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Séminaire internes 2018-2019

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

- 17 septembre 2018 : Céline Baudouin - Alkaline Volcanism associated with early stage of rifting : origin, differentiation & trace element partitioning

East African Rift exposes different stages of extension, from early stage rifting in Tanzania (Natron & Manyara basin) to oceanic accretion in Afar (Ethiopia). Due to its location and tectonic setting, Tanzanian volcanoes offers the opportunity to study the earliest stage of rift initiation and to constrain the origin of alkaline-CO2-rich magmas and magmatic evolution of the silica-undersaturated melts as well as associated carbonatitic magmatism.

- 24 septembre 2018 : Marine Boulanger - Melt migration and interactions in the lower oceanic crust : insights from Atlantis Bank interlayered series at IODP Hole U1473A (Southwest Indian Ridge)

Oceanic crust accretion processes at slow-spreading ridges are yet insufficiently constrained, especially for the lower crust. One of the key challenges is to understand how melts migrate through the lower crust and in what extent they interact with surrounding lithologies. For that purpose we studied a cumulate portion of lower crust exhumed at the Atlantis Bank Oceanic Core Complex, and sampled by drilling during IODP Exp. 360. The cumulate olivine gabbro presents intense layering which origins gave us new insights on magma migration, emplacement, crystallization and interaction processes. We found that the overall sequence displays melt/rock reactions or homogenization overprints developing at all stages of formation of the cumulate. This suggests that interaction processes, and thus the migration of melts in this heterogeneous environment are two of the prevailing key parameters controlling the crust and eruptive material composition.

- 22 octobre 2018 : Guillaume Florin - Influence of redox processes on germanium isotopic composition of ordinary chondrites

Ordinary chondrites (OCs) are undifferentiated meteorites composed of an assemblage of primitive components that underwent thermal metamorphism on their parent body. The three H, L, LL groups of OCs are distinguished by an increase in oxidizing conditions from the H group to the most oxidized L and LL groups. That has been highlighted by Δ17O-%Fa correlation and decrease in metal content from H ( 8%) to LL ( 2%). They are also characterized by an increase in germanium content, a moderately siderophile and volatile element, which is also sensitive to redox conditions. All these features have led authors to argue that the three OCs groups would at least come from three different parent bodies. On each OC parent body, decay of 26Al and 60Fe triggers thermal metamorphism and results in texture, mineralogy and chemistry modifications. They define petrographic types that range from the unequilibrated type 3 to the highly equilibrated type 6. This has been modeled in an "onion shell" structure, or through impact and reassembly mechanisms. In order to precise thermodynamic conditions of formation, as well as nebular versus parent bodies processes, we have investigated germanium elemental and isotopic variations of metal, silicate and sulfide phases in H, L and LL ordinary chondrites.

- 5 novembre 2018 : Camille Litty - Fluvial Sediment Dynamics and Erosional Mechanisms in the Western Peruvian Andes

Rivers have been recognized as one of the primary agents of erosion and controls on landscape evolution. During mountain denudation, rivers incise into bedrock, therbeby controlling the hillslope erosion processes. They also convey the erosion products supplied from upstream to sedimentary basins. In mountainous streams, coarse and fine sediment charateristics bear crucial information about the transport dynamics, the flow strengths of these streams, the sources of sediment, the mechanisms of erosion and transport and the controlling conditions such as uplift and precipitation. I will present some case studies allowing to understand the sediment routing through time and through various climatic conditions in Western Peru.

- 12 novembre 2018 : Apolline Mariotti - Impact of glacial-interglacial cycles on denudation rates in the Western Mediterranean

The interaction between climatic variations and surfaces processes (namely denudation) is still poorly understood (Herman and Champagnac, 2016 vs Willenbring and Jerolmack, 2016) and up to debate. As a way to constrain this interaction, we use high-resolution data of denudation rates, applied to archives that precisely document the effect of glacial-interglacial cycles, independently from the tectonic forcing. We use 10Be to quantify present denudation in the Var watershed (southern French Alps) as well as paleo-denudation rates for this same watershed preserved in two well documented sediments cores in the Mediterranean Sea. We also adresse methodology questions such as what is the seasonal effect on the cosmogenic 10Be concentrations and does the sediment granulometry have a predictable effect on the cosmogenic nuclides concentrations in quartz.

- 3 décembre 2018 : Antoine Crémades - Transition from rifting to convergence in a segmented margin : process and kinematics of inversion along the eastern Pyrenean-Provençal system

In recent decades, research applied to 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. Even if the understanding of these concepts is well advanced, the processes involved in the inversion of salt-rich rifts are poorly documented, especially during the early orogenic phase. This lack of knowledge is partly related to the mobility and solubility of salt, which disappears rapidly under the action of erosion leaving extremely complex « ghost » structures.

Furthermore, passive margins and rifts are often segmented by transfer zones, major crustal structures that lie at a high angle to the rift trend and that are locations of fault interaction where extensional strain is transferred or relayed from one structure to another. In relasionship with rift inheritence and because transfer zones are presented in both extensional and compressional regimes, rift transfer zones appear to play a key role in rift inversion and orogenesis, however this phenomenon has been sparsely studied. Therefore, the study of the processes and mechanisms controlling early inversion of salt-rich rift transfer zone appears to be a key point to improve our understanding of the mechanisms that control orogenesis.

With 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 transfer zones by studying the tectono-sedimentary 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. The Corbières therefore represents an ideal salt rich transfer zone that records early orogenesis.

- 10 décembre 2018 : Carlotta Ferrando - Melt transport and assimilation-precipitation processes through the heterogeneous lower oceanic crust : microstructural and petro-geochemical constraints from drill cores

About 55% of the mid-ocean ridge system spread at rates lower than 40 mm/y. There, the slow-spread oceanic crust presents an extremely heterogeneous structure, which is partly composed of serpentinized mantle rocks intruded by multiple gabbroic bodies. It is locally exposed at Oceanic Core Complexes (OCC), where in situ oceanic crust can be sampled. During my PhD thesis I studied two gabbroic sequences drilled at the Atlantis Massif OCC (30°N, Mid-Atlantic Ridge) and the Atlantis Bank OCC (32°S, 57°E, Southwest Indian Ridge). The combined macro- and microscopic observations I performed, together with geochemical analyses and numerical modelling, allowed me to investigate the magmatic and cooling processes that shape the oceanic crust formed at slow-spreading ridges.

- 17 décembre 2018 : Simon Couzinié - Decoding the zircon age-hafnium record of crust evolution : a case study from the French Massif Central

The continental crust has been extracted from the Earth mantle for at least 4 Ga but the mode and pace of new crust production through time both remain highly debated. In the past 10 years, extensive zircon U–Pb–Hf(–O) isotope databases have been interrogated to unravel the extent of crust production vs. reworking at a given time period. We examine the limitations of this approach by reconstructing the evolution of the crust segment today exposed in the eastern part of the French Massif Central. Our results identify two major inconsistencies between the geological record and the signal derived from statistical analysis of zircon U–Pb–Hf(–O) isotope data considered out of any petrological context, as generally performed in studies investigating crust evolution. Consequently, we posit that the global zircon record bears equivocal information which can only be resolved when additional constrains on the zircon host rocks are available.

- 14 Janvier 2019 : Lucile Pentecoste-Cuynet - Plasma studies and cosmo-chemical implications

This seminar will be the opportunity to describe what a plasma is, its potential applications and the studies that result. During this presentation, I will briefly discuss an example of a study conducted during one of my previous research projects : Plasma-Surface interactions in a Nuclear Fusion context. We will also make the connection between plasmas and your research projects : Plasmas in your characterization techniques. Finally, we will focus in particular on the study of plasma and the influence of electronic ionization on the isotopic fractionation of light elements. This study being part of the PHOTONIS Project, the cosmo-chemical implications will be discussed.

- 21 Janvier 2019 : David Bekaert - Isotopic constraints on the origin and nature of primitive materials in the solar system and on early Earth

During this seminar, I will give you an overview of three main sections of my thesis. The first one addresses the origin of primitive, volatile-rich materials in the solar system - mainly comets and carbonaceous chondrites. The second discusses the potential for these outer-solar system materials to have been scattered early in the inner solar system, and to have supplied terrestrial planets - including the Earth-Moon system - with volatile elements. The last part will be dedicated to the evolution of the atmosphere, in relation to the emergence of life on Earth. In particular, I will focus on a newly developed technique using Xe isotopes to set constraints on the widespread nature of early life.

- 28 Janvier 2019 : Bernard Marty - Ecotourisme à l’Archéen

- 4 Février 2019 : Ruben Rosenkranz - Onset of Mid-Miocene orogen-parallel extension in the Thakkhola-Mustang graben (central Nepal) as revealed by detrital apatite (U-Th-Sm)/He and Apatite FT ages : evidence for an orogen-scale transition from channel flow to underthrusting.

Apatite (U-Th-Sm)/He has the potential to rapidly assess the spatial distribution of exhumation rates from a given catchment. In my talk I will discuss the problems that affect the detrital application of the methodology, and elucidate some possible solutions to circumvent these issues. I show that a dataset from the Kali Gandaki river in central Nepal, along with a numerical model, usefully constrains the exhumation history of the Thakkhola-Mustang graben, with significant consequences for the understanding of the Himalayan geodynamics.

- 11 Mars 2019 : Présentations doctorants 1A

Marion Auxerre - Origine des Chondres Barrés

Xiaobai Ruan - Sr and Mg isotopic geochemistry in weathering reaction associated to bedrock landslides

- 18 Mars 2019 : Présentations doctorants 1A

Tachambalath Aswin Pradeep - Erosion, alteration and paleo-weathering in the Himalayas

Arbia Jouini - Perturbations biogéochimiques à la limite Crétacé-Paléogène : apport des isotopes du Soufre et du Calcium

- 25 Mars 2019 : Présentations doctorants

Cécile Deligny - Origin and timing of accretion of volatile elements in the inner Solar System : Constraints from in-situ analyses of achondrites

Rongsheng Yang - Environmental evolution since the Middle Eocene of the northeastern Tibetan Plateau based on clay mineralogical and geochemical records in the Xining Basin

- 8 Avril 2019 : Célia Dalou - Redox control on nitrogen isotope fractionation during planetary core formation

The origin and evolution of Earth’s nitrogen is often discussed by comparing the large variation of N isotopic compositions among Earth’s building blocks (chondrites) to the signatures of various terrestrial reservoirs. Here we demonstrate that planetary differentiation processes, such as core formation, may have significantly modified the N isotopic composition of the proto-Earth. During core-mantle differentiation, a significant amount of isotopically light N entered Earth’s core, producing an isotopic fractionation much larger than has been observed for other geochemical tracers of core formation. The magnitude of N isotopic fractionation varies significantly as a function of the redox history of the early Earth. Therefore, distinct N isotopic ratios among Earth’s reservoirs or between planetary bodies may reflect different planetary evolution processes as opposed to different N sources.

- 6 Mai 2019 : Michael Broadley - Noble gas constraints on the origin of volatiles in the deep mantle ; a Yellowstone case study

- 20 Mai 2019 : Yves Marrocchi / Guillaume Paris - Présentation sur la prospective des OSU de l’INSU

- 1 Juillet 2019 : Présentations doctorants 1A - the end

Matthieu Almayrac -

Julien Léger - Reconstruction de l’orogenèse précoce et des sources des sédiments dans la zone de liaison entre les Alpes et les Pyrénées (Crétacé supérieur - Paléogène)

publié mercredi 14 août 2013