Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We provide results of a detailed study of the first peridotite xenoliths of proven mantle origin reported from Bezymyanny volcano in the Klyuchevskoy Group, northern Kamchatka arc. The xenoliths are coarse spinel harzburgites made up mainly of Mg-rich olivine as well as subhedral orthopyroxene (opx) and Cr-rich spinel, and also contain fine-grained interstitial pyroxenes, amphibole and feldspar. The samples are unique in preserving the evidence for both initial arc mantle substrate produced by high-degree melt extraction and subsequent enrichment events. We show that the textures, modal and major oxide compositions of the Bezymyanny xenoliths are generally similar to those of spinel harzburgite xenoliths from Avacha volcano in southern Kamchatka. However, coarse opx from the Bezymyanny harzburgites has higher abundances of light and medium rare earth elements and other highly incompatible elements than coarse opx from the Avacha harzburgites. We infer that (1) the sub-arc lithospheric mantle beneath both Avacha and Bezymyanny (and possibly between these volcanoes) consists predominantly of harzburgitic melting residues, which experienced metasomatism by slab-related fluids or low-fraction, fluid-rich melts and (2) the degrees of metasomatism are higher beneath Bezymyanny. By contrast, xenolith suites from Shiveluch and Kharchinsky volcanoes 50-100 km north of the Klyuchevskoy Group include abundant cumulates and products of reaction of mantle rocks with silicate melts at high melt/rock ratios. The high melt flux through the lithospheric mantle beneath Shiveluch and Kharchinsky may be related to the asthenospheric flow around the northern edge of the sinking Pacific plate; lateral propagation of fluids in the mantle wedge south of the plate edge may contribute to metasomatism in the mantle lithosphere beneath the Klyuchevskoy Group volcanoes.
ISSN: 0377-0273

hal-00941258
https://hal.archives-ouvertes.fr/hal-00941258
DOI : 10.1016/j.jvolgeores.2012.12.022

Éditeur(s) : HAL CCSD PeerJ
Résumé : International audience
The adaptative bleaching hypothesis (ABH) states that, depending on the symbiotic flexibility of coral hosts (i.e., the ability of corals to ''switch'' or ''shuffle'' their algal symbionts), coral bleaching can lead to a change in the composition of their associated Symbiodinium community and, thus, contribute to the coral's overall survival. In order to determine the flexibility of corals, molecular tools are required to provide accurate species delineations and to detect low levels of coral-associated Symbiodinium. Here, we used highly sensitive quantitative (real-time) PCR (qPCR) technology to analyse five common coral species from Moorea (French Polynesia), previously screened using only traditional molecular methods, to assess the presence of low-abundance (background) Symbiodinium spp. Similar to other studies, each coral species exhibited a strong specificity to a particular clade, irrespective of the environment. In addition, however, each of the five species harboured at least one additional Symbiodinium clade, among clades A–D, at background levels. Unexpectedly, and for the first time in French Polynesia, clade B was detected as a coral symbiont. These results increase the number of known coral-Symbiodinium associations from corals found in French Polynesia, and likely indicate an underestimation of the ability of the corals in this region to associate with and/or ''shuffle'' different Symbiodinium clades. Altogether our data suggest that corals from French Polynesia may favor a trade-off between optimizing symbioses with a specific Symbiodinium clade(s), maintaining associations with particular background clades that may play a role in the ability of corals to respond to environmental change. How to cite this article Rouzé et al. (2017), An updated assessment of Symbiodinium spp. that associate with common scleractinian corals from Moorea (French Polynesia) reveals high diversity among background symbionts and a novel finding of clade B.
ISSN: 2167-8359

Droits : info:eu-repo/semantics/OpenAccess
hal-01430294
https://hal-sde.archives-ouvertes.fr/hal-01430294
https://hal-sde.archives-ouvertes.fr/hal-01430294/document
https://hal-sde.archives-ouvertes.fr/hal-01430294/file/Rouze-2017-PeerJ-Updated.pdf
DOI : 10.7717/peerj.2856

