Éditeur(s) : AIHP-GEODE : Archéologie Industrielle, Histoire, Patrimoine/Géographie- Développement Environnement de la Caraïbe Université des Antilles et de la Guyane. Service commun de la documentation Université des Antilles et de la Guyane SFHOM : Société Française d'Histoire d'Outre-Mer
Description : Le nouveau numéro de la Société française d'histoire d'outre-mer est consacré à la problématique des territoires de l'histoire antillaise. Un bilan de plusieurs décennies de recherches, de questions, d'interrogations mais aussi d'enseignements pour toute une génération d'universitaires. Les 9 intervenants présentent un résumé de leurs communications.
Siècle(s) traité(s) : 18
Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V14090
V14090

Éditeur(s) : HAL CCSD
Résumé : National audience
Les semelles métamorphiques sont situées à la base desgrandes ophiolites obductées. Elles sont principalement composéesd’amphibolites (métabasaltes à amphiboles ± grenat,clinopyroxène, plagioclase) fortement cisaillées et dont les conditionsmaximum de métamorphisme sont estimées à 800±100Cet 1.0±0.2 GPa. Leur formation a lieu au cours des 2 Ma suivantl’initiation des zones de subduction. Ces amphibolites sont interprétéescomme des portions de lithosphère océanique subduite,portions qui sont métamorphisées, dis-je, à haute températurepar transfert de chaleur depuis le coin de manteau sus-jacent quiformera la base de l’ophiolite obductée. Leur importante déformationau pic de métamorphisme est interprétée comme synchroneà leur accrétion au manteau de la plaque supérieure. Les semellesmétamorphiques sont donc des témoins directs de la dynamiqueprécoce des zones de subduction océanique. Leur pétrologie etleur déformation fournissent des contraintes majeures, et rares,sur l’évolution de la structure thermique et sur le comportementmécanique de l‘interface de subduction naissante. Cette étudeprésente des données structurales à plusieurs échelles, couplant desanalyses de terrain aux analyses EBSD sur des échantillons à amphibole± plagioclase ± clinopyroxene ± grenat de la semelle métamorphique.Les grains d’amphibole et de plagioclase sont caractériséspar une forte orientation préférentielle parallèle à la foliationet à la linéation. Cette fabrique est accompagnée par une forteorientation cristallographique préférentielle des amphiboles marquéepar un axe [001] marquant la linéation et la normale au plan(001) perpendiculaire à la foliation. Les plagioclases montrentune orientation cristallographique préférentielle faible voire nulle.Cette fabrique est similaire à celle observée dans les amphibolitescisaillées de base de croûte continentale. Les clinopyroxèneset les grenats présentent des degrés d’orientation intermédiaires.Ces deux phases forment des boudins dont l’axe long est orientéparallèlement à la foliation. Les porphyroclastes de clinopyroxèneprésentent une extinction ondulante et le développement de sousgrainsà leur périphérie. Les clinopyroxènes et les grenats agissentdonc comme phases ” dures ”, augmentant la résistance de laroche à la déformation. À l’initiation de la subduction, la partiesupérieure de la plaque plongeante est affectée par l’augmentationprogressive du degré de métamorphisme. Ceci entraîne une fortedéshydratation et la cristallisation de phases ” faibles ” (quartz,amphibole, plagioclase) et ” fortes ” (clinopyroxene, grenat). Larhéologie de l’interface de la subduction en est fortement affectée.Les unités de la semelle métamorphique (avec des minéralogies etdes conditions P-T-t différentes) accrétées aux péridotites de laplaque supérieure témoignent de changements rhéologiques majeuresà l’interface de la subduction au cours de l’histoire précocedes zones de subduction.
RST 2016, livre des résumés
Caen, France

