Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Constraining mantle deformation beneath plate boundaries where plates interact with each other, such as beneath active or halted mountain belts, is a particularly important objective of "mantle tectonics" that may bring a depth extent to the Earth's surface observation. Such mantle deformation can be mapped at scale lengths of several tens of kilometers through the analysis of seismological data and particularly by mapping seismic anisotropy from the splitting analysis of vertically-propagating SKS waves that largely reflect the strain-induced crystal preferred orientations of the rock-forming minerals within the upper mantle. In the present study, we analyse data from approximately 50 broadband seismic stations covering the Western Alps and we provide a coherent picture of upper mantle anisotropy beneath the belt. The large-scale anisotropy pattern is characterized by fast split directions that closely follow the trend of the belt. Moreover, the maximum anisotropy magnitude is not located beneath the internal zones of the belt but instead beneath external units. All suggests that the anisotropy is likely dominated by sublithospheric mantle deformation. We propose that the observed anisotropy pattern can be explained by recent or active mantle flow around the Eurasian slab presently plunging beneath the inner parts of the Alps.
ISSN: 0012-821X

hal-00617828
https://hal.archives-ouvertes.fr/hal-00617828
https://hal.archives-ouvertes.fr/hal-00617828/document
https://hal.archives-ouvertes.fr/hal-00617828/file/Barruol_SKS_Alpes_EPSL2011_hal.pdf
DOI : 10.1016/j.epsl.2010.12.040

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : L’art respire et inspire le monde, si bien qu’il ne peut être appréhendé isolément de son contexte, de son époque. La création contemporaine, quant à elle, par son caractère protéiforme et foisonnant, est le reflet singulier d’une planète devenue multipolaire et où, régulièrement, est mise en crise la notion de frontière. Au même moment, cette création est capable d’inventer des formes inédites, qui, à l’instar des utopies du xviiie siècle, ont pour vocation de construire de nouveaux espaces, de nouvelles contrées, sous l’angle d’un idéal mêlant éthique et esthétique. Dès lors, il convient de souligner sa possible faculté à « artialiser » le monde. Les biennales ou triennales, produits de l’industrie culturelle et par conséquent, sujettes aux effets de la mondialisation, ont rendu particulièrement visibles ces œuvres, en façonnant des territoires, des ar-t-chipels, suffisamment attractifs pour drainer, de fait, des flots de touristes en leur direction. Ce migra-r-teur, trouvant là des zones protégées, pourrait y expérimenter une possible façon d’habiter poétiquement un monde perçu comme inhospitalier.
Art feeds on and inspires the world so that it cannot be appreciated neither on its own nor out of its context. As for contemporary art by its protean character and its multiplicity, it is the spitting image of a planet that has become polarized where the notion of frontier is constantly changing. At the same time, contemporary art is capable of inventing original forms which, following the example of the xviiith century utopias, have the purpose of building new spaces, new territories, from the point of view of an ideal where ethics and aesthetics entertwine. Hence it is advisable to highlight its possible capacity to “artialise” the world. The biennial or triennal events, fruits of the cultural industry and consequently prone to the effects of globalisation, have made those pieces of art particularly visible, by shaping territories, ar-t-chipelagoes, attractive enough to draw, henceforth, flows of tourists in their direction. That migr-art-ist finding in those places, protected areas, could experiment there a potential way of living poetically in a world seen as hostile.
El arte respira e inspira al mundo de modo que no puede ser comprendido sin ser vinculado con su contexto, su época. La creación contemporánea por su parte, por su caracter proteiforme y abundante es el singular reflejo de un planeta que se ha vuelto multipolar donde se debate con frecuencia la noción de frontera. En el mismo momento, esta creación es capaz de inventar formar inéditas, que como las utopias del siglo xviii, tienen como vocación construir nuevos espacios, nuevos parajes en términos de un ideal a la vez ético y estético. Desde entonces, cabe subrayar su posible facultad para « artialiser » al mundo. Las bienales o trienales, productos de la industria cultural y por lo tanto sujetas a los efectos de la globalización han hecho visibles estas obras, al crear territorios, unos ar-te-chipielagos, lo suficientemente atractivos como para atraer a miles de turistas. Ese migrante del arte, al encontrar allí unas zonas protegidas podría experimentar una forma posible de ocupar poéticamente un mundo visto como inhóspito.

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.11291
http://journals.openedition.org/etudescaribeennes/11291

Éditeur(s) : Springer
Résumé : The Var turbidite system is a small sandy system located in the Ligurian Basin. It was deposited during the Pliocene-Quaternary in a flat-floored basin formed during the Messinian salinity crisis. The system was fed through time by the Var and Paillon canyons that connect directly to the Var and Paillon rivers. It is still active during the present sea-level highstand. Two main mechanisms are responsible for gravity-flow triggering in the Var turbidite system: (1) mass-wasting events affect mainly the upper part of the continental slope, in areas where volumes of fresh sediment delivered by rivers are highest, and result from the under-consolidation state of slope sediments and earthquakes, and (2) high-magnitude river floods resulting from melting of snow and convective rainfall during fall and spring seasons, and generating hyperpycnal turbidity currents at river mouths when the density of freshwater transporting suspended particles exceeds that of ambient seawater. Failure- and flood-induced gravity flows are involved through time in the construction of the Var Sedimentary Ridge, the prominent right-hand levee of the Var system, and sediment waves. Processes of construction of both the Var Ridge and sediment waves are closely connected. Sandy deposits are thick and abundant in the eastern (downchannel) part of the ridge. Their distribution is highly constrained by the strong difference of depositional processes across the sediment waves, potentially resulting through time in the individualization of large and interconnected sand bodies.
Geo-Marine Letters (0276-0460) (Springer), 2006-12 , Vol. 26 , N. 6 , P. 361-371

Droits : 2006 Springer
http://archimer.ifremer.fr/doc/2006/publication-2258.pdf
DOI:10.1007/s00367-006-0047-x
http://archimer.ifremer.fr/doc/00000/2258/

Éditeur(s) : HAL CCSD Springer/Terra Scientific Publishing Company
Résumé : International audience
We carried out a detailed paleomagnetic, rock-magnetic, and Thellier paleointensity study of all similar to 3.6 My Pliocene lava flow succession in southern Georgia. An earlier study (Camps et al., 1996) revealed that several consecutive lava flows record an intermediate polarity direction at the base of the section followed by a thick reverse polarity zone. The transitional field was interpreted as an excursion within chron 2Ar or all upper Cochiti-Gilbert reversal. New paleomagnetic data reported here have been obtained from nearby lava successions. In total, about 170 standard paleomagnetic cores belonging to 22 lava flows were collected during the 2005 sample collection campaign. Rock-magnetic experiments showed that the remanence is carried by Ti-poor titanomagnetite in most of the samples. The fraction of grains with multidomain magnetic structure does not seem to be important. Characteristic remanent magnetization was successfully determined oil all samples. The direct correlation with the original (Thoki) sequence, previous preliminary measurements of natural remanent magnetization (Sologashvili, 1986), and field observations allowed us to establish a new magnetic stratigraphy. The lower part of section is characterized by intermediate magnetic polarity followed by thick reversely magnetized lavas. The upper sequence, represented by 18 consecutive flows yielded normal magnetic polarity. The mean paleointensity of the intermediate field is drastically reduced with respect to the post-transitional field strength. Based on all available radiometric ages and new paleomagnetic data, it may be speculated that Gilbert-Gauss (R-N) reversal was recorded at the upper part of sequence. Lower intermediate polarity flows possibly represent a form of precursor of this reversal that is similar to the Matuyama-Brunhes geomagnetic transition.
ISSN: 1343-8832

hal-00413099
https://hal.archives-ouvertes.fr/hal-00413099

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The mantle above a subducting slab is the site of complex interactions between deformation, partial melting, fluid migration and magma transport. To constrain these interactions and their effects on olivine deformation, we analyze microstructures, crystal preferred orientations, and water contents of peridotite xenoliths entrained by andesites of the Avacha volcano, southern Kamchatka arc. These xenoliths are refractory spinel harzburgites that have coarse-grained microstructures with widely spaced subgrain boundaries and sinuous grain boundaries in olivine, consistent with deformation by dislocation creep under low deviatoric stress (< 13 MPa) and with a significant contribution from diffusional processes. Analysis of crystal preferred orientations (CPO) indicates dominant activation of high-temperature, low-stress {0kl}[100] slip systems in olivine and of(100)[001] in orthopyroxene. In most samples, coarse opx crystals, elongated parallel to the lineation, enclose small olivine grains in crystallographic continuity with neighbouring crystals, indicating crystallization of orthopyroxene at the expense of olivine as a result of reactive percolation of Si-rich fluids coeval with the high-temperature deformation. Secondary crystallization of interstitial orthopyroxene led locally to development of opx-rich lenses parallel to the foliation, characterized by a decrease in olivine grain size and dispersion of the olivine CPO without changing the dominant slip systems. Half of the samples also show acicular orthopyroxene aggregates with which is associated a fine-grained matrix composed of rounded strain-free olivine, orthopyroxene, spinel, and rare amphibole crystals. This matrix occurs pervasively along grain boundaries or forms millimeter-scale irregular lenses and anastomosing veinlets that crosscut the coarse crystals and their ductile deformation structures. Both acicular orthopyroxene and the fine-grained matrix are interpreted as resulting from reactive transport of H2O-rich fluids under static conditions, probably in the lithospheric mantle. Infrared analyses show that olivine contains 1-8 center dot 6 ppm by weight of water. These low water contents are similar to those observed in spinel peridotites from other subduction zones and probably record both the low solubility of water in olivine at low pressure and dehydration during exhumation of the xenoliths. Water contents in orthopyroxene are highly variable (25-506 ppm H2O), probably recording spatially heterogeneous interaction with fluids or melts and compositional disequilibrium in the studied samples. Change in the dominant percolation mechanism from porous flow to fracturing suggests cooling, consistent with the low temperatures estimated from pyroxene thermometry (< 800-900 degrees C). The Avacha xenoliths therefore record pervasive deformation of a region of the mantle under asthenospheric conditions, followed by its accretion to the base of the lithosphere, probably as a result of cooling of the mantle wedge. Percolation of Si-rich fluids or hydrous melts is recorded at all stages; this probably enhanced diffusion and lowered deviatoric stresses during ductile deformation, but did not change the dominant slip direction in olivine from [100] to [001].
ISSN: 0022-3530

hal-00456053
https://hal.archives-ouvertes.fr/hal-00456053
DOI : 10.1093/petrology/egp085

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We discuss mantle structure and dynamics under the Gibraltar arc. For that region, a large variety of geodynamic models has been proposed, and there was, up to recently, no consensus on which of these models is the best one to describe the geodynamic situation of the region. The key to distinguishing the different models probably lies in the upper mantle, and we propose two specially adapted seismological techniques that help to distinguish each of the two models that are more frequently invoked. These are, on one hand, the subduction-rollback (SR) model, and on the other, continental delamination or convective removal (CDCR). The first technique that we use is based on observations of dispersed P-wavetrains that are expected for certain ray directions. Observations made on the Gibraltar arc suggest the presence of subducted oceanic lithosphere under the Alboran Sea. The second technique is based on shear-wave splitting of SKS phases, and it allows us to look for the radially-oriented flow that must be present in the mantle beneath the Alboran Sea, for a CDCR mechanism. There are however no indications of any radial flow up to this point. Both approaches therefore suggest that subduction-rollback is the best model to explain the complex geodynamic situation under the region.
ISSN: 0040-1951

hal-01388041
http://hal.univ-reunion.fr/hal-01388041
http://hal.univ-reunion.fr/hal-01388041/document
http://hal.univ-reunion.fr/hal-01388041/file/Bokelmann_Gibraltar_Tphy2011_hal.pdf
DOI : 10.1016/j.tecto.2010.08.004

Éditeur(s) : HAL CCSD Springer-Verlag
Résumé : We provide evidence for a plume-like upwelling beneath the Eifel hotspot, Western Germany, by using teleseismic shear-wave splitting to resolve the anisotropy associated with upwelling flow that is spreading laterally into the asthenosphere. The variation in fast-polarization azimuth we find across the Eifel hotspot is explained by a model of slowly upwelling material that is horizontally being deflected or sheared in a parabolic asthenospheric flow (PAF) pattern toward west-southwest, a direction that correlates with Eurasian absolute plate motion. We suggest that the lack of an age progression for Eifel volcanism, which is expected for a fixed-upwelling model, is a result of (1) sporadic volcanism due to a low excess plume temperature and/or varying crustal stresses that periodically relax and facilitate eruption, and (2) complex upwelling flow pathways and/or Late Tertiary changes in the slow Eurasian plate motion. The success of the PAF model in fitting the data is remarkable given the small number of parameters (four) and the consistency with the plate motion direction determined from geology and/or geodesy. This suggests that a predictable mantle-anisotropy pattern may exist also for other hotspots driven by plume-like upwellings, and that splitting can be a useful diagnostic to differentiate between plume-like and alternative sources for mantle hotspots.
Mantle plumes - a multidisciplinary approach

hal-00407986
https://hal.archives-ouvertes.fr/hal-00407986
DOI : 10.1007/978-3-540-68046-8

