Éditeur(s) : Wiley-Blackwell
Résumé : The Climate Forecast System Reanalysis (CFSR) provides a wealth of information spanning 1979–2009 for investigation of ocean wind and wave climate. Preprocessing of the data is necessary to remove the dominant seasonal signals and to create time series of semimonthly averaged wind speed and significant wave height over a 0.5° global grid. We perform an empirical orthogonal function (EOF) analysis to extract the dominant space-time patterns. The results for the three major ocean basins show strong zonal structures in the winds and saturation of the swells corroborating prior works with various data sets. We reexamine the CFSR data in the frequency domain to identify periodic signals associated with published climate indices. The Fourier transform of the preprocessed time series generates spectra ranging from 1 month to 15 years period for an EOF analysis. The results demonstrate the spatial structures and periods of climate phenomena. The Arctic Oscillation dominates the Atlantic basin with a broad range of intra-annual signals off the European coasts. The Indian and Pacific Oceans are strongly influenced by inter-annual cycles of the El Niño Southern Oscillation (ENSO) and the Antarctica Oscillation. The Indian Ocean also has strong intra-annual components ranging from 50 to 80 days period. The ENSO proves to be a ubiquitous signal around the globe, and in particular, saturates the Pacific with strong influences in the equatorial region and the Southern Hemisphere Westerlies. A commonality of all basins is that the magnitude and the spatial structure of the intra-annual and inter-annual signals are similar suggesting a wide range of periods in each of the climate cycles examined.
Journal of Geophysical Research: Oceans (21699275) (Wiley-Blackwell), 2014-08 , Vol. 119 , N. 8 , P. 5563-5584

Droits : 2014. American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00210/32149/30606.pdf
http://archimer.ifremer.fr/doc/00210/32149/30607.pdf
DOI:10.1002/2013JC009729
http://archimer.ifremer.fr/doc/00210/32149/

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : We present whole-rock major- and trace-element and Nd–Sr–Pb radiogenic isotope data for Cretaceous igneous suites from eastern Cuba. These rocks are related to the Greater Antilles paleo-island arc magmatism and have three different igneous styles. Group 1 consists of tholeiitic basalts and rare basaltic andesites that have normal mid-ocean ridge basalt (N-MORB)-like compositions similar to those found in back-arc basin basalts (TiO2 = 1·2–2·9 wt%; La/Yb(N) = 0·7–0·9, Th/Nb = 0·06–0·08, and initial 208Pb/ 204Pb = 37·65–37·74). Group 2 comprises basaltic and rare basaltic andesitic subvolcanic dykes with major- and trace-element and isotopic compositions similar to those of island arc tholeiites (TiO2 = 0·7–1·4 wt%; La/Yb(N) = 0·6–0·9, Th/Nb = 0·06–0·68, and initial 208Pb/ 204Pb = 37·74–38·25). Group 3 is composed of low-Ti (TiO2 = 0·3–0·9 wt%) calcalkaline igneous rocks that have an unambiguous subduction-related character (La/Yb(N) = 1·1–5·0, Th/Nb = 0·35–1·55, and initial 208Pb/ 204Pb = 37·94–38·39). The parental magmas of the three groups formed by variable melting degrees (< 5–25%) of spinel lherzolite, with more depleted mantle sources for Groups 2 and 3 than Group 1. The trace-element and radiogenic isotope compositions of primitive Group 3 samples are strongly bimodal. One subgroup of samples is characterized by low Ta/Yb (0·02–0·03) and Th/La (0·10–0·13), slightly subchondritic Nb/Ta (13·3–17·3), and relatively high initial 206Pb/204Pb (18·57–18·62) and {varepsilon}Nd (7·6–9·4). The remaining primitive Group 3 samples have higher Ta/Yb (0·06–0·11) and Th/La (0·24–0·32), and highly subchondritic Nb/Ta (7·6–9·1), coupled with lower initial 206Pb/204Pb (18·24–18·29) and {varepsilon}Nd (3·4–5·5). These signatures were induced by two distinct slab components that mainly reflect the contributions of Cretaceous Atlantic marine and North American continental sediments, respectively. Nb/Ta in the first subgroup was influenced by melting of rutile-bearing subducted crust, whereas in the second it was inherited from recycled continental sediments. The involvement of Atlantic and North American sediments in Cuban Cretaceous magmatism indicates that the Proto-Caribbean (North American-Proto Atlantic) lithosphere subducted beneath the Greater Antilles arc during the Late Cretaceous (pre-Campanian), consistent with geotectonic models involving onset of SW-dipping subduction beneath the Greater Antilles paleo-arc during the Aptian. The variable mantle source depletion and magnitude of the subduction component probably reflect different settings across the arc, from the arc front to a back-arc spreading ridge.
ISSN: 0022-3530

hal-00406373
https://hal.archives-ouvertes.fr/hal-00406373
DOI : 10.1093/petrology/egm040

