Guérande – 10bis boulevard du 19-Mars-1962

Le diagnostic réalisé dans le cadre du projet d’aménagement du 10bis boulevard du 19-Mars-1962 à Guérande a concerné une emprise de 5 650 m2, diagnostiquée à hauteur de 5,2 % – soit 8,1 % sur les 3 615 m2 accessibles. Les contraintes d’accès, la faible largeur des tranchées réalisées ainsi que des conditions d’observation défavorables limitent la compréhension de la nature et de l’organisation des vestiges mis en évidence. Ceux-ci se répartissent sur l’ensemble de la parcelle avec cependant u..

A tectonic model for the juxtaposition of granulite- and amphibolite-facies rocks in the Eburnean orogenic belt (Sassandra-Cavally domain, Côte d’Ivoire)

The Sassandra-Cavally (SASCA) domain (SW Côte d’Ivoire) marks the transition between the Archean Kenema-Man craton and the Paleoproterozoic (Rhyacian) Baoule-Mossi domain. It is characterized by the tectonic juxtaposition of granulite-facies and amphibolite-facies rocks. Migmatitic grey gneisses, garnet–cordierite–sillimanite migmatitic paragneisses and garnet–staurolite-bearing micaschists reached peak pressure conditions ranging from ∼ 6.6 kbar at 620 °C to ∼ 10 kbar at 820 °C. These conditions are associated with the first recorded deformation D1 and correspond to a Barrovian geothermal gradient of ∼ 25 °C/km. Subsequent exhumation, associated with a second deformation D2, was marked by decompression followed by cooling along apparent geothermal gradients of ∼ 40 °C/km. A D3 deformation phase is marked by folding and local transposition of the regional S1/S2 foliation into E-W trending shear zones. LA-ICP-MS U–Pb dating of monazite, which displays complex internal structures, reveals four age groups correlated to textural position of monazite grains and analytical points: (1) rare relictual zones yield dates at the Archean-Paleoproterozoic transition (ca. 2400–2600 Ma); (2) a cluster of dates centered at ca. 2037 Ma on grains aligned along the S2 foliation of the migmatitic grey gneiss, attributed to D2; (3) a cluster of dates centered at ca. 2000 Ma, and (4) dates spreading from ca. 1978 to 1913 Ma, documented for the first time in the West African Craton monazites. The ages of the latter two groups are similar to the ones identified in the Guiana Shield, and could be attributed to a disturbance by fluids, to a periodic opening of U–Pb system or to an episodic crystallization of monazite during slow cooling lasting several tens of Myrs. These data allow to propose a model for the tectonic evolution of the SASCA domain at the contact between the Rhyacian Baoule-Mossi domain and the Archean Kenema-Man nucleus whereby crustal thickening is achieved by crustal-scale folding and is followed by and concomitant with lateral flow of the thickened partially molten crust accommodated by regional transcurrent shear zones. This combination of crustal thickening controlled by tectonic forces and gravity-driven flow leads to the juxtaposition of granulite- and amphibolite-facies rocks

Cryptic trans-lithospheric fault systems at the western margin of South America: implications for the formation and localization of gold-rich deposit superclusters

We present a review of frontier research advances in the investigation of cryptic structures that transect the South American Andes at oblique strike directions. The intersections between these cryptic structures and the superimposed Andean belt correlate with the spatial distribution of gold-rich mineral deposit clusters. The deposit clusters can be described as superclusters, as they comprise various gold deposit types that formed at multiple times throughout the Phanerozoic, impinging repeatedly on the structural intersections. However, the cryptic inherited fault structures are difficult to detect, because their deeper-seated roots are often overlain by younger supracrustal successions, and/or their exposed surface manifestations are structurally obscured by subsequent tectonic-magmatic activity. Thus, it also remains a challenge to constrain the nature and timing of formation, and the respective subsequent evolutionary path, of these proposed pre-Andean structures. Based on various case studies, we demonstrate that the localization of identified Phanerozoic gold deposit superclusters along the western South American margin is fundamentally controlled by structural inheritance often dating back to at least the Mesoproterozoic. Integration of multi-approach observations and datasets allows insights into a larger-scale tectonic history that showcases the successive inheritance of major structures originating from the Amazonian Craton, over the Paleozoic Gondwana margin, into the Cenozoic magmatic belts of the Andes, and even into recent fractures within the subducting oceanic Nazca plate, recording >1.2-billion-years of progressive structural inheritance and growth at one of the longest-lived tectonic margins in Earth history. In contrast to previous models of the spatial distribution of gold deposits, based on statistical approaches and spatial periodicity in self-organized systems focusing on single subduction and/or accretion episodes and belts, we propose that the structural inheritance and intersections are key to the localization of gold deposits in the Andes. In combination with bulk-geochemical data from magmatic rocks, we suggest that inherited structures maintained a trans-lithospheric connectivity to pre-fertilized gold enriched upper mantle reservoirs, which were tapped during multiple tectono-magmatic reactivation episodes

