• 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).
We are interested in further determine the physical and chemical conditions of formation of high temperature components of chondrites ( chondrules and refractory inclusions ), the origin and nature of their precursors, the chronology of their training and their accretion to form chondrites . The tools we use are those of the mineralogy and geochemistry including isotopic compositions (3 isotopes of oxygen but also the development of new isotopic tracers ) and the extinct radioactivities ( 10Be , 26Al , 53Mn , ...) . These isotopic measurements require analytical developments on the MC- ICPMS IPG (chemistry and coupled with laser ablation ) and ion probes CRPG Nancy . A key point of our goals is to put all the comments on the extraterrestrial material in quantitative models of the physical chemistry of the accretion disk .
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.
• 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)
We are developing this project the potential of isotopes as tracers If paleo- ocean temperatures ( temperature control the solubility of Si , resulting in reservoir effect of isotopic fractionation ) tracers diagenesis process, and plotters of the source of crustal magmas ( sedimentary rocks may have isotopic compositions If divided over the mantle ) . If the isotopic analyzes are made by laser abaltaion coupled to the MC- ICPMS and ion probe ims 1280. We study the BIFs , cherts and Archean granitoids
• 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.
• La compositions du noyau par calculs de dynamique moléculaire ab initio
Participants IPG: James Badro
Collaborations principales: John Brodholt (University College London)
We use molecular dynamics calculations ab initio (DFT - VASP - PAW - GGA ) to determine the density and propagation velocities of seismic waves in the liquid outer core of the Earth. The goal is to find the compositions of light elements that correspond to observations radial seismic models. We also seek to constrain the compositions low speeds layers that were discovered in the outer core is the limit with the seed ( F- layer) and the boundary with the mantle.
• 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 ai mis 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.
• 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.
• 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.
CRADLE (ANR défi de tous les savoirs) : Chondrite Recipe from Accretion Disk modeling and Laboratory Experiments
The goal of the project CRADLE (Chondrite Recipe from Accretion Disk modeling and Laboratory Experiments) is to attempt for the first time to (i) assemble observations and analyses made with an unprecedented resolution of several primitive chondritic meteorites and (ii) develop in parallel a numerical model of the Solar protoplanetary disk, which will be built to integrate all these new observations. We want to study whether numerical simulations based on our knowledge of the physics of the solar protoplanetary disk and of disks observed around protostars can reproduce the formation of primitive planetesimals such as the parent bodies of chondrites. One key aspect will be to integrate two different approaches, from astrophysics and from cosmochemistry. CRADLE is expected to advance our understanding of the early evolution of the disk, its physics and chemistry, and of the formation of planetesimals, which is the least understood step towards the formation of terrestrial planets.
The relevance of the project CRADLE comes from recent observations of accretion disks around young stars analogous to our forming Sun, and of chondritic meteorites. Chondrites are understood as "sediments" having accumulated in the accretion disk from materials formed very early in the Solar nebula or inherited from the presolar molecular cloud, making them a unique window on the early solar system. All these observations lead to several key questions related to the origin of the first solids and the first planetary objects in the protoplanetary disk. There is yet no model able to answer these questions. An apparent conflict exists between (i) the nature of chondrites, which are made from components (refractory inclusions, chondrules, fine-grained matrix) having very different origins in the accretion disk (based on parameters such as temperature, pressure, mineralogy, chemical and isotopic composition, ...) and formation ages extending over several million years, and (ii) our understanding of the standard dynamical, thermodynamical and chemical spatio-temporal evolution of the protoplanetary disk, which predict rapid evolution and mixing.
Recent developments of numerical codes allow designing simulations that are capable of following the infall of the presolar cloud, the formation and the evolution of the protoplanetary disk, and to take into account detailed physico-chemical constraints coming from the observations of chondritic meteorites. Similarly, recent analytical developments in the study of extra-terrestrial matter have made it possible to gather observations (such as the formation ages of the different components of a chondrite) that describe precisely the complexity of a chondrite. CRADLE is based on going back and forth between numerical simulations and chemical and isotopic measurements of chondrites, each part feeding into the other.
Participants IPG: Manuel Moreira
In this first phase of the project, financed by Labex UnivEarthS, we aim to demonstrate the feasibility of in situ dating of extraterrestrial surfaces by measuring cosmogenic isotopes, particularly those of rare gases (3He, 21Ne, ...). The objective is twofold. The first is to date the surfaces (Moon, Mars, satellites). the second is to help select samples for return to Earth (Asteroids, Mars).
• Collection and measurement of the isotopic composition of rare gases in the stratosphere
Participants IPG: Manuel Moreira
Thanks to CNES funding, we will build a sampling platform that will be placed in a stratospheric balloon. The scientific objective is to determine if isotopic fractionation of xenon exists at high altitude, and to constrain the process of loss of atmospheric xenon.