166 research outputs found
Un pouvoir dâabbĂ© en acte(s) : Raoul dâArgences, abbĂ© de FĂ©camp (1190-1219)
AprĂšs la conquĂȘte de 1204, tous les abbĂ©s bĂ©nĂ©dictins de Normandie deviennent des abbĂ©s royaux ; Philippe Auguste renforce ainsi les liens qui existaient depuis le XIIe siĂšcle entre le pouvoir capĂ©tien et les prĂ©lats normands. Ce moment reprĂ©sente un tournant dans lâhistoire de tous les monastĂšres de la principautĂ©. LâĂ©tude de lâabbatiat de Raoul dâArgences Ă la TrinitĂ© de FĂ©camp (1190-1219) contribue Ă mettre en lumiĂšre la politique des abbĂ©s autour de 1204. Ă travers lâexamen des actes de cet abbĂ©, cet article entend montrer que moins quâun temps dâinstabilitĂ©, le changement dâautoritĂ© royale a Ă©tĂ© un moment de renforcement du pouvoir abbatial Ă plusieurs titres, pour ce qui est de lâabbaye de FĂ©camp. LâĂ©tude des aspects diplomatiques et celle des objets de quarante-cinq chartes de Raoul concordent, et montrent que les abbĂ©s doivent aussi ĂȘtre considĂ©rĂ©s sous leur volet politique.As soon as Normandy was attached to the Royal domain, Philip II Augustus gave Royal status to all the Norman Benedictine abbots and reinforced links that existed since the XIIth century between the Capetian rulers and the Norman prelats. This moment represents a turn in the history of all the monasteries of the principality. The study of Raoul of Argences, abbot of la TrinitĂ© of FĂ©camp (1190-1219) has brought new light on the politics of Abbots around 1204. Following the examination of acts of this particular abbot, this article aims to show that far from being a moment of instability, the change of Royal power was a moment when abbatial authority was, in as far as the Abbey of FĂ©camp is concerned, reinforced. The study of the diplomatic aspects and the subject of forty-five charters of Raoul concord, and show that the political position of abbots must also be taken into consideration
Inner forearc sequence architecture in response to climatic and tectonic forcing since 150 ka : Hawhe's Bay, New Zealand
International audienceThe influence of eustasy, tectonic deformation, and sediment flux as controlling parameters on basin stratigraphy and depositional sequence development are largely accepted. Eustasy is usually considered as the dominant mechanism of sequence generation, especially for Pleistocene successions. In active subduction-margin settings, the high rates of tectonic deformation are expected to have a stronger influence on basin-fill architecture, while sediment flux is generally less well constrained, and therefore less frequently considered. The active Hikurangi subduction margin in New Zealand offers the opportunity to quantitatively assess the relative roles of tectonic, climatic, and eustatic drivers. We present a quantitative source-to-sink-like study of the late Pleistocene succession from the Hawke's Bay sector of the inner forearc domain (c. 150 ka to present). The interpretation of a grid of high-resolution marine seismic data, onland and offshore core and well descriptions, and the integration of geomorphic studies enabled identification of system tracts. In turn these comprise two sea-level-cycle depositional sequences (LPS1 and LPS2), including one complete 100 ka sequence (LPS1). Isopach maps of both sequences reveal changes in sediment distribution and preservation that reflect the relative roles of tectonic deformation and eustasy. Eustasy dominates development of sequence architecture at relatively short time scales (i.e., 100 kyrs). Four long-lasting depocenters are identified over the inner forearc domain and located in four subsiding basins (Kidnappers, Mahia, Lachlan, and Motu-o-Kura basins). Significant shifts of the depocenter location in the basins are correlated with eustatic sea-level changes. Estimates of sediment volumes and masses from isopach maps indicate higher mass accumulation rates during climato-eustatic extremes, which we correlated to the onland erosional response. Sediment distribution and landscape evolution are strongly influenced by the interaction of the structural deformation and sediment flux. We present paleogeographic reconstructions for the inner forearc domain coincident with two paleoclimatic extremes (Last Glacial Maximum and Holocene Optimum). These illustrate the importance of eustatic changes, structural deformation, and sediment flux on the pattern of sediment distribution, accumulation, and sequence architecture