insu-01388730
https://hal-insu.archives-ouvertes.fr/insu-01388730

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Microbathymetry data, in situ observations, and sampling along the 13°20′N and 13°20′N oceanic core complexes (OCCs) reveal mechanisms of detachment fault denudation at the seafloor, links between tectonic extension and mass wasting, and expose the nature of corrugations, ubiquitous at OCCs. In the initial stages of detachment faulting and high-angle fault, scarps show extensive mass wasting that reduces their slope. Flexural rotation further lowers scarp slope, hinders mass wasting, resulting in morphologically complex chaotic terrain between the breakaway and the denuded corrugated surface. Extension and drag along the fault plane uplifts a wedge of hangingwall material (apron). The detachment surface emerges along a continuous moat that sheds rocks and covers it with unconsolidated rubble, while local slumping emplaces rubble ridges overlying corrugations. The detachment fault zone is a set of anostomosed slip planes, elongated in the along-extension direction. Slip planes bind fault rock bodies defining the corrugations observed in microbathymetry and sonar. Fault planes with extension-parallel stria are exposed along corrugation flanks, where the rubble cover is shed. Detachment fault rocks are primarily basalt fault breccia at 13°20′N OCC, and gabbro and peridotite at 13°30′N, demonstrating that brittle strain localization in shallow lithosphere form corrugations, regardless of lithologies in the detachment zone. Finally, faulting and volcanism dismember the 13°30′N OCC, with widespread present and past hydrothermal activity (Semenov fields), while the Irinovskoe hydrothermal field at the 13°20′N core complex suggests a magmatic source within the footwall. These results confirm the ubiquitous relationship between hydrothermal activity and oceanic detachment formation and evolution.
ISSN: 1525-2027

hal-01571973
https://hal.archives-ouvertes.fr/hal-01571973
https://hal.archives-ouvertes.fr/hal-01571973v2/document
https://hal.archives-ouvertes.fr/hal-01571973/file/Escart-n_et_al-2017-Geochemistry%2C_Geophysics%2C_Geosystems.pdf
DOI : 10.1002/2016GC006775

Éditeur(s) : HAL CCSD
Résumé : International audience
EGU General Assembly 2014
Vienne, Austria

insu-01113701
https://hal-insu.archives-ouvertes.fr/insu-01113701

Éditeur(s) : HAL CCSD
Résumé : International audience
Metamorphic soles correspond to m to 500m thick tectonic slices welded beneath most of the large-scale ophiolites.They typically show a steep inverted metamorphic structure where the pressure and temperature conditions ofcrystallization increase upward (from 500100ºC at 0.50.2 GPa to 800100ºC at 1.00.2 GPa), with isogradssubparallel to the contact with the overlying ophiolitic peridotite. The proportion of mafic rocks in metamorphicsoles also increases from the bottom (meta-sediments rich) to the top (approaching the ophiolite peridotites). Thesesoles are interpreted as the result of heat transfer from the incipient mantle wedge toward the nascent slab (associatedwith large-scale fluid transfer and possible shear heating) during the first My of intra-oceanic subduction(as indicated by radiometric ages). Metamorphic soles provide therefore major constraints on early subductiondynamics (i.e. thermal structure, fluid migration and rheology along the nascent slab interface).We present a detailed structural and petrological study of the metamorphic sole from 4 major cross-sections alongthe Oman ophiolite. We show precise pressure–temperature estimates obtained by pseudosection modelling andEBSD measurements performed on both the garnet-bearing and garnet-free high-grade sole. Results allow quantificationof the micro-scale deformation and highlight differences in pressure–temperature–deformation conditionsbetween the 4 different locations, showing that the inverted metamorphic gradient through the sole is not continuousin all locations.Based on these new constraints, we suggest a new tectonic–petrological model for the formation of metamorphicsoles below ophiolites. This model involves the stacking of several homogeneous slivers of oceanic crust leadingto the present-day structure of the sole. In this view, these thrusts are the result of rheological contrasts between thesole and the peridotite as the plate interface progressively cools down. These slivers later underwent several stagesof retrogression (partly mediated by ascending fluids from the slab) from amphibolite- to prehnite/pumpellite-faciesconditions.
Geophysical Research Abstracts
Vienne, Austria