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present GPS observations in Morocco and adjacent areas of Spain from 15 continuous (CGPS) and 31 survey-mode (SGPS) sites extending from the stable part of the Nubian plate to central Spain. We determine a robust velocity field for the W Mediterranean that we use to constrain models for the Iberia-Nubia plate boundary. South of the High Atlas Mountain system, GPS motions are consistent with Nubia plate motions from prior geodetic studies. We constrain shortening in the Atlas system to <1.5 mm/yr. 95% confidence level. North of the Atlas Mountains, the GPS velocities indicate Nubia motion with respect to Eurasia, but also a component of motion normal to the direction of Nubia-Eurasia motion, consisting of southward translation of the Rif Mountains in N Morocco at rates exceeding 5 mm/yr. This southward motion appears to be directly related to Miocene opening of the Alboran Sea. The Betic Mountain system north of the Alboran Sea is characterized by WNW motion with respect to Eurasia at 1-2 mm/yr. paralleling Nubia-Eurasia relative motion. In addition, sites located in the Betics north of the southerly moving Rif Mountains also indicate a component of southerly motion with respect to Eurasia. We interpret this as indicating that deformation associated with Nubia-Eurasia plate motion extends into the southern Betics, but also that the Betic system may be affected by the same processes that are causing southward motion of the Rif Mountains south of the Alboran Sea. Kinematic modeling indicates that plate boundary geometries that include a boundary through the Straits of Gibraltar are most compatible with the component of motion in the direction of relative plate motion, but that two additional blocks (Alboran-Rif block, Betic Mountain block), independent of both Nubia and Eurasia are needed to account for the motions of the Rif and Betic Mountains normal to the direction of relative plate motion. We speculate that the southward motions of the Alboran-Rif and Betic blocks may be related to mantle flow, possibly induced by southward rollback of the subducted Nubian plate beneath the Alboran Sea and Rif Mountains.
ISSN: 0264-3707

hal-00475538
https://hal.archives-ouvertes.fr/hal-00475538
DOI : 10.1016/j.jog.2009.10.007

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The Ama Drime range located at the transition between the high Himalayan range and south Tibet is a N-S active horst that offsets the South Tibetan Detachment System (STDS). Within the horst, a paragneissic unit, possibly attributed to the upper Himalayan crystalline series, overly the lower Himalayan crystalline series Ama Drime orthogneissic unit containing large metabasite layers and pods that have experienced pressure >= 1.4 GPa. Combining structural analysis with new and published pressure-temperature (P-T) estimates as well as U-Th/Pb, Ar-39/Ar-40 and (U-Th)/He ages, the P-T-deformation-time (P-T-D-t) paths of the main units within and on both sides of the horst are reconstructed. They imply that N-S normal faults initiated prior to 11 Ma and have accounted for a total exhumation <= 0.6 GPa (22 km) that probably occurred in two phases: the first one until similar to 9 Ma and the second one since 6 to 4 Ma at a rate of similar to 1 mm/yr. In the Ama Drime unit, 1 to 1.3 GPa (37 to 48 km) of exhumation occurred after partial melting since similar to 30 Ma until similar to 13 Ma, above the Main Central Trust (MCT) and below the STDS when these two fault systems were active together. The switch from E-W (STDS) to N-S (Ama Drime horst) normal faulting between 13 and 12 Ma occurs at the time of propagation of thrusting from the MCT to the Main Boundary Thrust. These data are in favor of a wedge extrusion or thrust system rather than a crustal flow model for the building of the Himalaya. We propose that the kinematics of south Tibet Cenozoic extension phases is fundamentally driven by the direction and rate of India underthrusting.
ISSN: 0278-7407

hal-00486405
https://hal.archives-ouvertes.fr/hal-00486405
DOI : 10.1029/2009TC002551

