Cerium Stable Isotopic Composition of Non-Carbonaceous Chondrites

Abstract

The elemental and isotopic compositions of the rare earth elements (REE) reveal critical information about the physicochemical dynamics of the solar nebula. Cerium (Ce) is the most abundant REE in the Solar System. It has recently received renewed attention due to the decay of ¹³⁸La to ¹³⁸Ce, but its stable isotopic composition still requires a better comprehension. Here, we report the Ce stable isotopic compositions (¹⁴²Ce/¹⁴⁰Ce, expressed as δ¹⁴²Ce) of 18 well-characterized non-carbonaceous chondrites including 11 enstatite chondrites (EH and EL) and 6 ordinary chondrites (H, L, and LL) collected from the Antarctic, and one rumuruti chondrite collected from the Sahara Desert. The analyzed chondrites show relatively homogeneous δ¹⁴²Ce compositions within 0.01 ± 0.30‰ (n = 18; 2SD). This observation indicates lack of any resolvable effects of nebular physicochemical variables, such as differences in fO₂ and chemistry of the accretion regions, in different chondrites. A homogeneous isotopic composition among our analyzed samples also indicates a lack of evidence for any effects of thermal metamorphism on the δ¹⁴²Ce composition of chondrites. In addition, considering a wide range of weathering degrees in our samples, we do not observe any modifications resulting from weathering. Considering the refractory and lithophile behavior of Ce and the limited variation of δ¹⁴²Ce between various non-carbonaceous chondrite groups, their average will not be significantly different from the Ce isotopic composition of the Bulk Silicate Earth (BSE). We discuss the cosmochemical implications of our data and suggest extending the database of the stable isotopic composition of Ce and other REE in different types of chondrites and chondritic components.