B3 - Tracing the origin of the late veneer using nucleosynthetic isotope anomalies in siderophile elements

Research areas: Isotope geochemistry, cosmochemistry

Summary

The elevated abundances of highly siderophile elements (HSE) in the Earth's mantle are thought to reflect the late accretion of primitive material (the “late veneer”) to the mantle after core formation was complete. However, it is currently not known whether the late-accreted material is genetically linked to the main building material of the Earth, in which case it may consist of the leftover planetesimals remaining after the main accretion phase of terrestrial planets, or if, alternatively, the late veneer derives from an exotic source of planetesimals (perhaps even comets) unrelated to the building blocks of Earth. Distinguishing between these two contrasting possibilities is important for understanding the origin and composition of the late veneer, its relation to the formation of the Earth, and, more generally, the dynamics of the late stages of terrestrial planet formation.

This issue can be addressed using nucleosynthetic isotope anomalies, which arise through the heterogeneous distribution of one or several presolar components in the solar protoplanetary disk, and constitute a distinctive tracer of potential genetic relationships among planetary bodies.

The proposed study will focus on using nucleosynthetic Ru and Mo isotope anomalies in chondrites and lunar samples (1) to evaluate whether the late veneer and the main building blocks of the Earth share the same genetic heritage, (2) to establish a link (if any) between known groups of meteorites and late-accreted materials, and (3) to identify any changes in the origin and composition of these materials over time.

Some of the same samples will be analysed in subprojects A1, A2, and B1 for their age and chemical composition. The combined data, therefore, will constrain the chemical inventory and origin of the late-accreted material, and any temporal change thereof, with unprecedented detail.