Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The active collision zone around Taiwan orogen receives a variety of sedimentary inputs, including terrigenous flux from Taiwan and Chinese rivers, oceanic currents and atmospheric dust. In order to determine the present-day respective contributions of these different sources, we analysed the Pb and Sr isotopic compositions of late Quaternary sediments accumulated offshore east Taiwan. Samples from the Taiwan Coastal Range (andesites, sandstones, conglomerate and Peinan River terraces and suspended loads) have also been analysed to constrain the mean Taiwan isotopic signature. Mixing lines between the different sources of material indicate that the core located in the Okinawa Trough represents a mixture of about 60% of Taiwan, 30% of Chinese Loess and 10% of Yangtze River contributions. The southernmost core, located close to Luzon Are, is influenced by Taiwan (60%) and volcanic material (40%). The Sr and Pb isotopic compositions of samples cored in the Manila Trench and in the Huatung Basin are strongly influenced by the Taiwan signature, while the Ryukyu Trench core samples point to significant but variable contributions of Chinese Loess and Yangtze River. This work also reports Zn isotopic variations in the silicate fraction of these marine core samples. The overall variation in Zn isotopic compositions (expressed as 666 Zn) is greater than 0.3 per mil (parts per thousand) for an analytical precision of +/- 0.05 parts per thousand. The Zn isotopic signal for most of the marine core samples is similar to the literature data measured on sedimentary material, except for the Manila Trench core samples and the older sample from the Huatung Basin: they present values heavier by 0.2-0.3 parts per thousand, close to those obtained on all Taiwan rocks and Peinan River particulates. These results show: 1- the particular characteristics of Taiwan Zn isotopic compositions on a large scale; and: 2- the possible use of Zn isotopes as a tracer of material sources.
ISSN: 0009-2541

hal-00412214
https://hal.archives-ouvertes.fr/hal-00412214
DOI : 10.1016/j.chemgeo.2007.10.024

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We report new data on the geochemical evolution, metasomatic and deformation processes in the lower layers of cratonic lithospheric mantle based on a detailed study of extraordinarily fresh and large deformed peridotite xenoliths from the Udachnaya kimberlite pipe, Siberia. Based on our T-P estimates, the deformed peridotites are localized in a depth range of 170 to 220 km near the base of cratonic mantle. The degree of deformation is not correlated with the depth and equilibration temperatures of the xenoliths. The deformed peridotites are depleted in magmaphile major elements indicating their residual nature, but are enriched in incompatible trace elements, Fe and K. The deformed peridotites experienced a complex evolution, i.e., they were formed initially as high-degree melt extraction residues and later were subjected to three main stages of metasomatic modification. (1) An old, mostly cryptic metasomatism by melt/fluid of carbonatitic composition, which formed garnets with sinusoidal REE patterns (Smn/Ern > 1). (2) Silicate metasomatism, which led to the most significant changes in mineralogical and chemical composition of the deformed peridotites. (3) Fe and Ti metasomatism just before the entrainment of the deformed rocks into kimberlite magma. Enrichment of the peridotites in large-ion lithophile elements (K, Rb, Ba) is related to the formation of kelyphitic rims around garnet. The nature of the metasomatic agent of silicate metasomatism was evaluated from mass-balance of measured and calculated whole-rock compositions, ratios of highly incompatible elements (D < 0.1) and fractional crystallization modeling. All this evidence indicates that the agent of silicate metasomatism had a composition intermediate between that of kimberlites and HIMU OIB. The metasomatic processes responsible for the formation of deformed peridotites and precipitation of megacryst suites cannot be widespread at the base of the cratonic mantle. Rather, they are local features only existing in the cratonic mantle below kimberlite fields and localized along the metasomatic vein system.
ISSN: 0024-4937

hal-00941010
https://hal.archives-ouvertes.fr/hal-00941010
DOI : 10.1016/j.lithos.2012.11.014

