Wüstite in the fusion crust of Almahata Sitta sulfide-metal assemblage MS-166: Evidence for oxygen in metallic melts
Article first published online: 28 MAR 2013
© The Meteoritical Society, 2013.
Meteoritics & Planetary Science
Volume 48, Issue 5, pages 730–743, May 2013
How to Cite
Horstmann, M., Humayun, M., Harries, D., Langenhorst, F., Chabot, N. L., Bischoff, A. and Zolensky, M. E. (2013), Wüstite in the fusion crust of Almahata Sitta sulfide-metal assemblage MS-166: Evidence for oxygen in metallic melts. Meteoritics & Planetary Science, 48: 730–743. doi: 10.1111/maps.12097
- Issue published online: 13 MAY 2013
- Article first published online: 28 MAR 2013
- Manuscript Accepted: 30 JAN 2013
- Manuscript Received: 5 SEP 2012
- German Research Foundation
- NASA Cosmochemistry Program. Grant Numbers: NNX10AI37G, NNX12AH88G
Meteorite fusion crusts form during the passage of a meteoroid through the Earth's atmosphere and are highly oxidized intergrowths as documented by the presence of e.g., oxides. The porous and irregular fusion crust surrounding the Almahata Sitta sulfide-metal assemblage MS-166 was found highly enriched in wüstite (Fe1-xO). Frictional heating of the outer portions of the assemblage caused partial melting of predominantly the Fe-sulfide and minor amounts of the outer Ni-rich portions of the originally zoned metal in MS-166. Along with melting significant amounts of oxygen were incorporated into the molten fusion crust and mainly FeS was oxidized and desulfurized to form wüstite. Considerable amounts of FeS were lost due to ablation, whereas the cores of the large metal grains appear largely unmelted leaving behind metal grains and surrounding wüstite-rich material (matte). Metal grains along with the surrounding matte typically form an often highly porous framework of globules interconnected with the matte. Although textures and chemical composition suggest that melting of Fe,Ni metal occurred only partially (Ni-rich rims), there is a trace elemental imprint of siderophile element partitioning influenced by oxygen in the metallic melt as indicated by the behavior of W and Ga, the two elements significantly affected by oxygen in a metallic melt. It is remarkable that MS-166 survived the atmospheric passage as troilite inclusions in iron meteorites are preferentially destroyed.