A new NMR solution structure of the SL1 HIV-1(Lai) loopâloop dimer
Dimerization of genomic RNA is directly related with the event of encapsidation and maturation of the virion. The initiating sequence of the dimerization is a short autocomplementary region in the hairpin loop SL1. We describe here a new solution structure of the RNA dimerization initiation site (DIS) of HIV-1(Lai). NMR pulsed field-gradient spin-echo techniques and multidimensional heteronuclear NMR spectroscopy indicate that this structure is formed by two hairpins linked by six WatsonâCrick GC base pairs. Hinges between the stems and the loops are stabilized by intra and intermolecular interactions involving the A8, A9 and A16 adenines. The coaxial alignment of the three A-type helices present in the structure is supported by previous crystallography analysis but the A8 and A9 adenines are found in a bulged in position. These data suggest the existence of an equilibrium between bulged in and bulged out conformations in solution
Cenozoic tectonics of the Western Approaches Channel basins and its control of local drainage systems
International audienceLe domaine des Approches occidentales de la Manche constitue une zone clĂ© pour caractĂ©riser l'Ă©volution post-rift des marges continentales NW europĂ©ennes associĂ©es Ă la collision Afrique/Europe. MalgrĂ© les divers tĂ©moins des inversions cĂ©nozoĂŻques jalonnant le pourtour de la Manche, la structuration et l'amplitude des mouvements demeurent nĂ©anmoins incertaines au sein de la partie mĂ©ridionale française des Approches occidentales. Il en est de mĂȘme sur le rĂŽle de l'inversion de la mer du Nord dans la mise en place du Fleuve Manche qui drainait un bassin versant bien supĂ©rieur Ă la Manche actuelle durant les grandes rĂ©gressions plio-quaternaires et alimentait les Ă©ventails sous-marins Celtique et Armoricain en bas de pente. La rĂ©alisation des campagnes de sismique-rĂ©flexion haute rĂ©solution GEOMOC et GEOBREST03 dont les rĂ©sultats font l'objet de cet article permettent de rĂ©pondre Ă ces questions en complĂ©tant la connaissance gĂ©ologique de la Manche. Les nouvelles observations soulignent le diachronisme et le contraste de l'amplitude des mouvements du systĂšme de failles associĂ©es Ă l'inversion du bassin d'Iroise. Celle-ci se fait en deux Ă©pisodes: un Ă©pisode paroxysmal palĂ©ogĂšne dĂ©composĂ© en deux phases, Ă©ocĂšne (YprĂ©sien probable) et oligocĂšne, et un Ă©pisode nĂ©ogĂšne plus modĂ©rĂ© rĂ©activant partiellement les structures impliquĂ©es antĂ©rieurement. Les dĂ©formations se concentrent le long de l'accident nord Iroise (NIF) situĂ© dans le prolongement de la faille MĂ©dio-Manche et entraĂźne localement des plissements de la couverture sĂ©dimentaire Ă l'aplomb des accidents profonds. L'inversion induit ainsi un soulĂšvement de prĂšs de 700 m du plateau mĂ©dian situĂ© au sud de l'accident nord Iroise. La cartographie isochrone des sĂ©quences sismiques identifiĂ©es dĂ©montre Ă©galement le contrĂŽle majeur des structures tectoniques sur la mise en place des dĂ©pĂŽts nĂ©ogĂšnes. Le soulĂšvement de la partie orientale du bassin favorise ainsi la mise en place de vastes prismes progradants d'Ăąge miocĂšne supĂ©rieur, et contrĂŽle le dĂ©veloppement postĂ©rieur du rĂ©seau des palĂ©o-vallĂ©es constituant l'extrĂ©mitĂ© occidentale du fleuve Manche. Ce rĂ©seau prĂ©sente une gĂ©omĂ©trie en baĂŻonnette marquĂ©e par de brutaux changements de directions variant de N040 Ă N070, cette derniĂšre direction caractĂ©risant la plus grande partie des failles nĂ©ogĂšnes associĂ©es au bassin d'Iroise. Les palĂ©o-vallĂ©es se seraient dĂ©veloppĂ©es lors d'une chute du niveau marin au-delĂ du rebord de plate-forme et la stratigraphie Ă©tablie Ă travers cette Ă©tude amĂšne Ă placer le dĂ©but des incisions au PliocĂšne (ReurĂ©vien ou prĂ©-Tiglien). La chute amplifiĂ©e par l'inversion du bassin d'Iroise serait suivie d'un basculement tardif de la plate-forme externe Ă l'instar des observations rĂ©alisĂ©es sur de nombreuses marges du pourtour nord atlantique
Détail d'une structure régionale majeure par méthodes géophysiques combinées - cas de la faille de Fécamp-Lillebonne (Seine-Maritime, France)