Éditeur(s) : HAL CCSD MDPI
Résumé : International audience
Marine ecosystems cover about 70% of the planet surface and are still an underexploited source of useful metabolites. Among microbes, filamentous fungi are captivating organisms used for the production of many chemical classes of secondary metabolites bound to be used in various fields of industrial application. The present study was focused on the collection, isolation, screening and genotyping of pigmented filamentous fungi isolated from tropical marine environments around La Réunion Island, Indian Ocean. About 150 micromycetes were revived and isolated from 14 marine samples (sediments, living corals, coral rubble, sea water and hard substrates) collected in four different locations. Forty-two colored fungal isolates belonging to 16 families, 25 genera and 31 species were further studied depending on their ability to produce pigments and thus subjected to molecular identification. From gene sequence analysis, the most frequently identified colored fungi belong to the widespread Penicillium, Talaromyces and Aspergillus genera in the family Trichocomaceae (11 species), then followed by the family Hypocreaceae (three species). This study demonstrates that marine biotopes in La Réunion Island, Indian Ocean, from coral reefs to underwater slopes of this volcanic island, shelter numerous species of micromycetes, from common or uncommon genera. This unstudied biodiversity comes along with the ability for some fungal marine inhabitants, to produce a range of pigments and hues.
ISSN: 2309-608X

hal-01657071
http://hal.univ-reunion.fr/hal-01657071
http://hal.univ-reunion.fr/hal-01657071/document
http://hal.univ-reunion.fr/hal-01657071/file/14-%20Fouillaud%20et%20al.%2C%20J.%20of%20Fungi%202017.pdf
DOI : 10.3390/jof3030036

Éditeur(s) : HAL CCSD Geological Society
Résumé : Gem opals from Wegel Tena, Wollo Province, Ethiopia, occur in Oligocene rhyolitic ignimbrites. They display a unique geochemistry, with some samples yielding the highest Ba concentrations ever recorded. They are generally much richer in chemical impurities than opals from other localities. For example, the sum Al+Fe or the sum Na+Mg+Ca+K+Ba are often higher. These geochemical features make them easy to distinguish from other opals worldwide. We observed strong geochemical variations and some good positive correlations in our samples, such as Al+Fe vs. Na+Mg+Ca+K+Ba, Al vs Ca, or Ba vs Ca. This shows that the crystallography of opal has controlled, at least in part, the incorporation of chemical impurities, although opal is not well-crystallized. In addition, the multimodal distributions of several chemical impurities (e.g. U vs Sr, Al vs Ca, Ba vs Ca, etc.) suggest at least two origins of silica: weathering of feldspars and weathering of volcanic glass. In addition, opals from Wegel Tena contain numerous well-preserved microscopic plant fossils. Moreover, their host rock exhibits features typical of pedogenesis (abundant clays, desiccation cracks, and grain size sorting). We propose that the opals at Wegel Tena formed during the Oligocene period when volcanic emissions stopped for a time long enough to allow weathering of ingimbrites and therefore liberation of silica. This accompanied the formation of soil and development of plant life, and some plants were trapped in opal.
ISSN: 1467-7873

hal-00767555
https://hal.archives-ouvertes.fr/hal-00767555
DOI : 10.1144/1467-7873/10-MINDEP-058

Éditeur(s) : HAL CCSD
Résumé : Geothermal energy is considered as a green and infinite energy source at human scale. Currently, the yield of geothermal power plants is limited to temperatures of the operating fluid which 350 °C. From tectonic and volcanic activity at mid-ocean ridges, Iceland is a location where supercritical fluid extraction (T> 375 °C) can considered for the near future. Exploiting such fluids could theoretically multiply by a factor of ten the electrical power delivered by geothermal wells. Can such fluids circulate at the base of brittle oceanic crust? This work investigates the petrophysical properties of basalts in order to constrain geophysical observations in Iceland and predict the behavior of very high temperature geo-hydrothermal reservoirs. The first approach consisted in studying the physical properties of rocks that have hosted deep hydrothermal circulations at oceanic ridges. The study of these rocks at ODP Site 1256 shows that the porosity measured both in the field and in the lab is associated with amphibolite facies alteration minerals (T> 500 ° C). The second approach was to recreate in the laboratory the conditions of pressure, temperature and pore fluid pressure of high temperature to supercritical hydrothermal systems to predict the mechanical and electrical properties of basalts under these conditions. The mechanical results indicate that the brittle/ductile transition occurs at a temperature of about 550° C, where a strong permeability decrease is expected. The implementation and calibration of a new cell for measuring electrical conductivity at high temperature provide the first results for the interpretation of geophysical data. When applied to basaltic crustal conditions in Iceland, these results indicate that hydrothermal fluids could circulate, at least temporarily, in a supercritical state up to 5 km depth.
La géothermie est considérée comme une source d'énergie propre et inépuisable à échelle humaine. Actuellement, le rendement des centrales géothermiques est limité à l'exploitation de fluides de températures inférieures à 350 °C. L'association de l'activité tectonique et volcanique aux dorsales océaniques fait de l'Islande un lieu où l'extraction de fluides supercritiques (T> 375 °C) peut être envisagée. Cette exploitation pourrait multiplier par dix la puissance électrique délivrée par le système géothermal. Ces fluides peuvent-ils circuler dans la croûte océanique ? Ce travail propose de contraindre les observations géophysiques et de prédire le fonctionnement des réservoirs géo-hydrothermaux de très haute température par l'étude des propriétés physiques des basaltes. La première approche est focalisée sur l'étude de roches ayant accueilli une circulation hydrothermale par le passé. L'étude de ces roches au site ODP 1256, montre que leur porosité est associée à la présence de minéraux d'altération hydrothermale du facies amphibolite (T> 500 °C). La seconde approche a consisté à recréer, en laboratoire, les conditions des systèmes hydrothermaux, à très haute température, afin de prédire les propriétés mécaniques et électriques des basaltes dans ces conditions. Les résultats mécaniques indiquent que la transition fragile/ductile, souvent associée à une forte décroissance de perméabilité, intervient à une température d'environ 550 °C. La mise en place d'une cellule de mesure de la conductivité électrique de haute température a fourni les premiers résultats utiles à l'analyse des données géophysiques. Appliqués aux conditions de la croûte basaltique Islandaise, ces résultats indiquent que des fluides hydrothermaux pourraient circuler au moins transitoirement à l'état supercritique jusqu'à ~ 5 km de profondeur.
https://tel.archives-ouvertes.fr/tel-00591798