Éditeur(s) : HAL CCSD
Résumé : IODP Hole U1309D (IODP Exp. 304-305, 30°N) and ODP Site 1275 (ODP Lag 209, 15°45?N) sampled two oceanic core complexes, at the Mid-Atlantic Ridge. The recovered rocks are mostly gabbroic with some very primitive and olivine rich (Ol>70%). In Hole U1309D, trace element compositions of clinopyroxene and plagioclase poikiloblasts from olivine-rich rocks ndicate that they crystallized from the same melt in all lithologies. Olivine trace element compositions are in disequilibrium with the two other minerals. Olivine crystallographic preferred orientations are weak, with a relatively strong uncommon [001] concentration but consistent with deformation by dislocation creep with activation of the high temperature (010) [100] slip system, commonly described in asthenospheric mantle. The joint study of geochemical processes and microstructures in these rocks suggest a complex crystallization history in an open system with percolation of large volume of MORBtype melt and interaction with the depleted shallow mantle. Olivine-rich rocks are interpreted as the ultimate residue of these melt-mantle reaction processes. At Site 1275, the formation of the more evolved rocks of the gabbroic series is not related to the impregnation event creating olivine-rich rocks.
These rocks represent late magmatic injections, which are completely crystallized at depth as intrusivegabbroic bodies. The results presented in this thesis are consistent with the formation of oceanic core complexes associated with relatively strong magmatic activity, and with the crystallization of most of melt in the lithosphere without basaltic counterpart erupted on the seafloor.
Le puits IODP U1309D (Exp. IODP 304-305, 30°N) et le Site ODP 1275 (Leg ODP 209, 15°45'N) ont permis d'échantillonner deux core complexes océaniques de la dorsale Médio-Atlantique. Les roches récupérées sont principalement gabbroïques dont certaines très primitives et riches en olivine (ol >70%). Dans le puits U1309D, les compositions en éléments en trace des poeciloblastes de clinopyroxène et de plagioclase des roches riches en olivine indiquent qu'ils précipitent depuis le même magma dans toutes les lithologies. La composition en éléments en trace des olivines est en déséquilibre avec ces deux minéraux. Les fabriques cristallographiques de l'olivine sont faibles avec une concentration sur [001] inhabituelle, néanmoins compatibles avec une déformation plastique de haute température, avec l'activation du système de glissement (010) [100] communément décrit dans le manteau asthénosphérique. L'étude conjointe des caractéristiques géochimiques et microstructurales de ces roches met en lumière une histoire complexe de cristallisation dans un système ouvert où de larges volumes de magma de type MORB ont percolé et interagi avec le manteau appauvri superficiel. Ces roches riches en olivine représenteraient le résidu ultime de ces réactions liquide-manteau. Au site 1275, la formation des roches les plus évoluées de la série n'apparaît pas liée à l'événement d'imprégnation formant les roches riches en olivine. Ces roches correspondent à des injections tardives de magma qui ont entièrement cristallisé en profondeur sous forme de plutons intrusifs. Les résultats présentés dans ce mémoire sont compatibles avec une formation des core complexes océaniques associée à une activité magmatique relativement importante, et à une cristallisation complète de tout ou partie de ces magmas dans la lithosphère sans contre-partie volcanique en surface.
https://tel.archives-ouvertes.fr/tel-00354807

tel-00354807
https://tel.archives-ouvertes.fr/tel-00354807
https://tel.archives-ouvertes.fr/tel-00354807/document
https://tel.archives-ouvertes.fr/tel-00354807/file/these_MD.pdf

Éditeur(s) : HAL CCSD Nature Publishing Group
Résumé : International audience
The mantle and continental crust--Earth's main silicate reservoirs--have a lead isotope composition that is too radiogenic to have evolved from primitive Solar System material over 4.57 billion years1. To account for this imbalance, it has been suggested that unradiogenic lead may have partitioned into the metallic core2, 3, 4 or lower continental crust5. Alternatively, radiogenic lead could have been added to Earth later by meteorite impacts6. Unradiogenic lead was discovered in fragments of mantle rocks exhumed in the Horoman massif, Japan, implying that the mantle itself may provide a complementary reservoir of unradiogenic lead7. However, it is unclear why this unradiogenic component is not sampled by the melting that generates oceanic basalts8. Here we present double-spike lead isotope data for abyssal peridotite rocks, considered to represent suboceanic mantle, exposed on the Atlantic Ocean floor. We find that sulphides dated at about 1.83 billion years old and trapped as inclusions in silicate minerals preserve extremely unradiogenic lead isotope compositions. This unradiogenic lead could have been prevented from adding significantly to oceanic basalts if either the silicates shield the sulphide inclusions or if the sulphides reside in refractory mantle rocks that are rarely sampled during melting. We conclude that the lead isotope composition of the silicate Earth could be largely balanced by unradiogenic lead in sulphide in the mantle.
ISSN: 1752-0894

hal-00795575
https://hal.archives-ouvertes.fr/hal-00795575
DOI : 10.1038/ngeo1531