insu-01309369
https://hal-insu.archives-ouvertes.fr/insu-01309369

Éditeur(s) : HAL CCSD
Résumé : International audience
Metamorphic soles correspond to m to 500 m thick highly strained metamorphic rock units found beneath myloniticbanded peridotites at the base of large-scale ophiolites, as exemplified in Oman. Metamorphic soles aremainly composed of metabasalts deriving from the downgoing oceanic lithosphere and metamorphosed up togranulite-facies conditions by heat transfer from the mantle wedge. Pressure–temperature peak conditions areusually estimated at 1.00.2 GPa and 800100ºC. The absence of HP–LT metamorphism overprint implies thatmetamorphic soles have been formed and exhumed during subduction infancy. In this view, metamorphic soleswere strongly deformed during their accretion to the mantle wedge (corresponding, now, to the base of the ophiolite).Therefore, metamorphic soles and banded peridotites are direct witnesses of the dynamics of early subductionzones, in terms of thermal structure, fluid migration and rheology evolution across the nascent slab interface.Based on fieldwork and EBSD analyses, we present a detailed (micro–) structural study performed on samplescoming from the Sumeini window, the better-preserved cross-section of the metamorphic sole of Oman. Largedifferences are found in the deformation (CPO, grain size, aspect ratio) of clinopyroxene, amphibole and plagioclase,related to mineralogical changes linked with the distance to the peridotite contact (e.g., hardening due to theappearance of garnet and clinopyroxene).To model the incipient slab interface in laboratory, we carried out 5 hydrostatic annealing and simple-shear experimentson Griggs solid-medium apparatus. Deformation experiments were conducted at axial strain rates of 10-6s-1. Fine-grained amphibolite was synthetized by adding 1 wt.% water to a (Mid-Ocean Ridge) basalt powder asa proxy for the metamorphic sole (amphibole + plagioclase + clinopyroxene garnet assemblage). To synthetizegarnet, 2 experiments were carried out in hydrostatic conditions and with deformation at 800C with confiningpressure of 2 GPa. Another simple-shear experiment has been carried out at 800C and 1 GPa with fined-grainednatural garnet. With the aim of mimicking the early slab interface (between the metamorphic sole and bandedperidotites at the base of the ophiolite), 2 simple-shear deformation experiments with 2 layers have been carriedout at 800C and confining pressure of 1 GPa. The bottom layer was made of hydrated basalt powder and the toplayer was made of olivine.Fined-grained garnet-free amphibolite is significantly weaker than dunite but the appearance of harder mineralsin the amphibolite (garnet and clinopyroxene) has major implications on its rheological evolution. These resultsallow liking field observations of strain localization at the interface to the metamorphic sole formation
European Geosciences Union General Assembly 2016
Vienne, Austria

insu-01309394
https://hal-insu.archives-ouvertes.fr/insu-01309394

Éditeur(s) : HAL CCSD
Résumé : International audience
Understanding subduction rheology in both space and time has been a challenge since the advent of plate tectonics.We herein focus on "subduction infancy", which corresponds to the first 0-2 My immediately following subductionnucleation, when a newly born slab penetrates into the overriding plate mantle and heats up.The only remnants of this critical, yet elusive, geodynamic step are thin metamorphic soles, commonly found beneathpristine, 100-1000 km long portions of oceanic lithosphere emplaced on top of continents (i.e. ophiolites).In this study, we show how, during subduction infancy, transient mechanical properties of both the mantle and crustacross the subduction plate interface (during 100s ky) control and hinder the penetration of tectonic plates intothe mantle, and how this results in strong peaks of resistance and even slicing of their surface — leaving behindthin, chopped-off metamorphic slivers (i.e. metamorphic soles).These findings constrain the mechanical behaviour of the subduction plate interface (with implications for couplingprocesses and earthquake generation) as well as the properties of the crust and mantle. They also highlight the roleof fluids in enabling subduction to overcome this early resistance.
Geophysical Research Abstracts
Vienne, Austria