tel-00591798
https://tel.archives-ouvertes.fr/tel-00591798
https://tel.archives-ouvertes.fr/tel-00591798/document
https://tel.archives-ouvertes.fr/tel-00591798/file/THESE_MV_pro.pdf

Éditeur(s) : HAL CCSD Springer Verlag (Germany) Springer Verlag
Résumé : International audience
Arenal volcano is nearly unique among arc volcanoes with its 42 year long (1968–2010) continuous, small-scale activity erupting compositionally monotonous basaltic andesites that also dominate the entire, ~7000 year long, eruptive history. Only mineral zoning records reveal that basaltic andesites are the result of complex, open-system processes deriving minerals from a variety of crystallization environments and including the episodic injections of basalt. The condition of the mafic input as well as the generation of crystal-rich basaltic andesites of the recent, 1968–2010, and earlier eruptions were addressed by an experimental study at 200 MPa, 900–1,050 °C, oxidizing and fluid-saturated conditions with various fluid compositions [H2O/(H2O + CO2) = 0.3–1]. Phase equilibria were determined using a phenocryst-poor (~3 vol%) Arenal-like basalt (50.5−wt% SiO2) from a nearby scoria cone containing olivine (Fo92), plagioclase (An86), clinopyroxene (Mg# = 82) and magnetite (Xulvö = 0.13). Experimental melts generally reproduce observed compositional trends among Arenal samples. Small differences between experimental melts and natural rocks can be explained by open-system processes. At low pressure (200 MPa), the mineral assemblage as well as the mineral compositions of the natural basalt were reproduced at 1,000 °C and high water activity. The residual melt at these conditions is basaltic andesitic (55 wt% SiO2) with 5 wt% H2O. The evolution to more evolved magmas observed at Arenal occurred under fluid-saturated conditions but variable fluid compositions. At 1,000 °C and 200 MPa, a decrease of water content by approximately 1 wt% induces significant changes of the mineral assemblage from olivine + clinopyroxene + plagioclase (5 wt% H2O in the melt) to clinopyroxene + plagioclase + orthopyroxene (4 wt% H2O in the melt). Both assemblages are observed in crystal-rich basalt (15 vol%) and basaltic andesites. Experimental data indicate that the lack of orthopyroxene and the presence of amphibole, also observed in basaltic andesitic tephra units, is due to crystallization at nearly water-saturated conditions and temperatures lower than 950 °C. The enigmatic two compositional groups previously known as low- and high-Al2O3 samples at Arenal volcano may be explained by low- and high-pressure crystallization, respectively. Using high-Al as signal of deeper crystallization, first magmas of the 1968–2010 eruption evolved deep in the crust and ascent was relatively fast leaving little time for significant compositional overprint by shallower level crystallization.
ISSN: 0010-7999

hal-01115717
https://hal.archives-ouvertes.fr/hal-01115717
DOI : 10.1007/s00410-014-1040-4

