On going projects | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS

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Research Departments

Cosmochemistry, Astrophysics and Experimental Geophysics

  On going projects

•  Origine des CAIs, des chondres et des chondrites (projet Labex UnivEarthS, Programme National de Planétologie INSU)

 

Participants IPG: Marc Chaussidon, Sébastien Charnoz, Christa Gopel, Frédéric Moynier, Manuel Moreira,

Collaborations principales: Matthieu Gounelle & Emmanuel Jacquet MNHN (Paris); Andrei Gurenko, Evelyn Füri & Yves Marrocchi CRPG (Nancy); Mathieu Roskosz (Université de Lille); Knut Metzler, Addi Bischoff & Torsten Kleine (Université de Munster).

 

Nous sommes intéressés à déterminer plus précisément les conditions physico-chimiques de formation des composants haute température des chondrites (inclusions réfractaires et chondres), l'origine et la nature de leurs précurseurs, la chronologie de leur formation et de leur accrétion pour former les chondrites. Les outils que nous utilisons sont ceux de la minéralogie et de la géochimie avec notamment les compositions isotopiques (3 isotopes de l'oxygène mais aussi le développement de nouveaux traceurs isotopiques) et les radioactivités éteintes (10Be, 26Al, 53Mn, ...). Ces mesures isotopiques demandent des développements analytiques sur le MC-ICPMS de l'IPG (chimie et couplage avec l'ablation laser) et sur les sondes ioniques du CRPG de Nancy. Un point clef de nos objectifs est de replacer toutes les observations faites sur la matière extra-terrestre dans des modèles quantitatifs de la physico-chimie du disque d'accrétion.

 

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• Contraintes expérimentales sur l’origine des éléments volatils sur Terre (projet ANR jeune chercheur, PI Siebert) 

Participants IPGP : Julien Siebert, Frédéric Moynier, Brandon Mahan, Pierre Cartigny

Collaborations principales : Laurent Rémusat (MNHN, IMPMC, Paris) ; Manuel Munoz (ISTerre, Grenoble)

 

Volatile elements (e.g. H, C, S) have a fundamental role in planetary evolution. But how and when budgets of volatiles were set in planets and the mechanism of volatile depletion in planetary bodies remains poorly understood and represents a fundamental obstacle in understanding the chemical processing of terrestrial planets. Two main theories exist. Either Earth accreted ‘dry’, with Earth’s building blocks completely devoid of volatile elements. Then, the Earth’s complement of volatile elements was only established later, once the Earth was differentiated into a core and mantle, by the addition of a late veneer. Or, the Earth accreted ‘wet’ where volatiles where present during the main stages of accretion and differentiation of the Earth. The imprint of core formation on the geochemistry of siderophile and volatile elements of the present mantle can discriminate between these two competing scenarios. We will use core formation experiments and the geochemical signatures from metal-silicate equilibration of three siderophile and volatile elements sulfur, selenium, and tellurium. An original and complementary multi-techniques approach combining experiments at high pressure and high temperature, and high-resolution analyses on quenched samples will be developed to obtain new constraints on the origin of volatiles elements on Earth.

 

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• Les compositions isotopiques du Si comme traceur des paléo-températures des océans et de l'origine de la croûte continentale à l'archéen

 

Participants IPG: Marc Chaussidon, Frédéric Moynier, Pascal Philippot

Collaborations principales: Romain Tartese & François Robert MNHN (Paris); Nicolas Dauphas (Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago); Béatrice Luais CRPG (Nancy); Martin Guitreau (Isotope Geochemistry & Cosmochemistry Group, The University of Manchester), Steve Mojzis (Department of Geological Sciences, University of Colorado at Boulder)

 

Nous développons dans ce projet le potentiel des isotopes du Si comme traceurs des paléo-températures océaniques (la température contrôle la solubilité du Si, ce qui entraîne par effet réservoir des fractionnements isotopiques), traceurs des processus de diagenèse, et traceurs de la source des magmas crustaux (les roches sédimentaires peuvent avoir des compositions isotopiques du Si fractionnées par rapport au manteau). Les analyses isotopiques du Si sont faites par abaltaion laser couplée au MC-ICPMS et sonde ionique ims 1280. Nous étudions les BIFs, les cherts et les granitoïdes archéens.

