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Title: Characterising primitive chondrite components
Author: Duffy, Christina Mary
ISNI:       0000 0004 2706 723X
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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Primitive chondrite components in six carbonaceous chondrites, Bencubbin, HaH 237, Gujba, Isheyevo, Acfer 209 and Acfer 094 were studied to examine the complex thermal histories of individual particles. Significant information about the origin and evolution of the solar nebula is contained within primitive chondrite components including FeNi metals, sulphides, matrix material and calcium aluminium inclusions, allowing conclusions to be drawn about the conditions which prevailed in the early nebula. This thesis describes the analysis of meteoritic metal and other components in carbonaceous chondrites using a suite of complementary techniques including secondary electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), secondary ion mass spectrometry (nanoSIMS), grain-size frequency distribution (GSFD) and computed tomography. Metal is chosen as the primary comparative component as it is a common feature in carbonaceous chondrites and is an indication of the extent to which a sample has been exposed to thermal, metamorphic and alteration processes. EBSD results reveal a variation between chondrule-associated metal and matrix metal in CR chondrite Acfer 209 and the ungrouped chondrite Acfer 094 indicating a difference in formation and subsequent processing. TEM results demonstrated that evidence for aqueous alteration occurs on a sub-μm scale on the rims of FeNi metal grains in Acfer 094. FeNi metallic rims displayed regions of pitting corrosion and an enrichment in O and Ni accompanied by depletion in Fe. These features indicate interaction with an aqueous fluid. Grain-size frequency distribution analyses revealed a strong and common mode in the metal grain aspect ratios of three samples from the CB group of chondrites indicating a common deformational event. The presence of adjacent primitive components with varying chemical and crystallographic textures reveals that these samples were subject to a complex thermal history. Fine-grained matrix material in HaH 237 is heavily hydrated and shows no complementarity to chondrules which escaped aqueous alteration consistent with the X-wind model. In contrast, matrix material does show compositional complementarity to chondrules in Acfer 094 and Acfer 209. This suggests material for both components formed in the same region of a nebula conforming to the shock model where material formed on the disk.
Supervisor: Bland, Phil ; Russell, Sara ; McPhail, David Sponsor: ORIGINS Network ; Marie Curie
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral