Creusement de culs

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Creusement de culs
Volume 16, Issue 5 , July 1974 , Pages M71-M77
2004, Journal of Volcanology and Geothermal Research
2004, Journal of Volcanology and Geothermal Research
2004, Earth and Planetary Science Letters
2003, Journal of Volcanology and Geothermal Research
2001, Earth and Planetary Science Letters
Copyright © 1974 Published by Elsevier B.V.
Ore Geology Reviews, Volume 77, 2016, pp. 82-96
Geochemistry, Volume 80, Issue 1, 2020, Article 125594
Ore Geology Reviews, Volume 141, 2022, Article 104592
A detailed mapping and data from borings support the conclusion that there is a late lava flow inside the Papenoo valley, the main valley of Tahiti island. This last volcanic manifestation which took place 400,000 years ago came after the phase of erosion corresponding to the Illinoian glacial period. It is one of the four phases of erosion followed by filling observed in the cross section of the Papenoo valley.
Une cartographie de détail ainsi que les données de sondage montrent une coulée de vallée comblant le lit de la Papenoo, principale rivière de Tahiti. Cette manifestation volcanique tardive s'est produite il y a 400 000 ans et a interrompu une phase d'érosion correspondant à l'épisode glaciaire de l'Illinoian. Au total, 4 phases d'érosion suivies de remblaiements sont observées dans l'étude du profil transversal de la vallée de la Papenoo.
A quantitative geomorphological study has been made on 27 river basins in Tahiti-Nui volcanic island (French Polynesia) to reconstruct the erosional evolution of a young oceanic island subjected to heavy tropical rainfall. Tahiti-Nui is composed of a main shield volcano cut by two huge landslides on each side of a main E–W rift zone. The northern landslide depression was rapidly buried by the construction of a second shield, the late activity of which overflowed the crest and then filled the southern landslide depression. The island is now volcanically inactive and is deeply dissected by erosion. The present geometries of the river basins are first compared using dimensionless parameters derived from a digital elevation model. The original volcanic surfaces are then reconstructed to estimate the volumes removed by erosion and determine the average rates of long-term erosion. The basins developed on the flanks of the main shield are wider, shallower, and gentler than the basins incising the post-landslide second shield, indicating a higher degree of evolution. Rainfall concentration on the windward (eastern) side of the island also contributed to increase the vertical lowering of the volcanic relief and the enlargement of the valleys. The magnitude of erosion, however, is neither directly linked with the age of the units incised nor with the differential amounts of rainfall. Erosion rates determined over the last 1 Myr range between 10 − 3 km 3 kyr − 1 and 0.25 km 3 kyr − 1 . The highest values occur in the basins incising the main E–W rift zone and/or the lateral rims of the northern and southern landslide depressions. Long-term dissection has thus been enhanced along the geological discontinuities of the eruptive system. Deep erosion was first constrained along the axis of the main E–W rift zone, where numerous dykes compartmentalize the volcanic structure into large unstable blocks. Dykes most probably acted as mechanical discontinuities along which shallow gravitational landslides recurrently occurred. Such mass-wasting episodes produced significant amounts of debris, partly preserved as highly indurated sedimentary breccias of various ages exposed at various locations. Subsequent dissection of Tahiti-Nui was enhanced to the north and to the south, leading to the rapid evolution of the Papenoo and Taharuu drainage systems over the last 500 kyr. Long-term dissection on Tahiti-Nui has been responsible for the removal of at least 350 km 3 of volcanic material from the surface, and for the partial exhumation of a shallow intrusive complex partly composed of coarse-grained plutonic rocks (gabbros and syenites) in the central part of the eruptive system. Structurally controlled erosion is thus a key component of landscape evolution on such high-relief oceanic tropical islands.
