Éditeur(s) : HAL CCSD Springer-Verlag
Résumé : The seismology is the most effective method to explore the Structure of subduction zones to great depth. The distinguishing feature of the mantle in the subduction regions is the presence of hydrated phases, which transport water into the Earth's interior and release it with dramatic local consequences, triggering earthquakes and melting. The seismological detection of these hydrous phases and geo-dynamic interpretation of flow in the hydrous mantle depend on knowledge of the anisotropic elastic properties and the characteristics of the wave propagation in anisotropic media. In this paper we briefly recall the distinguishing features of anisotropic wave propagation and the observable parameters. We suggest the Vp/Vs ratio is a physically sound parameter than can be observed by seismology in anisotropic regions of the Earth, whereas the Poisson's ratio, which is often quoted, is not directly observable and does not correspond to the characteristics of wave propagation in an anisotropic or isotropic medium. We report for the first time the ratios of Vp/Vs1 and Vp/Vs2, where Vs1 is the fastest and Vs2 slowest S-wave velocities of an anisotropic media. We present the current knowledge of the anisotropic seismic properties of hydrous minerals in the upper mantle, transition zone, and lower mantle that are stable along low temperature geotherms associated with subduction, and identify which minerals are likely to influence seismological observations because they have very high volume fractions, or very high anisotropies, or both of these.;In the upper mantle antigorite and talc are exceptionally anisotropic (Vp 71% Vs 68% and Vp 65%, Vs 68%, respectively) and chlorite is also very anisotropic for S-waves (Vp 35%, Vs 76%). Comparatively less anisotropic are hornblende (Vp 27%, Vs 31%), used as proxy for tremolite in subduction zones, and clinohumite (21.8%, Vs 15.9%). Brucite at 4 GPa (Vp 26.5%, Vs 30.9%) and the dense hydrogen magnesium silicate (DHMS) phase A at 9GPa (Vp 9.3%, Vs 17.6%) are the only hydrous minerals stable in the upper mantle that have had their elastic properties measured at in situ mantle pressures. Except for the phase A, all these minerals are more anisotropic than olivine for at least one parameter (Vp, Vs, Vp/Vs1, or Vp/Vs2). In the transition zone the major phases hydrous wadsleyite and ringwoodite C have moderate to weak anisotropies (Vp 16.3%, Vs 16.5%, and Vp 1.9%, Vs 4.4%, respectively). The DHMS Superhydrous B has a moderate anisotropy (Vp 6.9%, Vs 11.6%). At greater depth the DHMS phase D Lit 24 GPa (Vp 10.8%, Vs 18.0%) is the only hydrous phase that can transport hydrogen from the transition zone into the lower mantle. The phase D is more anisotropic for S than P waves like many of the hydrous phases. From these data it is clear that hydrous phases are in general very anisotropic. However, pressure can play a strong role in reducing anisotropy. It is the case for brucite and talc, in which increasing pressure from ambient to 4 GPa reduces the anisotropy by about 50% for both P and S waves. In contrast, the anisotropy of the DHMS phase A does not change significantly with pressure.;Our picture of the seismic anisotropy of hydrated minerals remains incomplete; the elastic properties of many have not been measured even at ambient conditions (e.g., 10 angstrom phase and phase E) or not measured in their true elastic symmetry (e.g., clinochlore). The majority of hydrous minerals have not been measured at high pressure. and none related to hydrated mantle have been measured at elevated temperature. We have shown in the few cases where hydrous minerals have been measured as a function of pressure, that this variable has an important effect oil the velocity distribution and in most cases reduces the degree of anisotropy, hence we Would expect seismic anisotropy to play a key role in the determination of the shallow structure of subduction zones in the upper mantle.
Subduction zone geodynamics

