Gilchrist, Finley Jack (2025) Rhyolite Generation at a Migrating Volcanic Centre: Atitlán, Guatemala. PhD thesis, Birkbeck, University of London.
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Abstract
Super-eruptions are some of the most devastating natural events on Earth. Each event is unique, so study of as many eruption deposits as possible is vital to understand the circumstances that can lead to their formation. Several factors are tied to the formation of massive volumes of eruptible magma, and one of these is migration of the source of magma from the mantle. To examine this, we have studied the Atitlán Volcanic centre (AVC). This centre lies in the central Guatemalan segment of the Central American volcanic arc (CAVA), where volcanism is strongly controlled by trenchwards migration and where large pumice eruptions are relatively commonplace. The AVC has produced several super-eruptions in the last 14 Ma, the most recent being the 75 ka, 510 km3 (dense rock equivalent) Los Chocoyos (LCY) eruption. This eruption produced at least four different magmas including three rhyolites that are divided by mineralogy and K2O content. The eruption’s vents (and likely the feeding magma body) lay in-between the old and new positions of the arc, now represented by the Atitlán caldera. Isotopic values of the stratovolcanoes grow more radiogenic inland and the LCY magmas have intermediate isotope values between the two extremes. The high-K LCY rhyolite had the largest volume of the LCY magmas, and petrogenetic modelling shows that it was formed by fractional crystallisation of stratovolcano magmas. Extraction of magma from the width of the centre and subsequent homogenisation can explain the intermediate isotopic signature of the LCY magmas compared to the stratovolcano endmembers. Migration therefore has a strong control on both the positioning of large-volume rhyolite magma bodies, and on their compositions. As shown by Volcán Atitlán, magmatism has now migrated outside of the caldera margins and explosive activity has ceased. The longevity of these systems is therefore also controlled by arc migration.
Metadata
| Item Type: | Thesis |
|---|---|
| Copyright Holders: | The copyright of this thesis rests with the author, who asserts his/her right to be known as such according to the Copyright Designs and Patents Act 1988. No dealing with the thesis contrary to the copyright or moral rights of the author is permitted. |
| Depositing User: | Acquisitions And Metadata |
| Date Deposited: | 03 Jul 2025 16:40 |
| Last Modified: | 22 Sep 2025 07:19 |
| URI: | https://eprints.bbk.ac.uk/id/eprint/55877 |
| DOI: | https://doi.org/10.18743/PUB.00055877 |
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