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : Las Islas Canarias, situadas en la región macaronésica, acogen ecosistemas terrestres y marinos de valiosa riqueza ecológica y paisajística, representativos de las áreas culturales y biogeográficas de su entorno; hasta el punto de albergar tres Reservas de la Biosfera reconocidas por la UNESCO. La diversidad y riqueza de este marco insular ya fue elogiada por grandes científicos como Alexander von Humboldt o Charles Darwin. Sin embargo, actualmente la presión ejercida sobre el medio por parte del desarrollo urbanístico y la industria turística, motor económico del archipiélago, pone en peligro estos frágiles ecosistemas; lo que ha generado un profundo debate entre crecimiento económico y turístico, y desarrollo sostenible y conservación. El presente artículo trata, desde una óptica divulgativa, de acercar al lector al medio que caracteriza las Islas Canarias e introducirlo en el marco donde se desarrolla parte importante de la actividad turística en España, uno de los países que más turistas recibe año a año.
Les îles Canaries, situées dans la région de la ‘Macaronésica’ (l’Est de l’Océan Atlantique), abritent des écosystèmes marins et terrestres très précieux, tant du point de vue écologique que paysager. Ils sont représentatifs de les zones biogéographiques de sa région et comptent trois Réserves da Biosphère reconnues par l’UNESCO. De grands scientifiques comme Alexander Von Humboldt et Charles Darwin ont fait l’éloge de la richesse de la biodiversité de cet archipel. Cependant, actuellement, la pression anthropique, notamment en liaison avec le développement touristique et tous les enjeux économiques qui l’accompagnent, mettent en danger les écosystèmes des Canaries ; ce constat a ouvert un large débat sur les enjeux autour des développements économique et touristiques et leurs dérives. Notre article propose de mettre l’accent sur les caractéristiques des îles Canaries et de replacer les processus de développements touristiques dans leur contexte pour ouvrir la réflexion sur les conditions nécessaires pour d’un développement durable.
The Canary Islands, located in the region of 'Macaronésica' (Este of Atlantic Ocean), are home to marine and terrestrial ecosystems very valuable, both ecological and landscape. They are representative of the bio-geographic zones of the region and there are three Biosphere Reserves da recognized by UNESCO. Great scientists such as Alexander Von Humboldt and Charles Darwin have praised the richness of the biodiversity of this archipelago. However, at present, anthropogenic pressure, including in relation to tourism development and all economic issues that accompany it, endanger ecosystems Canary Islands. This has opened a broad debate on the issues surrounding economic development and tourism and their excesses. Our article proposes to focus on the characteristics of the Canary Islands and put the process of tourist developments in their context to open reflection on the necessary conditions for sustainable development.
Canaries

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.1302
http://journals.openedition.org/etudescaribeennes/1302

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

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

Éditeur(s) : HAL CCSD American Association for the Advancement of Science
Résumé : International audience
Sediments cored along the southwestern Iberian margin during Integrated Ocean Drilling Program Expedition 339 provide constraints on Mediterranean Outflow Water (MOW) circulation patterns from the Pliocene epoch to the present day. After the Strait of Gibraltar opened (5.33 million years ago), a limited volume of MOW entered the Atlantic. Depositional hiatuses indicate erosion by bottom currents related to higher volumes of MOW circulating into the North Atlantic, beginning in the late Pliocene. The hiatuses coincide with regional tectonic events and changes in global thermohaline circulation (THC). This suggests that MOW influenced Atlantic Meridional Overturning Circulation (AMOC), THC, and climatic shifts by contributing a component of warm, saline water to northern latitudes while in turn being influenced by plate tectonics.
ISSN: 0036-8075

hal-01054316
https://hal.archives-ouvertes.fr/hal-01054316
DOI : 10.1126/science.1251306

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : This paper discusses the hypothesis that small tunas and the various species found in association with drifting fads (such as "mahi-mahi", rainbow runner, wahoo, etc.) may be biologically trapped by such a strong association. Massive seeding of drifting artificial fads was observed worldwide during recent years. In this hypothesis, we suggest that fads may alter some biological characteristics of epipelagic populations associated with them: migration, growth, condition factors, predation and natural mortality. As fads are most often used in the equatorial currents, they tend to exhibit zonal drift. Therefore, the associated populations would be artificially transferred from one part of the ocean to another, when they would show different movement patterns in the absence of fads. Natural logs were probably beneficial in terms of ecology and evolution, because they tend to accumulate in convergence areas, most often considered as rich forage areas. Now, fads are seeded in offshore areas, which are not necessarily favourable for tuna feeding. This apparently strong association between fishes and drifting fads may then produce an unexpected biological impact on tuna populations and their associated fauna. The plan is to test this hypothesis in the Atlantic, developing an ad hoc research programme based on tagging, biological and physiological studies, in association to an analysis of high resolution fishery data before and after the development of the fad fishery.Original Abstract: Cet article discute l'hypothese selon laquelle les petits thons et les differentes especes associees a des DCP derivants (comme les coryphenes, elagatis, thazards, etc.) pourraient etre pris dans un piege biologique resultant de cette forte association. Le deploiement massif de DCP artificiels derivants a ete constate a l'echelle mondiale au cours des dernieres annees. Dans cette hypothese, ces DCP, colonises en permanence par de grandes fractions de populations epipelagiques, pourraient modifier les caracteristiques biologiques des especes concernees: leur migration, leur croissance, leurs facteurs de condition, la predation et la mortalite naturelle. Les DCP etant plus frequemment utilises dans les courants equatoriaux, ils tendent a deriver zonalement. Ainsi, les populations associees seraient artificiellement transferees d'un bord a l'autre de l'ocean, alors qu'elles manifesteraient d'autres types de deplacements en l'absence de DCP. Les debris naturels etaient probablement benefiques sur le plan de l'ecologie et de l'evolution car ils s'accumulent dans des zones de convergence le plus souvent considerees comme des zones riches en nourriture. Maintenant, les DCP sont mouilles au large, dans des zones qui peuvent ou non etre favorables a l'alimentation des thons. Cette association apparemment forte entre poissons et DCP derivants pourrait alors causer un impact biologique inattendu sur les populations pelagiques (thons et faune accompagnante). L'objectif est de tester cette hypothese dans l'Atlantique au moyen d'un programme de recherche s'appuyant sur du marquage et des etudes biologiques et physiologiques, parallelement a une analyse des donnees de peche (tailles et CPUE, avant et apres le deploiement des DCP derivants).