Éditeur(s) : Université de Bretagne Occidentale
Résumé : ln Java island, a number of quaternary volcanoes are Iocated in a back-arc position relative to the Sunda arc volcanie axis. These volcanie centers show an important variability in the petrologic composition of their products (potassic calc-alkali, shoshonitie, alkali potassie and alkali u/trapotassie leucitic series).
L'île de Java comporte, à l'arrière de l'axe volcanique de l'arc de la Sonde, un grand nombre de volcans quaternaires dont les laves présentent une grande diversité pétrologique (séries calco-alcalines potassiques, shoshonitiques, alcalines potassiques, alcalines ultrapotassiques à leucite). Ces édifices arrière-arc, mis en place à la faveur de fractures majeures obliques par rapport à l'axe de l'arc, se situent à des distances très variables de la fosse (profondeurs du plan de Benioff comprises entre 200 et 650 km). Le but de ce travail est la caractérisation géochimique (éléments en trace et isotopes Sr-Nd-Pb) des laves arrière-arc de cette région, leur comparaison avec celles des magmas de l'axe de l'arc, et la discussion de l'origine des variations observées.

Droits : UBO
http://archimer.ifremer.fr/doc/00034/14540/11815.pdf
http://archimer.ifremer.fr/doc/00034/14540/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Our understanding of the contribution of interspecific interactions to functional diversity in nature lags behind our knowledge of spatial and temporal patterns. Although two-species mutualisms are found in all types of ecosystems, the study of their ecological influences on other community members has mostly been limited to third species, while their influence on entire communities remains largely unexplored. 2. We hypothesized that mutualistic interactions between two respective ant species and an epiphyte mediate the biological traits composition of entire invertebrate communities that use the same host plant, thereby affecting food webs and functional diversity at the community level. 3. Aechmea mertensii (Bromeliaceae) is both a phytotelm ('plant-held water') and an ant-garden epiphyte. We sampled 111 bromeliads (111 aquatic invertebrate communities) associated with either the ant Pachycondyla goeldii or Camponotus femoratus. The relationships between ants, bromeliads and invertebrate abundance data were examined using a redundancy analysis. Biological traits information for invertebrates was structured using a fuzzy-coding technique, and a co-inertia analysis between traits and abundance data was used to interpret functional differences in bromeliad ecosystems. 4. The vegetative traits of A. mertensii depended on seed dispersion by C. femoratus and P. goeldii along a gradient of local conditions. The ant partner selected sets of invertebrates with traits that were best adapted to the bromeliads' morphology, and so the composition of the biological traits of invertebrate phytotelm communities depends on the identity of the ant partner. Biological traits suggest a bottom-up control of community structure in C. femoratus-associated phytotelmata and a greater structuring role for predatory invertebrates in P. goeldii-associated plants. 5. This study presents new information showing that two-species mutualisms affect the functional diversity of a much wider range of organisms. Most biological systems form complex networks where nodes (e. g. species) are more or less closely linked to each other, either directly or indirectly, through intermediate nodes. Our observations provide community-level information about biological interactions and functional diversity, and perspectives for further observations intended to examine whether large-scale changes in interacting species/community structure over broad geographical and anthropogenic gradients affect ecosystem functions.
ISSN: 0269-8463

hal-00817509
https://hal.archives-ouvertes.fr/hal-00817509

Éditeur(s) : HAL CCSD
Résumé : International audience
Background: Everyone is subject to environmental exposures from various sources, with negative health impacts (air, water and soil contamination, noise...) or with positive effects (e.g. green space). Studies considering such complex environmental settings in a global manner are rare.Aims: We propose to use data mining techniques to create a composite exposure index with a data-driven approach, in view to assess the environmental burden experienced by populations. We illustrate this approach on a large French metropolitan area.Methods: The study was carried out in the Great Lyon area (France, 1,260,348 inhabitants in 2007, 527 km²) at the census block group (BG) scale. Indicators on NO2 annual concentrations, noise levels, proximity to green spaces and to industrial plants, and road traffic were synthetized using Multiple Factor Analysis (MFA), which allows to explore the relations between exposures and BGs without a priori knowledge, and to synthetize indicators of different types. Hierarchical clustering was then used to create BG classes. Results: The four first components of the MFA explained respectively 23, 14, 13 and 12% of the total variance. Clustering in 3 classes group: 1) BGs far from industries, greener and with less noise and air pollution than the average; 2) BGs close to industries with less green spaces and air pollution than the average; and 3)BGs far from industries but with higher levels of noise, air pollution and traffic. Greater numbers of classes were tested in order to assess a variety of clustering.Conclusions: We present a data driven approach using data mining techniques, which seem overlooked for cumulative exposure assessment in complex environmental settings. Although it cannot be applied directly for risk or health effect assessment, the resulting index can help to identify hot spots of cumulative exposure, to prioritize urban policies or to compare the environmental burden across study areas in an epidemiological framework.
Environment and Health – Bridging South, North, East and West. Conference of ISEE, ISES and ISIAQ.
Basel, Switzerland

hal-01432884
https://hal.archives-ouvertes.fr/hal-01432884
https://hal.archives-ouvertes.fr/hal-01432884/document
https://hal.archives-ouvertes.fr/hal-01432884/file/Poster_2013_ISEE_20130711.pdf

Éditeur(s) : HAL CCSD
Résumé : International audience
Pollen records, marine faunal associations and stable isotope compositions of sediments from Rhodes, Greece, have been determined to track environmental changes in the eastern Mediterranean during the Early and Middle Pleistocene. A detailed chronostratigraphic curve, based on magnetostratigraphic data, was obtained by correlating pollen spectra with the Mediterranean oxygen isotopic curve of Ocean Drilling Program Site 975. Five sedimentary sequences that correspond to marine oxygen isotope stage (MIS) 31–27 and to MIS 20–17 have been investigated in the confined Tsampika microbasin. High-amplitude Pinus variations confirm glacio-eustatic changes deduced from changes in marine faunal associations and sedimentary depositional environments. Reflecting climatic cycles identified in the marine carbonate oxygen isotope record, eight vegetation successions (characterized by the dominance first of mesothermic elements, then of mid- and high-altitude elements with Pinus, and ending with maxima in herb and steppe elements) have been documented. Most of them were probably driven by changes in insolation occurring in high northern latitudes (obliquity impact) during the late Early Pleistocene and early Middle Pleistocene.
Journal of the Geological Society, London

hal-00470360
https://hal.archives-ouvertes.fr/hal-00470360

Éditeur(s) : HAL CCSD Wiley
Résumé : Question: To establish a habitat classification based on functional group co-occurrence that may help the drawing up of conservation plans. Location: Riverine forest fragments in the Grand-duché de Luxembourg, Europe. Methods: Forest fragments were surveyed for their abundance of vascular plants. These were clustered into emergent groups according to 14 life-traits related 10 plant dispersal, establishment and persistence. Forest fragments were classified according to similar distribution of the identified emergent groups. Environmental factors were related to the emergent group richness in each forest type using generalized linear models. Results: Contrary to former species centred classification, only two groups of forests, each with clearly different emergent group composition and conservation requirements. Were detected: (1) swamp forests characterized by anemogamous perennials, annuals and hydrochorous perennials and (2) moist forests characterized by barochorous perennials, small geophytes and zoochorous phanerophytes. From a conservation point of view, priority should he given to large swamp forest with intact flooding regimes his is in accordance with the high wind and water dispersal capacities of their typical emergent groups. For the moist forests. conservation priorities should he high forest connectivity and historical continuity since dispersal and establishment of their characteristic emergent groups arc highly limited. Conclusions: The described methodology, situated at an intermediate integration level between the individual species and whole community descriptors. takes advantage of both conservation plans built for single species and the synthetic power of bread ecological measures.
ISSN: 1402-2001

