Mn-rich chondrule rims in CO3 chondrites: Implications for the composition of nebular dust

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Jillian Kirk, Myriam Telus, Pranvera Hyseni, Fatima Jorge-Chavez, Vanessa Mendoza, Steven J. Desch, Dale Burns, Steven Simon

Icarus, In Press, Journal Pre-proof, Available online 14 July 2026

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“Highlights

  • CO3 chondrules exhibit rims enriched in Mn, made of high-Ca and low-Ca pyroxene.
  • Mn-rich chondrule rims likely formed from a complex process in the nebula.
  • Nebular dust may have been the source of Mn-rich rims.”

“Chondrules are small igneous particles that formed in the protoplanetary disk and make up the bulk of chondrites. Chondrule rims offer insights into the composition of dust in the solar nebula and the conditions and heating mechanisms associated with chondrule formation. High-resolution elemental mapping of pristine CO3 chondrite thin sections revealed igneous chondrule rims enriched in manganese, a moderately volatile element (MVE), which is sensitive to thermal processing. These chondrule rims have not previously been characterized, in part due to their small thicknesses (30 m). Characterization of Mn-rich rims in CO3 chondrites reveals that this enrichment exists in a variety of textures, some of which are associated with non-igneous fine-grained rims, while many clearly formed from a melt. Mn-rich pyroxenes in CO3 chondrule rims are also enriched in Na, K, and Cr, as compared to pyroxene in host chondrules (i.e., chondrules hosting the Mn-rich rims) and no-rim chondrules (chondrules without Mn-rich rims). These enrichments seem to be the result of nebular processing of chondrules as opposed to parent-body processing, as enrichments do not correlate with petrologic subtypes. Pyroxene with similar enrichments in these elements occur within igneous chondrule rims seen in CR chondrites, indicating that these rims may have formed across different locations and times in the nebula. Previous studies have suggested that MVE enrichment of chondrule rims occurred during interaction with MVE-enriched nebular gas. Our results could support an alternative scenario involving accretion of MVE-enriched dust onto solidified chondrules, which subsequently experienced varying degrees of thermal processing, possibly facilitated by a planetesimal or planetary embryo bow shock, resulting in MVE-enriched chondrule rims. Future work is needed to validate this idea. This study highlights the potential role of outgassing planetesimals and/or planetary embryos as a source of MVE-rich dust in the solar nebula.”

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