Mineralogy of volatile‐rich clasts in brecciated meteorites

Abstract

AbstractMeteoritic breccias are valuable samples as they can contain rare materials from the early solar system as clasts. Volatile‐rich, CI‐ and CM‐like clasts may represent parent body lithologies, which cannot be found as individual meteorites in today's meteorite collections. In order to reveal a better knowledge about the presence and chemical characteristics and variability of volatile (water‐bearing) materials in the early solar system these clasts play an important role. Such materials may have been available as the volatile component during the accretion of terrestrial planets. To understand the distribution of volatile‐rich materials in the solar system, we studied CI‐ and CM‐like clasts in brecciated meteorites including polymict ureilites, HEDs, CR, CB, CH, and ordinary chondrites. CI‐like clasts occur throughout all of the mentioned meteorite groups, whereas the CM‐like clasts have only been identified in HEDs and ordinary chondrites. The abundance of volatile‐rich clasts in general decreases in the order CH > CR > ureilites > HEDs > CB > OC > R. The mineralogy of CI‐like clasts is similar to CI chondrites, but their compositions of phyllosilicates differ. The mineralogy of CM‐like clasts clearly links them to CM chondrites. They must have been delivered to the HED parent body by low‐velocity impacts after differentiation and volcanism, as there is no evidence for high shock and heating processes. Additionally, we propose that CI‐like clasts in the CR, CB, and CH chondrites are a primary component of the appropriate parent bodies (accretionary breccias). Conversely, the CI‐like clasts in polymict ureilites and HEDs represent an infall as (micro)meteorites or as low‐velocity impactors, which happened after the accretion and differentiation of the appropriate parent bodies.