Magnetite-bubble aggregates at mixing interfaces in andesite magma bodies

Edmonds, M. and Brett, A. and Herd, R. A. and Humphreys, M. C. S. and Woods, A. (2014) Magnetite-bubble aggregates at mixing interfaces in andesite magma bodies. In: The Role of Volatiles in the Genesis, Evolution and Eruption of Arc Magmas. Special publication, 410 (410). The Geological Society, London, pp. 95-121. ISBN 9781862396890

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Official URL: http://sp.lyellcollection.org/content/early/2014/0...

Abstract

Magnetite is a particularly favourable site for heterogeneous bubble nucleation in magma and yet only very rarely is evidence for this preserved due to the myriad of processes that act to overprint such an association. The possibility of bubble-magnetite aggregates in magmas carries with it interesting implications for the fluid mechanics of magma bodies and for the magma mixing process responsible for the formation of andesites. We use image analysis and statistical methods to illustrate a spatial association between magnetite and bubbles in mafic enclaves. There is a large range in magnetite contents in the enclaves (up to 7.5%) which is related to the porosity of the enclaves, indicating a mechanism of enrichment of the mafic magma in magnetite. In the andesite there is no spatial association between bubbles and magnetite and the magnetite content of the andesite is small. We suggest a mechanism for enclave formation whereby in vapour-saturated magma, bubbles nucleate on magnetite. Upon intrusion into the base of an andesite magma body, these bubble-magnetite aggregates rise and ‘sweep up’ other magnetites, resulting in the accumulation of aggregates at the magma interface. Instabilities lead to the flotation of enclaves, characterized by enrichment in magnetite and bubbles.

Item Type: Book Section
Additional Information: The paper is embargoed until the 14th of August 2015. The final version has been published by The Geological Society of London here: http://dx.doi.org/10.1144/SP410.7.
Uncontrolled Keywords: 2014AREP; IA68;
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
06 - Part-III Projects
08 - Green Open Access
Journal or Publication Title: Geological Society, London, Special Publications
Volume: 410
Page Range: pp. 95-121
Identification Number: 10.1144/SP410.7
Depositing User: Sarah Humbert
Date Deposited: 10 Oct 2014 17:17
Last Modified: 01 Sep 2015 16:53
URI: http://eprints.esc.cam.ac.uk/id/eprint/3119

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