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15303/12636.pdf
http://archimer.ifremer.fr/doc/00042/15303/

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy B - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
Peridotites exhumed in the footwall of axial detachment faults at slow-spreading ridges are highly serpentinized. Most mid-ocean ridge detachment settings are magmatically active and hydrous fluid circulation in and near the fault has been shown to be influenced by the presence of melt or magmatic lithologies. Our working area along the Southwest Indian Ridge (62–65°E) is nearly amagmatic and represents an end-member to study the hydrous alteration of exhumed peridotites without these magmatic influences. We use an integrated petrological approach combining microstructural, mineralogical and chemical observations to unravel the sequence of serpentinization in 272 dredged samples of variably serpentinized peridotites and to document the circulation of serpentinizing fluids in and near the exhumation faults. We find that serpentine recrystallization and veins overprint the initial serpentinite mesh texture in ∼25% of the samples. Oxygen isotope data suggest that this sequence developed at relatively high temperatures (271–336°C) and under increasing fluid–rock ratios, from near stoichiometry for mesh texture formation to >10 during recrystallization. Increasing fluid supersaturation relative to serpentine favors the replacement of mesh texture lizardite by chrysotile and polygonal or polyhedral serpentine. We attribute local recrystallization into antigorite to moderate Si-metasomatism, possibly following pyroxene serpentinization. We do not observe the more pronounced Si-metasomatism leading to talc replacing serpentine that is reported for the more magmatically active Mid-Atlantic Ridge detachment settings and is attributed to prior leaching of magmatic rocks. Scales of preferential fluid pathways in our samples evolved from pervasive and close-spaced (<500 µm) microfractures during the formation of the initial serpentine mesh texture, to centimeter-thick planar domains of enhanced fluid flux, spaced at ∼10 cm intervals and probably grouped in corridors that may be up to ∼100 m across. Serpentine minerals are enriched in some fluid-mobile elements (Cl, B, U) relative to the peridotite protolith, and several elements (Al, Fe, Si, Cu, As, Sb, REE) are redistributed at the millimeter to decimeter scale. Serpentinizing fluids were seawater-derived, probably mildly alkaline (small to no europium anomalies), reducing and H2-enriched (formation of magnetite). These fluids may have been similar to, though warmer than, those venting at the ultramafic-hosted Lost City hydrothermal fluid (30°N, Mid-Atlantic Ridge).
ISSN: 0022-3530

hal-01174047
https://hal.archives-ouvertes.fr/hal-01174047
DOI : 10.1093/petrology/egv014

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : International audience
New geodynamical data from West Africa bring consistent informations on the pre-Mesozoic reconstruction within a large area running from the western Sahara to the Colombian cordillera. These new data support a Neoproterozoic Ocean (WANO) between the Amazonian (AMC) and West African (WAC) cratons previously to the Iapetus and Rheic oceans. We delineate 31 blocs detached from the surrounding three continents: NAC (North American Craton), AMC and WAC. 7 came from the WAC margin, 7 from the NAC, 6 from the AMC and 11 from an intermediate volcano sedimentary domain (COB) built on a 1200-1000 Ma oceanic crust. These imbricated blocks formed a tight mosaic by the Hercynian/Alleghanian tectonic event which gave way to the Pangea super-continent. But, during the Atlantic Ocean opening these blocks began to move. They were separated by new oceanic basins. However, previously to the Pangea, blocks from the COB domain formed two sets of garlands located on the northwestern Gondwana margin. The northern one moved to the North until the Silurian to collide the NAC (Taconic tectonic event) meanwhile the southern one remains on the Gondwana margin. All together were gathered by the Carboniferous/Permian time. Then, the framework for the opening of the Atlantic Ocean was not totally disconnected from the "Variscan" collage and many variscan weakness zones were re-used as initial breaking zones. Beyond this tectonic impact, the pre-mesozoic assemblage allows us to compare this "Caribbean" island arc with another one: the Indonesian "Banda" arc. Thus, West Africa is a geological key area for correlations between the Caribbean, the Appalachian, the Brazilian "Nordeste" and the West European domains and for the understanding of the Atlantic Ocean opening process.
EISSN: 1777-5817

hal-00842747
https://hal.archives-ouvertes.fr/hal-00842747
DOI : 10.2113/gssgfbull.184.1-2.5