hal-01031884
https://hal.archives-ouvertes.fr/hal-01031884

Éditeur(s) : HAL CCSD European Geosciences Union
Résumé : International audience
Measurements of branch xylem density, D_x, were made for 1466 trees representing 503 species, sampled from 80 sites across the Amazon basin. Measured values ranged from 240 kg m^?3 for a Brosimum parinarioides from Tapajos in West Pará, Brazil to 1130 kg m^?3 for an Aiouea sp. from Caxiuana, Central Pará, Brazil. Analysis of variance showed significant differences in average D_x across the sample plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that geographic location and plot accounted for 33% of the variation with species identity accounting for an additional 27%; the remaining "residual" 40% of the variance accounted for by tree to tree (within species) variation. Variations in plot means, were, however, hardly accountable at all by differences in species composition. Rather, it would seem that variations of xylem density at plot level must be explained by the effects of soils and/or climate. This conclusion is supported by the observation that the xylem density of the more widely distributed species varied systematically from plot to plot. Thus, as well as having a genetic component branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing and in a predictable manner. Exceptions to this general rule may be some pioneers belonging to Pourouma and Miconia and some species within the genera Brosimum, Rinorea and Trichillia which seem to be more constrained in terms of this plasticity than most species sampled as part of this study.
ISSN: 1810-6277

hal-00298004
https://hal.archives-ouvertes.fr/hal-00298004
https://hal.archives-ouvertes.fr/hal-00298004/document
https://hal.archives-ouvertes.fr/hal-00298004/file/bgd-5-2003-2008.pdf

Éditeur(s) : HAL CCSD IOP Publishing
Résumé : We present the results of an inter-laboratory comparison of EPMA analysis at low voltage (5-6 kV) of three monophasic alloy steel samples. The aim of the work was to obtain an estimate of the present situation of low-voltage analysis of steel and identify needs for improvement. EPMA analyses of the samples were conducted by seven participant groups using electron microprobes and scanning electron microscopes of different kind, equipped with wavelength- and/or energy-dispersive X-ray spectrometers, and employing their own methodology of analysis. The results using WDS showed essentially an underestimation of the Cr contents, with relative deviations from the reference values ranging from -0.7 % to -17 %, and an overestimation of Fe and Ni, with relative deviations from the reference composition ranging from -4 % to +30 %, and from +14 % to +42 %, respectively. The relative deviations obtained by using EDS showed larger scatter, ranging from -16 % to +54 % for Cr, -0.4 % to +66 % for Fe and from +13 % to +90 % for Ni. Reasons for the differences observed and the scatter of results are discussed.
ISSN: 1757-8981

hal-00813999
https://hal.archives-ouvertes.fr/hal-00813999
DOI : 10.1088/1757-899X/32/1/012014

Éditeur(s) : Gauthier-Villars
Résumé : The mangroves of Senegal are limited to the inlet of the Casamance - a river with very low discharge - and to the Sine-Saloum. The mineralogical and geochemical analysis of sediments (derived from 30 deep bore-holes) shows the thickness of the mangrove substrate, which overlies the continental terminal formation. Kaolinite and smectite account for over 90% of the clay fraction. The former is derived from the continental terminal whereas the latter is of marine origin. The chemical composition of the mangrove sediments is remarkably stable and clays play an overwhelming role in the preservation of organic matter and pyrite. Since 1968, a drought in Senegal has caused an important increase in the salinity levels of streams and water-tables; a considerable modification of vegetation zones in the Casamance, especially manifest in the extension of bare flats locally known as "tannes" at the expense of mangroves and marked changes in the morphology and geochemistry of mangrove soils. Compared to most mangrove areas in the humid tropics, mangroves in Senegal are characterized by a very fragile equilibrium.
Oceanologica Acta, Special issue (0399-1784) (Gauthier-Villars), 1982

