Multiple melting in a four-layered barred-olivine chondrule with compositionally heterogeneous glass from LL3.0 Semarkona
Article first published online: 19 FEB 2013
© The Meteoritical Society, 2013.
Meteoritics & Planetary Science
Volume 48, Issue 3, pages 445–456, March 2013
How to Cite
Rubin, A. E. (2013), Multiple melting in a four-layered barred-olivine chondrule with compositionally heterogeneous glass from LL3.0 Semarkona. Meteoritics & Planetary Science, 48: 445–456. doi: 10.1111/maps.12069
- Issue published online: 18 MAR 2013
- Article first published online: 19 FEB 2013
- Manuscript Accepted: 17 DEC 2012
- Manuscript Received: 15 OCT 2012
- NASA Cosmochemistry. Grant Number: NNG06GF95G
Chondrule K7p from LL3.0 Semarkona consists of four nested barred-olivine (BO) chondrules. The innermost BO chondrule (chondrule 1) formed by complete melting of an olivine-rich dustball. After formation, the chondrule was incorporated into another olivine-rich dustball. A second heating event caused this second dustball to melt; the mesostasis and some of the olivine in chondrule 1 were probably also melted at this time, but the chondrule 1 structure remained largely intact. At this stage, the object was an enveloping compound BO chondrule. This two-step process of melting and dustball enshrouding repeated two more times. The different proportions of olivine and glass in chondrules 1–4 suggest that the individual precursor dustballs differed in the amounts of chondrule fragments they contained and the mineral proportions in those fragments. The final dustball (which ultimately formed chondrule 4) was somewhat more ferroan; after melting, crystallizing, and quenching, chondrule 4 contained olivine and glass with higher FeO and MnO contents than those of the earlier formed chondrules. Subsequent aqueous alteration on the LL parent body transformed the abundant metal blebs and stringers at the chondrule surface into carbide, iron oxide, and minor Ni-rich metal. Portions of the mesostasis underwent dissolution, producing holes and adjacent blades of more resistant material. Much of the glass in the chondrule remained isotropic, even after minor hydration and leaching. The sharp, moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution.