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Séminaires internes 2019 - 2020

Contact : Jessica Flahaut (flahaut@crpg.cnrs-nancy.fr)

- 4 Novembre 2019 : Julien Boulliung - Solubilité, spéciation et diffusion de l’azote dans les verres et liquides silicatés

Résumé : L’origine de l’azote (N) sur Terre, et les échanges entre ses différents réservoirs (atmosphère, manteau et noyau) au cours de son évolution sont aujourd’hui encore largement débattus. Peu de données portant sur le comportement de l’azote lors des processus de haute température sont disponibles. Pour mieux comprendre les mécanismes d’incorporation de N dans les silicates fondus (magma), une série d’expérience d’équilibre gaz-liquide silicaté a été réalisée à haute température (1425°C) et à pression atmosphérique (1 bar), pour différentes compositions de silicates et différentes conditions de fugacité d’oxygène (fO2) (de IW-8 à IW). Les teneurs en N dans les verres obtenus ont été déterminées par SIMS (spectrométrie de masse des ions secondaires) et spectrométrie de masse gaz rare (VG-5400 et Noblesse HR). La spéciation de l’azote dans les verres silicatés a été étudiée par spectroscopie Raman. Les résultats montrent un effet fondamental de la fO2 et de la composition du silicate sur la solubilité de N dans les silicates fondus. Ces nouvelles données permettent de contraindre la solubilité de N à la surface de l’océan magmatique terrestre en équilibre avec une atmosphère réduite riche en azote.

- 18 Novembre 2019 : Antoine Crémades - Transition from rifting to convergence in a segmented margin : processes and kinematics of inversion along the eastern Pyrenean-Provençal system

Résumé : In recent decades, research into the understanding of orogenic systems has been strongly influenced by the notion of inheritance, and particularly by the concepts of (1) the formation and evolution of passive margins that are inverted to form orogenic belts and (2) salt tectonics as a major controlling factor during the evolution of rifts and orogenesis. Due to salt mobility and solubility, the understanding of the processes involved in the inversion of salt rich rifts are poorly documented, especially in transfer zones, major crustal structures that lie at a high angle to the rift trend and where strain is relayed from one structure to another. Using a tectono-stratigraphic field approach coupled with paleomagnetism and raman paleothermometry, this doctoral project aims to improve our understanding of inversion processes in and around salt rich rift transfer zones by studying the tectono stratigraphic architecture of a case study : the Corbières transfer zone between the eastern Pyrenees and Provençal domains. As a result of the gentle shortening in the eastern Pyrenees during orogenesis, this salt rich transfer zone preserves pre—(rift related) and syn—(orogen related) inversion structures. In this talk, I will present part of the tectono-stratigraphic study witch allows us to reinterpret previously identified Pyrenean compressional structures (Eocene) as extensional structures that developed during early Jurassic to early Cretaceous (Mesozoic rifting) in relation to active salt tectonics processes. These old extensional structures allow us to open the debate on (1) the influence of Alpine Tethys (Lias-Dogger) and the Pyrenean (Aptian-Albian) distensive systems at their intersection in the Corbières and (2) their implication as inherited template for younger tectonic phases (Apto-Albian rifting, Pyrenean orogeny, and Gulf of Lion rifting).

- 11 Décembre 2019 (Exceptionnellement le Mercredi) : Delphine Klaessens - Melt migration and dunite formation in the mantle section of the Oman ophiolite

Résumé : The processes of melt migration in the mantle, particularly beneath mid-oceanic ridges, are still largely debated. Ophiolite mantle section contains dunite bodies that are viewed as melt-rock reaction products, resulting from complete dissolution of pyroxene in peridotites, and interpreted as relics of conduits for focused melt flow. We combine structural observations and geochemical data on peridotites from the Oman ophiolite, the world’s largest and best-exposed oceanic lithosphere segment. We observe three types of dunite throughout the mantle section : (1) a dunitic layer beneath the crust corresponding to a melt storage and reaction zone, called the Moho Transition zone (MTZ) ; (2) concordant and discordant dunitic dykes occurring sporadically throughout the whole section ; (3) concordant dunitic bands at the base of the ophiolite section. We have analyzed highly siderophile (HSE - Os, Ir, Ru, Pt, Pd and Re) and lithophile (in progress) element compositions of the three types of dunite and of their associated host harzburgite to investigate their origin. Our results show Os isotope signatures consistent with abyssal peridotite values, and limited variation in Mg# and HSE abundances for harzburgites. In contrast, dunites have compositions coherent with their structural contexts. Their Mg#, HSE spectra and Os isotopes all imply increasing interaction with melt from the base to the summit.

- 16 Décembre 2019 : Gaston Giuliani - Idée de cadeaux pour Noël : un saphir de la Haute-Loire ou de l’Atlantique ?

Résumé : Gem sapphire deposits from the basaltic Cenozoic magmatism of the French Massif Central (FMC) were eroded by the Loire River and its tributaries Allier and other minor creeks. New placers formed downstream near Gien near Orléans up to the beach of Brétignolles-sur-mer on the Atlantic Ocean. The present contribution compares the mineralogy (habits, solid and melt inclusions) and geochemistry (trace elements and O-isotopes) of sapphires from the FMC, Gien and Brétignolles-sur-mer in order to discuss the ability of the Loire River to transport corundum from the central part of France to its estuary at the Atlantic Ocean, once upon a time prior to the construction of dams.

- 20 janvier 2020 : Sylvain Breton - Dynamique des surfaces planétaires à partir des statistiques de cratères d’impact

Résumé : Impact crater are often used in the study of planetary surfaces. On the one hand, statistics on crater number provide the age of the surface, on the other hand, their shapes reflect the surface processes they witnessed. This study combines the statistic and morphology approaches in order to investigate the timing and intensity of sedimentary and volcanic processes of planetary surfaces. The use of crater depth measurements add a dimension to frequency distributions with the introduction of size and depth frequency distribution (SDFD). SDFSs can be interpreted in term of crater obliteration rates thanks to crater chronology models. We also developed models of crater population taking into account obliteration. Mars surface is highly cratered with many craters displaying signs of modifications by volcanic process, sedimentation and erosion. We interpreted SDFDs using a classic crater chronology system, to produce global maps of obliteration at different epochs of Mars. During Noachian, obliteration rates reach several thousands m/Gy, but rapidly decrease during early Hesperian and are close to 0 during Amazonian. Obliteration on the province of Tharsis decreased slower, suggesting a persistence of volcanic activity until early Amazonian. Northern lowlands witness Amazonian obliteration rates one order of magnitude higher than the rest of the planet, which may indicate the continuous formation of Vastitas Borealis during middle Amazonian. In addition to our global approach, we computed recent obliteration rates from mapping of high resolution images on landing sites of rover missions. Mawrth Vallis and Oxia Planum present significant obliteration rates, especially on units containing hydrated minerals.

- 27 janvier 2020 : Présentation des services numériques de l’UL - exceptionnellement à 14h

- 3 Février 2020 : Gen Ito - Infrared spectroscopy and field portable instrumentation for planetary exploration

Summary : Future missions to planetary objects are expected to have increasingly more human and rover components in surface exploration. To aid the explorers in conducting scientific tasks, portable instruments will likely be invaluable. Currently, knowledge of instrument suitability and most effective incorporation strategies are not sufficiently developed. As one of the first steps in this development process, we assess the fundamental capabilities of portable imaging technique in providing critical information for geological field work on planetary surfaces. Portable imaging, operating in the thermal infrared (8–13 μm), captured crucial data regarding rock/mineral types at field sites analogous to planetary settings. Value brought forth by portable infrared imaging is substantial, and this technique has the potential to benefit effective geological field work, which may lead to maximizing scientific return from missions. This finding and accompanying analyses presented here serve as a foundation for further development of instruments and mission strategies.

- 10 Février 2020 : Valentin Casola

- 23 Mars 2020 : Yves Marrocchi - Conditions de formation des premiers solides du Système Solaire

publié mardi 16 septembre 2014