hal-00420893
https://hal.archives-ouvertes.fr/hal-00420893

Éditeur(s) : Oxford Univ Press
Résumé : In subduction zones, melting and dehydration of the subducted slab introduce material into the mantle wedge and modify its chemical and isotopic composition. As a consequence, island arc lavas differ significantly from mid-ocean ridge basalts and ocean island basalts. In some arcs, the composition of lavas is strongly influenced by the sedimentary material introduced with the slab; in others, magma composition is mainly affected by aqueous fluids released by the slab. The Lesser Antilles arc is known for its extreme continental-crust-like signature but for some Lesser Antilles lavas subducted sediments are barely involved and enrichment in fluid-mobile elements (Ba, U, Sr, Pb, etc.) is the dominant feature. Here we evaluate whether La/Sm is a quantitative proxy of sediment involvement in volcanic arcs, and we relate dehydration and melting processes to the temperature and pressure conditions of the slab. We use Martinique as a case study because in this island both dehydration and sediment melting fingerprints coexist. We measured major and trace elements for about 130 age-constrained samples, carefully chosen to cover all volcanic phases of Martinique (25 Ma to present). Using these results we demonstrate that: (1) weathering does not modify the La/Sm ratio; (2) fractional crystallization of amphibole and/or garnet does not increase La/Sm by more than 20%; (3) rare earth element transfer from wall-rock to magma during fractionation is not significant; (4) melting of the mantle source increases La/Sm by only about 20%. As a consequence, we show that the proportion of slab sediment incorporated in the mantle wedge controls the La/Sm ratio of the source. The observed correlations between La/Sm and Nd and Hf isotopic compositions indicate that the effect of sediment addition is the overwhelming factor: La/Sm is a good proxy for slab sediment proportion in Martinique. We observe a geographical gradient between slab dehydration and sediment melting on the island. Whereas lavas located on the western side of the island display a clear sedimentary input in their source, lavas located on the eastern side of the island, closer to the trench, are clearly influenced by dehydration of the subducted slab. In addition, the aqueous fluids clearly come from the subducted basalt and they did not interact with the overlying sediments. The influence of sediment added to the source of the magmas increases from the eastern part to the western part of the island. We relate this geographical change to the pressure and temperature conditions at the slab surface. Sediments probably cross their solidus under Martinique and hydrous melting is triggered. Finally, we show that under all volcanic arcs where the signature of sediments overwhelms the signature of fluids, the slab surface reaches P-T conditions that allow the subducted sediments to melt. Inversely, under most volcanic arcs where the signal of aqueous fluids dominates over sediment melts, the subducted slab is not hot enough for the sedimentary pile to melt.
Journal Of Petrology (0022-3530) (Oxford Univ Press), 2012-12 , Vol. 53 , N. 12 , P. 2441-2464

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00113/22392/20234.pdf
DOI:10.1093/petrology/egs055
http://archimer.ifremer.fr/doc/00113/22392/

Éditeur(s) : HAL CCSD Cambridge University Press (CUP)
Résumé : International audience
Upper Triassic volcanic and sedimentary rocks of the Mamonia Complex in southwestern Cyprus are exposed in erosional windows through the post-Cretaceous cover, where the Mamonia Complex is tectonically imbricated with the Troodos and Akamas ophiolitic suites. Most of these Upper Triassic volcanic rocks have been considered to represent remnants of Triassic oceanic crust and its associated seamounts. New Nd and Pb isotopic data show that the whole Mamonia volcanic suite exhibits features of oceanic island basalts (OIB). Four rock types have been distinguished on the basis of the petrology and chemistry of the rocks. Volcanism began with the eruption of depleted olivine tholeiites (Type 1) and oceanic island tholeiites (Type 2) associated with deep basin siliceous and/or calcareous sediments. The tholeiites were followed by highly phyric alkali basalts (Type 3) interbedded with pelagic Halobia-bearing limestones or white reefal limestones. Strongly LREE-enriched trachytes (Type 4) were emplaced during the final stage of volcanic activity. Nd and Pb isotopic ratios suggest that tholeiites and mildly alkali basalts derived from partial melting of heterogeneous enriched mantle sources. Fractional crystallization alone cannot account for the derivation of trachytes from alkaline basalts. The trachytes could have been derived from the partial melting at depth of mafic material which shares with the alkali basalts similar trace element and isotopic compositions. This is corroborated by the rather similar isotopic compositions of the alkali basalts and trachytes. The correlations observed between incompatible elements (Nb, Th) and {varepsilon}Nd and Pb isotopic initial ratios suggest that the Mamonia suite was derived from the mixing of a depleted mantle (DMM) and an enriched component of High µ (µ = 238U/204Pb, HIMU) type. Models using both Nd and Pb isotopic initial ratios suggest that the depleted tholeiites (Type 1) derived from a DMM source contaminated by an Enriched Mantle Type 2 component (EM2), and that the oceanic tholeiites (Type 2), alkali basalts (Type 3) and trachytes (Type 4) were derived from the mixing of the enriched mantle source of the depleted tholeiites with a HIMU component. None of the Mamonia volcanic rocks show evidence of crustal contamination. The Upper Triassic within-plate volcanism likely erupted in a small southerly Neotethyan basin, located north of the Eratosthenes seamount and likely floored by oceanic crust.
ISSN: 0016-7568

insu-00353657
https://hal-insu.archives-ouvertes.fr/insu-00353657
DOI : 10.1017/S0016756806002937