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
IODP Site U1309 was drilled at Atlantis Massif, an oceanic core complex, at 30 degrees N on the Mid-Atlantic Ridge (MAR). We present the results of a bulk rock geochemical study (major and trace elements) carried out on 228 samples representative of the different lithologies sampled at this location. Over 96% of Hole U1309D is made up of gabbroic rocks. Diabases and basalts cross-cut the upper part of the section; they have depleted MORB compositions similar to basalts sampled at MAR 30 degrees N. Relics of mantle were recovered at shallow depth. Mantle peridotites show petrographic and geochemical evidence of extensive melt-rock interactions. Gabbroic rocks comprise: olivine-rich troctolites (>70% modal olivine) and troctolites having high Mg# (82-89), high Ni (up to 2300 ppm) and depleted trace element compositions (Yb 0.06-0.8 ppm); olivine gabbros and gabbros (including gabbronorites) with Mg# of 60-86 and low trace element contents (Yb 0.125-2.5 ppm); and oxide gabbros and leucocratic dykes with low Mg# (<50), low Ni (similar to 65 ppm) and high trace element contents (Yb up to 26 ppm). Troctolites and gabbros are amongst the most primitive and depleted oceanic gabbroic rocks. The main geochemical characteristics of Site U1309 gabbroic rocks are consistent with a formation as a cumulate sequence after a common parental MORB melt, although (lack of systematic) downhole variations indicate that the gabbroic series were built by multiple magma injections. In detail, textural and geochemical variations in olivine-rich troctolites and gabbronorites suggest chemical interaction (assimilation?) between the parental melt and the intruded lithosphere. Site U1309 gabbroic rocks do not represent the complementary magmatic product of 30 degrees N volcanics, although they sample the same mantle source. The bulk trace element composition of Site U1309 gabbroic rocks is similar to primitive MORB melt compositions; this implies that there was no large scale removal of melts from this gabbro section. The occurrence of such a large magmatic sequence implies that a high magmatic activity is associated with the formation of Atlantis Massif. Our results suggest that almost all melts feeding this magmatic system stays trapped into the intruded lithosphere.
ISSN: 0012-821X

hal-00413562
https://hal.archives-ouvertes.fr/hal-00413562
DOI : 10.1016/j.epsl.2008.12.034

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study analyzes the active tectonics within the northwestern and southeastern extensions of the Pambak-Sevan-Syunik fault (PSSF), a major right-lateral strike-slip fault cutting through Armenia. Quantifying the deformations in terms of geometry, kinematics, slip rates and earthquake activity, using cosmogenic 3He, OSL/IRSL and radiocarbon dating techniques, reveal different behaviors between the two regions. Within the northwestern extension, in the region of Amasia, the PSSF bends to the west and splits into two main WNW–ESE trending reverse faults defining a compressional pop-up structure. We estimate an uplift rate and a shortening rate of 0.5 ± 0.1 mm/y and 1.4 ± 0.6 mm/y, respectively. This suggests that most of the ∼2 mm/y right lateral movement of the PSSF seems to be absorbed within the Amasia pop-structure. Within the southeastern extension, the PSSF shows signs of dying out within the Tsghuk Volcano region at the southernmost tip of the Syunik graben. There, the tectonic activity is characterized by a very slow NS trending normal faulting associated with a slight right-lateral movement. Slip rates analyses (i.e. vertical slip rate, EW stretching rate at 90° to the fault, and right-lateral slip rate of ∼0.2 mm/y, ∼0.1 mm/y and ∼0.05 mm/y, respectively) lead to the conclusion that the right lateral movement observed further north along the PSSF is mainly transferred within other active faults further west within the Karabagh (Hagari fault or other structures further northwestwards). Comparing our slip rates with those estimated from GPS data suggests that most of the deformation is localized and seismic, at least within the Tsghuk region. The geometrical and kinematic pattern observed within the two terminations of the PSSF suggests that the fault and its surrounding crustal blocks are presently rotating anticlockwise, as also observed within the GPS velocity field. This is consistent with the recent kinematic models proposed for the Caucasus-Kura-South Caspian region and brings a new insight into the present geodynamics of Armenia.
ISSN: 1040-6182

hal-01307342
https://hal.archives-ouvertes.fr/hal-01307342
DOI : 10.1016/j.quaint.2015.05.021

