Volatiles are fundamental to many aspects of kimberlite magmatism. However, the volatile compositions and concentrations are poorly defined. Enrichment of H in kimberlitic olivines, many of which are xenocrysts, suggests high water content, but the extent to which H exchanges between these xenocrysts and kimberlite magmas remains unclear. This study investigates zonation of H in kimberlite-hosted xenolith and macrocrystic olivines using Fourier transform infrared spectroscopy to constrain the extent of re-equilibration. Data show that, depending on locality, xenolith olivines exhibit either no H-zonation, or substantial H-depletion in their rims. Macrocrysts feature similar trends to xenolith olivines from the same intrusion. In terms of the rim:core ratio of H, strongly zoned olivines average ~0.5, whereas poorly zoned olivines average at ~0.9 (macrocrysts) or 1.0 (xenolith olivines). Locality-specific H-zonation could result from different magmatic thermal regimes, water concentrations, or ascent durations. If the magmas that contained weakly zoned olivines were anhydrous, their restricted zoning requires ascent durations (< 20 min at 1100 °C) that are considerably shorter than published estimates (~1-24 hr at 1100 °C). These findings suggest that elevated magmatic water concentrations minimized loss of H from olivine in these kimberlites, showing that non-equilibrated xenocrysts could indirectly record high water concentrations in the form of weak H-zonation. Strong H-depletion patterns in olivines from other kimberlites may reflect lower initial magmatic water concentrations, or loss of fluid to country rocks. Future studies could compare H-zonation to temperature and ascent rate estimates, and field relationships to better elucidate the causes of locality-specific H-zonation. An apparent correlation between diamond grade and H-zonation warrants further investigation. / This thesis includes an Electronic Appendix, available at http://dalspace.library.dal.ca
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/14103 |
| Date | 08 August 2011 |
| Creators | Hilchie, Luke Jonathan, Hilchie, Luke |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
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