insu-01309386
https://hal-insu.archives-ouvertes.fr/insu-01309386

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Despite decades of petrological and geochemical studies, the nature and setting of obducted ophiolites remain controversial: the influence of supra-subduction zone environments on pre-existing oceanic lithosphere is yet to assess, and the processes leading to subduction/obduction initiation are still poorly constrained. Our study documents successive influx of slab-derived fluids and progressive strain localization within the upper mantle in a supra-subduction environment during the first few My of the subduction history. We focus on strongly sheared mafic amphibolites intruding peridotites near the mantle–crust transition of the New Caledonia obducted ophiolite and ~ 50 to 100 m above the basal thrust contact of the ophiolite. These m- to hm-long and several m-thick shear bands are interpreted as inherited small-scale intrusions of mafic melts, probably dikes or sills, which were derived from a moderately refractory mantle source refertilized by supra-subduction zone fluids. 40Ar/39Ar age constraints on pargasite at ca. 90 Ma suggest that they could be inherited from the former Pacific west-dipping subduction.Secondary deformation of these mafic intrusions is intimately associated to three major stages of fluid infiltration: (1) the first stage of deformation and metasomatism is marked by syn-kinematic growth of Ca-amphibole (at 700–800 °C and 3–5 kbar) with a distinctive supra-subduction zone signature, and controlled later channelization of aqueous fluids. 40Ar/39Ar dating on magnesio-hornblende indicates that this deformation episode occurred at ca. 55 Ma, coincident with east-dipping subduction initiation; (2) the main metasomatic stage, characterized by the development of a phlogopite-rich matrix wrapping peridotites and amphibolite boudins, points to the percolation of alkali-rich aqueous fluids at still high temperature (650–750 °C); (3) the last, low temperature (< 600 °C) metasomatic stage results in the formation of deformed veinlets containing talc, chlorite and serpentine.
ISSN: 0024-4937

hal-01306664
https://hal.archives-ouvertes.fr/hal-01306664
https://hal.archives-ouvertes.fr/hal-01306664/document
https://hal.archives-ouvertes.fr/hal-01306664/file/Soret_2016_Strain_localization.pdf
DOI : 10.1016/j.lithos.2015.11.022

Éditeur(s) : HAL CCSD
Résumé : International audience
Understanding subduction rheology in both space and time has been a challenge since the advent of plate tectonics. We herein focus on "subduction infancy", that is the first ~1-5 My immediately following subduction nucleation, when a newly born slab penetrates into the upper plate mantle and heats up. The only remnants of this critical yet elusive geodynamic step are thin metamorphic soles, commonly found beneath pristine, 100-1000 km long portions of oceanic lithosphere emplaced on continents (i.e., ophiolites).Through the (i) worldwide compilation of pressure-temperature conditions of metamorphic sole formation augmented by pseudosection thermodynamic modeling, (ii) calculations of the viscosity of materials along the plate interface and (iii) generic numerical thermal models, we provide a conceptual model of dynamic plate interface processes during subduction infancy (and initiation s.l.).We show in particular how major rheological switches across the subduction interface control slab penetration, and the formation of metamorphic soles. Due to the downward progression of hydration and weakening of the mantle wedge with cooling, the lower plate (basalt, sediment) and the upper plate (mantle wedge) rheologies equalize and switch over a restricted temperature-time-depth interval (e.g., at ~800°C and ~1 GPa, during 0.1-2 My, for high-temperature metamorphic sole formation). These switches result in episodes of maximum interplate mechanical coupling, thereby slicing the top of the slab and welding pieces (basalt, sediment) to the base of the mantle wedge. Similar mechanical processes likely apply for the later, deeper accretion and exhumation of high-temperature oceanic eclogites in serpentinite mélanges, or for the accretion of larger tectonic slices.This model provides constraints on the effective rheologies of the crust and mantle and general understanding, at both rock and plate scale, for accretion processes and early slab dynamics.
AGU Fall Meeting 2015
San Francisco, United States

