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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 : S. Morosi - Présentation des services numériques de l’UL

- 10 Février 2020 : Valentin Casola - Manteau source et genèse des magmas parents des carbonatites : les principales ressources en terres rares sur Terre

Résumé : Les carbonatites sont des magmas inhabituels, riches en carbone. Ils peuvent être formés par la fusion d’une source elle-même riche en C, ou par de faibles degrés de fusion d’un manteau pauvre en C (<80 ppm C) suivi d’une différenciation extrême et / ou d’une immiscibilité. En plus de l’intérêt scientifique, comprendre leur formation présente un intérêt économique puisque les carbonatites sont associées aux plus gros gisements de Terres Rares sur Terre. Dans le cadre de cette thèse, des xénolithes mantelliques (péridotites) ont été collectés autour de l’Oldoinyo Lengai (Rift est-africain, REA), le seul volcan actuellement actif émettant des carbonatites, afin de déterminer les compositions modales, chimiques et isotopiques du manteau source des carbonatites, ainsi que son histoire en termes de métasomatisme. Ces xénolithes ont fait l’objet d’une étude pétrographique et géochimique qui révèlent une histoire mantellique et métasomatique complexe. Par ailleurs, des analyses δ18O et δ13C (SIMS) ont été réalisées sur les carbonates présents dans ces xénolithes. Ces carbonates ont longtemps été considérés comme des arguments clés pour soutenir une source riche en C. Cependant, ces nouvelles données isotopiques vont à l’encontre d’un modèle d’enrichissement en carbone du manteau source des carbonatites sous forme de carbonates mantelliques puisque les carbonates considérés seraient des phases d’altération de surface. Par ailleurs, Le manteau sous le REA est très marqué par un métasomatisme silicaté et hydraté (illustré par des veines à phlogopites/ amphiboles/ ilménites/diopsides riches en Cr). Le caractère fertile de ces veines (par rapport à la lherzolite hôte), ainsi que leurs teneurs en C cinq fois plus élevées que la péridotite hôte, laisse à penser que ce métasomatisme joue un rôle important dans la formation de magmas primaires spécifiques pouvant former des carbonatites par différenciation et immiscibilité. Cette hypothèse a été testée par des expériences de fusion de ces veines naturelles en piston cylindre.

- 17 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.

- 2 Mars 2020 : Yves Marrocchi - Timescale and conditions of formation of the first solids of the solar system

Chondrites are leftover solids from the evolution of the solar protoplanetary disk 4.56 Gyr ago. They are composed of varying proportions of four main components : refractory inclusions, chondrules, Fe-Ni metal and matrix material. These materials were subsequently accreted together to form the asteroidal parent bodies that represent the source of unequilibrated meteorites. Refractory inclusions are high temperature assemblages composed of crystalline silicates and oxides rich in calcium and aluminum. They are the oldest recognized objects in Solar System with an absolute age of 4.5685 Gyr. Chondrules are silicate spherules that represent the most abundant solid formed during the evolution of the protoplanetary disk. However, due to a fragmentary understanding of processes involved, the timescale and the conditions of formation of these primordial solids remains very enigmatic and controversial. During this seminar, I will present new isotopic results that allows the condensation and agglomeration timescales of the first solids of the solar system to be quantified. By coupling petrographic observations and isotopic measurements, I will also discuss how recycling processes led to the formation of chondrules. These results will be used to discuss the conditions of formation and evolution of the solar protoplanetary disk.

- 9 Mars 2020 : Nicolas Bott - The surface of airless bodies in the Solar system

Résumé : Airless bodies (i.e. bodies with no or very tenous atmosphere) are of an incredible diversity in term of size, color and composition. This tell us the complex story of our Solar system, its nature and its evolution. Not protected by a gaseous shell such as on Earth, airless bodies’ surfaces undergo an intense alteration called space weathering, composed of several processes like micrometeorites bombardment or cosmic rays irradiation. Depending on their initial composition, they can either darken or brighten, redden or blueing. Thus, it is crucial to study airless bodies as a whole to figure out their initial composition and of the Solar system. During this seminar, I will present the different bodies I focused on till now, the main conclusions we can draw about them, and my project at CRPG.

- 30 Mars 2020 : Alessandro Maltese - On the Accretion of the Earth and a New Perspective on the Evolution of its Early Crust-Mantle System

Summary : The reconstruction of Earth’s earliest history, from its accretion to the formation of the first continents, is strongly limited by the availability of samples from that time. Despite this limitation, the accessible rock record comprises a compositionally diverse spectrum of different groups of meteorites, lunar and ancient terrestrial rocks, as well as remnants of those. Determination of their chemical and isotopic compositions has allowed to partly constrain the origin of material and the physical processes that formed and shaped the Earth during its early stages. During the seminar, I will present an overview of Earth’s accretion and early differentiation history. Mostly, this will be done from an (isotope) geochemical perspective and within the context of the work conducted during my PhD. I will discuss a mix of potentially useful contributions made, as well as some of the problems that I am currently facing. In detail, I will discuss how the element abundances observed in bulk silicate Earth (BSE) potentially trace the accretion and differentiation path of the Earth, what the Archean Lu-Hf record might teach us about ancient geodynamics, and how/if Hadean components within these rocks fit into the picture.

- 6 Avril 2020 : Présentations 1A - Nicolas Schnuriger + Carolina Dantas-Cardoso + Maxime Piralla

- 11 Mai 2020 : Présentations 1A - Yujin Jegal + Marius Huber




publié mardi 16 septembre 2014