Description du projet
Focus sur l’évolution de la croûte terrestre et l’origine de la tectonique des plaques
Le zircon, plus vieux minéral terrestre, est au cœur d’un grand nombre d’études sur l’évolution de notre planète. En l’occurrence, nos connaissances sont restées limitées aux informations géochimiques conservées dans les différentes stries de croissance identifiables dans les cristaux de zircon. Le projet MILESTONE, financé par l’UE, repoussera les limites des connaissances actuelles à une échelle analytique différente, celle d’inclusions minérales de 10-20 µm d’apatite et de feldspath encapsulées dans des zircons. L’analyse géochimique intégrée des zircons et de leurs inclusions, pour des milliers de zircons d’âge et de provenance différents, sera utilisée pour dater l’origine de la tectonique des plaques, ainsi que pour développer un modèle global de l’évolution de la croûte continentale depuis l’Hadéen (c’est-à-dire >4 Ga) jusqu’à aujourd’hui, une période durant laquelle la Terre est devenue progressivement, ou plus soudainement, une planète habitable.
Objectif
The continental crust is the principal record of conditions on Earth during the past 4.4 billion years, yet how it formed and evolved through time remains unresolved. Zircon lies at the core of crustal evolution studies, and yet our knowledge has remained restricted to the geochemical information that can be extracted from this mineral with current techniques. This CoG moves the debate to a different scale analytically, to the scale of mineral inclusions encapsulated within zircons. A key motivation is the recent analytical breakthrough in the microanalysis of minute samples, which was achieved by the PI and the team he led at the University of Bristol, using state-of-the-art instruments similar to those now available at the PI’s host laboratory.
The integrated analysis of Sr and Pb isotopes of mineral inclusions, along with the trace elements, U-Pb, Hf and O isotopes analysis of their host zircons, for over 5000 zircons of different ages and provenance, will provide new and different information to that available from the 'zircon only' record – ultimately to i) probe the inferred transition from intraplate- to subduction-related magmatism associated with the onset of plate tectonics; ii) date this transition and its duration precisely in different places; iii) develop a global model of continental crust evolution from the Hadean (i.e. >4 Ga) to the Present, in which the Earth has progressively, or more suddenly, become a habitable planet. These goals will be achieved through:
1. Building a worldwide collection of inclusion-bearing zircons with a range of ages and provenance (WP1).
2. Evaluating changes in the degree of differentiation of the newly generated continental crust through time, using the Sr isotope record of apatite inclusions (WP2).
3. Addressing changes in the tectonic settings of new crust formation, using the Pb isotope record of feldspar inclusions (WP3).
4. Modelling the variation in the new crust thickness through space and time (WP4).
Champ scientifique
Programme(s)
Régime de financement
ERC-COG - Consolidator GrantInstitution d’accueil
75794 Paris
France