Éditeur(s) : HAL CCSD Centre National de la Recherche Scientifique
Résumé : Une étude stratigraphique, sédimentologique et magnétique a été réalisée sur la partie supérieure d'une terrasse alluviale de l'oued Adaila, dansla plaine d'El Ma Labiod (nord-est de l'Algérie). Cette terrasse renferme un niveau très riche en matériel archéologique appartenant à la civilisation atérienne, dont l'âge dépasse 35 000 ans. Du point de vue sédimentologique, les sédiments sont dominés par la fraction limoneuse suivie par les sables fins et grossiers. Du point de vue stratigraphique, la succession de dépôts à éléments grossiers recouverts par des éléments fins correspond à des niveaux fluviatiles avec des mises en place à débit contrasté. Les courbes cumulatives ont un faciès dit " parabolique " et témoignent d'un sédiment immature et peu évolué. Les résultats de l'étude magnétique concordent avec les précédents. Ils révèlent une forte concentration en grains magnétiques dans la partie médiane de la coupe (foyer) et une faible concentration à la base (Unité L) contemporaine d'un climat sec. Les grains magnétiques, de taille variable (polydomaine, monodomaine et superparamagnétique), sont portés par la magnétite et la maghémite de faible champ coercitif, ainsi que par la goethite et l'hématite de fort champ coercitif. Les courbes de la susceptibilité magnétique en fonction de la température et les courbes de la décomposition de l'ARI (spectres de coercivité) confirment ces résultats.
ISSN: 1142-2904

hal-00750185
https://hal.archives-ouvertes.fr/hal-00750185

Éditeur(s) : HAL CCSD
Résumé : International audience
Objective The objective of the study was to investigate the joint effect of occupational exposure to asbestos, and tobacco and alcohol consumption, on the risk of laryngeal cancer among men. Methods We used data from a large population-based case–control study conducted in France. We estimated two-way and three-way interactions between asbestos exposure (never vs ever exposed), tobacco consumption ( extless20 vs ≥20 pack-years) and alcohol consumption ( extless5 vs ≥5 drinks per day). The interaction on an additive scale was assessed by estimating the relative excess risk due to interaction (RERI) and the attributable proportion due to interaction, and the interaction on a multiplicative scale was assessed by estimating the multiplicative interaction parameter (ψ). Multiplicative interactions were also assessed using fractional polynomials for alcohol drinking, tobacco smoking and asbestos exposure. Results When compared with light-to-moderate smokers and drinkers never exposed to asbestos, the increase in laryngeal cancer risk was smallest among light-to-moderate drinkers and smokers exposed to asbestos (OR=2.23 (1.08 to 4.60)), and highest among heavy smokers and drinkers ever exposed to asbestos (OR=69.39 (35.54 to 135.5)). We found an additive joint effect between asbestos exposure and alcohol consumption (RERI=4.75 (−4.29 to 11.12)), whereas we observed a more than additive joint effect between asbestos exposure and tobacco consumption (RERI=8.50 (0.71 to 23.81)), as well as between asbestos exposure, and tobacco and alcohol consumption (RERI=26.57 (11.52 to 67.88)). However, our results did not suggest any interaction on a multiplicative scale. Conclusions Our results suggest that asbestos exposure, in combination with tobacco and alcohol exposure, accounted for a substantial number of laryngeal cancer cases. Our findings therefore highlight the need for prevention in activities, such as construction work, where exposure to asbestos-containing materials remains
Occupational and Environmental Medicine

hal-01269904
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01269904
DOI : 10.1136/oemed-2015-102954
PUBMED : 26403532