Gillot at al. (2004) question the conclusions of Clément et al. (2002) about the occurrence of a recent debris avalanche event in Tahiti Nui volcano, together with their interpretation of the central depression of the island as the scar of a huge landslide. We show in this reply that this latter process is the only one capable of forming such a “horseshoe-shaped” depression. In addition, the brecciated deposits which cover the flat floor of this structure cannot be generated through another mechanism, such as fluviatile erosion.
Errors are quoted at 1σ. The ages measured in this study (Table 11, Fig. 3) generally confirm the previous radiometric data from Tahiti-Nui (e.g. [7,9,14,29]). The K/Ar determinations obtained on flows from the main shield volcano are in agreement with the available stratigraphic control (Fig. 4).
Geological mapping, accurate K/Ar dating and geochemical analyses of lavas allow a detailed reconstruction of the geological history of Tahiti-Nui Island (French Polynesia). The exposed volcanic activity is first characterized by the construction of a main shield from 1.4 Ma to 870 ka, with a maximum aerial eruptive rate around 2 km 3 /kyr. Lavas from this early building stage are alkaline, slightly silica-undersaturated, with 87 Sr/ 86 Sr and 143 Nd/ 144 Nd compositions rather constant and close to the enriched mantle II type. Vent locations were first concentrated along a main E–W rift zone, which was responsible for the lateral collapse of the northern and southern flanks of the main shield, around 0.87 Ma ago. The subsequent activity was first restricted to the northern depression, corresponding to an eruptive rate of about 5 km 3 /kyr in the period 850–760 ka. Significant variations in La/Sm, 87 Sr/ 86 Sr and 143 Nd/ 144 Nd occur in lavas erupted immediately after the main northern landslide, indicating a sudden increase in the extent of partial melting likely caused by the decompression subsequent to collapse. However, the later activity declined, and the lavas exhibit a gradual change toward strongly silica-undersaturated basanites, likely indicating a decreasing extent of partial melting of the upper mantle. The evolution of radiogenic isotope ratios over time indicates a change in the source toward more depleted compositions, until around 500 ka. Post-erosion volcanic activity, following an apparent hiatus of 240 kyr, exhibits similar major and trace element and isotope compositions. The volcano-structural and geochemical evolution of Tahiti-Nui and the overall alkaline character of the lavas from other eruptive complexes of the Society alignment suggest a relative weakness (low temperature and low eruptive rate) of the Society plume compared to the Hawaiian hot-spot.
Occurrences of debris avalanche deposits newly identified in Tahiti (Society Islands) and Ua Huka (Marquesas Archipelago) are described and interpreted here. In both islands, the breccias are located within horseshoe-shaped residual calderas. In Tahiti, the epiclastic formations, up to 500 m thick, lie on the floor of the central depression and in the valley of the northwards running Papenoo River. In Ua Huka, the breccias crop out within a depression limited by a semicircular crest in four bays along the southern coast. Their thickness is ca. 100 m. A few clasts collected in the Tahitian breccias and some rocks forming their substratum have been dated (K–Ar datings) and analysed (major and trace elements, Sr–Nd isotopes) for this study. Using these data, we show that the debris avalanche(s) occurred in Tahiti Nui at the end of the growth of the shield volcano (between 570 000 and 390 000 years ago), maybe in consequence of the emplacement of the plutonic body which occupies the central part of the caldera. In Ua Huka, the collapse took place nearly 3 Ma ago, between the construction of the shield volcano and that of the inner one. The southwards orientation of the caldera, like that of the neighbouring island Nuku Hiva, might reflect a preferential direction of weakness in the substratum of the central Marquesas.
In previous contributions [31,35], we have shown that azimuthal anisotropy can be strongly perturbed in the vicinity of hotspot structures; indeed, no clear seismic anisotropy has been observed to date at active ocean island hotspots. The ‘normal’ APM-parallel result at KOS is then particularly interesting since this very young island (1.4 Ma [16]) might have been expected to feature no azimuthal anisotropy, as is the case for Tahiti (∼1 Ma [36]) and the southern part of the Big Island of Hawaii [31,35]. The measurement at KOS suggests that any possible active member of the Caroline chain (yet to be discovered) is so distant and/or weak that the plume flow does not affect asthenospheric mantle fabrics beneath KOS.
