Item – Thèses Canada

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Numéro d'OCLC
828089766
Titre
High resolution structural investigation of synthetic and natural 2:1 clay-mineral assemblages using advanced sample preparation and electron microscopy imaging techniques
Diplôme
Thesis / Dissertation ETD
Éditeur
McGill University 2012
Notes
Doctor of Philosophy (Department of Earth and Planetary Sciences)
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Résumé
In this study, X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and conventional TEM (CTEM) of Pt-C replicas are used to characterize both synthetic and natural 2:1 clay minerals from a variety of geological environments. In manuscript 1, reference samples of illite and expandable 2:1 clay minerals (i.e., smectite-group minerals, vermiculite and rectorite) varying in interlayer charge were investigated to characterize their interlayer expansion after treatment with octadecylammonium (nC=18) cations. The results of this study show that the treatment of ultrathin sections of 2:1 clay minerals with nC=18 cations and their subsequent investigation under the HRTEM provide information on the distribution of layer charges and layer-charge heterogeneities that cannot be obtained with conventional techniques of sample preparation. The major objective of manuscript 2 is to test whether oxalate catalyzes the crystallization of saponite at low temperatures and pressures. Additionally, the experiments of this study allow the investigation of the expansion behaviour and the structure of newly formed saponite crystals after exchange with n-alkylammonium cations in HRTEM lattice-fringe images. As these clay minerals are interpreted to replicate by template-catalyzed polymerization and transmit the charge distribution from layer to layer, the formation of 2:1 layer silicates with a variable layer-charge has significant implications for the abiotic origin of life. The finding that polar organic molecules such as oxalic acid catalyze clay-mineral formation in the laboratory is of great relevance to what processes may have occurred on carbonaceous chondrites and on the primitive, outgassing Earth that finally led to the evolution of life. In manuscript 3, I investigated the role of oxalate in promoting the nucleation of 2:1 silicate layers of saponite within the low-charge, smectite-like interlayers of rectorite. This study was aimed to test the interc
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Sujet
Earth Sciences - Mineralogy