Éditeur(s) : HAL CCSD
Résumé : International audience
Abstract A careful re-examination of the well-known written documents pertaining to the 2,750-year-long historical period of Mount Etna was carried out and their interpretation checked through the high-accuracy archeomagnetic method (>1,200 large samples), combined with the 226Ra-230Th radiochronology. The magnetic dating is based upon secular variation of the direction of the geomagnetic field (DGF) and estimated to reach a precision of  ±40 years for the last 1,200 years, and ±100 to 200 years up to circa 150 B.C. Although less precise, the 226Ra-230Th method provides a unique tool for distinguishing between historic and prehistoric lavas, which in some cases might have similar DGFs. We show that despite the abundance of details on ancient historical eruptions, the primary sources of information are often too imprecise to identify their lava flows and eruptive systems. Most of the ages of these lavas, which are today accepted on the geological maps and catalogues, were attributed in the 1800s on the basis of their morphology and without any stratigraphical control. In fact, we found that 80% of the “historically dated” flows and cones prior to the 1700s are usually several hundreds of years older than recorded, the discrepancies sometimes exceeding a millennium. This is proper the case for volcanics presumed of the “1651 east” (actually ∼1020), “1595” (actually two distinct flows, respectively, ∼1200 and ∼1060), “1566” (∼1180), “1536” (two branches dated ∼1250 and ∼950), “1444” (a branch dated ∼1270), “1408” (lower branches dated ∼450 and ∼350), “1381” (∼1160), “1329” (∼1030), “1284” (∼1450 and ∼700), “1169 or 812” (∼1000) eruptions. Conversely, well-preserved cones and flows that are undated on the maps were produced by recent eruptions that went unnoticed in historical accounts, especially during the Middle Ages. For the few eruptions that are recorded between A.D. 252 and 750 B.C., none of their presumed lava flows shows a DGF in agreement with that existing at their respective dates of occurrence, most of these flows being in fact prehistoric. The cinder cones of Monpeloso (presumed “A.D. 252”) and Mt. Gorna (“394 B.C.”), although roughly consistent magnetically and radiochronologically with their respective epochs, remain of unspecified age because of a lack of precision of the DGF reference curve at the time. It is concluded that at the time scale of the last millennia, Mount Etna does not provide evidence of a steady-state behavior. Periods of voluminous eruptions lasting 50 to 150 years (e.g., A.D. 300–450, 950–1060, 1607–1669) are followed by centuries of less productive activity, although at any time a violent outburst may occur. Such a revised history should be taken into account for eruptive models, magma output, internal plumbing of the volcano, petrological evolution, volcano mapping and civil protection.
Bulletin of Volcanology / Bull Volcanic Eruptions

hal-00315967
https://hal.archives-ouvertes.fr/hal-00315967
DOI : 10.1007/s00445-007-0121-x

Éditeur(s) : Amer Geophysical Union
Résumé : In the Atlantic Ocean, the northward export of warm surface water is compensated by a southward flow of cold North Atlantic Deep Water (NADW). The NADW is transported southward along the American continental margin within the Deep Western Boundary Current (DWBC). Some tracer and float observations have shown that part of the DWBC water flows eastward along the equator. Here we present three meridional velocity sections which give an instantaneous image of the top-to-bottom zonal circulation along the equatorial Atlantic. They reveal the presence of Equatorial Deep Jets (EDJs) between 1 degrees 30'N and 1 degrees 30'S, alternating eastward-westward currents with short vertical scale, surrounded by columns of eastward currents (the Extra Equatorial Jets or EEJs) at 2 degreesN and 2 degreesS. In addition to direct velocity measurements, tracer distributions give indications of water-mass feeding of the EDJs and EEJs by the DWBC.
Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2001-03 , Vol. 28 , N. 5 , P. 819-822

Droits : 2001 AGU
http://archimer.ifremer.fr/doc/00000/10369/9567.pdf
http://archimer.ifremer.fr/doc/00000/10369/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In the southeastern corner of the Tyrrhenian basin, in the central Mediterranean Sea, a tight alignment of earthquakes along a well-defined Benioff zone marks one of the narrowest active trenches worldwide, where one of the last fragment of the former Tethys ocean is consumed. Seismic tomography furnishes snapshot images of the present-day position of this slab, and seismic anisotropy allows to reconstruct the past kinematics of the subduction process. Using seismic anisotropy fast directions as a proxy for the present and past mantle flow, we look backward for the seismic traces of the slab motion through the western-central Mediterranean mantle, from the starting locus of subduction toward its present day position. The result of combining independent data sets provides a coherent pattern of anisotropy that illustrates an example of slab rollback from its initiation point to its present-day position.
ISSN: 0012-821X

hal-01389115
http://hal.univ-reunion.fr/hal-01389115
http://hal.univ-reunion.fr/hal-01389115/document
http://hal.univ-reunion.fr/hal-01389115/file/Lucente_medit_EPSL2006_hal.pdf
DOI : 10.1016/j.epsl.2005.10.041

