Aqueous alteration of CM carbonaceous chondrites
- 出版日期：2004.
- 页数：1 v. :
- 第一责任说明：Lysa J. Chizmadia.
- 分类号：a283
- ISBN：0496168177(ebk.) :
MARC全文
02h0029488 20120618160344.0 cr un||||||||| 120618s2004 xx ||||f|||d||||||||eng | 3156109 0496168177(ebk.) : CNY371.35 NGL NGL NGL a283 Chizmadia, Lysa J. Aqueous alteration of CM carbonaceous chondrites [electronic resource] : constraints on early solar system processes / Lysa J. Chizmadia. 2004. 1 v. : digital, PDF file. Adviser: Brearley, Adrian J. Thesis (Ph.D.)--The University of New Mexico, 2004. Chondrule mesostasis is amorphous and therefore metastable. The accretionary fine-grained rims around the chondrules and other components have high surface area to volume ratios. The 3--5 mum Fe-Ni metal grains found within the fine-grained rims are easily oxidized. These three components of CM carbonaceous chondrutes should be sensitive to the aqueous alteration experienced by these meteorites. Light optical microscope observations and electron microprobe analyses (EMPA) indicate that all of the chondrule mesostases are no longer glassy, but have been replaced by hydrous phyllosilicates. This is counter to one of the main pieces of evidence in support of the pre-accretionary alteration model. Scanning electron microscope observations and EMPA indicate that Fe-Ni metal grains are present in the fine-grained rims of Y-791198, and that they are rare, averaging less than 1 per rim. Transmission electron microscope observations demonstrate that the fine-grained rims of Y-791198 are not composed of crystalline phases, but of amorphous materials with Fe-rich sulfide grains. The fine-grained rims are similar in texture, mineralogy and composition to GEMS-type IDPs (glass-embedded metal and sulfide). Therefore, it seems likely that the precursor materials to fine-grained rims were dominantly amorphous materials and Fe-rich sulfide grains with primary nebular phases such as olivine and Fe-Ni metal grains. These observations are most consistent with the parent-body alteration model, involving a high pH fluid, which accounts for the survival of Fe-Ni metal grains with contact with an oxidizing aqueous fluid. Aqueous alteration of CM chondrites progressed from replacing the chondrule mesostases with hydrated phyllosilicates, to the hydration of the amorphous rim materials, to the precipitation of nanocrystalline serpentine from the hydrated amorphous materials, to the development of fibrous serpentine, to the growth of coarse-grained serpentine, and finally to the formation of Fe3＋-rich cronstedtite and tochilinite. Chondrites (Meteorites) ; Chondrules. Electronic dissertations. aeBook. aCN bNGL http://pqdt.bjzhongke.com.cn/Detail.aspx?pid=VamO5p4vXKA%3d NGL Bs1545 rCNY371.35 ; h1 bs1204