Éditeur(s) : HAL CCSD Elsevier
Résumé : "Tectonically emplaced" mantle rocks include subcontinental, suboceanic, and subarc mantle rocks that were tectonically exhumed from the upper mantle and occur:(i) as dispersed ultramafic bodies, a few meters to kilometers in size, in suture zones and mountain belts (i.e., the "alpine," or "orogenic" peridotite massifs - De Roever (1957), Thayer (1960), Den Tex (1969));(ii) as the lower ultramafic section of large (tens of kilometers) ophiolite or island arc complexes, obducted on continental margins (e.g., the Oman Ophiolite and the Kohistan Arc Complex - Coleman (1971), Boudier and Coleman (1981), Burg et al. (1998));(iii) exhumed above the sea level in ocean basins (e.g., Zabargad Island in the Red Sea, St. Paul's islets in the Atlantic and Macquarie Island in the southwestern Pacific - Tilley (1947), Melson et al. (1967), Varne and Rubenach (1972), Bonatti et al. (1981)).The "abyssal peridotites" are samples from the oceanic mantle that were dredged on the ocean floor, or recovered from drill cores (e.g., Bonatti et al., 1974; Prinz et al., 1976; Hamlyn and Bonatti, 1980).Altogether, tectonically emplaced and abyssal mantle rocks provide insights into upper mantle compositions and processes that are complementary to the information conveyed by mantle xenoliths (See Chapter 2.05). They provide coverage to vast regions of the Earth's upper mantle that are sparsely sampled by mantle xenoliths, particularly in the ocean basins and beneath passive continental margins, back-arc basins, and oceanic island arcs.Compared with mantle xenoliths, a disadvantage of some tectonically emplaced mantle rocks for representing mantle compositions is that their original geodynamic setting is not exactly known and their significance is sometimes a subject of speculation. For instance, the provenance of orogenic lherzolite massifs (subcontinental lithosphere versus upwelling asthenosphere) is still debated (Menzies and Dupuy, 1991, and references herein), as is the original setting of ophiolites (mid-ocean ridges versus supra-subduction settings - e.g., Nicolas, 1989). In addition, the mantle structures and mineralogical compositions of tectonically emplaced mantle rocks may be obscured by deformation and metamorphic recrystallization during shallow upwelling, exhumation, and tectonic emplacement. Metamorphic processes range from high-temperature recrystallization in the stability field of plagioclase peridotites ( Rampone et al., 1993) to complete serpentinization (e.g., Burkhard and O'Neill, 1988). Some garnet peridotites record even more complex evolutions. They were first buried to, at least, the stability field of garnet peridotites, and, in some cases to greater than 150 km depths ( Dobrzhinetskaya et al., 1996; Green et al., 1997; Liou, 1999). Then, they were exhumed to the surface, dragged by buoyant crustal rocks ( Brueckner and Medaris, 2000).Alternatively, several peridotite massifs are sufficiently well preserved to allow the observation of structural relationships between mantle lithologies that are larger than the sampling scale of mantle xenoliths. It is possible in these massifs to evaluate the scale of mantle heterogeneities and the relative timing of mantle processes such as vein injection, melt-rock reaction, deformation, etc... Detailed studies of orogenic and ophiolitic peridotites on centimeter- to kilometer-scale provide invaluable insights into melt transfer mechanisms, such as melt flow in lithospheric vein conduits and wall-rock reactions (Bodinier et al., 1990), melt extraction from mantle sources via channeled porous flow ( Kelemen et al., 1995) or propagation of kilometer-scale melting fronts associated with thermalerosion of lithospheric mantle ( Lenoir et al., 2001). In contrast, mantle xenoliths may be used to infer either much smaller- or much larger-scale mantle heterogeneities, such as micro-inclusions in minerals ( Schiano and Clocchiatti, 1994) or lateral variations between lithospheric provinces ( O'Reilly et al., 2001).The abyssal peridotites are generally strongly affected by oceanic hydrothermal alteration. Most often, their whole-rock compositions are strongly modified and cannot be used straightforwardly to assess mantle compositions (e.g., Baker and Beckett, 1999). However, even in the worst cases the samples generally contain fresh, relic minerals (mainly clinopyroxene) that represent the only available direct information on the oceanic upper mantle in large ocean basins, away from hot-spot volcanic centers. In situ trace-element data on clinopyroxenes from abyssal peridotites provide constraints on melting processes at mid-ocean ridges (Johnson et al., 1990).In this chapter, we review the main inferences on upper mantle composition and heterogeneity that may be drawn from geochemical analyses of the major elements, lithophile trace elements, and Nd-Sr isotopes in tectonically emplaced and abyssal mantle rocks. In addition we emphasize important insights into the mechanisms of melt/fluid transfer that can be deduced from detailed studies of these mantle materials.
Treatise on Geochemistry Update12.04

hal-00407944
https://hal.archives-ouvertes.fr/hal-00407944
DOI : 10.1016/B0-08-043751-6/02004-1

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

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

Éditeur(s) : HAL CCSD International Phycological Society
Résumé : International audience
We studied a group of monoraphid diatom species (Bacillariophyceae, Achnanthidiaceae) found in the marine coastal environment of tropical islands of the Caribbean Sea, western Atlantic Ocean, Indian Ocean, South Pacific Ocean, the Adriatic Sea and the Black Sea. Based on light and electron microscope examination, Madinithidium was formally described as a genus new to science with the generitype defined as Madinithidium undulatum. The characteristic features of the valve structure are a strongly developed sternum and raphe sternum, transapical striae formed by a single areola (macroareolae) positioned in small depressions, elevated virgae and coaxial internal central raphe endings. Furthermore, the striae of both raphe and sternum valves are closed by finely perforated hymenes. Madinithidium and Achnanthidium species are difficult to identify correctly with light microscopy since their valves are small and finely structured. Four species recently described from the western Indian Ocean and assigned to Achnanthidium sensu lato – Achnanthidium capitatum, A. flexuistriatum, A. pseudodelicatissimum and A. scalariforme – possessed morphological features permitting their placement into Madinithidium gen. nov. The above-mentioned species were formally transferred to the new genus.
ISSN: 2330-2968

hal-01333391
https://hal-univ-perp.archives-ouvertes.fr/hal-01333391
DOI : 10.2216/14-21R2

Éditeur(s) : AGU
Résumé : Submarine canyons are narrow but deep submarine valleys that extend for hundreds of meters. They represent the most impressive structures that shape the present morphology of passive continental margins. They can occur off the mouth of rivers: the Tagus, Zaire, Amazon, and Orinoco in the Atlantic; the Indus in the Indian Ocean; and the Var, Rhone, and Ebro in the Mediterranean. Some are at times disconnected from any stream mouth such as the Nazare canyon, off Portugal, despite the fact that it is close to the coast. Some were connected to a river mouth during lowstands of sea level, such as the Wilmington canyon in the northwest Atlantic, or the Blackmud canyon in the northeast Atlantic.
EOS, Transactions American Geophysical Union (0096-3941) (AGU), 2004-07-06 , Vol. 85 , N. 27 , P. 257

