bédard, Cees R. van Staal, Shoufa Lin, Tong Hong, and Kai Wang. "Geology of the Liuyuan Complex, NW China: A Permian back-arc basin ophiolite at the southern edge of the Central Asian orogenic belt." GSA Bulletin, January 9, 2023. http://dx.doi.org/10.1130/b36736.1.

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Located in the southern margin of the Central Asian orogenic belt, the stratigraphy and tectonic setting of the mafic 290−280 Ma Liuyuan Complex have been controversial for decades, with workers arguing for a forearc ophiolite or a continental rift setting. Here, we present the results of a detailed field study, where the Liuyuan Complex was subdivided into troctolite, melatroctolite, layered gabbro, varitextured olivine gabbro, hornblende gabbro, plagiogranite, sheeted dike, and mafic tectonite, in addition to previously identified and studied basalt and chert. All contacts between the igneous facies are intrusive, with gabbroic rocks separated from the overlying basalt by a well-developed and laterally continuous sheeted dike complex. Based on their geochemical affinities, two groups of basalt were identified: group I (low-TiO2) and group II (high-TiO2). A modeled liquid line of descent, assuming perfect mineral fractionation, with a liquidus temperature of 1212 °C, pressure of 1 kbar, fO2 at the quartz-fayalite-magnetite (QFM) buffer, and initial melt H2O of 0.5 wt%, provides an excellent fit to group I lavas, with group II basalts interpreted as having formed from a distinct arc source. The stratigraphy, extended trace-element patterns, and tectonic fingerprinting of the lavas suggest the Liuyuan Complex formed as an ophiolite in a fast-spreading back-arc basin, a setting inconsistent with previously proposed tectonic models for the southern Central Asian orogenic belt. We expand on a tectonic model that proposes the Liuyuan Complex formed as a back-arc to the recently identified Ganquan arc. The back-arc basin was then consumed in a north-dipping subduction zone beneath the active margin of composite Siberia. The magmatic center of this arc migrated southward, likely caused by slab roll-back, with the Liuyuan Complex becoming the basement of an arc. Exhumation of the Liuyuan Complex took place by 267 Ma, as constrained by the age of a subaerial dacite that unconformably overlies the basalts of the Liuyuan Complex.

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Journal articles on the topic 'Active tectonique'

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