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Séminaires internes 2020 - 2021

Contact : Jessica Flahaut (jessica.flahaut@univ-lorraine.fr)

A partir du 29 octobre 2020, les séminaires internes seront assurés à 100% en virtuel sur Microsoft Teams (voir lien reçu par email)

- 14 Septembre 2020 : Présentations nouveaux doctorants 2019-2020 - Yujin Jegal - Development of in-situ Rb-Sr isotopic measurements by LA-ICP-MS and SIMS for small-scale dating of geological processes : Preliminary results

- 21 Septembre 2020 : Marion Auxerre - Cristallisation des olivines dans les chondres macro-porphyrique et barrés

Résumé : Les chondres, principal constituant des chondrites (météorites primitives) font partis des premiers objets à se former dans le Système Solaire. Ces chondres sont de petites gouttelettes de liquide silicaté de quelques millimètres, partiellement ou complètement fondues. D’un point de vue textural, Les chondres sont divisés en deux catégories : les chondres porphyriques avec 80 % (M-P, m-P, POP, PO, PP) et les chondres non-porphyriques avec 20 % (BO, RP…). Parmi ces chondres, ceux dits barrés (BO) et macro-porphyriques (M-P) ont la particularité d’être composés de très peu de cristaux d’olivines (<5 cristaux en barre pour les BO et automorphes pour les M-P). Cependant, des récentes études expérimentales montrent des désaccords sur leur formation (Lofgren 1987, Libourel et al., 2019, Faure et al., in prep). Contrairement à ce qui était supposé jusqu’à aujourd’hui, les BO se formeraient lors d’un refroidissement lent et non rapide. Les chondres M-P, quant à eux, subiraient une surchauffe pour limiter la nucléation des cristaux (+ΔT) et non une souschauffe (-ΔT). Ces observations donnent ainsi des informations complémentaires sur la formation des chondres. Ainsi l’objectif de cette thèse vise à comprendre la cristallisation des olivines selon certaines contraintes thermiques et d’observer leur morphologie (nombre et taille). Pour cela, des séries d’expériences ont été réalisées avec différents degrés de surchauffe (+ΔTmax= 230°C), de souschauffe (-ΔTmax= 70°C) et de taux de refroidissement (100-50-10-5-2°C/h), pour plusieurs compositions. Les résultats montrent que pour former peu de cristaux automorphes dans un liquide silicaté, il est nécessaire que le liquide subisse une surchauffe (+ΔT) et un refroidissement lent de quelques degrés par heure (<2°C/h). Ces nouvelles données viennent apporter des contraintes thermiques sur la formation de ces objets extraterrestres et donc sur les conditions qui régnaient lors de la formation du Système Solaire.

- 5 Octobre 2020 : Présentations nouveaux doctorants 2019-2020 - Marius Huber + Carolina Dantas Cardoso

Marius Huber - Dynamics of giant landslides and their contribution to Himalayan erosion

Carolina Dantas Cardoso - Continuous isotopic tracing of crustal fluids transfer related to natural (seismic/volcanic) or anthropogenic hazards

- 12 Octobre 2020 : Présentations nouveaux doctorants 2019-2020 - Nicolas Schnuriger + Maxime Piralla

Nicolas Schnuriger- Redox conditions of the formation of chondrules and their precursors

Maxime Piralla - Origin and chronology of the first objects in the early solar system

- 19 Octobre 2020 : Alessandro Maltese - Element, Isotope, and Model Constraints on the Accretion of the Earth and its Early Differentiation History

Summary : During the seminar, I will present some of the work conducted during my PhD and share my perspective on aspects of Earth’s accretion history and its chemical differentiation during the Archean. In detail, I will discuss how the element abundances of bulk silicate Earth (BSE) potentially trace the accretion and differentiation path of the Earth, the opportunity this presents for the U-Th-Pb system, and how new Lu-Hf data from the Bastar craton, India, fit into the context of the global Archean Hf record.

- 26 Octobre 2020 : Cécile Deligny - Origin of volatile elements and timing of their accretion in the inner Solar System

Summary : Volatile elements (H, N) control the evolution of planetary bodies, and they have been essential ingredients for the development of life on Earth. Nonetheless, the origin of volatiles and the timing of their accretion on inner Solar System planets remains a subject of debate and controversy in planetary science. H and N isotopes offer a powerful tool for assessing the contribution from solar, meteoritic, or cometary volatile reservoirs to the terrestrial planets because the relative proportion of their two isotopes varies dramatically across the Solar System. (1) Angrites are derived from the earliest generation of differentiated planetesimals, and are thus key to constraining the source(s) and timing of volatile delivery to planetary bodies in the inner Solar System. We investigate the H and N isotopic signatures of angrite melts by in-situ secondary ion mass spectrometry analyses of mineral-hosted melt inclusions and interstitial glass in the volcanic angrites D’Orbigny and Sahara 99555. The most primitive melt trapped in Mg-rich olivines in D’Orbigny is characterized by carbonaceous chondrite-like H and N isotopic compositions. Given the very old crystallisation ages of these angrites, our findings imply that nitrogen- and water-rich objects were present in the terrestrial planet-forming region within the first 4 Myr after the formation of Ca-Al-rich inclusions (CAIs, the oldest materials in the Solar System). (2) Mars is a planetary embryo, and Hf-W data indicate that it accreted very rapidly in the inner Solar System. So-called SNCs (Shergottites, Nakhlites, Chassignites) are meteorites that originate from Mars. H and N isotope measurements are powerful tools to constrain the signature and origin of primordial volatiles trapped in SNCs and, by inference, in the Martian mantle. The goal of this study was to target pristine phases such as melt inclusions and mesostasis (partially recrystallized glass) for in-situ measurements of their nitrogen content and isotopic ratios to access the most primitive melt of the Nakhlites and Chassignites reservoirs. Preliminary results will be presented during the seminar.

- 2 Novembre 2020 : Caroline Lotout -Petrochronology and P-T-t path in high grade metamorphic rocks

Summary : Deciphering duration and conditions of metamorphism in orogenic systems is crucial to understand large-scale tectonic processes. In the last decades, the development of thermodynamic modelling has fundamentally improved the quantitative constraints on the P–T conditions experienced by metamorphic rocks. In the meantime, instrumental advances in isotopic and elemental analysis led to the advent of petrochronology, an emerging discipline that investigates the petrological evolution of minerals by integrating their textural, isotopic and elemental record. After a brief introduction to the most used approaches for linking petrogenesis, P–T and time, I will first present a comprehensive P-T-t study of an eclogite-facies rock from the Najac Massif (south French Massif Central), using a combination of P-T estimates, trace element analysis, garnet Lu-Hf and Sm-Nd dating, apatite and zircon U-Pb dating (Lotout et al., 2018). Recently acquired new U-Pb, O, Hf and trace element of these zircon crystals, directly in thick section, provide new insights on their petrogenesis during high-grade metamorphism. Finally, I will present and discuss the main objective of the 3 years postdoc I just started : “Conditions and duration of High tempeRature metamOrphism in large hot orogeNs assessed through petrochronolOgy : insights from Grenville TECtonics”, which will be conducted between the CRPG & Memorial University of Newfoundland (Canada).

- 9 Novembre 2020 : Arbia Jouini - Perturbations biogéochimiques à la limite Crétacé-Paléogène : apport des isotopes du soufre et du calcium

La limite Crétacé-Paléogène (KPg) (66Ma) est l’une des grandes crises environnementales du Phanérozoïque dont la cause est toujours débattue : un impact météoritique et/ou un volcanisme intense. Les changements climatiques et biotiques complexes qui se sont produits pendant la transition du Maastrichtien tardif au début du Danien ont été bien étudiés et documentés pour le cycle du carbone, cependant les conséquences de ces perturbations sur les cycles du soufre et le calcium ne sont pas encore bien comprises. En effet, les fortes émissions de CO2 et H2SO4 dans l’atmosphère durant cette période ont probablement contribué à une acidification et à une crise de la production carbonatée océanique susceptibles d’affecter différents aspects du cycle du S et du Ca. Comprendre la dynamique de ces deux cycles, qui peuvent varier en réponse à de nombreux facteurs environnementaux d’intérêt à la KPg (volcanisme, altération,...), est essentiel pour interpréter les mécanismes globaux qui sous-tendent l’événement. De plus, en raison de leurs liens étroits avec les cycles du carbone et de l’oxygène, cela permettra d’étudier les effets qu’une telle perturbation aurait sur la chimie des océans ainsi que d’éventuelles réponses géochimiques qui pourraient avoir lieu pour la stabiliser. Pour mieux contraindre le comportement des cycles océaniques du S et du Ca à travers cette crise, ce projet de thèse vise à reproduire les enregistrements en δ34Socéan et δ44Caocéan à haute résolution autour de la limite (entre 68 et 64 Ma) à partir d’échantillons de foraminifères planctoniques et benthiques monospécifiques du site ODP 1209C (Leg 198) afin de répondre aux questions suivantes : (1) Comment les cycles océaniques du S et du Ca ont réagi aux changements environnementaux avant et après l’extinction de masse KPg, de façon à améliorer notre compréhension de la nature de leurs perturbations qui étaient en partie entravées par la faible résolution temporelle des enregistrements existants pour cette période. (2) Quelles sont les implications paléoenvironnementales de ces nouvelles données, comment s’ajoutent-elles aux divers modèles/hypothèses biogéochimiques entourant l’événement d’extinction de masse KPg. (3) Et finalement est-ce que les enregistrements isotopiques du S et du Ca à haute résolution peuvent être utilisées afin de détecter les changements rapides des cycles biogéochimiques tout au long de cette période.