insu-01242103
https://hal-insu.archives-ouvertes.fr/insu-01242103

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
In ophiolites and in present-day oceanic crust formed at fast spreading ridges, oceanic plagiogranites are commonly observed at, or close to the base of the sheeted dike complex. They can be produced either by differentiation of mafic melts, or by hydrous partial melting of the hydrothermally altered sheeted dikes. In addition, the hydrothermally altered base of the sheeted dike complex, which is often infiltrated by plagiogranitic veins, is usually recrystallized into granoblastic dikes that are commonly interpreted as a result of prograde granulitic metamorphism. To test the anatectic origin of oceanic plagiogranites, we performed melting experiments on a natural hydrothermally altered dike, under conditions that match those prevailing at the base of the sheeted dike complex. All generated melts are water saturated, transitional between tholeiitic and calc-alkaline, and match the compositions of oceanic plagiogranites observed close to the base of the sheeted dike complex. Newly crystallized clinopyroxene and plagioclase have compositions that are characteristic of the same minerals in granoblastic dikes. Published silicic melt compositions obtained in classical MORB fractionation experiments also broadly match the compositions of oceanic plagiogranites; however, the compositions of the coexisting experimental minerals significantly deviate from those of the granoblastic dikes. Our results demonstrate that hydrous partial melting is a likely common process in the root zone of the sheeted dike complex, starting at temperatures exceeding 850A degrees C. The newly formed melt can either crystallize to form oceanic plagiogranites or may be recycled within the melt lens resulting in hybridized and contaminated MORB melts. It represents the main MORB crustal contamination process. The residue after the partial melting event is represented by the granoblastic dikes. Our results support a model with a dynamic melt lens that has the potential to trigger hydrous partial melting reactions in the previously hydrothermally altered sheeted dikes. A new thermometer using the Al content of clinopyroxene is also elaborated.
ISSN: 0010-7999

hal-00534058
https://hal.archives-ouvertes.fr/hal-00534058
DOI : 10.1007/s00410-010-0502-6

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Subduction infancy corresponds to the first few million years following subduction initiation, when slabs start their descent into the mantle. It coincides with the transient (yet systematic) transfer of material from the top of the slab to the upper plate, as witnessed by metamorphic soles welded beneath obducted ophiolites. Combining structure–lithology–pressure–temperature–time data from metamorphic soles with flow laws derived from experimental rock mechanics, this study highlights two main successive rheological switches across the subduction interface (mantle wedge vs. basalts, then mantle wedge vs. sediments; at ∼800 °C and ∼600 °C, respectively), during which interplate mechanical coupling is maximized by the existence of transiently similar rheologies across the plate contact. We propose that these rheological switches hinder slab penetration and are responsible for slicing the top of the slab and welding crustal pieces (high- then low-temperature metamorphic soles) to the base of the mantle wedge during subduction infancy. This mechanism has implications for the rheological properties of the crust and mantle (and for transient episodes of accretion/exhumation of HP-LT rocks in mature subduction systems) and highlights the role of fluids in enabling subduction to overcome the early resistance to slab penetration.
ISSN: 0012-821X

hal-01383368
http://hal.upmc.fr/hal-01383368
http://hal.upmc.fr/hal-01383368/document
http://hal.upmc.fr/hal-01383368/file/Agard_2016_Plate_interface.pdf
DOI : 10.1016/j.epsl.2016.06.054

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Expeditions 304 and 305 of the Integrated Ocean Drilling Program cored and logged a 1.4 km section of the domal core of Atlantis Massif. Postdrilling research results summarized here constrain the structure and lithology of the Central Dome of this oceanic core complex. The dominantly gabbroic sequence recovered contrasts with predrilling predictions; application of the ground truth in subsequent geophysical processing has produced self-consistent models for the Central Dome. The presence of many thin interfingered petrologic units indicates that the intrusions forming the domal core were emplaced over a minimum of 100-220 kyr, and not as a single magma pulse. Isotopic and mineralogical alteration is intense in the upper 100 m but decreases in intensity with depth. Below 800 m, alteration is restricted to narrow zones surrounding faults, veins, igneous contacts, and to an interval of locally intense serpentinization in olivine-rich troctolite. Hydration of the lithosphere occurred over the complete range of temperature conditions from granulite to zeolite facies, but was predominantly in the amphibolite and greenschist range. Deformation of the sequence was remarkably localized, despite paleomagnetic indications that the dome has undergone at least 45 degrees rotation, presumably during unroofing via detachment faulting. Both the deformation pattern and the lithology contrast with what is known from seafloor studies on the adjacent Southern Ridge of the massif. There, the detachment capping the domal core deformed a 100 m thick zone and serpentinized peridotite comprises similar to 70% of recovered samples. We develop a working model of the evolution of Atlantis Massif over the past 2 Myr, outlining several stages that could explain the observed similarities and differences between the Central Dome and the Southern Ridge.
ISSN: 0148-0227

hal-00617528
https://hal.archives-ouvertes.fr/hal-00617528
https://hal.archives-ouvertes.fr/hal-00617528/document
https://hal.archives-ouvertes.fr/hal-00617528/file/2010JB007931.pdf
DOI : 10.1029/2010JB007931

Éditeur(s) : HAL CCSD Météo et Climat
Résumé : International audience
Le premier volet du projet Cyprim vise à mieux identifier les précurseurs des cyclogenèses et des précipitations intenses en région méditerranéenne. Cet article en présente les principaux résultats. Il est question des ingrédients météorologiques à l'origine de ces systèmes, de la grande à la mésoéchelle, des causes des fortes intensités, localisations et parfois stationnarité des récipitations associées. Le coeur de l'article présente des méthodes d'identification des anomalies de tourbillon potentiel liées à l'occurrence d'événements précipitants intenses et dresse une climatologie de ces anomalies. Les perspectives d'exploitation de cette information pour améliorer la qualité des prévisions sont évoquées. ENGLISH VERSION: The first part of the CYPRIM project (Cyclogenesis and intense precipitations in the Mediterranean region) aims at a better identification of the precursor structures of cyclogenesis and heavy precipitation in the Mediterranean region. This article presents the main results. It mentions the meteorological ingredients from which these systems originate from the large to themesoscale, the reasons for large intensities, the localization and sometimes stationarity of the associated precipitations. The heart of the article shows methods for identifiying potential vorticity anomalies involved in the occurrence of heavy precipitation events and sets up a climatology of these anomalies.The perspectives of the usefulness of this information for improving forecast quality are discussed.
ISSN: 0026-1181

insu-00448250
https://hal-insu.archives-ouvertes.fr/insu-00448250
DOI : 10.4267/2042/28828

Éditeur(s) : HAL CCSD Elsevier
Résumé : Two peat sequences were sampled in the vicinity of the main mining districts of the Vosges Mountains: Sainte-Marie-aux-Mines and Plancher-les-Mines. Lead isotopic compositions and excess lead fluxes were calculated for each of these radiocarbon-dated sequences. Geochemical records are in very good agreement with the mining history of the area, well known over the last millennium. Except for an anomaly corresponding to the Middle Bronze Age which has not yet been resolved, there is no clear geochemical evidence of local metal production in the Vosges before the 10th century as excess lead deposition archived between 500 BC and 500 AD is attributed to long-range transport of polluted particulate matter. The approach described here can be applied to other mining districts where archaeological evidence is scarce or even lacking, but where past exploitation is suspected.
ISSN: 0375-6742

hal-00512409
https://hal.archives-ouvertes.fr/hal-00512409
DOI : 10.1016/j.gexplo.2010.05.004