 

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High precision isotopic measurements of heavy elements in extra-terrestrial materials: origin and age of the solar system volatile element depletion (projet ERC, PI Moynier).

 

Participants IPG: Frédéric Moynier, Julien Siebert, James Badro, Alkis Giourgatis, Julien Moureau, Chizu Kato, Emily Pringle, Paolo Sossi.

The objectives of this proposal are to develop new cutting edge high precision isotopic measurements to understand the origin of the Earth, Moon and solar system volatile elements and link their relative depletion in the different planets to their formation mechanism. We develop and use high precision stable isotopic measurements of moderately volatile elements such as Zn, Rb or Ga.

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Study of the core-mantle differentiation and core composition by combining experimental petrology and isotope geochemistry.

 

Participants IPG: Frédéric Moynier, Julien Siebert, James Badro, Alkis Giourgatis, Julien Moureau, Nicolas Wehr, Brandon Mahan, Emily Pringle, Chizu Kato, Paolo Sossi

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• La compositions du noyau par calculs de dynamique moléculaire ab initio

 

Participants IPG: James Badro

Collaborations principales: John Brodholt (University College London)

 

Nous utilisons ici les calculs de dynamique moléculaire ab initio (DFT – VASP – PAW – GGA) afin de déterminer la densité et les vitesses de propagation des ondes sismiques dans le noyau externe liquide de la Terre. Le but est de trouver les compositions en éléments légers qui correspondent aux observations des modèles sismiques radiaux.

Nous cherchons aussi a contraindre la compositions des couches de basses vitesses qui ont été découvertes dans le noyau externe a la limite avec la graine (F-layer) et à la limite avec le manteau.

 

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• Core-Mantle Interactions

 

Participants IPG: James Badro, Edouard Kaminski

 

The dynamics of the Earth's mantle is controlled by thermochemical convection. Compared to a chemically homogeneous system, the Earth's mantle has three sources of density anomalies that interact with thermal anomalies and determine the overall thermal evolution of the planet. First, chemical anomalies generated by partial melting and magmatic differentiation at the surface of the planet. The second source of anomalies, called primitive, corresponds to inhomogeneities in the deep Earth as a result of the primordial formation and differentiation of the planet. In particular, the existence of a terrestrial magma ocean in the early stages of Earth's evolution - the basal magma ocean hypothesis - played an important role in the generation of a density contrast between the shallow mantle and deep mantle. Despite the fact that a primitive source has been integrated into the convection models in the last 10 years, the constraints on the nature and origin remain scarce. A third source of chemical anomalies corresponds to chemical reactions at the core-mantle boundary. Traditionally considered fairly limited because they involve reactions between solids and liquids, these interactions could be a major source of chemical evolution of the mantle if liquid is present at the base of the mantle - or has been for a significant period time - as postulated in the basal magma ocean hypothesis.

Our aim is to provide experimental constraints on the equilibria between solid silicate / liquid silicate / metal at the bottom of the magma ocean and to integrate them into models of the formation, differentiation and evolution of Earth's mantle.

 

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Core Formation and Core Composition

 

Participants IPG: James Badro, Julien Siebert

 

The Earth grew by the collisional accretion of a range of small rocky bodies and Moon- to Mars-sized planetesimals. The Earth, as well as the interior of the large planetary embryos, was sufficiently hot to have substantially melted, allowing the segregation of dense, immiscible molten iron to form a core, separated from the residual overlying silicate mantle.

As the Earth grew, metal from the cores of accreted embryos likewise sank to its centre, after temporarily accumulating (or not…) at the base of a silicate Magma Ocean. The hidden elemental inventory of the core was therefore set very early during Earth’s history by the ambient conditions in prevailing in the Magma Ocean. The chemical (elemental and isotopic) imprint of this process is still still present in the geological record today, and can be used to lead an effective investigation of the processes and conditions of core formation.

 

The preference of different elements for molten iron, relative to coexisting silicate melt, is highly variable and sensitive to temperature, pressure and oxidation state. By assessing which elements are missing from the silicate portion of the Earth, and using laboratory experiments to constrain the partitioning of elements between iron and silicate melts, the conditions under which the core was formed can be determined.