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00246/35744/34252.pdf
http://archimer.ifremer.fr/doc/00246/35744/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
ISSN: 0098-0331

hal-01083748
https://hal-agroparistech.archives-ouvertes.fr/hal-01083748
DOI : 10.1007/s10886-009-9673-x

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : Traditional measures of diversity, namely the number of species as well as Simpson's and Shannon's indices, are particular cases of Tsallis entropy. Entropy decomposition, i.e. decomposing gamma entropy into alpha and beta components, has been previously derived in the literature. We propose a generalization of the additive decomposition of Shannon entropy applied to Tsallis entropy. We obtain a self-contained definition of beta entropy as the information gain brought by the knowledge of each community composition. We propose a correction of the estimation bias allowing to estimate alpha, beta and gamma entropy from the data and eventually convert them into true diversity. We advocate additive decomposition in complement of multiplicative partitioning to allow robust estimation of biodiversity.
ISSN: 1932-6203

hal-01189953
https://hal.archives-ouvertes.fr/hal-01189953
DOI : 10.1371/journal.pone.0090289
PRODINRA : 259795
PUBMED : 24603966

Éditeur(s) : HAL CCSD Wiley
Résumé : 1. Niche theory proposes that species differences underlie both coexistence within communities and the differentiation in species composition among communities via limiting similarity and environmental filtering. However, it has been difficult to extend niche theory to species-rich communities because of the empirical challenge of quantifying niches for many species. This has motivated the development of functional and phylogeny-based approaches in community ecology, which represent two different means of approximating niche attributes. 2. Here, we assess the utility of plant functional traits and phylogenetic relationships in predicting community assembly processes using the largest trait and phylogenetic data base to date for any set of species-rich communities. 3. We measured 17 functional traits for all 4672 individuals of 668 tree species co-occurring in nine tropical rain forest plots in French Guiana. Trait variation was summarized into two ordination axes that reflect species niche overlap. 4. We also generated a dated molecular phylogenetic tree based on DNA sequencing of two plastid loci (rbcL and matK) comprising 97% of the individuals and 91% of the species in the plots. 5. We found that, on average, co-occurring species had greater functional and, to a lesser extent, phylogenetic similarity than expected by chance. 6. We also found that functional traits and their ordination loadings showed significant, albeit weak, phylogenetic signal, suggesting that phylogenetic distance provides pertinent information on niche overlap in tropical tree communities. 7. Synthesis. We provide the most comprehensive examination to date of the relative importance of environmental filtering and limiting similarity in structuring tropical tree communities. Our results confirm that environmental filtering is the overriding influence on community assembly in these species-rich systems.
ISSN: 0141-6707

hal-01032423
https://hal.archives-ouvertes.fr/hal-01032423
DOI : 10.1111/j.1365-2745.2012.01966.x

Résumé : Le cycle biologique du principal stock de crevettes pénéïdes (Penaeus subtilis) exploité sur le plateau continental guyanais est court (18 mois environ). Les variabilités intra et inter annuelles de l'abondance des individus appartenant aux différentes composantes des premières phases du cycle (larves, post-larves, juvéniles) sont considérées comme très fortes, ce phénomène étant exacerbé par le double changement de milieu au cours du cycle, passage d'un habitat en eau salée à celui en eau douce, puis retour au premier. La pêcherie de la flottille crevettière guyanaise est ainsi basée sur un stock au renouvellement rapide et variable, aussi l'optimisation de sa gestion implique une meilleure compréhension des mécanismes de recrutement des crevettes et notamment leur facteurs de variation. Ainsi, depuis octobre 1992 une étude est conduite pour analyser ces mécanismes de recrutement. Elle s'intègre dans un programme de coopération régionale entre l'IFREMER et le Ministère de l'Agriculture, de l'Elevage et des Pêches du Surinam financé par des fonds FEDER et du FIC, et elle est menée par l'IFREMER dans la Zone Economique Exclusive française et par le laboratoire du Département des pêches du Surinam sur le plateau surinamien. Le programme prévoit une série de huit campagnes en mer qui seront conduites en parallèle par chacun des deux laboratoires Français et Surinarnien sur les plateaux de Guyane (campagnes RESUBGUY) et du Surinam (campagnes RESUBSUR) afin d'analyser le phénomène de recrutement sur la plus large échelle possible d'observation (plateau guyano-surinamien). Deux campagnes annuelles ont été programmées pour chaque pays, en mai et en octobre. La périodicité de ces campagnes est fonction des résultats des travaux conduits par l'IFREMER et l'ORSTOM sur la phase pré-recrutée de Penaeus subtilis qui ont mis en évidence deux principales périodes annuelles distinctes de recrutement (avril-mai; septembre-octobre). Cette campagne est la quatrième de la série initiée en octobre 1992. L'étude n'est pas limitée à l'examen des seules captures de crevettes Penaeus subtilis, puisqu'elle incluse également l'analyse de la composition des prises accessoires des crevettiers. Les "by-catches" considérées dans ce travail sont surtout représentées par la crevette "sea-bob", Xiphopenaeus kroyeri, ainsi que par les principales espèces de poissons d'intérêt commercial (ou ayant une forte probabilité de le devenir dans un futur proche). Enfin, une attention particulière a également été portée sur les captures accidentelles de tortues marines afin d’en estimer l’importance réelle.

Droits : 1994 Ifremer
http://archimer.ifremer.fr/doc/00076/18750/16321.pdf
http://archimer.ifremer.fr/doc/00076/18750/

Éditeur(s) : Elsevier
Résumé : Sediment cores acquired in 2004 off the Rhone prodelta show consistent anomalous methane concentrations of up to 87,440 ppm. Methane compositional and isotopic data support a biogenic origin, although there are a few sites that show strongly depleted delta C-13 values (-53%o PDB) suggesting a mixed source for the gas (biogenic and thermogenic). Anomalous methane concentrations (samples with more than 90 ppm) are discussed and integrated with organic carbon data, sedimentary rates and ADCP profiles. Highest gas concentrations were found directly off the river mouth (20-40 m water depth) and where the IFREMER models point to the thickest accumulation (> 2 m) in response to the Rhone flood event. In areas unaffected by the high flux of organic matter and rapid/thick flood deposition, or in between flood events, the conditions for methanogenesis and gas accumulation have not been met; in these areas, the physical and biological reworking of the surficial sediment may effectively oxidize and mineralize organic matter and limit bacterial methanogenesis in the sub-surface. We propose that in the Rhone prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried, effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial.
Marine Geology (0025-3227) (Elsevier), 2006-12 , Vol. 234 , N. 1-4 , P. 215-231

Droits : 2006 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2006/publication-2396.pdf
DOI:10.1016/j.margeo.2006.09.005
http://archimer.ifremer.fr/doc/00000/2396/

Éditeur(s) : HAL CCSD Elsevier
Résumé :  
Tree species-rich tropical rainforests are characterized by a highly variable quality of leaf litter input to the soil at small spatial scales. This diverse plant litter is a major source of energy and nutrients for soil microorganisms, particularly in rainforests developed on old and nutrient-impoverished soils. Here we tested the hypothesis that the variability in leaf litter quality produced by a highly diverse tree community determines the spatial variability of the microbial respiration process in the underlying soil. We analyzed a total of 225 litter-soil pairs from an undisturbed Amazonian rainforest in French Guiana using a hierarchical sampling design. The microbial respiration process was assessed using substrateinduced respiration (SIR) and compared to a wide range of quality parameters of the associated litter layer (litter nutrients, carbon forms, stoichiometry, litter mass and pH). The results show that the variability of both litter quality and SIR rates was more important at large than at small scales. SIR rates varied between 1.1 and 4.0 mg g_1 h_1 and were significantly correlated with litter layer quality (up to 50% of the variability explained by the best mixed linear model). Total litter P content was the individual most important factor explaining the observed spatial variation in soil SIR, with higher rates associated to high litter P. SIR rates also correlated positively with total litter N content and with increasing proportions of labile C compounds. However, contrary to our expectation, SIR rates were not related to litter stoichiometry. These data suggest that in the studied Amazonian rainforest, tree canopy composition is an important driver of the microbial respiration process via leaf litter fall, resulting in potentially strong plant-soil feedbacks. .
ISSN: 0038-0717

hal-01032139
https://hal.archives-ouvertes.fr/hal-01032139
DOI : 10.1016/j.soilbio.2011.01.018

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present an integrated study of geochemistry, petrofabrics and seismic properties of strongly sheared eclogites from the Chinese Continental Scientific Drilling (CCSD) project in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. First, geochemical data characterize diverse protoliths of the studied eclogites. The positive Eu- and Sr-anomalies, negative Nb anomaly and flat portion of heavy rare earth elements in coarse-grained rutile eclogites (samples B270 and B295) suggest a cumulate origin in the continental crust, whereas the negative Nb anomaly and enrichment of light rare earth elements in retrograde eclogites (samples B504, B15 and B19) imply an origin of continental basalts or island arc basalts. Second, P-wave velocities (V-p) of three typical eclogite samples were measured under confining pressures up to 500 MPa and temperatures to 700 degrees C. At 500 MPa and room temperature, the mean V-p reaches 8.50-8.53 km/s in samples B270 and B295 but drops to 7.86 km/s in sample B504, and the P-wave anisotropy changes from 1.7-2.7% to 5.5%, respectively. The pressure and temperature derivatives of V-p are larger in the retrograde eclogite than in fresh ones. Third, the electron backscatter diffraction (EBSD) measurements of the eclogites reveal random crystal preferred orientation (CPO) of garnet and pronounced CPO of omphacite, which is characterized by a strong concentration of [001]-axes sub-parallel to the lineation and of (010)-poles perpendicular to the foliation. The asymmetric CPO of omphacite in sample B270 recorded a top-to-the-south shear event during subduction of the Yangtze plate. The calculated fastest V-p is generally sub-parallel to the lineation, but a different deformation environment during exhumation could form second-order variations in omphacite CPO and affect the V-p distribution in eclogites (e.g., the fastest V-p is at similar to 35 degrees from the foliation in sample 13295). Comparison between measured and calculated seismic properties indicates that the CPO of omphacite controls the seismic anisotropy of eclogites at high pressure, and compositional layering and retrograde minerals will increase the anisotropy. Calculated P-wave velocities agree well with velocities measured at 500 MPa and room temperature for fresh eclogites, but much higher than those of retrograde eclogite. As a case study, the laboratory-derived V-p-P and V-p-T relationships were used to estimate P-wave velocities of eclogites and peridotites beneath the Western Superior Province, Canada. The results indicate that besides the fabric-induced anisotropy, the direction dependence of pressure and temperature derivatives of V-p can significantly increase seismic anisotropy of eclogites with depth, which results in eclogites being an important candidate for the seismic anisotropy in the upper mantle. Due to their very high density and velocity, garnet-rich eclogites within peridotite could be detected in seismic reflections in subduction zones.
ISSN: 0040-1951

hal-00463512
https://hal.archives-ouvertes.fr/hal-00463512
DOI : 10.1016/j.tecto.2008.09.027

