Chondrite diversity revealed by chromium, calcium and magnesium isotopes

Chondrites are undifferentiated meteorites that can provide information on the compositions of materials in the early solar System, including the building blocks of the terrestrial planets. While most chondrites belong to well-defined groups based on their mineralogy and chemical composition, a minor fraction have unusual characteristics and are classified as ungrouped chondrites. These ungrouped chondrites reflect the diversity of chondritic materials in the early solar system; however, they are not as well stud-ied as grouped meteorites and their origins are poorly understood. In this study, we present high -precision mass-independent Cr, Ca and Mg isotope data for 17 ungrouped chondrites. The epsilon 54Cr and epsilon 48Ca (epsilon expresses parts per ten thousand mass-independent isotope deviation) data for ungrouped chon-drites also provide important constraints for assessing their relationships to the known chondrite groups, and the radiogenic Mg isotope ratios (mu 26Mg*) can be used to track the early solar system history. We also present the first high-precision data for a Kakangari (KC) chondrite, an enstatite chondrite, and for four enstatite-rich meteorites. The epsilon 54Cr and epsilon 48Ca values for the KC are-0.44 +/- 0.04 and-1.30 +/- 0.25, respec-tively, and epsilon 48Ca value for SAH 97096 (EH3) is-0.19 +/- 0.22 that overlaps with that of those of Earth -Moon system and ordinary chondrites. All the carbonaceous chondrite-like (CC) ungrouped chondrites show positive epsilon 54Cr and epsilon 48Ca values, and all the non-carbonaceous chondrite-like (NC) ungrouped chon-drites and KCs (also belong to the NC trend) show zero or negative epsilon 54Cr and epsilon 48Ca values. This observa-tion confirms the CC-NC dichotomy for primitive solar system materials. LEW 87232 (KC) also shows the highest 55Mn/52Cr ratio and epsilon 53Cr value amongst all the chondrites. There is a positive trend between 55Mn/52Cr ratios and epsilon 53Cr values among all the chondrites that mostly reflects a mixing between mul-tiple chondritic components. Previously it has been reported that there is a bulk 26Al-26Mg correlation line amongst chondrites. This correlation has been interpreted as being due to mixing of CAIs (high 27Al/24Mg ratios and mu 26Mg* values) and other silicate material (e.g., chondrules and matrix). By provid-ing additional 26Al-26Mg chondrite data, we show that there is no 26Al-26Mg correlation line for the chon-drites, ruling out the two-endmember (i.e., CAIs and other silicates) mixing model.(c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).