The evolution of planetesimal reservoirs revealed by Fe-Ni isotope anomalies in differentiated meteorites

• Early- and late-formed planetesimals formed from the same mix of dust components. • Many differentiated meteorites share an isotopic signature with CR chondrites. • The CR reservoir was established early and remained isolated throughout disk history. • CI chondrites are the only CC type not represented in differentiated meteorites. • CI chondrites formed late by photoevaporation and/or in a distinct disk reservoir. Differentiated meteorites sample planetesimals formed earlier than the parent bodies of chondritic meteorites. To evaluate whether these two generations of planetesimals formed from the same or distinct materials, we have analyzed the Fe and Ni isotopic compositions for a large set of differentiated meteorites, representing approximately 26 distinct parent bodies. Most of these samples are genetically related to the carbonaceous chondrite (CC)-type reservoir, which is thought to represent some portion of the outer disk. The new data reveal that early and late CC planetesimals cover a similar range of Fe and Ni isotopic compositions, indicating that all these bodies accreted from the same mixture of dust components, either in a long-lived pressure structure of the disk or in different substructures containing the same materials. Many differentiated meteorites have an isotopic composition similar to the late-formed CR chondrites, indicating that the CR chondrite reservoir was established early and remained isolated for essentially the entire disk lifetime. Finally, CI chondrites are the only CC chondrites whose isotopic composition is not represented among differentiated meteorites. Thus, planetesimals with CI chondrite-like isotopic compositions represent a late burst of planetesimal formation and possibly formed by a distinct mechanism and/ or in a different location from the other CC planetesimals.