From no whinge scenarios to viability tree

Avoiding whinges from various and potentially conflicting stakeholders is a major challenge for sustainable development and for the identification of sustainability scenarios or policies for biodiversity and ecosystem services. It turns out that independently complying with whinge thresholds and constraints of these stakeholders is not sufficient because dynamic ecological-economic interactions and uncertainties occur. Thus more demanding no whinge standards are needed. In this paper, we first argue that these new boundaries can be endogenously exhibited with the mathematical concepts of viability kernel and viable controls. Second, it is shown how these no whinge kernels have components, such as harvesting of resources, that should remain within safe corridor while some other components, in particular biodiversity, have only lower conservation limits. Thus, using radar charts, we show how this no whinge kernels can take the shape of a tree that we name viability tree. These trees of viability capture the idea that the unbounded renewal potential of biodiversity combined with a bounded use of the different ecosystem services are crucial ingredients for the sustainability of socio-ecosystems and the design of no whinge policies reconciling the different stakeholders involved

Exploring the vertebrate fauna of the Bird’s Head Peninsula (Indonesia, West Papua) through DNA barcodes

Biodiversity knowledge is widely heterogeneous across the Earth's biomes. Some areas, due to their remoteness and difficult access, present large taxonomic knowledge gaps. Mostly located in the tropics, these areas have frequently experienced a fast development of anthropogenic activities during the last decades and are therefore of high conservation concerns. The biodiversity hotspots of Southeast Asia exemplify the stakes faced by tropical countries. While the hotspots of Sundaland (Java, Sumatra, Borneo) and Wallacea (Sulawesi, Moluccas) have long attracted the attention of biologists and conservationists alike, extensive parts of the Sahul area, in particular the island of New Guinea, have been much less explored biologically. Here, we describe the results of a DNA-based inventory of aquatic and terrestrial vertebratecommunities, which was the objective of a multidisciplinary expedition to the Bird's Head Peninsula (West Papua, Indonesia) conducted between 17 October and 20 November 2014. This expedition resulted in the assembly of 1005 vertebrate DNA barcodes. Based on the use of multiple species-delimitation methods (GMYC, PTP, RESL, ABGD), 264 molecular operational taxonomic units (MOTUs) were delineated, among which 75 were unidentified and an additional 48 were considered cryptic. This study suggests that the diversity of vertebrates of the Bird's Head is severely underestimated and considerations on the evolutionary origin and taxonomic knowledge of these biotas are discussed.Fieldwork and laboratory activities were supported by the Lengguru 2014 Project (www.lengguru.org), conducted by the French National Research Institute for Sustainable Development (IRD), the Indonesian Institute of Sciences (LIPI) with the Research Centre for Biology (RCB), and the Politeknik KP Sorong, with the help of the Institut Français in Indonesia (IFI) and the French embassy in Jakarta, with corporate sponsorship from COLAS SA Company (Environment Department), Total Foundation, ABS, Wasco, Veolia Eau, SDV-Bolloré,Peer reviewe

Contribution of mantle plumes, crustal thickening and greenstone blanketing to the 2.75–2.65Ga global crisis

International audienceAssuming that the period 2.75–2.65 Ga corresponds to a single, but global, geodynamic event, we investigate—through numerical experiments—the mechanisms that could have led to the profound continental reworking that occurred at that time. Although the extent of the crisis at the Earth’s surface pledges in favour of the involvement of mantle plumes, our numerical experiments suggest that the thermal impact of mantle plumes is unlikely to explain both the amplitude and timing of the thermal anomaly, as observed in the Superior Province (Canada) and the Yilgarn Craton (Australia). Similarly, moderate crustal thickening can not lead to significant reworking of the continental crust within the observed time constraint. Crustal thickening with a factor ≥1.5 is also unlikely because it is not consistent with the moderate metamorphic grade observed at the surface of many Archaean cratons. Burial of a radiogenic crust under a 10 km thick greenstone cover also falls short of explaining, not so much the amplitude and the extent, but the timing of the thermal anomaly. In contrast, the combination of the thermal anomaly related to the greenstone blanketing effect with the heat transfer from a plume head spreading at the top of the thermal boundary layer can adequately explain the amplitude, the timing, and the extent of the 2.75–2.65 Ga crisis.Our favoured model involves a global rearrangement of convection cells in the deep mantle and formation of multiple mantle plumes. The greenstones emplaced at the surface and the plumes that spread in the thermal boundary layer contributed to heat the crust from both above and below. This produced massive crustal partial melting that reached its climax ca. 40 Myr after the emplacement of the plumes and associated greenstone cover rocks. This led to gravitational instabilities in the crust, as dense greenstone cover rocks began to sink into the thermally softened crust and granite domes rose in response. The extraction of heat-producing elements toward the upper part of the crust has contributed to the cooling and stabilisation of the cratons. This succession of events, which is not incompatible with plate-tectonic processes, may have profoundly changed the nature of the crust exposed at the surface and could explain the contrasting geochemical signatures of Archaean and post-Archaean shales

