Microchondrule-bearing clast in the Piancaldoli LL3 meteorite: a new kind of type 3 chondrite and its relevance to the history of chondrules

摘要: In the Piancaldoli LL3 chondrite, we found a mm-sized clast containing ~100 chondrules 0.2–64 μm in apparent diameter (much smaller than any previously reported) that are all of same textural type (radial pyroxene; FS1–17). This clast, like other 3 chondrites, has fine-grained Ferich opaque silicate matrix, sharply defined chondrules, abundant low-Ca clinopyroxene and minor troilite Si- Cr-bearing metallic Fe,Ni. However, very high modal matrix abundance (63 ± 8 vol. %), unique characteristics absence microscopically-observable olivine indicate is new kind chondrite. Most have FeO-rich edges, chondrule size inversely correlated with chondrule-core FeO concentration (the first reported correlation composition). Chondrules acquired Fe by diffusion from Fe-rich material during mild metamorphism, possibly before final consolidation rock. Microchondrules (those ⩽ 100 diameter) also another chondrite Rio Negro L regolith breccia. groups, microchondrule appears to be anticorrelated mean size, viz. 0.02–0.04 % H CO chondrites ⩽0.006 L, LL, CV chondrites. Microchondrules probably formed process normal-sized droplet chondrules: melting pre-existing dustballs. Because most compound collisions between type, suggest dust grains were mineralogically sorted nebula aggregating into The sizes craters, which resulted similarly-sized while they plastic, size-sorting (of dustballs) occurred formation, aerodynamic processes nebula. We predict kinds exist contain abundances, size-ranges proportions types different known groups.