Résumé : Ce travail vise à mettre en place un système de fusion de sources d'information basé sur la Théorie des Fonctions de Croyance (TFC) et adapté aux contextes des images forestières. La TFC engendre des temps de calcul importants lorsque la cardinalité du cadre de discernement devient grande. Ainsi, nous avons proposé en premier lieu une méthode de réduction du référentiel de définition permettant d'éviter l'explosion combinatoire en restreignant le calcul sur les hypothèses estimées pertinentes et déterminées à partir des histogrammes des classes issues de la phase d'apprentissage. Ensuite, nous avons proposé des techniques d'estimation de fonctions de masse spectrales, texturales, contextuelles et structurelles. L'information multi-fractale a été utilisée comme signature de texture, ainsi l'image de Hôlder a constitué une source d'information pour l'estimation de la masse texturale. Un autre apport consiste à proposer une approche de transfert de masse basée sur l'information contextuelle, en exploitant l'image des couronnes d'arbres comme une source déduite. L'implémentation d'algorithmes de détection de couronnes d'arbres nous a permis d'extraire des mesures sur les couronnes que nous avons utilisées en tant qu'attributs pour l'estimation des fonctions de masse. Nos expérimentations montrent des taux de classification assez satisfaisants et une adéquation de notre approche de fusion à une classification à l'arbre près
This thesis aims to develop an information source fusion system based on belief functions theory (BFT) and adapted t forest images context (especially high resolution images). Applications of BFT to image classification result in th assignment of each image point to a c1ass or a subset of classes based on the mass functions estimation expressing th belief of an event. BFT leads to significant computation time when the cardinality of the set of definition become large. Thus, we first proposed a method to reduce the frame of discernment in order te avoid the combinatorial explosio by restricting the calculation on the hypotheses of the set of definition deduced from the classes histograms determine from the learning phase. Then, we proposed spectral, texturai, contextual and structural mass functions technique estimation. Multi-fractal information was used as texture signature and Hôlder image has been a source ( information for estimating the texturai mass. Another contribution is the integration of trees crowns image as derive source and the proposai of an approach to mass transfer based on contextual information inside and outside a crown. Th implementation of detection trees crowns algorithms allowed us to extract measurements on trees. These measurement are used as attributes for mass functions estimation. Our experiments and comparisons with other methods show quit satisfactory classification rate with spectral and textural approaches and adequacy of our fusion approach to contextu and structural information for trees classification

http://www.theses.fr/2011AGUY0434/document

Éditeur(s) : HAL CCSD International Association for Energy Economics
Résumé : International audience
In this paper we propose to determinate and to test a set ofstatistical parameters (20)to estimate the predictability of the global horizontal irradiation time series and thereby propose a new prospective tool indicating the expected error regardlessthe forecasting methodsa modeller can possibly implement. The mean absolute log return, which is a tool usually used in econometry, proves to be a very good estimator. Some examples of the use of this tool are exposed, showing the interest of this statistical parameter in concrete cases of predictions or optimizations.
ISSN: 0195-6574

hal-01180041
https://hal.archives-ouvertes.fr/hal-01180041
https://hal.archives-ouvertes.fr/hal-01180041/document
https://hal.archives-ouvertes.fr/hal-01180041/file/discriminent_param.pdf

Éditeur(s) : Centre français du littoral
Résumé : This study presents the first results of an ongoing research program that aims to derive thematic maps of the intertidal lagoon of Arcachon (SW Atlantic coast of France) from space imagery. At this stage, we present the results of the tests performed on Formosat-2 imagery. Several classification strategies have been tried with the aim to discriminate the sedimentary facies and the main species of the lagoon. The classes calculated by an optimized unsupervised clustering method, based on simulated annealing global minimization technique, were used to train a supervised classification algorithm. This approach allowed us to derive a bio-sedimentary map which overall accuracy is about 84%. Also, this method has the advantage of describing the fraction of vegetation cover of the seagrass.
Cette étude présente les premiers résultats d’un vaste programme de recherche qui ambitionne de définir une méthode de cartographie des platiers intertidaux du Bassin d’Arcachon (France) par télédétection. Les résultats présentés ici concernent les tests effectués sur l’imagerie Formosat-2 dans le but de discriminer les sédiments et les principales espèces végétales de la lagune. Le résultat d'une classification non supervisée optimisée par la méthode du recuit simulé est ensuite utilisé pour entraîner une classification par minimum de distance. Cette approche permet d’obtenir une carte des faciès bio-sédimentaires dont la précision est estimée à plus de 84 %. Cette méthode présente, en outre, un excellent potentiel pour la détermination du pourcentage de couvert végétal des herbiers à zostères.
Paralia (1760-8716) (Centre français du littoral), 2008 , N. 10 , P. 563-572

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00254/36572/35110.pdf
DOI:10.5150/jngcgc.2008.054-L
http://archimer.ifremer.fr/doc/00254/36572/

Éditeur(s) : HAL CCSD American Physical Society
Résumé : International audience
Using contact dynamics simulations, we compare the effect of rolling resistance at the contacts in granular systems composed of disks with the effect of angularity in granular systems composed of regular polygonal particles. In simple shear conditions, we consider four aspects of the mechanical behavior of these systems in the steady state: shear strength, solid fraction, force and fabric anisotropies, and probability distribution of contact forces. Our main finding is that, based on the energy dissipation associated with relative rotation between two particles in contact, the effect of rolling resistance can explicitly be identified with that of the number of sides in a regular polygonal particle. This finding supports the use of rolling resistance as a shape parameter accounting for particle angularity and shows unambiguously that one of the main influencing factors behind the mechanical behavior of granular systems composed of noncircular particles is the partial hindrance of rotations as a result of angular particle shape.
ISSN: 1539-3755

hal-00594891
https://hal.archives-ouvertes.fr/hal-00594891
https://hal.archives-ouvertes.fr/hal-00594891/document
https://hal.archives-ouvertes.fr/hal-00594891/file/Estrada2010ReSubmitV2.pdf
ARXIV : 1105.4418