Droits : 2004 AGU
http://archimer.ifremer.fr/doc/00071/18201/15769.pdf
DOI:10.1029/2004EO270001
http://archimer.ifremer.fr/doc/00071/18201/

Éditeur(s) : Yale University
Résumé : Data from a hydrographic section carried out in January-March 1994 offshore from the eastern coast of South America from 50S to 10N, are used to quantify the full-depth exchanges of water between the western boundary currents and the ocean interior. In the upper and intermediate layers, the westward transport associated with the southern branch of the South Equatorial Current was 49 Sv at the time of the cruise. The transports of the central and northern branches in the upper 200 m were 17 Sv and 12 Sv, respectively. After subtraction of the parts that recirculate in the subtropical, subequatorial, and equatorial domains, the fraction of the South Equatorial Current that effectively contributes to the warm water export to the North Atlantic is estimated at 18 Sv. The poleward boundary of the current southern branch is at 31S through the whole thickness of the subtropical gyre, but the latitude of the northern boundary varies from 7 degrees 30'S at the surface to 27S at 1400 m depth. The estimated latitude of its bifurcation into the Brazil Current and North Brazil Undercurrent also varies downward from about 14S at the surface to 28S at a depth of 600 m.In the North Atlantic Deep Water, eastward flows exceeding 10 Sv are observed at 3 degrees -4 degrees of latitude in both hemispheres, at 10S, and at 34S-30S. Between 4S and 17S, a net westward flow with an estimated transport of 19 Sv reinforces the southward deep western boundary current. Cyclonic circulations of Antarctic Bottom Water along the western boundaries of the Argentine and Brazil basins have amplitudes of 15 Sv and 13 Sv, respectively, exceeding those of the interbasin exchanges. The net alongshore transport of this water mass between the hydrographic section and the continental slope reverses to a southward direction from 13S to 27S, probably in relation with an eastward shift of the equatorward near-bottom boundary current at these latitudes.
Journal of Marine Research (0022-2402) (Yale University), 2000-11 , Vol. 58 , N. 6 , P. 1007-1039

Droits : 2000 Yale University
http://archimer.ifremer.fr/doc/2000/publication-803.pdf
DOI:10.1357/002224000763485782
http://archimer.ifremer.fr/doc/00000/803/

Éditeur(s) : Université Paul Sabatier, Toulouse III
Résumé : The marine phytoplankton in the ocean represents only less than 1% of global biomass. Phytoplankton performs half of all photosynthesis. This autotrophic biomass in ocean is then an essential element in the climate regulation through processes as carbon dioxide absorption during the photosynthesis. Therefore, we need to estimate precisely this biomass as well as the processes which affect it. Using remotely sensed data (altimetry and ocean colour) and a coupled physical/biogeochemical model (MERCATOR-OPA/NPZDDON), Rossby waves and their influence on phytoplankton biomass are specifically studied in the North Atlantic Ocean. Their features and their influences on surface chlorophyll concentrations were analysed. Through the different mechanisms identified, we estimated that these waves can induce local increases from 60% to 150% of the estimated primary production.
Même si l'océan ne représente que moins de 1% de la biomasse liée aux plantes sur la terre, il est responsable de près de la moitié de la photosynthèse nette de la biosphère. Cette biomasse est par conséquent un élément essentiel dans la régulation du climat à travers par exemple le cycle océanique du carbone. Il est donc nécessaire d'estimer correctement cette biomasse ainsi que les processus qui l'affectent. A l'aide de données satellites altimétriques et couleur de l'eau et d'un modèle couplé physique/biogéochimie (MERCATOR-OPA / NPZDDON), les ondes de Rossby et leur influence sur cette biomasse sont spécifiquement étudiées dans l'océan Atlantique Nord. Leurs propriétés et leur influence sur les concentrations en chlorophylle de surface sont analysées. Au travers des mécanismes mis en jeu identifiés, nous estimons que ces ondes peuvent entraîner une augmentation locale comprise entre 60% et 150% de la production primaire estimée.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2005/these-2454.pdf
http://archimer.ifremer.fr/doc/00000/2454/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
IODP Hole U1309D (Atlantis Massif, Mid-Atlantic Ridge 30 degrees N) is the second deepest hole drilled into slow spread gabbroic lithosphere. It comprises 5.4% of olivine-rich troctolites (->70% olivine), possibly the most primitive gabbroic rocks ever drilled at mid-ocean ridges. We present the result of an in situ trace element study carried out on a series of olivine-rich troctolites, and neighbouring troctolites and gabbros, from olivine-rich intervals in Hole U1309D. Olivine-rich troctolites display poilkilitic textures; coarse-grained subhedral to medium-grained rounded olivine crystals are included into large undeformed clinopyroxene and plagioclase poikiloblasts. In contrast, gabbros and troctolites have irregularly seriate textures, with highly variable grain sizes, and locally poikilitic clinopyroxene oikocrysts in troctolites. Clinopyroxene is high Mg# augite (Mg# 87 in olivine-rich troctolites to 82 in gabbros), and plagioclase has anorthite contents ranging from 77 in olivine-rich troctolites to 68 in gabbros. Olivine has high forsterite contents (82-88 in olivine-rich troctolites, to 78-83 in gabbros) and is in Mg-Fe equilibrium with clinopyroxene. Clinopyroxene cores and plagioclase are depleted in trace elements (e.g., Yb-cpx similar to 5-11 x Chondrite), they are in equilibrium with the same MORB-type melt in all studied rock-types. These compositions are not consistent with the progressively more trace element enriched (evolved) compositions expected from olivine rich primitive products to gabbros in a MORB cumulate sequence. They indicate that clinopyroxene and plagioclase crystallized concurrently, after melts having the same trace element composition, consistent with crystallization in an open system with a buffered magma composition. The slight trace element enrichments and lower Cr contents observed in clinopyroxene rims and interstitial grains results from crystallization of late-stage differentiated melts, probably indicating the closure of the magmatic system. In contrast to clinopyroxene and plagioclase, olivine is not in equilibrium with MORB, but with a highly fractionated depleted melt, similar to that in equilibrium with refractory oceanic peridotites, thus possibly indicating a mantle origin. In addition, textural relationships suggest that olivine was in part assimilated by the basaltic melts after which clinopyroxene and plagioclase crystallized (impregnation). These observations suggest a complex crystallization history in an open system involving impregnation by MORB-type melt(s) of an olivine-rich rock or mush. The documented magmatic processes suggest that olivine-rich troctolites were formed in a zone with large magmatic transfer and accumulation, similar to the mantle-crust transition zone documented in ophiolites and at fast spreading ridges.
ISSN: 0009-2541