Éditeur(s) : Elsevier Sci Ltd
Résumé : Several marine geophysical data and piston-coring surveys acquired during the last decade allow one to better understand the close dynamic interactions between the sand-rich Orinoco turbidite system and the compressional structures of the Barbados prism. These interactions have been active since Eocene time as illustrated by the study of outcrops onshore Barbados Island. Because of strong morphologic and tectonic control in the east-Caribbean active margin, the present-day Orinoco turbiditic pattern system does not exhibit a classic fan geometry. The sea-floor geometry between the slope of the front of the Barbados prism and the slope of the South-American margin induces the convergence of the turbidite channels toward the abyssal plain, at the front of the accretionary prism. Also, whereas in most passive margins the turbidite systems are organized upstream to downstream as canyon, channel-levee and lobes, here, due to the tectonic control, the sedimentary system is organized upstream to downstream as channel-levee, canyons and channelized lobes. Indeed, at the edge of the Orinoco platform, the system has multiple sources with several distributaries and downstream the channel courses are complex with frequent convergences or divergences that are emphasized by the effects of the undulating seafloor tectonic morphologies associated with active thrust tectonics and mud volcanism. On top of the accretionary prism, turbidite sediments are filling transported piggy-back basins whose timing of sedimentation vs. deformation is complex. While erosion processes are almost absent on the highly subsiding Orinoco platform and in the upper part of the turbidite system, they develop mostly between 2000 and 4000 m of water depth, above the compressional structures of the Barbados prism (canyons up to 3 km wide and 300 m deep). In the abyssal plain, the main turbiditic channel develops toward the east and connects with the Vidal mid-Atlantic channel. The sediments transported in this channel are filling several elongated basins linked with fracture zones (notably the Barracuda Basin), and finally end their course in the Puerto-Rico trench, the deepest morphologic depression of the region. Piston-cores have demonstrated that turbidite sediments above the accretionary prism and in the abyssal plain are mostly coarse sandy deposits covered by recent pelagic planktonic-rich sediments, which corresponds to slower sand deposition during the post-glacial sea level rise. Numerical stratigraphic modelling suggests that during the last glacial event, the main depocentres were located above the tectonic prism and in the abyssal plain, at the front of the prism and that, during the Holocene eustatic rise, a large accommodation space formed on the shelf confining sedimentation mostly on the Orinoco deltaic platform and producing a starvation downstream in the turbidite system.
Marine And Petroleum Geology (0264-8172) (Elsevier Sci Ltd), 2015-06 , Vol. 64 , P. 76-103

Droits : 2015 Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00252/36373/34913.pdf
DOI:10.1016/j.marpetgeo.2014.12.015
http://archimer.ifremer.fr/doc/00252/36373/

Éditeur(s) : HAL CCSD
Résumé : International audience
The "South-Dominica" archaeological mission of the French ministry of foreign affairs has started work in 2005. Designed to enlighten the archaeological terra incognita dominicana, this research has essentially been dedicated to the early ceramic occupation of the island. Our work has been based on the analysis of the few collections already existing, on systematic survey campaigns and on an important test pit program. This lecture will be concentrating on the presentation of the Soufrière site excavation. The Soufriere site, found in the seventies, is composed of an important early cedrosan saladoid occupation covered by volcanic deposits. The data obtained during this excavation, associated with other results of the "South Dominica" archaeological mission, incites us to think about a revision of the territories associated to the complexes in the Lesser Antilles.
La mission archéologique "Sud-Dominique" du ministère français des affaires étrangères a débuté ses travaux en 2005. Destinées à en finir avec la terra incognita dominicana archéologique, ces recherches sont essentiellement consacrées à l'étude du premier peuplement agro-céramique de l'île. Le travail de la mission archéologique repose sur l'étude de séries anciennes, des campagnes de prospections systématiques et un important programme de sondages. Notre présentation se concentrera sur la fouille que nous avons menée du site de Soufrière dans le sud de la Dominique. Ce gisement identifié dans les années 1970 correspond à une importante occupation saladoïde cedrosane ancienne qui a été recouverte par des dépôts volcaniques. Les données obtenues lors de cette fouille associées à l'ensemble des résultats obtenus en 3 années par la mission archéologique Sud-Dominique nous incitent à nous interroger sur la nécessité d'une révision des territoires associés à la notion de complexe dans les Petites Antilles.
XXII Conference of the International Association of Caribbean Archaeology
Kingston, Jamaica