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Ultraslow spreading at mid-ocean ridges limits melting due to on-axis conductive cooling, leading to the prediction that peridotites from these ridges are relatively fertile. To test this, we examined abyssal peridotites from the Gakkel Ridge, the slowest spreading ridge in the global ocean ridge system. Major and trace element concentrations in pyroxene and olivine minerals are reported for 14 dredged abyssal peridotite samples from the Sparsely Magmatic (SMZ) and Eastern Volcanic (EVZ) Zones. We observe large compositional variations among peridotites from the same dredge and among dredges in close proximity to each other. Modeling of lherzolite trace element compositions indicates varying degrees of non-modal fractional mantle melting, whereas most harzburgite samples require open-system melting involving interaction with a percolating melt. All peridotite chemistry suggests significant melting that would generate a thick crust, which is inconsistent with geophysical observations at Gakkel Ridge. The refractory harzburgites and thin overlying oceanic crust are best explained by low present-day melting of a previously melted heterogeneous mantle. Observed peridotite compositional variations and evidence for melt infiltration demonstrates that fertile mantle components are present and co-existing with infertile mantle components. Melt generated in the Gakkel mantle becomes trapped on short length-scales, which produces selective enrichments in very incompatible rare earth elements. Melt migration and extraction may be significantly controlled by the thick lithosphere induced by cooling at such slow spreading rates. We propose the heterogeneous mantle that exists beneath Gakkel Ridge is the consequence of ancient melting, combined with subsequent melt percolation and entrapment.
ISSN: 0016-7037

hal-01307003
https://hal.archives-ouvertes.fr/hal-01307003
DOI : 10.1016/j.gca.2015.11.017

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) : Elsevier Sci Ltd
Résumé : The quantity and the source of organic matter preserved in the Recent turbiditic channel-levees systems around 4000 m-depth off the Congo River were determined using bulk geochemical approaches (Rock-Eval, elemental and isotopic analyses) as well as molecular and optical analyses on selected samples. These mud-rich sediments contain high amount of organic matter (3% Corg on average), the origin of which is a mixture of terrestrial higher-plant debris and deeply oxidized phytoplanktonic material. Although the relative contribution of continental source versus marine source of the organic matter cannot be precisely quantified, the continental fraction appears significant (at least 70-80%) especially for such depths and distances from the coast. The organic matter distribution appears very homogeneous at different scales, from the single turbiditic event to the entire levee, and changes in accumulation rates have a little impact on the quantity and quality of preserved organic matter. With a petroleum potential around 4.5 kg HC per t rock, the fine-grained turbiditic sediments in the Congo deep-sea system could be regarded as an analog of gas-prone source rocks for the deep offshore of the Atlantic margins. Finally, the Congo deep-sea turbiditic system is a major conveyor of organic carbon to the deep ocean. Further studies are needed to evaluate the efficiency of such systems for the storage of continental organic matter into the deep ocean in relation to sea-level and climatic changes. (C) 2010 Elsevier Ltd. All rights reserved.
Marine And Petroleum Geology (0264-8172) (Elsevier Sci Ltd), 2010-05 , Vol. 27 , N. 5 , P. 995-1010

Droits : 2010 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/00006/11700/9285.pdf
DOI:10.1016/j.marpetgeo.2010.02.006
http://archimer.ifremer.fr/doc/00006/11700/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Fault affecting silicoclastic sediments are commonly enriched in clay minerals. Clays are sensitive to fluid–rock interactions and deformation mechanisms; in this paper, they are used as proxy for fault activity and behavior. The present study focuses on clay mineral assemblages from the Point Vert normal fault zone located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep in SE France. In this area, the Annot sandstones were buried around 6–8 km below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The fault affects arkosic sandstone beds alternating with pelitic layers, and displays throw of about thirty meters. The fault core zone comprises intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The foliated sandstones display clay concentration along S–C structures characterized by dissolution of K-feldspar and their replacement by mica, associated with quartz pressure solution, intense microfracturation and quartz vein precipitation. The gouge is formed by a clayey matrix containing fragments of foliated sandstones and pelites. However, a detailed petrographical investigation suggests complex polyphase deformation processes. Optical and SEM observations show that the clay minerals fraction of all studied rocks (pelites and sandstones from the damage and core zones of the fault) is dominated by white micas and chlorite. These minerals have two different origins: detrital and newly-formed. Detrital micas are identified by their larger shape and their chemical composition with a lower Fe–Mg content than the newly-formed white micas. In the foliated sandstones, newly-formed white micas are concentrated along S–C structures or replace K-feldspar. Both types of newly formed micas display the same chemical composition confirmed microstructural observations suggesting that they formed in the same conditions. They have the following structural formulas: Na0.05 K0.86 (Al 1.77 Fe0.08 Mg0.15) (Si3.22 Al0.78) O10 (OH)2. They are enriched in Fe and Mg compared to the detrital micas. Newly-formed chlorites are associated with micas along the shear planes. According to microprobe analyses, they present the following structural formula: (Al1,48 Fe2,50 Mg1,84) (Si2,82 Al1,18) O10 (OH)8. All these data suggest that these clay minerals are synkinematic and registered the fault activity. In the gouge samples, illite and chlorite are the major clay minerals; smectite is locally present in some samples.In the foliated sandstones, Kubler Index (KI) ((001) XRD peak width at half height) data and thermodynamic calculations from synkinematic chlorite chemistry suggest that the main fault deformation occurred under temperatures around 220 °C (diagenesis to anchizone boundary). KI measured on pelites and sandstones from the hanging and footwall, display similar values coherent with the maximal burial temperature of the Annot sandstones in this area. The gouge samples have a higher KI index, which could be explained by a reactivation of the fault at lower temperatures during the exhumation of the Annot sandstones formation
ISSN: 0191-8141

hal-01172423
https://hal.archives-ouvertes.fr/hal-01172423
DOI : 10.1016/j.jsg.2015.03.012

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
We report new textural and chemical data for 10 garnet peridotite xenoliths from the Udachnaya kimberlite and examine them together with recent data on another 21 xenoliths from the 80-220 km depth range. The samples are very fresh (LOI near zero), modally homogeneous and large (>100 g). Some coarse-grained peridotites show incipient stages of deformation with <10 % neoblasts at grain boundaries of coarse olivine. Such microstructures can only be recognized in very fresh rocks, because fine-grained interstitial olivine is strongly affected by alteration, and may have been overlooked in previous studies of altered peridotite xenoliths in the Siberian and other cratons. Some of the garnet peridotites are similar in composition to low-opx Udachnaya spinel harzburgites (previously interpreted as pristine melt extraction residues), but the majority show post-melting enrichments in Fe and Ti. The least metasomatized coarse peridotites were formed by 30-38 % of polybaric fractional melting between 7 and 4 GPa and ≤1-3 GPa. Our data together with experimental results suggest that garnet in these rocks, as well as in some other cratonic peridotites elsewhere, may be a residual mineral, which has survived partial melting together with olivine and opx. Many coarse and all deformed garnet peridotites from Udachnaya underwent modal metasomatism through interaction of the melting residues with Fe-, Al-, Si-, Ti-, REE-rich melts, which precipitated cpx, less commonly additional garnet. The xenoliths define a complex geotherm probably affected by thermal perturbations shortly before the intrusion of the host kimberlite magmas. The deformation in the lower lithosphere may be linked to metasomatism.
ISSN: 0010-7999

hal-00941252
https://hal.archives-ouvertes.fr/hal-00941252
DOI : 10.1007/s00410-013-0855-8

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Spinel (± plagioclase) peridotite xenoliths from the Tallante and Los Perez volcanic centres in the eastern Betics (SE Spain) range from depleted (clinopyroxene-poor) harzburgites to fertile (clinopyroxene-rich) lherzolites and orthopyroxene-free wehrlites. Significantly, only one harzburgite, which is depleted in heavy rare earth elements (HREE), retains the imprint of ca. 20% ancient melting of an original garnet lherzolite source. In contrast, REE abundances of other harzburgites and lherzolites from the eastern Betics have been increased by melt-rock reaction. The whole-rock and mineral compositions of these mantle rocks are largely controlled by three types of modal metasomatism: 1) common clinopyroxene-orthopyroxene addition and olivine consumption which increased FeOt, SiO2 and Al2O3, and decreased MgO compared to the refractory melting products; 2) subordinate orthopyroxene dissolution and precipitation of clinopyroxene and olivine, which led to higher FeOt and MgO and lower SiO2 than in common (orthopyroxene-rich) lherzolites; and 3) rare orthopyroxene consumption and olivine addition that caused higher FeOt and lower SiO2 compared to the original melting residues. These mineral modal and major element variations have been produced mostly by interactions with relatively FeOt-rich/SiO2-poor melts, likely derived from a peridotite-pyroxenite lithospheric mantle with a highly heterogeneous isotopic composition. Melting of the lithospheric mantle in the western Mediterranean was triggered by upwelling of the asthenosphere induced by back-arc extension in the Late Oligocene-Early Miocene. Trapping of small fractions of exotic melts in whole-rocks — likely the parental magmas of Miocene back-arc dykes that intruded the Betic crust — caused local disequilibrium between the trace element signatures and Pb isotopic compositions of clinopyroxene and whole-rock. Subsequent interaction with SiO2-undersaturated magmas, similar to the parental melts of the Pliocene alkali basalts that host the xenoliths, promoted orthopyroxene consumption and clinopyroxene-olivine enrichment at locations close to magma conduits, and finally generated orthopyroxene-free wehrlites. This event constitutes the last episode of the Cenozoic magmatic evolution of the westernmost Mediterranean which is recorded in the mantle xenoliths from the eastern Betics.
ISSN: 0024-4937

