Defining the Baseline of the REE Stable Isotope Variations in Solar System Materials: Earth

Abstract

Mass-dependent fractionations (MDFs) of stable isotopes record critical information regarding the origin and evolution of planetary materials [1]. Studies of MDF of refractory lithophile elements (RLEs) can provide insights into condensation/evaporation and planetary accretion processes in the early solar system. For example, the lighter calcium isotope composition observed in carbonaceous meteorites compared to that of the bulk silicate Earth, enstatite and ordinary chondrites [2, 3] may be due to the contribution of refractory dust [4, 5], which has a light Ca isotope composition [6, 7]. In contrast, titanium, another RLE with a similar chemical behavior in the early solar system, was found to have uniform isotope compositions among different groups of meteorites including carbonaceous chondrites [8]. A potential explanation for the dichotomy of these two refractory elements could be connected to the higher 50% condensation temperature of Ti relative to Ca [9]. The isotopic results suggest that no Ti net loss took place from the CAI-forming region, while not all Ca condensed in the CAIs [7, 8]. Clearly, more proxies are needed to better understand the processes that occurred during the condensation of the solar nebula.