Droits : info:eu-repo/semantics/OpenAccess
hal-00961335
https://hal.univ-antilles.fr/hal-00961335
https://hal.univ-antilles.fr/hal-00961335/document
https://hal.univ-antilles.fr/hal-00961335/file/soufriA_repaperfinal.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Imaging deep active volcanic areas remains a challenge in our understanding of their activity and evolution, especially in subduction zones. Study of magnetic anomalies is appropriate to access such dynamics in depth. The magnetic anomaly pattern of the Lesser Antilles Arc (LAA) subduction is studied through Curie Point Depth (CPD), interpreted as the depth of the 580 °C isotherm, and developed to better assess the deep thermal structure of the arc. The depth of the estimated CPD exhibits a complex topography. Keeping in mind the overall uncertainty associated with this method, a main doming is evidenced below the Guadeloupe archipelago. Its apex is shifted towards the ancient arc, suggesting a very hot state of the fore-arc/arc domain. To better understand the LAA thermal state, we perform 2D thermo-mechanical simulations of the subduction zone. Recalling that magnetite is a serpentinization by-product, we simulate water transfer triggered by slab dehydration to test the assumption of fore-arc serpentinization suggested by the positive magnetic anomaly in the vicinity of the Guadeloupe archipelago. In this area, the subduction-induced arc lithosphere hydration and related weakening trigger a fast heating of the upper plate by basal convective removal. This process of fast arc lithosphere thinning may apply where simultaneously the volcanic arc is split in two and normal convergence is high enough. As serpentinization strongly decreases P-wave velocity, we propose a new interpretation of a published seismic profile below Guadeloupe. The seismic layer previously interpreted as the arc lower crust may rather be a layer of serpentinized mantle, as supported by spatial correlations between gravimetric and magnetic anomalies. Consequently, at the scale of Guadeloupe Island, the fore-arc Moho would be shallower than initially assumed, with a dome shape more consistent with both the extensive deformation active since the Oligocene in the inner fore-arc and the CPD doming.
ISSN: 0040-1951

Droits : http://creativecommons.org/licenses/by-nc-nd/
insu-01505300
https://hal-insu.archives-ouvertes.fr/insu-01505300
https://hal-insu.archives-ouvertes.fr/insu-01505300/document
https://hal-insu.archives-ouvertes.fr/insu-01505300/file/Gailler-2017.pdf
DOI : 10.1016/j.tecto.2017.03.014

Éditeur(s) : HAL CCSD Blackwell Publishing
Résumé : International audience
Pliocene and Pleistocene deposits from Grande-Terre (Guadeloupe archipelago, French Lesser Antilles) provide a remarkable example of an isolated carbonate system built in an active margin setting, with sedimentation both controlled by rapid sea-level changes and tectonic movements. Based on new field, sedimentological and palaeontological analyses, these deposits have been organized into four sedimentary sequences (S1 to S4) separated by three subaerial erosion surfaces (SB0, SB1 and SB2). Sequences S1 and S2 ('Calcaires inférieurs à rhodolithes') deposited during the late Zanclean to early Gelasian (planktonic foraminiferal Zones PL2 to PL5) in low subsidence conditions, on a distally steepened ramp dipping eastward. Red algal-rich deposits, which dominate the western part of Grande-Terre, change to planktonic foraminifer-rich deposits eastward. Vertical movements of tens of metres were responsible for the formation of SB0 and SB1. Sequence S3 ('Formation volcano-sédimentaire', 'Calcaires supérieurs à rhodolithes' and 'Calcaires à Agaricia') was deposited during the late Piacenzian to early Calabrian (Zones PL5 to PT1a) on a distally steepened, red algal-dominated ramp that changes upward into a homoclinal, coral-dominated ramp. Deposition of Sequence S3 occurred during a eustatic cycle in quiet tectonic conditions. Its uppermost boundary, the major erosion surface SB2, is related to the Cala1 eustatic sea-level fall. Finally, Sequence S4 ('Calcaires à Acropora') probably formed during the Calabrian, developing as a coral-dominated platform during a eustatic cycle in quiet tectonic conditions. The final emergence of the island could then have occurred in late Calabrian times.
ISSN: 1469-3496