hal-01553092
https://hal.archives-ouvertes.fr/hal-01553092
DOI : 10.1016/j.lithos.2016.12.011

Éditeur(s) : Elsevier
Résumé : The combined use of Lu-Hf and Sm-Nd isotope systems potentially offers a unique perspective for investigating continental erosion, but little is known about whether, and to what extent, the Hf-Nd isotope composition of sediments is related to silicate weathering intensity. In this study, Hf and Nd elemental and isotope data are reported for marine muds, leached Fe-oxide fractions and zircon-rich turbidite sands collected off the Congo River mouth, and from other parts of the SE Atlantic Ocean. All studied samples from the Congo fan (muds, Fe-hydroxides, sands) exhibit indistinguishable Nd isotopic composition (epsilon(Nd)similar to - 16), indicating that Fe-hydroxides leached from these sediments correspond to continental oxides precipitated within the Congo basin. In marked contrast, Hf isotope compositions for the same samples exhibit significant variations. Leached Fe-hydroxide fractions are characterized by epsilon(Hf) values (from -1.1 to +13) far more radiogenic than associated sediments (from -7.1 to -12.0) and turbidite sands (from -27.2 to -31.6). epsilon(Hf) values for Congo fan sediments correlate very well with Al/K (i.e. a well-known index for the intensity of chemical weathering in Central Africa). Taken together, these results indicate that (1) silicate weathering on continents leads to erosion products having very distinctive Hf isotope signatures, and (2) a direct relationship exists between epsilon(Hf) of secondary clay minerals and chemical weathering intensity. These results combined with data from the literature have global implications for understanding the Hf-Nd isotope variability in marine precipitates and sediments. Leached Fe-hydroxides from Congo fan sediments plot remarkably well on an extension of the 'seawater array' (i.e. the correlation defined by deep-sea Fe-Mn precipitates), providing additional support to the suggestion that the ocean Hf budget is dominated by continental inputs. Fine-grained sediments define a diffuse trend, between that for igneous rocks and the,seawater array', which we refer to as the 'zircon-free sediment array' (epsilon(Hf)=0-91 epsilon(Nd)+3.10). Finally, we show that the Hf-Nd arrays for seawater, unweathered igneous rocks, zircon-free and zircon-bearing sediments (epsilon(Hf)= 1.80 epsilon(Nd)+2.35) can all be reconciled, using Monte Carlo simulations, with a simple weathering model of the continental crust. (C) 2008 Elsevier B.V. All rights reserved.
Earth and Planetary Science Letters (0012-821X) (Elsevier), 2009 , Vol. 277 , N. 3-4 , P. 318-326

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-6451.pdf
DOI:10.1016/j.epsl.2008.10.028
http://archimer.ifremer.fr/doc/00000/6451/

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : The Fars arc accommodates the oblique convergence between the Arabic plate and the Iran block. Many geological observations suggest block rotations from regional to local scales. We present palaeomagnetic investigations in the Fars arc and its eastern termination, the Zagros-Makran syntaxis. Sixty-four sites have been sampled covering the Palaeocene Pabdeh Fm. to Mio-Pliocene Agha-Jhari Fm., the latest being the most sampled formation. We document pre-tilting components in all formations. However, coarse fractions of Agha-Jhari clastics formation retain a post-tilting remagnetization. As a whole, block rotations rarely exceed 20 degrees. In the western Fars arc, clockwise and counter-clockwise rotations of small amplitudes are consistent with the torsions observed near the strike slip Kazerun and Mangarak faults. In the Zagros Makran syntaxis, counter-clockwise and clockwise rotations are observed, respectively, in the western and eastern part. This pattern is consistent with an amplification of the shape of the syntaxis. Between Zagros and Makran, palaeomagnetic data support that the present-day arcuate shape of the arc is secondary. We assume that most of the block rotations took place during the Plio-Pleistocene, during a blocking stage of the Zagros-Makran syntaxis. We emphasize the role of Oman Peninsula which plays as an indenter for the propagation of the Fars thrust belt.
ISSN: 0956-540X

hal-00411142
https://hal.archives-ouvertes.fr/hal-00411142
DOI : 10.1111/j.1365-246X.2008.03732.x