Composition and origin of fluids associated with lode gold deposits in a Mesoarchean greenstone belt (Warrawoona Syncline, Pilbara Craton, Western Australia) using synchrotron radiation X-ray fluorescence

International audienceMicrothermometry and Raman spectroscopy techniques are routinely use to constrain ore-fluids δ18O and molar proportions of anhydrous gas species (CO2, CH4, N2). However, these methods remain imprecise concerning the ore-fluids composition and source. Synchrotron radiation X-ray fluorescence allows access to major and trace element concentrations (Cl, Br and K, Ca, Fe, Cu, Zn, As, Rb, Sr) of single fluid inclusion. In this paper, we present the results of the combination of these routine and newly developed techniques in order to document the fluids composition and source associated with a Mesoarchaean lode gold deposit (Warrawoona Syncline, Western Australia). Fluid inclusion analyses show that quartz veins preserved records of three fluid inclusion populations. Early fluids inclusions, related to quartz veins precipitation, are characterized by a moderate to high Br/Cl ratio relative to modern seawater, CO2±CH4±N2, low to moderate salinities and significant base metal (Fe, Cu, Zn) and metalloid (As) concentrations. Late fluid inclusions trapped in secondary aqueous fluid inclusions are divided into two populations with distinct compositions. The first population consists of moderately saline aqueous brines, with a Br/Cl ratio close to modern seawater and a low concentration of base metals and metalloids. The second population is a fluid of low to moderate salinity, with a low Br/Cl ratio relative to modern seawater and significant enrichment in Fe, Zn, Sr and Rb. These three fluid inclusion populations point to three contrasting sources: (1) a carbonic fluid of mixed metamorphic and magmatic origin associated with the gold-bearing quartz precipitation; (2) a secondary aqueous fluid with seawater affinity; and (3) a surface-derived secondary aqueous fluid modified through interaction with felsic lithologies, before being flushed into the syncline. Primary carbonic fluids present similar characteristics than those ascribed to Mesoarchaean lode gold deposits. This suggests similar mineralization processes for mid- and Mesoarchaean lode gold deposits despite contrasting fluid–rock interaction histories. However, in regard to the protracted history documented in the Warrawoona Syncline, we question the robustness of the epigenetic crustal continuum model, as ore-fluid characteristics equally support an epigenetic or a polyphased mineralization process

Protracted fluid-rock interaction in the mid-Archaean and implication for gold mineralization: Example from the Warrawoona Syncline (WA).

International audienc

Protracted fluid-rock interaction in the mid-Archaean and implication for gold mineralization: Example from the Warrawoona Syncline (WA).

International audienc

Efficient transmission of 'Candidatus Phytoplasma prunorum' is delayed by eight months due to a long latency in its host-alternating vector

UMR BGPI Equipe 6 ; UMR DAP Equipe DGBPublication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699Understanding at which spatiotemporal scale a disease causes significant secondary spread has both theoretical and practical implications. We investigated this issue in the case of European stone fruit yellows (ESFY), a quarantine vector-borne phytoplasma disease of Prunus trees. Our work was focused on the processes underlying disease spread: the interplay between the life cycles of the pathogen ('Candidatus Phytoplasma prunorum') and of the vector (Cacopsylla pruni). We demonstrated experimentally that C. pruni has only one generation per year and we showed that, at least in southeastern France, C. pruni migrates between conifers in mountainous regions (where it overwinters) and Prunus spp. at lower altitude (where it breeds). In acquisition-inoculation experiments performed with C. pruni over its period of presence on Prunus spp., both immature and mature C. pruni were hardly infectious (0.6%) despite effective phytoplasma acquisition and multiplication. We demonstrated that most immature vectors born on infected plants reach their maximum phytoplasma load (107 genomes per insect) only after migrating to conifers and that, after a life-long retention of the phytoplasma, their transmission efficiency was very high (60%) at the end of winter (when they migrate back to their Prunus host). Thus, most transmissions occur only after an effective latency of 8 months, following vector migrations and overwintering on conifers in mountainous regions. From this transmission cycle, we can infer that local secondary spread of ESFY in apricot orchards is marginal, and recommend that disease management strategies take more into account the processes occurring at a regional scale, including the role of wild Prunus spp. in ESFY epidemics