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UBC Theses and Dissertations

Volcanology of the A154N kimberlite at Diavik : implications for eruption dynamics Moss, Stephen William

Abstract

Eruptions of kimberlite volcanoes are a poorly-understood phenomena, as there been no historical eruptions of kimberlite, and primary deposits and edifices of kimberlite volcanoes are rarely preserved. In particular, the styles of explosion, magma fragmentation, and primary deposition of kimberlite remain unclear. This thesis comprises field and laboratory study of five kimberlite deposits within the A154N kimberlite volcano at Diavik, NWT, Canada. These studies provide critical descriptive and semi-quantitative data on the geometries, component variations, and relative agerelationships of deposits. These data are collected in order to link volcanic deposits with eruption processes in the following ways: A) Pyroclastic kimberlite hosted by the A154N pipe is shown to derive from a different kimberlite volcano. Thus, kimberlite volcanoes can act as receptacles for primary volcanic products from the eruptions of adjacent kimberlite pipes, leading to a ‘cross-fertilizing’ distribution of magma batches. B) Image analysis, based on manual and computer-assisted digitization, is used to establish characteristic properties of olivine crystals in intrusive coherent kimberlite, including modal %, size range, shape variability, and population parameters. These properties serve as a baseline in understanding kimberlite eruption style and fragmentation. C) Study of A154N deposits documents phase separation of kimberlite magmas in time and space during ascent and records an evolution in phase proportions (crystals: melt: gas) within and/or between emplacement events. Phase separation can determine the surface expression of kimberlite volcanoes, the degree of melt separation from olivine crystals during eruption and, thus, the amount of preserved crystallized kimberlite around olivine crystals in deposits. D) Measured and estimated physical properties of kimberlite magmas are combined with 3-D models for conduit geometry to show eruption durations of minutes to hours for the A154N volcano. E) Observations of primary pyroclastic products in kimberlite deposits show eruptions can both modify the sizes, shapes and distributions of olivine crystals and separate melt from olivine. Relative changes in the proportion of these two parameters as preserved in deposits may serve as a proxy for kimberlite eruption intensity. Finally, these volcanic processes are shown to have direct implications for the distribution of diamonds within kimberlite pipes.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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