hal-00760906
https://hal.archives-ouvertes.fr/hal-00760906
DOI : 10.1111/j.1365-3091.2011.01311.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The formation age of the Siberian cratonic mantle is not well established as yet. Re–Os data on various mantle-derived materials have shown that it contains Archaean components, but the reported Re-depletion ages show a broad variation range (3.4 to 1 Ga) and are commonly ≤ 2 Ga for peridotite xenoliths. We report Hf and Nd isotope data for cpx and garnet separated from nine refractory spinel and garnet peridotite xenoliths from the Udachnaya kimberlite. The cpx from low-opx spinel harzburgites show extremely high εHf values, from + 607 to + 2084, which testify to long-term evolution of these rocks with high Lu/Hf ratios, consistent with their residual origin and near absence of post-melting enrichments in the Lu–Hf system. Such high εHf values are unusual for cpx from other cratonic peridotites and are higher than those reported for depleted cpx in off-cratonic peridotites. The clinopyroxenes from low-opx spinel harzburgites yield Hf model ages from 1.9 to 1.7 Ga while the cpx from high-opx spinel harzburgites yield Hf model ages from 3.0 to 1.9 Ga. When plotted together, they define a Lu/Hf isochron with an age of 1.80 Ga, which we consider as a robust estimate of the formation age (melt extraction event) because it is obtained on residual rocks that show no evidence for HREE and Hf enrichments and because the model ages for three out of four individual samples are similar to each other. The cpx have high εNd of + 94 to + 123, which are inconsistent with their low Sm/NdPM of < 1 and yield no meaningful age estimates. The consistently high, positive εNd in these cpxs can be interpreted in terms of long-term evolution of refractory peridotites with high Sm/Nd, followed by relatively recent LREE enrichments.We infer that a significant part of the lithospheric mantle in the central Siberian craton may have been formed during a major event (or a series of events) at around 1.8 Ga. Older ages reported for the central Siberian craton may refer to less common materials from cratonic or other domains formed in the Archaean that were later incorporated into the cratonic roots. The transition from the “Archaean” to “modern” tectonic regimes in Siberia and possibly elsewhere may have taken place at 1.8–1.9 Ga rather than at ~ 2.5 Ga, i.e. in the second half of the Paleoproterozoic rather than at the Archaean–Proterozoic boundary, at which time the asthenospheric mantle became generally too cold to experience high-degree melting on a large scale. The ~ 1.8 Ga formation age of the Siberian cratonic mantle is coeval with that for a major part of the ancient continental crust in the central Siberian craton. The temporal crust–mantle links may be explained either by the generation of the initial source materials for continental crust in the same melting event that formed the residual peridotites or, alternatively, by subduction and melting of pre-existing proto-lithosphere destabilized by a major mantle upwelling that formed the residual mantle.
ISSN: 0009-2541

hal-01115519
https://hal.archives-ouvertes.fr/hal-01115519
DOI : 10.1016/j.chemgeo.2014.10.018

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) : Nature Publishing Group
Résumé : Submarine mud volcanoes are important sources of methane to the water column. However, the temporal variability of their mud and methane emissions is unknown. Methane emissions were previously proposed to result from a dynamic equilibrium between upward migration and consumption at the seabed by methane-consuming microbes. Here we show non-steady-state situations of vigorous mud movement that are revealed through variations in fluid flow, seabed temperature and seafloor bathymetry. Time series data for pressure, temperature, pH and seafloor photography were collected over 431 days using a benthic observatory at the active Hakon Mosby Mud Volcano. We documented 25 pulses of hot subsurface fluids, accompanied by eruptions that changed the landscape of the mud volcano. Four major events triggered rapid sediment uplift of more than a metre in height, substantial lateral flow of muds at average velocities of 0.4m per day, and significant emissions of methane and CO2 from the seafloor.
Nature Communications (2041-1723) (Nature Publishing Group), 2014-11-11 , Vol. 5 , P. 1-8

Droits : 2014 Macmillan Publishers Limited. All rights reserved.
http://archimer.ifremer.fr/doc/00245/35601/34137.pdf
http://archimer.ifremer.fr/doc/00245/35601/34138.pdf
DOI:10.1038/ncomms6385
http://archimer.ifremer.fr/doc/00245/35601/