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Melting experiments were performed on a silica-rich peridotite composition at 10-17 GPa to determine majoritic garnet-melt partition coefficients (D) for major and trace elements. Our results show that D for many elements, including Na, Sc, Y and rare earth elements (REE), varies significantly with increasing pressure or proportion of majorite component. Lu and Sc become incompatible at 17 GPa, with D decreasing from 1.5 at 10 GPa to 0.9 at 17 GPa. As predicted from lattice strain, log D for isovalent cations entering the large site of majoritic garnet exhibits a near-parabolic dependence on ionic radius. Our data are used to refine a previously published predictive model for garnet-melt partitioning of trivalent cations, which suffered from a lack of calibration in the 10-20 GPa range. Our results suggest that Archean Al-depleted komatiites from Barberton (South Africa) may have been generated by partial melting of dry peridotite at depths between 200 and 400 km. We also speculate that transition zone diamonds from Kankan (Guinea), which contain inclusions of majoritic garnet, may have formed from the partial reduction of CO2-rich magmas that subsequently transported them to the surface. This hypothesis would provide an explanation for the REE patterns of majoritic garnet trapped within these diamonds, including Eu anomalies. Finally, we show that segregation of majoritic garnet-bearing cumulates during crystallisation of a deep Martian magma ocean could lead to a variety of Lu/Hf and Sm/Nd ratios depending on pressure, leading to a range of ε143Nd and ε176Hf isotope signatures for potential mantle sources of Martian rocks.
ISSN: 0024-4937

hal-00767567
https://hal.archives-ouvertes.fr/hal-00767567
DOI : 10.1016/j.lithos.2012.06.013

Éditeur(s) : HAL CCSD Springer-Verlag Berlin Heidelberg
Résumé : International audience
The main biological function of reaction wood is to act as " muscle " for trees, enabling them to control their posture. The key property to achieve this function is the development of high mechanical stress during the formation of reaction wood cells, called " maturation strains ". Actually, reaction wood formation is basically the asymmetric formation of wood around the tree circumference, with higher maturation strains on the side where reaction wood is formed than on the opposite side. This asymmetry enables stems to bend upward or to compensate for the downward bending induced by gravity. At the cross section level, the performance in this biological function is linked not only to the magnitude of this asymmetry but also to an effect of the cross-sectional size (diameter) of the stem. Eccentric growth and variations in wood mechanical stiffness are second order effects that can modify this performance. Differences in maturation strains between reaction and non-reaction woods are related to their specific cell wall structure and composition. The swelling of the cell wall matrix during maturation and the effect of microfibril angle explain the differences in maturation strains between normal and compression wood. However, this mechanism fails in explaining the high maturation shrinkage of tension wood, and several hypotheses at the molecular levels are still under debate. How trees perceive their gravitational disequilibrium is also an open question for physiologists. Integrative biomechanical modelling (from the polymer level to the cell wall, cross section and whole tree levels) enables defining key variables that explain the performance of reaction wood as a system that insures the stem motricity. Maturation strains can be precisely measured only in recently formed wood at the tree surface, but their changes during the whole tree life can also be estimated by retrospective dendrochronological analysis through structural markers of reaction wood. Lastly, wood in living trees ensures general storage, defence, vascular and skeletal functions, that ask general questions about synergies and trade-offs as the structural characteristics of reaction wood can affect all these functions.
The Biology of Reaction Wood

ISBN : 978-3-642-10813-6
hal-01452085
https://hal.archives-ouvertes.fr/hal-01452085
https://hal.archives-ouvertes.fr/hal-01452085/document
https://hal.archives-ouvertes.fr/hal-01452085/file/Chap_Gril_al_Biomechanical_action_biological_functions_2014.pdf

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : 9 pages
International audience
Potentially hazardous asteroids and comets have hit Earth throughout its history, with catastrophic consequences in the case of the Chicxulub impact. Here we reexamine one of the mechanisms that allow an impact to have a global effect—the release of climate-active gases from sedimentary rocks. We use the SOVA hydrocode and model ejected materials for a sufficient time after impact to quantify the volume of gases that reach high enough altitudes (> 25 km) to have global consequences. We vary impact angle, sediment thickness and porosity, water depth, and shock pressure for devolatilization and present the results in a dimensionless form so that the released gases can be estimated for any impact into a sedimentary target. Using new constraints on the Chicxulub impact angle and target composition, we estimate that 325 ± 130 Gt of sulfur and 425 ± 160 Gt CO2 were ejected and produced severe changes to the global climate.
ISSN: 0094-8276

hal-01639659
https://hal.archives-ouvertes.fr/hal-01639659
DOI : 10.1002/2017GL074879