hal-00420916
https://hal.archives-ouvertes.fr/hal-00420916
DOI : 10.1016/j.chemgeo.2009.02.013

Éditeur(s) : HAL CCSD
Résumé : The Deep Basin of the Gulf of Mexico (DBGM) extends over eastern Mexico, the southeastern part of the United States, west of the Atlantic Ocean. This study, based on the interpretation and integration of seismic profiles, exploration wells and outcrop studies, focus on the deep part of the Gulf of Mexico, where bathymetry varies from 200 to 3750 m, thus comprising both the continental slope and the abyssal plain. The first part of this thesis focus on the description of the sedimentary infill of the western part of the Gulf of Mexico, in the Veracruz State, and to its geodynamic controls. The geodynamic evolution of the Deep Basin of the Gulf of Mexico (DBGM) begins during the Triassic-Jurassic with the break-up and the opening of a continental rift, in the southern part of the North American lithospheric plate. This opening induced a relative movement of the Yucatan Block towards the southeast. This intra-continental rifting episode was followed by a stage of post-rift thermal subsidence in the basins of the continental margin in the west, coeval with oceanic accretion in the DBGM. The thermal subsidence of the margin was subsequently modified by the Laramian orogeny, which impacted strongly the overall architecture of the margin as well as its litho-stratigraphic evolution, inducing the deposition of siliciclastic deposits in various morphotectonic provinces: i.e., near the tectonic front of the Sierra Madre Oriental (SMO), within the adjacent Chicontepec foreland basin, over the Tuxpan Platform (Golden Lane), across the continental slope and up to the deep abyssal plain, these two last morphotectonic provinces belonging to the DBGM. During the Early Paleogene, the effects of the thermal subsidence of the passive margin were stressed by the tectonic load of the Laramian orogen (i.e., the Sierra Madre Oriental, SMO), thus allowing the development of a foreland basin flexural. In this geodynamic framework, the main sedimentary transfers developed from the tectonic front "SMO" in the west, towards the DBGM in the east, the main source for clastic sediments being linked to the erosion of the "SMO" mountains. During the Paleocene and the Early Eocene, the architecture of the silici-clastic syn-tectonic sediments deposited in submarine fans was characterized by sliding, turbidites with A and B Bouma facies, as well as levees and channels. After the stop of the flexural subsidence, the thermal subsidence of the passive margin resumed during the Late Eocene, the Oligocene and the Neogene, allowing the development of a new sedimentary prism, prograding eastwards toward the DBGM. This sedimentary infill was again made up of levees-channels, sand bars and delta systems. During the Neogene, an extensional system with listric faults and roll-over features developed across the slope of the DBGM, due to an active detachment developing within overpressured Eocene-Oligocene clays. This gravitational gliding of Neogene series accounted also for the development of compressional features at the toe of the slope. Approximately 60% of the Miocene siliciclastic sediments have been trapped in growth strata and slope basins associated with this complex gravitational system, ranging from river-delta features towards gravity slides associated with slump facies. The second part of this thesis aims at a quantification of these various processes, including the construction of balanced cross sections, forward Thrustpack kinematic modelling coupling the development of a basal detachment, lithospheric flexure, erosion and sedimentation, as well as subsequent stratigraphic modelling with the Dionisos software, the later aiming at predicting the sand versus clay ratios in Neogene siliciclastic deposits of the DBGM and its surroundings.
Le bassin profond du Golfe du Mexique (BPMG) est localisé à l'est du Mexique, au sud-est des États-Unis et à l'ouest de l'Océan Atlantique. Cette étude de la partie profonde du Golfe du Mexique est basée sur l'intégration de données de sismique, de forages pétroliers et d'études de terrain; elle comprend toute la pente continentale et la plaine abyssale, avec une bathymétrie qui varie de 200 à 3750 m. La première partie de cette thèse est consacrée à la description du remplissage sédimentaire de la bordure occidentale du Golfe du Mexique, dans le secteur de Veracruz, en liaison avec son évolution géodynamique. L'évolution géodynamique du BPMG commence au Trias-Jurassique avec la rupture et la propagation d'un rift continental, dans le secteur sud de la plaque nord américaine. Cette ouverture et le déplacement relatif vers le sud-est du bloc crustal du Yucatan sont à l'origine du BPGM. Cette géodynamique de rift continental est suivie d'une étape post-rift accompagnée de l'océanisation du bassin. Les bassins de la marge passive ont poursuivi leur évolution sous l'effet de la subsidence thermique à l'ouest du Golfe du Mexique, tandis que de la croûte océanique se formait dans le BPGM. Cette subsidence thermique de la marge a ensuite été perturbée par l'orogénèse Laramienne, qui a remodelé l'architecture stratigraphique silico-clastique des dépôts du Tertiaire entre les éléments morphotectoniques suivants: lefront tectonique de la Sierra Madre Orientale (SMO), le bassin d'avant-pays Chicontepec, la Plateforme de Tuxpan-Faja de Oro, la pente continentale et la plaine abyssale, ces deux dernières provinces morphotectoniques appartenant au BPGM. Pendant le Paléogèneinférieur, les effets de la subsidence thermique de la marge passive ont été accentués par la charge tectonique de l'orogénèse laramienne (SMO), permettant ainsi le développement d'un bassin flexural d'avant-pays. Au cours de cette étape, les principaux transferts sédimentaires se sont effectués du front tectonique "SMO" vers le BPGM. La source principale de sédiments clastiques est liée à l'érosion de la chaîne de montagnes "SMO". Pendant le Paléocène et l'Éocène inférieur, l'architecture des premiers sédiments silico-clastiques syn-tectoniques déposés dans des éventails sous-marins sont caractérisés par des figures de glissement, des faciès turbiditiques A et B de Bouma, des chenaux-levées. Après l'arrêt de la subsidence flexurale, la subsidence thermique de la marge passive s'est poursuivie pendant l'Éocène supérieur, l'Oligocène et le Néogène, permettant le développement d'un nouveau prisme sédimentaire progradant. Les remplissages sédimentaires sont encore constitués de chenaux et de levées, avec des barres de sable associées à des systèmes deltaïques sur la plateforme. Pendant le Néogène, un système de failles listriques s'est développé sur la pente du BPGM, au-dessus d'une surface de décollement située, dans la région d'étude, dans les argiles de l'Éocène-Oligocène. Ce système de failles de croissance a piégé plus de 60% des sédiments silico-clastiques du Miocène. Ce remplissage sédimentaire évolue latéralement de faciès fluviaux deltaïques vers des faciès de pente affectés de glissements gravitaires et associés à des turbidites. La deuxième partie de cette thèse est consacrée à une approche quantitative basée sur des modélisations structurales (coupes équilibrées et modélisations cinématiques directes avec Thrustpack, couplant décollement gravitaire, flexure lithosphérique, érosion et sédimentation), puis sédimentaires (prise en compte des transferts de matériel clastique depuis la partie émergée de la chaîne jusqu'au bassin profond, à l'aide du logiciel Dionisos, afin de mieux comprendre les processus de piégeage des sédiments grossiers dans les structures de croissance et les bassins perchés de la marge.
https://tel.archives-ouvertes.fr/tel-00435120

