FeNi metal condensation and evolution in the Early Solar System: a study of germanium isotopes and siderophile elements in Ordinary and Bencubbinite primitive chondrites
The formation and subsequent chemical evolution of FeNi metal phases is critical for understanding the development of the early Solar System. Despite numerous studies on metal phases in chondrites, the effect of metal condensation at moderate temperatures, as well as of metal heating and oxidation in nebular and protoplanetary environment, is still under debate. By using a combined approach of germanium isotopic quantification and siderophile in-situ measurements in bulk and separated phases of Bencubbinites carbonaceous chondrites (CB) and ordinary chondrites, this thesis aims to provide new constraints on: (1) the formation of metal via condensation and metallic precursors melting and (2) the processes that can account for the elemental and isotopic difference between the H, L and LL chondrites and metal evolution with metamorphism. The results show that the two groups of CB are distinguishable using 𝝳74/ 70Gebulk, providing insights into kinetic and equilibrium condensation processes. Variations in 𝝳74/70Ge during metal condensation are shown to be the result of evaporation / recondensation processes that are not recorded by major or refractory elements. A large variation in siderophile element content in the metal of H primitive ordinary chondrites has been identified, as well as a positive 𝚫74/ 70GemetaI-silicates• This suggests local oxidation state variation and metal-silicate interactions during heating event(s) in the disk. The thesis also highlights that the H, Land LL groups are resolvable with 𝝳74/70Ge of bulk and metal. These variations are positively correlated with 𝚫17O and % Fa across the ordinary chondrites sequence and suggests the accretion of an increasing proportion of oxidising components with a high 𝝳74/70Ge and 𝚫17O composition from H to L to LL groups. Because the oxidising component contains Ge it suggests that it cannot be ice or water but more likely a silicate phase. These conclusions highlight the high potential of germanium isotopes to record processes leading to metal formation and evolution.