Shear wave splitting measurements, in conjunction with studies of shear wave velocity structure, indicate that the Ontong–Java Plateau (OJP) large igneous province (LIP) has a thick, compositionally distinct root that diverts asthenospheric mantle flow beneath the Pacific plate. The OJP, the largest of Earth’s LIPs, stands 2 km above adjacent Pacific abyssal plains and is composed of mantle plume derived volcanics erupted at 122 and 90 Ma. Surface wave tomography of the Plateau reveals a seismically slow upper mantle root that extends approximately to 300 km depth. The thickness and juxtaposition of the Plateau and the mantle root imply that the OJP is the preserved ‘head’ of a rising mantle plume formed in situ when the LIP erupted. Thus, it is a far-traveled body currently moving northwestwards with the Pacific plate. Shear wave splitting at four seismic stations along the northern margin of the OJP varies systematically: the fast axis of seismic anisotropy at three stations on the NE OJP margin trend NW, parallel to hotspot-defined Pacific absolute plate motion; at a fourth station, on the NW margin of the Plateau, the fast shear wave trend is NE. Upper mantle flow directions delineated by the shear wave splitting could thus represent mantle flow diverted around the leading, northwestern face of the rheologically strong, chemically distinct OJP root. In sum, the Plateau and its deep root appear to be similar to continental tectosphere, except for contrasting seismic velocities.
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Travaux de la Société d’orthopédie et de traumatologie de l’Ouest (SOO). Réunion de Nantes, juin 2015. Mémoire original
Revue de Chirurgie Orthopédique et Traumatologique, Volume 103, Issue 6, 2017, p. 663
Journal of Surgical Research, Volume 202, Issue 1, 2016, pp. 188-195
Revue de Chirurgie Orthopédique et Traumatologique, Volume 104, Issue 5, 2018, pp. 415-419
Revue de Chirurgie Orthopédique et Traumatologique, Volume 103, Issue 3, 2017, pp. 227-230
Revue du Rhumatisme Monographies, Volume 86, Issue 2, 2019, pp. 84-91
Revue de Chirurgie Orthopédique et Traumatologique, 2021
© 2016 Elsevier Masson SAS. All rights reserved.
La position over the top du tunnel métaphysaire fémoral lors de ligamentoplastie extra-physaire de LCA selon Clocheville semblerait être responsable d’une anisométrie négative. Jusqu’à présent, le suivi des enfants opérés selon cette technique pédiatrique se limitait au dépistage d’une épiphysiodèse iatrogène et à la recherche d’une instabilité clinique postopératoire. L’objectif de cette étude était de mesurer la laxité résiduelle par des tests objectifs, de quantifier la récupération musculaire, ainsi que d’évaluer la qualité de vie et la reprise des activités sportives de ces patients.
Onze patients d’âge moyen de 13,5 ans ont été revus au recul moyen de 2,1 ans. Ils ont été soumis à des tests cliniques objectifs (arthromètre GnRB ® et dynamomètre CON-TREX ® ), ainsi qu’à des questionnaires subjectifs (IKDC et KOOS).
Aucune différence significative n’a été retrouvée entre genou sain et genou opéré, que ce soit pour le GNRB ® à 134 N ( p = 0,79), ou celui à 200 N ( p = 0,98). Le système Con-Trex ® a permis de mesurer un pourcentage médian de récupération du quadriceps de 80,7 % (52,2–114,5) concernant la puissance musculaire (60°/s) et de 81,2 % (51,6–109,6) pour la réponse musculaire (180°/s). Le score IKDC subjectif médian était de 94,73/100 (73,68–98,93). Parmi nos patients, 72,7 % ont repris le sport en compétition.
