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Chondrules as probes of the physico-chemical conditions of the disc

As we suggested in the last quadrennial, the chondrules from primitive meteorites are complex objects that consist, in part, of lithic fragments that were inherited from differentiated planetesimals and a nebular component resulting from the interaction between these fragments and the gas. As such, chondrules provide unique markers for the early evolution of the accretion disc. In the next research project, we will identify their conditions of formation and of differentiation in a systematic study (ICP- MS laser ; collaboration with Georesources in Nancy, France ; ion probe) of the distribution of trace elements (including Ge, Ni, Ir, and REE) between the silicate, metallic, and sulphurated phases and their isotopic signatures (including Ge, Fe, S, O, and the noble gases). We will endeavour to evaluate the possible genetic relationships between these primitive bodies and differentiated meteorites (such as iron meteorites and achondrites). The study of vitreous or fluid inclusions (e.g., microthermometry) trapped in the ferromagnesian minerals of chondrules or achondrites will be the tool of choice used to determine the composition and physico-chemical conditions of fluids and primary magmas. Our current experimental potential allows us to obtain solubility data for moderately volatile elements in silicate liquids at high temperature by monitoring the activities and partial pressures of these species ; our second phase will focus on assessing the composition of nebular gas and the partial pressures of a number of species (including PSiO(g), PFe(g), PS2(g), and PNa(g)) during the formation of chondrules. Particular attention will also be given to the quantification of isotopic fractionation during interaction processes.