- 16 Novembre 2020 : Julien Léger - Reconstructing early orogenesis and sediment sources in the linking zone between the Alps and the Pyrenees (Late Cretaceous – Paleogene)

Summary : The thermal and dynamic behaviour of the crust during the onset and earliest phases of orogenesis are poorly constrained, most often due to strong overprinting by later phases. In addition, the initiation and early development of foreland basins is poorly understood. In the Pyrenees, where overall convergence was relatively low, recent in-situ zircon U-Th/He thermochronology studies (thesis of S. Ternois at CRPG) have identified a thermal cooling signal in the easternmost orogen that is clearly due to early convergence ( 70 Ma ago). In addition, pioneering double-dating (U/He & U/Pb) of detrital zircons documents the gradual unroofing of the growing early orogenic edifice that can be directly linked to early foreland basin infill. Paleogeographic reconstructions (G. Frasca’s post-doctoral work at CRPG) show that Pyrenean orogenesis was diachronous, initiating earlier to the east. Due to the Oligocene opening of the Liguro-Provençal Basin that largely destroyed the orogen east of the Pyrenees this record is today preserved only in Upper Cretaceous-Paleogene depocenters of the Corbières to Provencal foreland. When and how did these flexural depocenters first develop ? From where was sediment supplied and how did the source area relief evolve (sediment flux) ? As this area lies in the linking zone between the Pyrenees and the younger and partly synchronous Alpine orogeny, the foreland should record the gradual transfer of sediment supply and convergence from one orogeny to the other. To address these questions, we conduct (1) a U/He & U/Pb laser ablation double-dating (LADD) study of detrital zircons from Corbières and Provencal Upper Cretaceous-Paleogene basins, and (2) a numerical modelling study which will provide insights on the long-term and large-scale thermochronological signal recorded by foreland basins. Our analytical procedure is similar to the previous work of S. Ternois, but numerous changes have been made regarding the employed instruments (lasers, ICP, volumetric microscopy). During this talk, I will present these changes, the analytical difficulties we’ve been facing so far, and the first scarce results of the LADD and numerical modelling studies.

- 23 Novembre 2020 : Laurette Piani - Earth’s water may have been inherited from material similar to enstatite chondrite meteorites

Summary : I will present our recently published paper, in which we report the H content and isotopic composition of enstatite chondrites and discuss their potential contribution to the Earth’s water budget.

- 30 Novembre 2020 : Matthieu Almayrac - Noble gas behaviour in cometary ices under irradiation

Summary : The detection of noble gases (Ar, Kr and Xe) degassed by Comet 67P and studied by the Rosetta spacecraft highlights the necessity to document the behaviour of volatile elements on icy bodies. Specifically, xenon isotopes revealed a unique composition within the comet, and provided the first direct evidence of the contribution of comets to the primitive Earth atmosphere. However, fundamental questions remain as to whether the isotopic signature measured in the coma is representative of the composition of the ice, and how the isotopic composition of the ice may have evolved from the initial gas phase during its formation ? We have developed, in the noble gas lab, an experimental setup to create cometary ice analogues from mixtures of water, nitrogen and noble gases. Using this setup, my PhD work aims to understand the elemental and isotopic fractionations that can occur for noble gases and nitrogen during their trapping in, and release from, ice under a variety of interstellar and protoplanetary disk conditions (temperature, pressure, and irradiation by solar-like photons). We anticipate this work will help to put more constraints on the role of comet in delivering volatiles to the rocky planets.

- 7 Décembre 2020 : Xiaobai Ruan - Geochemistry in weathering reaction associated to bedrock landslides in SE Tibet

Summary : To test how the silicate weathering play its role in the “uplift driven climate change” hypothesis, it’s important to learn about landslide weathering, because it’s a relatively direct way to test whether silicate weathering is really enhanced in the active orogenic belt, and whether it plays as a CO2 sink. It has been shown that in active mountain belts weathering in bedrock landslides controls the variability in solute load of these mountain rivers. In particular, bedrock landsliding can promote the collection and slow percolation of surface runoff in highly fragmented rock debris and create favourable conditions for weathering. Under temperate or tropical climatic conditions of the Southern Alps of New Zealand or the Taiwan orogeny, the chemistry of surface water chemistry from landslide seepages are characterised by higher total dissolved solids (TDS) and calcium (Ca) concentration, higher relative abundances of potassium (K) and sulphate (SO4) in the cationic and anionic charges, respectively, than in the nearby catchment unaffected by active landslides. However, the significance of the weathering of bedrock landslides is currently unknown under high-altitude periglacial climatic conditions that might be more prevalent during glacial periods of the Quaternary, and in regions dominated by granitoid lithology. Here, we have investigated the solute load of landslide seepages and other mountain rivers in the Zayu catchment, SE Tibet. This valley is characterised by a large climatic gradient, from periglacial conditions near its source in the NE at altitude >4.5km to tropical evergreen forest in the SW near the Chinese-Indian border at altitude <1.5km. In addition recent bedrock landslides occur at all latitudes. The difference in the chemical characteristics of landslide seepages and nearby stream are similar to the previous findings at low altitude, while the landslide seepages have nearly identical chemical characteristics than their nearby rivers at high altitude. In detail, the seepages have a greater contribution from carbonate dissolution and a greater proportion of SO4 in the anionic charge, likely related to the oxidation of recently exposed sulphide, but no statistically resolvable difference in K. Given the large difference in weathering conditions from the NE, with water temperature 2°C to the SW with water temperature 20°C, we hypothesise that high-altitude periglacial conditions are likely to reduce the slow percolation of surface runoff in highly fragmented rock debris since frozen water cannot chemically weather the rocks while the frizzing-defrizzing cycles in the non-landslides areas will act as a physical enhancement of the surface contact between the water and the minerals, greatly reducing the difference with landslide deposits on that matter. In consequence, we propose that periglacial conditions and associated rapid frizzing cycles are likely to enhance weathering in similar manner than landslides are in more temperate climatic conditions.

- 14 Décembre : Aswin Tachambalath - Erosion, Alteration and Paleo-weathering in the Himalaya

Summary : Continental weathering contributes to substantial drawdown of atmospheric carbon via alteration of silicate minerals and transfer of organic carbon to sedimentary reservoirs. Weathering plays a pivotal role in evolution of earth’s surface, driving exogenic cycles of elements and influence climate. With the general goal to better understand the Himalayan paleo erosion, my thesis focuses on to refine a quantitative approach of the silicate weathering flux from the Himalayas following a source to sink approach. Weathering budget rely primarily on the difference between the source-rock and a preserved detrital sediment. The first step is to obtain a reliable record of continuous, dated detrital sediments which are preserved from diagenesis. It’s also important to assess the composition of source rock. The Himalayan system presents large difference in crustal maturity, hence of composition, among the different Himalayan and Transhimalayan formations must be taken into account. Acid leaching of the sediments is refined to retrieve carbonate free major element compositions reflecting silicate weathering signal. Source rock composition is constrained using Himalayan head water sediments representing to the best the Geological formations. Special attention is paid to decipher potential bias from diagenesis, and to take into account sediment sorting control on major element compositions. This presentation will review these aspects of the study and laying a foundation to use detrital sediments and sedimentary records to understand paleo erosion.

- 18 Janvier : Xiaoyu Zhou - A method to suppress isobaric and polyatomic interferences for measurements of highly siderophile elements in desilicified geological samples

Summary : I`m going to present a method to determine the concentrations of highly siderophile elements (HSEs : Ru, Pd, Re, Os, Ir, Pt) and osmium isotopic ratios by ICP-MS and TIMS, respectively, which was the part of work during my PhD. Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Carius tube or high pressure asher) is the most common method used to extract HSEs from geological samples. Recently, it has been recognized that additional HF-desilicification is necessary to better recover HSEs, potentially contained within silicate or oxide minerals in mafic samples, which cannot be dissolved solely by inverse aqua regia. However, the abundance of interfering elements tends to increase in the eluent when conventional ion-exchange purification procedures are applied to desilicified samples. Therefore, I developed an improved purification method to determine HSEs in desilicified samples. This method enables the reduction of the ratios of isobaric and polyatomic interferences, relative to the measured intensities of HSE isotope masses, to less than a few hundred parts per million. Furthermore, the total procedural blanks are either comparable to or lower than conventional methods. Thus, this method allows accurate and precise HSE measurements in mafic and ultramafic geological samples, without the need for interference corrections. Moreover, the problem of increased interfering elements, such as Zr for Pd, and Cr for Ru, is circumvented for the desilicified samples.

- 1er Février : Julia Neukampf - TBD




publié mardi 11 août 2015