Chondrite diversity revealed by chromium, calcium and magnesium isotopes

1,2KeZhu朱柯,3Martin Schiller,2Frédéric Moynier,3Mirek Groen,4Conel M. O’D. Alexander,5Jemma Davidson,5Devin L.Schrader,6Addi Bischoff,3Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2022.12.014]
1Freie Universität Berlin, Institut für Geologische Wissenschaften, Malteserstr. 74-100, 12249 Berlin, Germany
2Université Paris Cité, Institut de Physique du Globe de Paris, CNRS UMR 7154, 1 rue Jussieu, Paris 75005, France
3Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5–7, Copenhagen DK-1350, Denmark
4Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, Washington, DC 20015, USA
5Buseck Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287-6004, USA
6Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany
Copyright Elsevier

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 studied 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 ε54Cr and ε48Ca (ε expresses parts per ten thousand mass-independent isotope deviation) data for ungrouped chondrites also provide important constraints for assessing their relationships to the known chondrite groups, and the radiogenic Mg isotope ratios (μ26Mg*) 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 ε54Cr and ε48Ca values for the KC are -0.44 ± 0.04 and -1.30 ± 0.25, respectively, and ε48Ca 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 ε54Cr and ε48Ca values, and all the non-carbonaceous chondrite-like (NC) ungrouped chondrites and KCs (also belong to the NC trend) show zero or negative ε54Cr and ε48Ca values. This observation confirms the CC-NC dichotomy for primitive solar system materials. LEW 87232 (KC) also shows the highest 55Mn/52Cr ratio and ε53Cr value amongst all the chondrites. There is a positive trend between 55Mn/52Cr ratios and ε53Cr values among all the chondrites that mostly reflects a mixing between multiple 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 μ26Mg* values) and other silicate material (e.g., chondrules and matrix). By providing additional 26Al-26Mg chondrite data, we show that there is no 26Al-26Mg correlation line for the chondrites, ruling out the two-endmember (i.e., CAIs and other silicates) mixing model.

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