Multi-isotope (N, O, Ti, and Cr) study of C1 and CM-like clasts—Probing unsampled C1 material

Abstract

A multi-element isotope (N, O, Ti, and Cr) study was conducted on C1 and CM-like clasts hosted in achondrites and chondrite breccias to understand the genesis of these chondritic clasts. The mineralogy, O, and N isotopes confirm that CM-like clasts in howardites and polymict eucrites closely resemble CM chondrite-like material. The O and Cr isotope composition of C1 clasts in CR chondrites overlaps with those of CR chondrites, implying either formation in a similar nebular environment or resemblance to local CR material that underwent more extensive in situ alteration. Notably, these clasts are less enriched in ¹⁵N than bulk CR chondrites. In contrast, C1 clasts in ureilites are enriched in ¹⁵N relative to the Earth's atmosphere by ~100‰ setting them apart from any other known solar system material. They display elevated ¹⁷O and ¹⁸O values and lie along the CCAM line. In addition, a C1 clast from an ureilite represents the most ⁵⁴Cr-enriched and ⁵⁰Ti-depleted endmember among the carbonaceous chondrites. Altogether, these isotopic characteristics suggest that C1 clasts in ureilites represent material not sampled by any known meteorite group. Overall, this study highlights the presence of primitive, isotopically distinct materials in the early outer solar system, some of which were transported to the inner solar system to the accretion region of the host parent bodies.