tel-00435120
https://tel.archives-ouvertes.fr/tel-00435120
https://tel.archives-ouvertes.fr/tel-00435120/document
https://tel.archives-ouvertes.fr/tel-00435120/file/thesealzaga.pdf

Éditeur(s) : Wiley-blackwell Publishing, Inc
Résumé : P>Torsvik et al. recently presented a revised model for the opening of the South Atlantic Ocean. According to these authors, this new plate tectonic model is internally consistent and consistent with globally balanced plate motion solutions and takes into account realistic intraplate deformation. However, this model shows a number of kinematic and geological problems that we underline here, together with some comparisons with the new kinematic model recently proposed by Moulin et al.
Geophysical Journal International (0956-540X) (Wiley-blackwell Publishing, Inc), 2010-10 , Vol. 183 , N. 1 , P. 20-28

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00014/12504/9878.pdf
DOI:10.1111/j.1365-246X.2010.04727.x
http://archimer.ifremer.fr/doc/00014/12504/

Éditeur(s) : Blackwell science
Résumé : Patterns of mitochondrial DNA (mtDNA) variation were used to analyse the population genetic structure of southwestern Indian Ocean green turtle (Chelonia mydas) populations. Analysis of sequence variation over 396 bp of the mtDNA control region revealed seven haplotypes among 288 individuals from 10 nesting sites in the Southwest Indian Ocean. This is the first time that Atlantic Ocean haplotypes have been recorded among any Indo-Pacific nesting populations. Previous studies indicated that the Cape of Good Hope was a major biogeographical barrier between the Atlantic and Indian Oceans because evidence for gene flow in the last 1.5 million years has yet to emerge. This study, by sampling localities adjacent to this barrier, demonstrates that recent gene flow has occurred from the Atlantic Ocean into the Indian Ocean via the Cape of Good Hope. We also found compelling genetic evidence that green turtles nesting at the rookeries of the South Mozambique Channel (SMC) and those nesting in the North Mozambique Channel (NMC) belong to separate genetic stocks. Furthermore, the SMC could be subdivided in two different genetic stocks, one in Europa and the other one in Juan de Nova. We suggest that this particular genetic pattern along the Mozambique Channel is attributable to a recent colonization from the Atlantic Ocean and is maintained by oceanic conditions in the northern and southern Mozambique Channel that influence early stages in the green turtle life cycle.
Molecular Ecology (0962-1083) (Blackwell science), 2007 , Vol. 16 , N. 1 , P. 175-186

Droits : 2007 Blackwell
http://archimer.ifremer.fr/doc/2007/publication-2185.pdf
DOI:10.1111/j.1365-294X.2006.03122.x
http://archimer.ifremer.fr/doc/00000/2185/