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
1. A substantial fraction of the freshwater available in neotropical forests is impounded within the rosettes of bromeliads that form aquatic islands in a terrestrial matrix. The ecosystem functioning of bromeliads is known to be influenced by the composition of the contained community but it is not clear whether bromeliad food webs remain functionally similar against a background of variation in the understorey environment. 2. We considered a broad range of environmental conditions, including incident light and incoming litter, and quantified the distribution of a very wide range of freshwater organisms (from viruses to macroinvertebrates) to determine the factors that influence the functional structure of bromeliad food webs in samples taken from 171 tank-bromeliads. 3. We observed a gradient of detritus-based to algal-based food webs from the understorey to the overstorey. Algae, rotifers and collector and predatory invertebrates dominated bromeliad food webs in exposed areas, whereas filter-feeding insects had their highest densities in shaded forest areas. Viruses, bacteria and fungi showed no clear density patterns. Detritus decomposition is mainly due to microbial activity in understorey bromeliads where filter feeders are the main consumers of microbial and particulate organic matter (POM). Algal biomass may exceed bacterial biomass in sun-exposed bromeliads where amounts of detritus were lower but functional diversity was highest. 4. Our results provide evidence that tank-bromeliads, which grow in a broad range of ecological conditions, promote aquatic food web diversity in neotropical forests. Moreover, although bromeliad ecosystems have been categorised as detritus-based systems in the literature, we show that algal production can support a non-detrital food web in these systems.
ISSN: 0046-5070

hal-00819103
https://hal.archives-ouvertes.fr/hal-00819103

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Several recent studies have documented that reactions between melt and crystal mush in primitive gabbroic rocks (via reactive porous flow) have an important control in the formation of the lower oceanic crust and the evolution of MORBs. In this context, olivine-rich rocks can form either by fractional crystallization of primitive melts or by open system reactive percolation of pre-existing (possibly mantle-derived) olivine matrix. To address this question, we performed in-situ trace element analyses (by LA-ICP-MS) of olivine from the Erro-Tobbio ophiolite Unit (Ligurian Alps), where mantle peridotites show gradational contacts with an hectometer-scale body of troctolites and plagioclase wehrlites, and both are cut by later decameter-wide lenses and dykes of olivine gabbros. Previous studies inferred that troctolites and olivine gabbros represent variably differentiated crystallization products from primitive MORB-type melts. Olivines in the three rock types (mantle peridotites, troctolites, olivine gabbros) exhibit distinct geochemical signature and well-defined elemental correlations. As expected, compatible elements (e.g. Ni) show the highest concentrations in peridotites (2580–2730 ppm), intermediate in troctolites (2050–2230 ppm) and lowest in gabbros (1355–1420 ppm), whereas moderate incompatible elements (e.g. Mn, Zn) show the opposite behaviour. By contrast, highly incompatible elements like Zr, Hf, Ti, HREE are variably enriched in olivines of troctolites, and the enrichment in absolute concentrations is coupled to development of significant HFSE/REE fractionation (ZrN/NdN up to 80). AFC modelling shows that such large ZrN/NdN ratios in olivines are consistent with a process of olivine assimilation and plagioclase crystallization at decreasing melt mass, in agreement with textural observations. In-situ trace element geochemistry of olivine, combined with microstructural investigations, thus appears a powerful tool to investigate reactive percolation and the origin of olivine-rich rocks in the lower oceanic crust.
ISSN: 0016-7037

hal-01419938
https://hal.archives-ouvertes.fr/hal-01419938
DOI : 10.1016/j.gca.2016.06.029

Éditeur(s) : HAL CCSD
Résumé : International audience
This paper deals with texture classification using a multifractal approach. More precisely we analyse the singularity/regularity exponent that compose the textures because they theoretically carry most of the information. The analysis is made using the Legendre spectrum. Then a parameter vector is computed to describe this spectrum in order to classify the textures with an unsupervised k-means classifier. The resulting algorithm is evaluated against a classification directly based on the textures.
ICSP Proceedings
Beijing, China

hal-00602270
https://hal.archives-ouvertes.fr/hal-00602270