There is a rather extensive metal-silicate partitioning dataset in the published literature, but it is restricted to low pressures (P<25 GPa) and temperatures (T<2500 °C), much lower than the actual conditions at which the core formed. All core formation models are therefore based on thermodynamic modelling and extrapolation, and suffer from large inaccuracies and invalid assumptions. We have put tremendous efforts in recent years to push the P and T limits of the measurements, and we can now reproduce the conditions that prevailed during core formation in the lab, using the laser-heated diamond anvil cell.

The aim of this project is to measure new metal–silicate partitioning data at very high pressure and temperature, to probe P and T domains that have never been reached before, to reproduce the conditions under which the core formed in the laboratory, and to measure directly the compositions of our synthetic primitive “cores” and “mantles”, rather than model them through extrapolations.

Our main goal is to find a pathway and a process (or series of processes) that produce a core and a mantle that are consistent with the geophysical (density and bulk seismic velocity in the core) and geochemical (siderophile trace-element and isotopic composition of the mantle) observables: any successful model of core formation needs to reproduce the observed concentrations of all the elements in Earth’s silicate mantle. We will also help addressing outstanding issues such as the inventory of volatile elements early in Earth’s accretion (during core formation), as well as the constraints that puts on the Late Veneer that brought most volatile elements to the Earth after the core formed. We will then use modelling to explore a wide range of accretion scenarios, to find those that satisfy best the elemental abundance and isotopic constraints.

 

 

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Generation and Subsidence of Primitive Mantle Reservoirs

 

Participants IPG: James Badro

Collaborations principales: Philippe Gillet (Ecole polytechnique fédérale de Lausanne)

 

Current geochemical models of the Earth suggest that the mantle contains a number of hidden geochemical reservoirs. These reservoirs must have formed very early on, early enough to witness core formation. They also must have been deep, in order to isolate them from the convecting mantle over 4.5 billion years of existence. The most efficient process for producing large-scale chemical heterogeneities (or reservoirs) is fractional crystallisation and/or partial melting. The first few 100 million years after the formation of the Earth saw widespread melting of the mantle, a state known as “Magma Ocean”, due to impacting, short-lived radioactivity, and gravitational heating due to core formation. During subsequent solidification, Earth’s magma ocean experienced a global differentiation that left a strong compositional imprint on the resulting mantle, and created large-scale reservoirs that may have (at least partially) survived to the present day. To a large extent, present-day compositional structures in the mantle may be leftovers of these primordial reservoirs.

 

We propose here to determine the composition the various deep primordial reservoirs created during early mantle differentiation, and their potential subsidence to this day. For this, we will lead an experimental geochemical investigation on two fronts: (1) trace-element partitioning between deep mantle phases, and (2) trace-element partitioning between the solid and molten silicates.

We propose to look at the partitioning of a suite of lithophile and siderophile trace elements, both between solid lower-mantle minerals (perovskite), and between solid and liquid silicates. By linking this to trace-element concentrations in the upper-mantle (which is a sturdy geochemical observable), we will determine the depth and extent of the magma ocean (was it global, partial, transient, permanent?) as well as the compositional characteristic of the various reservoirs that are left behind.

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Origine et évolution des atmosphères planétaires

 

Participants IPG: Manuel Moreira, Sébastien Charnoz

  • Présence d’une atmosphère solaire durant l’accrétion ?
  • La nature des corps parents
  • La chronologie de la formation des atmosphères planétaires
  • La fuite du xénon
  • Le dégazage actuel du manteau de la Terre
    • Dorsales : le système mondial
    • Points chauds : exemple des Açores
    • Subduction : exemple de Santorin
    • Les processus de dégazage
  • La composition du manteau et de l’atmosphère archéens
  • La composition du manteau actuel – les challenges analytiques
    • Krypton et Xénon
    • Le néon
  • Le matériel extra-terrestre dans les sédiments marins
    • Contraindre les flux de micro-météorites au cours du temps
    • Une subduction possible dans le manteau : le cas des back-arcs
  • Implantation du vent solaire
    • Approche de laboratoire : le cosmotron
    • Mesure dans les grains du sol lunaire