International audienceLa faille de Lillebonne-FĂ©camp est une faille normale-dĂ©crochante dextre (Hauchard et Laignel, 2008 ; Wazi, 1988), orientĂ©e N150° (orientation armoricaine) Ă regard vers l'ouest, Ă rejet vertical variable (150 m dans le secteur de Bolbec, 40 m dans le secteur de Lillebonne). Il s'agit d'une structure gĂ©ologique rĂ©gionale majeure qui traverse le Pays de Caux sur plus de 25 km et se prolonge en Manche au large de FĂ©camp en prenant progressivement une orientation E-O. Au sud, cette structure n'atteindrait pas la Seine et viendrait buter contre l'accident de Notre-Dame-de-Gravenchon-Villequier, orientĂ© N060° (orientation varisque). A l'Ă©chelle du Bassin de Paris, cette structure s'inscrit dans la continuitĂ© des failles de la Seine, de Rambouillet et d'Etampes, et prĂ©sente la mĂȘme orientation que la structure du Bray. Dans le paysage structural du Pays de Caux, la faille de Lillebonne-FĂ©camp est Ă©galement associĂ©e Ă de larges structures plicatives Ă faible pendage, globalement parallĂšles Ă la faille (Ragot, 1988). En 2017, des investigations gĂ©ophysiques ont Ă©tĂ© rĂ©alisĂ©es par le BRGM dans le secteur de Bolbec pour amĂ©liorer les connaissances gĂ©ologiques et structurales dans la zone. L'interprĂ©tation et la corrĂ©lation conjointe des profils gĂ©o-Ă©lectriques, sismiques et de la carte gravimĂ©trique a permis de confirmer la thĂšse de Ragot sur la gĂ©omĂ©trie en faisceau de la faille, et de proposer une nouvelle carte structurale pour le secteur de Bolbec
Experimental evidence for the shallow production of phonolitic magmas at Mayotte
Since May 2018 till the end of 2021, Mayotte island has been the locus of a major submarine volcanic eruption characterized by the offshore emission of more than 6.5 km of basanitic magma. The eruption occurred along a WNWâESE trending submarine ridge on the east flank of the island where, in addition, several seemingly recent phonolitic bodies were also identified close to the island. To define realistic scenarios of magma ascent and potentially predict the style of an upcoming event, it is crucial to have a precise understanding on the plumbing system operating below volcanoes. The putative relationships between basanites emitted by the new volcano and these recent phonolites have been experimentally explored by performing crystallization experiments on a representative basanite over a large range of pressures (up to 400 MPa). The results show that the crystallization of basanite at crustal levels (12â15 km) yields a phonolitic residual liquid containing up to 3â4 wt% after 65 wt% of an assemblage of olivineplagioclaseamphiboleclinopyroxenebiotitemagnetiteilmeniteapatite. The final iron content of the residual phonolitic liquids is strongly controlled by the depth/pressure of fractionation. Fe-rich phonolites from the submarine ridge are produced at 6â8 km depth, while a shallower differentiation (4â5 km) results in the production of liquids with trachyteâbenmoreite affinities. If the fractionation process occurs at depths higher than 8 km, the resulting phonolitic melts are progressively enriched in â but depleted in FeO*, ie unlike those erupted. We therefore conclude that phonolitic magma production and storage at Mayotte is a rather shallow process.Depuis mai 2018 et jusquâĂ la fin de lâannĂ©e 2021, lâĂźle de Mayotte a Ă©tĂ© le scenario dâune Ă©ruption volcanique sous-marine majeure caractĂ©risĂ©e par lâĂ©mission en mer de plus de 6,5 km de magma basanitique. LâĂ©ruption sâest produite le long dâune ride sous-marine orientĂ©e ONOâESE sur le flanc est de lâĂźle oĂč, entre autre, plusieurs corps phonolitiques dâ aspect rĂ©cent ont Ă©galement Ă©tĂ© identifiĂ©s Ă proximitĂ© de lâĂźle. Pour dĂ©finir des scĂ©narios rĂ©alistes dâascension du magma et potentiellement prĂ©voir le style dâun Ă©vĂ©nement Ă venir, il est crucial dâavoir une comprĂ©hension prĂ©cise du systĂšme de plomberie magmatique opĂ©rant sous les volcans. Les relations gĂ©nĂ©tiques potentielles entre les basanites Ă©mises par le nouveau volcan et ces phonolites rĂ©centes ont Ă©tĂ© explorĂ©es expĂ©rimentalement en effectuant des expĂ©riences de cristallisation sur une basanite reprĂ©sentative, et ce sur une large gamme de pressions (jusquâĂ 400 MPa). Les rĂ©sultats montrent que la cristallisation de la basanite Ă des profondeurs crustales (12â15 km) produit un liquide rĂ©siduel phonolitique contenant jusquâĂ 3â4 % en poids (pd.%) de HO, aprĂšs la prĂ©cipitation dâau moins 65 pd.