Étude Chimique Et Isotopique Des Alliages Métalliques Dans Les Météorites Primitives

Résumé: Unequilibrated chondrites are objects formed early in the solar system and were only slightly altered after their formation. The study of this group informs us about the physical and chemical conditions of evolution of primitive materials in the solar system. In this study, we developed an analytical method for measuring the abundance of trace elements in two adjacent constituent phases of metal particles in chondrites by using the NanoSIMS. The Quantification of the concentrations of minors and trace elements (Ni, Co, Cu, Pt, Ir, W, Rh, Au) in kamacite and taenite in Fe-Ni grains in Krymka (type LL3.2) and Bremervörde (type H /L3.9) allows us to point out the process responsible for the formation of metal in the solar system. The study of the distribution of trace elements between kamacite and taenite shows a completion of a state of chemical equilibrium between the two phases in all grains. The diagrams of elementary ratios [Element]/[Ni] in kamacite and taenite were used to constrain the metamorphic temperature of Krymka to about 446 ± 9°C and for Bremervörde to about 595 ± 30°C. The partition coefficients of the elements between the two phases are likely governed by the ionic radius of the main oxidation state of the elements. Based on the metamorphism temperature and the Ni diffusivity in Fe-Ni, we estimated the cooling rate of the parent body in the range of 0.5-1K/My for both chondrites.

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