Description du projet
Un regard plus attentif sur les 4,4 milliards d’années d’histoire de la Terre
Des chercheurs vont porter un regard inédit sur l’évolution de la Terre, d’il y a 4,4 milliards d’années à nos jours, et de l’atmosphère au noyau. Le projet MEET, financé par le CER, se penchera sur l’évolution de la composition du manteau, qui entoure le noyau de la Terre, et sur celle de la croûte. Il étudiera la formation de la croûte, le recyclage de la croûte dans le manteau et les échanges entre la croûte et l’hydrosphère en se basant sur la composition des inclusions fondues et des minéraux hôtes typiques du manteau (olivine) et de la croûte (zircon). En fusionnant la modélisation géodynamique avec des modèles de surface et de climat, le projet s’intéressera de manière plus approfondie à l’évolution des taux de croissance et de recyclage de la croûte au fil du temps, à la concentration et l’origine d’eau et des halogènes dans le manteau profond, ainsi qu’à l’apparition et aux mécanismes de la tectonique des plaques sur Terre.
Objectif
Efforts to reconstruct the early Earth evolution lack critical information on the contents of mobile and volatile elements and their isotope signatures in the mantle and crust. Fortunately, this information is preserved in inclusions of melt in relicts of olivine from komatiites and picrites, and zircons from mafic and felsic rocks. In Aim I, we will use compositions and temperatures of primary mantle-derived melts reconstructed from the study of melt inclusions in olivine from komatiites and picrites to constrain the evolution of mantle composition. We will further study crust-formation, crust-mantle recycling, and crust-hydrosphere exchange based on composition of melt inclusions and host zircons. We will analyse a wide range of volatile elements and their isotopes in homogenized melt inclusions and the elemental and isotopic compositions of host olivines and zircons. The samples come from 24 localities of komatiites and picrites originating at different cratons between 3.7 and 0.06 Ga, and detrital and magmatic zircons with ages from 4.4 Ga to present. We will apply published and new models to constrain the temperatures and compositions of mantle and crustal sources. In Aim II, geodynamic modelling will relate our observations to the evolution of mantle convection, crustal production and recycling, and plate tectonics (PT). We will couple geodynamic modelling with surface and climate models and use derived geochemical proxies to test our hypotheses on the importance of surface processes in evolution of PT. We will thus address several fundamental issues: the rate of crustal growth and recycling through time; the cause and timing of the onset of large-scale subduction and PT, and factors controlling its evolution; concentration and origin of H2O and halogens in the deep mantle, and the extent (if any) of core-mantle interaction. MEET will, therefore, offer an unprecedented look at the evolution of Earth from 4.4 Ga to today, and from the atmosphere to the core.
Champ scientifique
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Régime de financement
ERC-SyG - Synergy grantInstitution d’accueil
38058 Grenoble
France