% dâun assemblage dâolivineplagioclaseamphiboleclinopyroxĂšnebiotitemagnĂ©titeilmĂ©niteapatite. La teneur finale en fer des liquides phonolitiques rĂ©siduels est fortement contrĂŽlĂ©e par la profondeur/pression de cristallisation. Les phonolites riches en fer de la dorsale sous-marine sont produites Ă 6â8 km de profondeur, tandis quâune diffĂ©renciation moins profonde (4â5 km) entraĂźne la production de liquides Ă affinitĂ©s trachyteâbenmoreite. Si le processus de fractionnement se produit Ă des profondeurs supĂ©rieures Ă 8 km, les liquides phonolitiques rĂ©sultants sont progressivement enrichis en SiOâAlO mais appauvris en FeO*, câest-Ă -dire diffĂ©rents des phonolites naturelles. Nous concluons donc que la production et le stockage de magma phonolitique Ă Mayotte est un processus plutĂŽt superficiel
Crise sismo-volcanique de Mayotte : rĂ©activation et Ă©volution en-direct dâune ride volcanique sur la pente est de lâĂźle mise en lumiĂšre par la bathymĂ©trie et la rĂ©flectivitĂ© multifaisceaux.
International audienc
The East-Mayotte new volcano in the Comoros Archipelago: structure and timing of magmatic phases inferred from seismic reflection data
Pleistocene Tectono-magmato-volcanic events recorded east of Mayotte - insights for the ongoing seismo-volcanic crisis
The offshore eastern Mayotte area has been extensively studied since the outbreak of the seismo-volcanic crisis in May 2018. Several oceanographic surveys have been carried out by REVOSIMA â https://doi.org/10.18715/MAYOTTE.REVOSIMA (MAYOBS cruises -https://doi.org/10.18142/291) for monitoring purpose, or for academic research (SISMAORE - https://doi.org/10.17600/18001331 and SCRATCH cruises - https://doi.org/10.17600/18002274). They offer a complete coverage of the eastern slope and abyssal plain with multibeam bathymetry and backscatter imagery, sub-bottom profiler (SBP), and several sediment cores. This set of data offers the opportunity to describe the morphology of the area and details the first tens of meters of the sedimentary succession on the abyssal plain.We discover several features including faults, domes and massive chaotic deposits that developed or occurred during Quaternary in the vicinity of the new Fani Maore Volcano. Domes are interpreted as forced folds related to the intrusion of a large sill at depth. The main fault crossing the largest forced fold is a succession of en-echelon segments with vertical throws of up to 8 meters and a preferential N130° strike compatible with the present day regional dextral context. Analysis of the SBP profiles reveals that faulting and doming associated to sill intrusion occurred simultaneously, and together with the deposition of two massive (several km3) and chaotic lobes at the foot of the Mayotte slope. Sediment cores collected over or close to the massive deposits indicate a mixed bioclastic-volcanoclastic content with a large amount of pumices, whose aspect and chemical composition are identical to volcanic edifices located on the upper slope (Horseshoe Volcano) or onshore (Petite-Terre). Backscatter imagery also reveals streaks that cover the lobes and trace back to the same upper slope area. Analysis of bioclasts from a core catcher stopped in the upper part of the deposit shows a large variety of foraminifers, shells fragments, with a little proportion originating from the upper-slope and shelf. We propose that these massive lobe deposits might have occurred as the pumice-dominated material ejected at HV or PT flows downslope, thus reworking and incorporating a substantial amount of hemipelagic deposits along the slope and over the abyssal plain. These observations suggests that a tectono-magmato-volcanic event occurred during recent geological time (Late Pleistocene according to early estimations). At least one comparable set of similar and synchronous features appears on our dataset thus implying the occurrence of a similar event, earlier in the Pleistocene. The correlations between these events and the activity at HV and PT volcanic centers are critical, as it would provide a recurring scenario to compare with present day seismo-volcanic crisis at Mayotte.This work is funded by REVOSIMA, ANR funded COYOTES project, and internal BRGM Project PDEV MAYOTTE.COmores & maYotte : vOlcanisme, TEctonique et Sismicit
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