Abstract
Mt. Taranaki is a dormant volcano, lying to the south-west of the North Island, New Zealand, ~400 km west of the Hikurangi Trough. This thesis addresses gaps in knowledge over the nature of magma production, evolution and storage, primarily through the analysis of melt inclusions from a range of Holocene deposits, for major element, trace element and dissolved volatile contents.Firstly, melt inclusion compositions are examined for the effects of post entrapment alteration. Clinopyroxene-hosted glasses made up the highest proportion of melt inclusions analysed. Commonly used equilibrium tests were evaluated for suitability for use on the range of melt compositions and compared to experimental data from this study and literature.
Secondly, melt inclusion compositions are used to discuss the magma source, magma evolution through the crust and the relationship between bulk andesitic compositions erupted from the summit vent and basaltic magmas erupted from the satellite cone, Panitahi. Melt inclusion compositions suggest that crystal fractionation drove magma evolution, and that the Panitahi magmas may be representative of parent magmas to those erupted at the summit. Diverse inclusion compositions suggest that evolution is complex and storage in a diverse range of ‘melt pockets’ is likely.
Magma storage conditions were evaluated using thermobarometric calibrations. Models were evaluated for appropriateness and compared to test predictions. Overall, outputted magma storage conditions are diverse within single eruptive episodes, suggesting the tapping of melts from multiple areas within the plumbing system.
Finally, high-temperature and pressure equilibrium experiments were run to better explore magma storage. A number of experiments aligned with the results of thermobarometry, and results suggested that melt volatile contents are likely undersaturated. However, the key conclusion is the requirement for higher temperature and pressure conditions and longer run times in future experiments.
| Date of Award | 7 May 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Alison C Rust (Supervisor) & Richard A Brooker (Supervisor) |