Éditeur(s) : HAL CCSD CRC Press Taylor & Francis Group
Résumé : aucun
Water-Rock Interaction XIII

hal-00857370
https://hal.archives-ouvertes.fr/hal-00857370

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Properly assessing the extent and magnitude of fault ruptures associated with large earthquakes is critical for understanding fault behavior and associated hazard. Submarine faults can trigger tsunamis, whose characteristics are defined by the geometry of seafloor displacement, studied primarily through indirect observations (e.g., seismic event parameters, seismic profiles, shipboard bathymetry, coring) rather than direct ones. Using deep-sea vehicles, we identify for the first time a marker of coseismic slip on a submarine fault plane along the Roseau Fault (Lesser Antilles), and measure its vertical displacement of ∼0.9 m in situ. We also map recent fissuring and faulting of sediments on the hangingwall, along ∼3 km of rupture in close proximity to the fault's base, and document the reactivation of erosion and sedimentation within and downslope of the scarp. These deformation structures were caused by the 2004 M w 6.3 Les Saintes earthquake, which triggered a subsequent tsunami. Their characterization informs estimates of earthquake recurrence on this fault and provides new constraints on the geometry of fault rupture, which is both shorter and displays locally larger coseismic displacements than available model predictions that lack field constraints. This methodology of detailed field observations coupled with near-bottom geophysical surveying can be readily applied to numerous submarine fault systems, and should prove useful in evaluating seismic and tsunamigenic hazard in all geodynamic contexts.
ISSN: 0012-821X

insu-01557932
https://hal-insu.archives-ouvertes.fr/insu-01557932
https://hal-insu.archives-ouvertes.fr/insu-01557932/document
https://hal-insu.archives-ouvertes.fr/insu-01557932/file/EPSL-2006-escartin.pdf
DOI : 10.1016/j.epsl.2016.06.024

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Rainbow is a dome-shaped massif at the 36°14′N nontransform offset along the Mid-Atlantic Ridge. It hosts three ultramafic-hosted hydrothermal sites: Rainbow is active and high temperature; Clamstone and Ghost City are fossil and low temperature. The MoMARDREAM cruises (2007, 2008) presented here provided extensive rock sampling throughout the massif that constrains the geological setting of hydrothermal activity. The lithology is heterogeneous with abundant serpentinites surrounding gabbros, troctolites, chromitites, plagiogranites, and basalts. We propose that a W dipping detachment fault, now inactive, uplifted the massif and exhumed these deep-seated rocks. Present-day deformation is accommodated by SSW-NNE faults and fissures, consistent with oblique teleseismic focal mechanisms and stress rotation across the discontinuity. Faults localize fluid flow and control the location of fossil and active hydrothermal fields that appear to be ephemeral and lacking in spatiotemporal progression. Markers of high-temperature hydrothermal activity (∼350°C) are restricted to some samples from the active field while a more diffuse, lower temperature hydrothermal activity (<220°C) is inferred at various locations through anomalously high As, Sb, and Pb contents, attributed to element incorporation in serpentines or microscale-sulfide precipitation. Petrographic and geochemical analyses show that the dominant basement alteration is pervasive peridotite serpentinization at ∼160–260°C, attributed to fluids chemically similar to those venting at Rainbow, and controlled by concomitant alteration of mafic-ultramafic units at depth. Rainbow provides a model for fluid circulation, possibly applicable to hydrothermalism at oceanic detachments elsewhere, where both low-temperature serpentinization and magmatic-driven high-temperature outflow develop contemporaneously, channeled by faults in the footwall and not along the detachment fault.
ISSN: 1525-2027

hal-01115281
https://hal.archives-ouvertes.fr/hal-01115281
https://hal.archives-ouvertes.fr/hal-01115281/document
https://hal.archives-ouvertes.fr/hal-01115281/file/Andreani_et_al-2014-Geochemistry%2C_Geophysics%2C_Geosystems.pdf
DOI : 10.1002/2014GC005269

