Evolution géodynamique du bassin carbonifère de Laval

National audienc

Numerical modelling of the drag finishing process at a macroscopic scale to optimize surface roughness improvement on additively manufactured (SLM) Inconel 718 parts

International audienc

A LREE-depleted component in the Afar plume: Further evidence from Quaternary Djibouti basalts

International audienceMajor, trace element and isotopic (Sr, Nd, Pb) data and unspiked K–Ar ages are presented for Quaternary (0.90–0.95 Ma old) basalts from the Hayyabley volcano, Djibouti. These basalts are LREE-depleted (Lan/Smn = 0.76–0.83), with 87Sr/86Sr ratios ranging from 0.70369 to 0.70376, and rather homogeneous 143Nd/144Nd (εNd = + 5.9–+ 7.3) and Pb isotopic compositions (206Pb/204Pb = 18.47–18.55, 207Pb/204Pb = 15.52–15.57, 208Pb/204Pb = 38.62–38.77). They are very different from the underlying enriched Tadjoura Gulf basalts, and from the N-MORB erupted from the nascent oceanic ridges of the Red Sea and Gulf of Aden. Their compositions closely resemble those of (1) depleted Quaternary Manda Hararo basalts from the Afar depression in Ethiopia and (2) one Oligocene basalt from the Ethiopian Plateau trap series. Their trace element and Sr, Nd, Pb isotope systematics suggest the involvement of a discrete but minor LREE-depleted component, which is probably an intrinsic part of the Afar plum

Wrench-Related Dome Formation and Subsequent Orogenic Syntax Bending in a Hot Orogen (Variscan Ibero-Armorican Arc, the Ouessant Island, France)

During the Carboniferous collision stage, the West European Variscan orogen was affected by oblique convergence, wrenching, plate-scale oroclinal bending, and widespread exhumation of the deep crust. One of these exhumed units forms the Leon dome located on the northern flank of the Ibero-Armorican Arc in the western part of the Armorican massif. Structural field data from the Ouessant Island reveal kinematic changes between 330 and 300 Ma that affected the northwestern margin of the Leon dome. This margin underwent two ductile deformation phases with opposite strike-slip shear senses. Dextral strike-slip wrenching combined with orogen-normal shortening, orogen-parallel stretching, and local top-to-the-NE shearing occurred during the Leon dome formation and exhumation of its gneissic core at 330-310 Ma. During tightening of the Ibero-Armorican Arc at similar to 300 Ma, more localized sinistral wrenching reactivated the northwestern boundary of the Leon dome. The resulting N70 degrees E trending sinistral Porspoder-Ouessant shear zone together with its conjugate dextral South Armorican shear zone controlled the lateral escape of the Leon-North-Central Armorican rigid tectonic wedge triggered by indentation of the Cantabrian orocline at the core of the Ibero-Armorican Arc

Response of different benthic indices to diverse human pressures

International audienceThe interest in benthic indicators for soft-bottom marine communities has dramatically increased after a rather long period of relative stagnation due to the need for new tools to assess the status of marine waters, called for by the Clean Water Act and the Water Framework Directive. Our expertise on ben- thic communities has permitted us to gather a vast amount of data from diverse water bodies under unpolluted and polluted conditions (e.g., accidental oil spill, sewage, long-term anthropogenic estuarine constraints) in tidal estuaries, harbours, and on the coastal shelf from Atlantic Ocean and Mediterranean Sea. We compared the results of four biotic indices on the various available datasets: Shannon-Wiener H diversity, AMBI and BO2A, which divide the species into Ecological Groups, and ITI, which divides the species into trophic groups, and the agreement of Best Professional Judgement (BPJ) on the assessment of ecological conditions. Benthic indicators as "sentinel species", which is a particular species that by its presence or its relative abundance warns of possible unbalances in the surrounding environment or dis- tortions in community functions, was also tested. Indicators, BPJ and opportunist sentinel species gave similar ECoQS for the different sampling sites. We discuss the use of Biological Indicators as 'objective' or 'subjective' alternatives for assessing soft-bottom communities, and propose to employ simple methods such as BPJ and taxonomy sufficiency in such diagnostic approaches