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Microstructures and crystallographic preferred orientation (CPO) of anorthosite samples interlayered in the upper and lower gabbro sections in the Oman ophiolite were analyzed in this paper. In the anorthosites registering the dynamics of the melt lenses, foliation is flat lying and starts to develop a few meters below the root zone of the sheeted dike complex (RZSDC). Microstructures and CPO of these rocks were developed in response to four different mechanisms: (1) density-controlled settling of plagioclase on the lens floor, (2) deposition of anorthosites related to convection currents, (3) melt compaction, and (4) uncompacted melt accumulation. In these anorthosites, the poles to (010) of plagioclase are parallel to the flow plane of convection, whereas the [100] axes and poles to (001) express the convection flow direction and the axis of convection rolls, respectively. The effect of subsidence of melt lens floor is recorded immediately below the RZSDC and is characterized by the rapid (but progressive) development of dipping foliation and lineation, reflecting the increase of deformation downsection. The degree of foliation and CPO development in the anorthosites is directly related to the distance of the center of the melt lenses before the subsidence starts. Despite the uncertain origin of the anorthosites from the lower gabbro section, all the samples lost the magmatic microstructural characteristics and presently are reequilibrated aggregates. However, they still preserve plagioclase CPO, where some of these patterns present similarities with the anorthosites from the upper gabbro section, but no evidence of intracrystalline deformation under high temperatures.
ISSN: 0278-7407

hal-00617446
https://hal.archives-ouvertes.fr/hal-00617446
DOI : 10.1029/2010TC002697

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This manuscript reports on a novel field experiment carried out on a microtidal beach in Camargue, France. For the first time in the field, a comprehensive description of the groundwater dynamics under sandy beach swash zone is presented. A cross-shore network of 15 buried pressure sensors is combined with terrestrial LiDAR measurements to study the swash-groundwater dynamics. The presented data focus on the decay of a moderate storm which allows to monitor the evolution of the groundwater pressure field in response to the retreat of the swash zone. Both horizontal and vertical head gradients are measured within the porous sand soil to estimate the groundwater flow field using Darcy’s law. Time-averaged analysis demonstrates the presence of a rather consistent groundwater circulation pattern under the swash zone, shifting offshore with the swash zone. The main tendency is an offshore directed flow, with infiltration/exfiltration in the upper/lower parts of the swash zone. Time-resolved analysis highlights the typical groundwater response to swash events which consists mainly of an overall infiltration flow during the bed inundation by the swash tongue, a seaward flow during the swash retreat and, for long backwash events, a localized exfiltration flow under the next incoming uprush.
ISSN: 0309-1708

hal-01412450
https://hal.archives-ouvertes.fr/hal-01412450
DOI : 10.1016/j.advwatres.2016.09.009

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The dynamics of mantle plumes and the origin of their associated swells remain some of the most controversial topics in geodynamics. Here we construct a numerical model of the mantle flow beneath the French Polynesia region. Our study is based on a new regional seismic tomography model, which high resolution allows obtaining information at the scale of plumes. We find excellent correlations between the observed and the modeled dynamic swells, between the modeled flow pattern and the active volcanism and between the buoyancy fluxes obtained from our numerical model and the ones deduced from the swells morphology. These outstanding fits reveal for the first time that a direct link exists between the surface observations and mantle flows.
ISSN: 0094-8276

hal-01236157
http://hal.univ-reunion.fr/hal-01236157
http://hal.univ-reunion.fr/hal-01236157/document
http://hal.univ-reunion.fr/hal-01236157/file/Adam_South_Pacific_Superswell_GRL2010.pdf
DOI : 10.1029/2010GL042534

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We present the results of a paleomagnetic study of seven new volcanic sections (146 flows) from Kerguelen Archipelago. For two of these sections, preliminary (;40;Ar/;39;Ar) ages are reported to aid in the calibration of the paleomagnetic results. The primary contribution of this report, however, is a compilation of these new data with those already published in order to describe statistically the characteristics of the paleomagnetic field as recorded by the Kerguelen flood basalts. In total, 258 paleomagnetic directions sampled at 13 stratigraphic sections through the lava pile are available and span an approximately 5 Ma window: from 25 to 30 Ma. The composite section represents at least 11 polarity zones that are correlated to the reference geomagnetic polarity timescale. Our approach is to investigate the average normal and reversed polarity field directions over this 5 Ma window. We calculated a paleomagnetic pole found to be located at ;λ; = 85.5°N, = 189.3°E (A;95; = 2.3°, K = 16.5, N = 233). This pole is in close agreement with the coeval paleomagnetic poles obtained from different worldwide places when analyzed in the Indo-Atlantic hot spot reference frame. In the statistical analysis we tackle the specific question: Is the secular variation isotropic? This question is directly related to the occurrence of a longitudinal confinement of the virtual geomagnetic poles, which is still a matter of debate among paleomagnetists. By means of statistical tests we show that the paleomagnetic data from Kerguelen agree with an isotropic model for paleosecular variation. Finally, we present adjustments to Camps and Prévot's (1996) statistical model, developed for some Northern Hemisphere latitudes, to the Southern Hemisphere paleomagnetic data from Kerguelen.
ISSN: 0148-0227

hal-00407636
https://hal.archives-ouvertes.fr/hal-00407636
https://hal.archives-ouvertes.fr/hal-00407636/document
https://hal.archives-ouvertes.fr/hal-00407636/file/pcamps-JGR2007.pdf
DOI : 10.1029/2006JB004648

Éditeur(s) : Institut de Ciències del Mar de Barcelona, CSIC
Résumé : Acoustic and core data have recently been collected on the shelf break and the upper part of the slope of the south Aquitaine continental margin. They reveal the major role played by mass-flow gravity processes in deposit erosion and redistribution, modelling of the sea-bed, and transfer of sediment toward the deep-sea. The study region is bounded in the south by the Capbreton canyon. The northern area, which shows a smooth morphology, is characterised by small-scale deformations due to sediment creep or low-amplitude slide processes. The deformations are associated with mini listric-like faults that bound packets of sediments in which the deposit geometry is typical of constructional sediment waves. These sediment waves result from the interaction of depositional and gravity deformation processes. In the southern area, closer to the canyon, wave-like structures are still present but mostly of smaller size. They only result from gravity deformation processes without any evidence of constructional processes. In the vicinity of the Capbreton canyon, the shelf break and upper slope have a much more uneven morphology with sedimentary reliefs, escarpments and depressions directed toward the canyon thalweg. The depressions look like slide scars, and could be the result of regressive slides initiated at the top of the canyon flank. The age of the sliding event responsible for the formation of the depression observed today could be middle to upper Quaternary. Since their formation, these depressions act as conduits that channel the transfer of shelf sediment into the canyon, as demonstrated by the occurrence of a meandering channel on the sea-floor of one depression.
Scientia Marina (0214-8358) (Institut de Ciències del Mar de Barcelona, CSIC), 2006-06 , Vol. 70 , N. 1 , P. 89-100

Droits : 2006 Institut de Ciències del Mar de Barcelona
http://archimer.ifremer.fr/doc/2006/publication-3960.pdf
http://archimer.ifremer.fr/doc/00000/3960/

Éditeur(s) : Université de La Rochelle, Ecole doctorale Gay Lussac
Résumé : The thesis work is part of the very current issue on mass mortality outbreaks affecting Pacific oyster, C. gigas, spat and juveniles and questions about the involvement of pesticides in this phenomenon. The first part of this thesis was devoted to study the effects of pesticides on hemocyte parameters in the Pacific oyster (in vitro and in vivo). The immunomodulator effect of selected pesticides (alone or in mixture) has been explored principally through flow cytometry. The second part concerned the study of the effects of a pesticides mixture on OsHV-1 itself. No direct effects have been reported on the viral particles in presence of the pollutants. Moreover, pesticide effects on Pacific oysters were also explored through experimental pathology assays after treatment of animals with a polluant mixture. Results showed that pesticide treated oysters appeared more susceptible to the viral infection in experimental conditions. The third part concerned the study of autophagy in the Pacific oyster, C. gigas. The publication of the complete genome in 2012 has opened up new possibilities for the study of innate immunity in this species. The study of autophagy for the first time in oysters consisted in a first step in the in silico search for genes involved in this pathway and the corresponding proteins by Western blotting. Then, the role of this important process in innate immunity has been explored through reproduction infections tests with or without modulators of autophagy. Results showed that autophagy appeared as involved in defence mechanisms against viral and bacterial infection in Pacific oysters.
Le travail de thèse s’inscrit dans la problématique très actuelle des mortalités massives de naissain et de juvéniles d’huîtres creuses, C. gigas, et des questionnements autour de l’implication des pesticides dans ce phénomène. La première partie de la thèse a été consacrée à l’étude des effets de pesticides sur les capacités hémocytaires de l’huître creuse (in vitro et in vivo). L’effet immunomodulateur des xénobiotiques sélectionnés (seul ou en mélange) a été exploré principalement au travers de la cytométrie en flux. La deuxième partie de la thèse a concerné l’étude des effets d’un mélange de pesticides sélectionnés sur le virus OsHV-1 et l’infection qu’il induit chez l’huître creuse. Les effets des pesticides sur le virus lui-même ont été évalués. Les expériences réalisées non pas permis de mettre en évidence dans les conditions testées, de dégradation des particules virales en présence des polluants. D’autre part, leurs effets sur les huîtres elles-mêmes ont été explorés après traitement des animaux avec un mélange de pesticides lors d’essais de pathologie expérimentale. Il a ainsi pu être montré que des huîtres préalablement comtaminées par un mélange de pesticides à des concentrations retrouvées dans l’environnement semblaient être plus sensibles à l’infection virale. La troisième partie de la thèse a concerné l’étude de l’autophagie chez l’huître creuse, C. gigas. La publication du génome complet de cette espèce en 2012 a ouvert de nouvelles possibilités pour étudier l'immunité innée. L’étude de l’autophagie réalisée pour la première fois chez l’huître creuse a consisté lors d’une première étape en la recherche in silico de gènes impliqués dans cette voie et des protéines correspondantes par western blotting. Puis, le rôle de ce processus important dans l’immunité innée a été exploré au travers d’essais de reproduction d’infections en présence ou non de modulateurs de l’autophagie. Les résultats obtenus semblent montrer que l’autophagie soit un processus important pouvant être impliqué dans les capacités de défense de l’huître creuse vis-à-vis d’infections virales et bactériennes.

Droits : 2014 Université de La Rochelle
http://archimer.ifremer.fr/doc/00226/33740/32149.pdf
http://archimer.ifremer.fr/doc/00226/33740/

Éditeur(s) : HAL CCSD World Scientific
Résumé : The present paper presents a laboratory experiment of rip current circulations over a moveable bed. The rip current characteristics over four distinct beach morphologies, exhibiting more or less developed nature-like bar-rip morphology,were investigated. For each video run, the same off shore shore-normal waves were generated by the wave maker with the same mean water level in order to study the sensitivity of the rip current characteristics as a function of the beach morphology only. In each case, a 1-hour video run was used to track a large number (~30) of drifters released within the surf zone. Image coordinates were then rectifie d to still water level Cartesian coordinates to compute drifter velocities, mean characteristics and surf zone rete ntion rates. Results show the presence of classic rip current patterns with counter-rotating cells and a relatively narrowoffshore-directed jet with, for three of the situations, a reasonably symmetric shape. Non-surprisingly, it was found that rip current intensity increases with increasing relative depth of the rip channel. The wave-driven circulations were strongly unstable. Computed standard deviation in fl ow intensity and direction provides high resolution information on the spatial variability of the rip current insta bilities with, for instance, highly-pulsating and weakly directionally variable offshore-directed flow in the rip channel. Conversely to what was previously hypothesized in the literature, there was hardly trace of vortices being shed offs hore and drifters exiting the surf zone compartment were not systematically caught by a pulsating jet. The cause for drifter exiting the semi-enclosed surf zone compartment remains, however, elusive and deserves further investigations. The computed surf zone retention rates (~90%) were of the order of those previously observed in the field, with no clear relationship with the mean rip current velocity or relative depth of the rip channel. Further video-runs will have to be analyzed to explore potential explanations
Proceedings of Coastal Dynamics 2009 Impacts of Human Activities on Dynamic Coastal Processes

ISBN : 978-981-4282-46
hal-00854534
https://hal.archives-ouvertes.fr/hal-00854534

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Rheological properties of mantle minerals and rocks at temperatures (T) appropriate to much of Earth's lithosphere have remained poorly constrained, even though past experimental studies on olivine single crystals and polycrystalline aggregates have quantified the high-temperature creep mechanisms (T > 1200 degrees C). Consequently, we have performed deformation experiments on crystals of San Carlos olivine at lower temperatures, from 900 degrees to 1200 degrees C, in triaxial compression along the [101](c) direction. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at differential stresses of 100 to 500 MPa. Several samples were deformed at constant displacement rate and others at constant load, in order to provide insight into possible effects of work-hardening. Under the deformation conditions investigated, little evidence of work-hardening was observed. The data follow a power-law dependence on stress, as in previous high-temperature deformation studies. The samples were, however, considerably weaker than predicted by the experimentally determined high-temperature constitutive equation for olivine crystals of this orientation from the study of Bai et al. (1991). The mechanical behavior correlates instead with the weaker of the two mechanisms (flow laws) that contribute to the high-temperature constitutive equation. Thus, our experiments demonstrate that published high-temperature constitutive equations overestimate the strength of lithospheric mantle and that the transition to low-temperature creep occurs at lower temperatures than previously inferred. Citation: Demouchy, S., S. E. Schneider, S. J. Mackwell, M. E. Zimmerman, and D. L. Kohlstedt (2009), Experimental deformation of olivine single crystals at lithospheric temperatures, Geophys. Res. Lett., 36, L04304, doi: 10.1029/2008GL036611.
ISSN: 0094-8276

hal-00420070
https://hal.archives-ouvertes.fr/hal-00420070
DOI : 10.1029/2008GL036611