Le manque de puissance de cette étude n’a pas permis de montrer de différence significative en termes de laxité résiduelle en position de détente des transplants sur GnRB ® , alors qu’un différentiel moyen de +0,4 mm était observé. Bien que des techniques pédiatriques de ligamentoplasties transphysaires soient de plus en plus proposées, la technique de Clocheville reste pour nous une alternative chirurgicale séduisante chez les sujets les plus jeunes, sans risque majeur d’épiphysiodèse iatrogène malgré son caractère théoriquement anisométrique.
L’incidence des ruptures de ligaments croisés antérieurs (LCA) chez l’enfant aux cartilages de croissance ouverts est estimée à 350 à 400 nouveaux cas par an en France [1]. Le développement de nouvelles activités sportives et le niveau d’exigence du sport de haut niveau pourraient être à l’origine de cette augmentation [2]. Le déterminisme de la lésion du LCA est fonction de l’âge avec 90 % des lésions intra-corporéales du LCA survenant après l’âge de 12 ans [1], [3]. Alors que la place du traitement conservateur reste encore discutée [4], [5], la présence d’une instabilité subjective, d’une laxité clinique et/ou d’une lésion méniscale imposent une chirurgie précoce [6], [7]. Depuis plus de 15 ans, de nombreuses équipes proposent des reconstructions par techniques transphysaires dont les modalités pédiatriques consistent en la réalisation de tunnels centrés [8], [9], verticaux [10], [11] et de petits diamètres [12]. Ils retrouvent des troubles de croissance faibles à modérés, mais sur de petits effectifs [13], [14], [15], [16]. Aucune étude n’a cherché à évaluer objectivement et très précisément les laxités résiduelles antéro-postérieures de ces ligamentoplasties, facteur pronostique majeur de survenue de lésions cartilagineuses et méniscales irréversibles. Le but de cette étude était d’évaluer la récupération fonctionnelle des patients opérés d’une ligamentoplastie de Clocheville à l’aide de questionnaires subjectifs, de mesurer leur laxité résiduelle et quantifier la récupération musculaire avec l’hypothèse que la laxité des genoux opérés était supérieure à celle des genoux sains controlatéraux du fait de l’anisométrie du transplant.
Onze patients ont été inclus dans cette étude rétrospective sur 12 opérés entre janvier 2008 à décembre 2013. Pendant cette période, tous les enfants présentant une rupture du LCA à cartilages de croissance ouverts ont été opérés selon la technique de ligamentoplastie extra-physaire de Clocheville [17]. Les suites opératoires étaient marquées par une immobilisation plâtrée par cruro-pédieux de 45 jours, permettant la consolidation de la tranchée tibiale épiphysaire garante d’une bonne stabilité
La cohorte comportait 10 garçons pour une fille d’un âge moyen de 13,5 ans (11,5–16,2). Le recul moyen après la chirurgie était de 2 ans et 1 mois (9 mois–5 ans 11 mois). Les enfants ont été opérés entre la 9 e et la 20 e semaine suivant une rupture du LCA.
Sur les IRM au moment du diagnostic, les lésions méniscales rencontrées étaient au nombre de 4 sur les 11 patients (36,4 %), trois portant sur le ménisque médial et une sur le ménisque latéral. Un seul cas a nécessité une suture par la technique
L’évaluation fonctionnelle subjective a permis de rapporter un score IKDC subjectif médian très satisfaisant de l’ordre de 94,7 %. Ce résultat est semblable aux 94 % que Bonnard et al. [20] ont retrouvé sur une série de 57 cas de ligamentoplasties de Clocheville au recul moyen de 2 ans. Une seule autre étude de plus de 40 enfants [1] rapportait un IKDC moyen en dessous de nos résultats de l’ordre de 92 % sur un total de 102 enfants dont 63 ont été opérés selon la technique de Clocheville.
Le GnRB ® a permis de m
Échangistes amateurs en plan à trois
Partouze brésilienne en pleine nature
Une blonde se prend une grosse