Éditeur(s) : Copernicus Gesellschaft Mbh
Résumé : During the GWADASEIS cruise (Lesser Antilles volcanic arc, February-March 2009) a very high resolution (VHR) seismic-reflection survey was performed in order to constrain Late Quaternary to Present faulting. The profiles we obtained evidence frequent "ponding" of reworked sediments in the deepest areas, similar to the deposition of Mediterranean "homogenites". These bodies are acoustically transparent (few ms t.w.t. thick) and are often deposited on the hanging walls of dominantly normal faults, at the base of scarps. Their thickness appears sufficient to compensate (i.e. bury) co-seismic scarps between successive earthquakes, resulting in a flat and horizontal sea floor through time. In a selected area (offshore Montserrat and Nevis islands), piston coring (4 to 7m long) was dedicated to a sedimentological analysis of the most recent of these particular layers. It corresponds to non-stratified homogenous calcareous silty sand (reworked calcareous plankton and minor volcanoclastics). This layer can be up to 2 m thick, and overlies fine-grained hemipelagites. The upper centimeters of the latter represent the normal RedOx water/sediment interface. Pb-210 and Cs-137 activities lack in the massive sands, while a normal profile of unsupported Pb-210 decrease is observed in the hemipelagite below, together with a Cs-137 peak corresponding to the Atmospheric Nuclear Experiments (1962). The RedOx level was thus capped by a recent instantaneous major sedimentary event considered as post-1970 AD; candidate seismic events to explain this sedimentary deposits are either the 16 March 1985 earthquake or the 8 October 1974 one (M-w = 6.3 and M-w = 7.4, respectively). This leads to consider that the syntectonic sedimentation in this area is not continuous but results from accumulation of thick homogenites deposited after the earthquakes (as observed in the following weeks after Haiti January 2010 event, McHugh et al., 2011). The existence of such deposits suggests that, in the area of study, vertical throw likely results from cumulated effects of separated earthquakes rather than from aseismic creep. Examination of VHR profiles shows that all major co-seismic offsets are recorded in the fault growth sequence and that co-seismic offsets can be precisely estimated. By using a sedimentation rate deduced from Pb-210 decrease curve (0.5 mmyr(-1)) and taking into account minor reworking events detected in cores, we show that the Redonda system may have been responsible for five > M-6 events during the last 34 000 yr. The approach presented in this work differs from fault activity analyses using displaced sets of isochronous surfaces and postulating co-seismic offsets. Combining VHR seismic imagery and coring we can decipher co-seismic vs. slow continuous displacement, and thus actually estimate the amplitude and the time distribution of major co-seismic offsets.
Natural Hazards And Earth System Sciences (1561-8633) (Copernicus Gesellschaft Mbh), 2012 , Vol. 12 , N. 5 , P. 1755-1767

Droits : Author(s) 2012. CC Attribution 3.0 License.
http://archimer.ifremer.fr/doc/00089/20040/21990.pdf
DOI:10.5194/nhess-12-1755-2012
http://archimer.ifremer.fr/doc/00089/20040/

Éditeur(s) : HAL CCSD
Résumé : International audience
Ce texte, issu d’une thèse de doctorat soutenue en 1991, traite de la vulnérabilité des populations exposées au volcan Cotopaxi en Equateur. L’accent est placé sur les représentations du risque, les aspects sociaux et socio-économiques ainsi que sur la cartographie de cette vulnérabilité.
Enseigner les risques naturels. Pour une géographie physique revisitée

Droits : info:eu-repo/semantics/OpenAccess
ISBN : 2-86912-059-4
hal-01184813
https://hal.archives-ouvertes.fr/hal-01184813
https://hal.archives-ouvertes.fr/hal-01184813/document
https://hal.archives-ouvertes.fr/hal-01184813/file/D%27Ercole%201994%20Mesurer%20le%20risque%20CHAM%27S%20compressed.pdf

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 Springer
Résumé : Subduction is a major process that plays a first-order role in the dynamics of the Earth. The sinking of cold lithosphere into the mantle is thought by many authors to be the most important source of energy for plates driving forces. It also deeply modifies the thermal and chemical structure of the mantle, producing arc volcanism and is responsible for the release of most of the seismic energy on Earth. There has been considerable achievements done during the past decades regarding the complex interactions between the various processes acting in subduction zones. This volume contains a collection of contributions that were presented in June 2007 in Montpellier (France) during a conference that gave a state of the art panorama and discussed the perspectives about "Subduction Zone Geodynamics". The papers included in this special volume offer a unique multidisciplinary picture of the recent research on subduction zones geodynamics. They are organized into five main topics: Subduction zone geodynamics, Seismic tomography and anisotropy, Great subduction zone earthquakes, Seismogenic zone characterization, Continental and ridge subduction processes. Each of the 13 papers collected in the present volume is primarily concerned with one of these topics. However, it is important to highlight that papers always treat more than one topic so that all are related lighting on different aspects of the complex and fascinating subduction zones geodynamics.
https://hal.archives-ouvertes.fr/hal-00808864

ISBN : 978-3-540-87974
hal-00808864
https://hal.archives-ouvertes.fr/hal-00808864

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