Éditeur(s) : HAL CCSD Chicago, IL : American Medical Association, [2013]-
Résumé : International audience
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ISSN: 2168-6068

Droits : info:eu-repo/semantics/OpenAccess
inserm-01491176
http://www.hal.inserm.fr/inserm-01491176
http://www.hal.inserm.fr/inserm-01491176/document
http://www.hal.inserm.fr/inserm-01491176/file/2017%2C%20Cordel%20-%20main%20characteristics%20of%20zika%20virus%20exanthema%20in%20Guadeloupe.pdf
http://www.hal.inserm.fr/inserm-01491176/file/2017%20Cordel%20-%20main%20characteristics%20of%20zika%20virus%20exanthema%20in%20Guadeloupe-Fig1.pdf

Éditeur(s) : HAL CCSD EDP Sciences
Résumé : Cette communication présente les principaux résultats du projet ExtraFlo sur l'estimation des pluies et crues extrêmes. A partir d'un jeu de données conséquent de plusieurs milliers de stations, une procédure d'inter-comparaison a permis d'évaluer les performances d'une trentaine d'implémentations différentes issues de différentes combinaisons (modèle probabiliste, méthode d'estimation, cadre local / régional / mixte local et régional). Le projet ExtraFlo a permis de mettre en évidence le manque de robustesse des approches basées sur le traitement statistique d'une série de quelques dizaines d'années d'observation. Des alternatives intéressantes existent, basées sur l'exploitation des records de pluie et de débit à l'échelle d'une région, de la collecte de données historiques quand cela est possible, de méthodes de simulation basées sur le couplage d'un générateur d'averses avec un modèle hydrologique pour la transformation des pluies en débit, ou des traces morphologiques laissées par les crues anciennes.
ISSN: 0018-6368

hal-01054313
https://hal.archives-ouvertes.fr/hal-01054313
DOI : 10.1051/1hb/2014010

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Hydrothermal circulation at ultramafic-hosted sites supports a large variety of high-and low-temperature hydrothermal vents and associated ecosystems. The discovery of abundant fossil vesicomyid and thyasirid shell accumulations at the ridge crest, approximately 2.5 km east of the active Rainbow vent field on the Mid-Atlantic Ridge (MAR, 36 degrees 13'N), increased our knowledge regarding the diversity of vent communities at slow spreading ridges. Bivalve molluscs of the family Vesicomyidae were represented by the genus Phreagena. Here we present the first record of this genus in the Atlantic Ocean. This second vesicomyid species known from the MAR, Phreagena sp., was found to be associated with a Thyasira species that is affiliated with T. southwardae (at the Logatchev vent field on the MAR) and with T. vulcolutre (in the Gulf of Cadiz). These two clams have close relationships with seep taxa along the continental margin, and were likely associated with sedimented vent fields. delta O-18 and delta C-13 analyses of the shells suggested that the burrowing bivalve Thyasira could incorporate isotopically light carbon, derived from the oxidation of methane in the sediment, while the signature of Phreagena sp. shells denoted a different carbonate source. C-14 dating of the shells denoted that the hydrothermal activity in the Rainbow area began at least similar to 25.5 kyr BP, which is similar to the model of the hydrothermal vent field distribution that was proposed for the Logatchev hydrothermal site. The results provide new insight regarding the diversity of chemosynthetic fauna on the MAR over geologic time. Ultramafic-hosted, on-axis sedimented vent fields extend the range of habitats for chemosynthetic communities, underlying the need to further explore the geology of these types of environments on slow-spreading ridges and to determine their role in the ecology of deep-sea vent communities.
ISSN: 1525-2027

hal-00523467
https://hal.archives-ouvertes.fr/hal-00523467
https://hal.archives-ouvertes.fr/hal-00523467/document
https://hal.archives-ouvertes.fr/hal-00523467/file/G3-Lartaud-_-al.pdf
DOI : 10.1029/2010GC003079