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      The lateral growth and coalesence of magma systems

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          Abstract

          Thermal and mechanical models of magma reservoir growth need to be reconciled with deformation patterns and structural relationships observed at active magma systems. Geophysical observations provide a series of short time-scale snap-shots (10 0–10 2 years) of the long-term growth of magmatic bodies (10 3–10 6 years). In this paper, we first review evidence for the growth of magmatic systems along structural features and the associated deformation patterns. We then define three distinct growth stages, (1) aligned melt pockets, (2) coalesced reservoirs, (3) highly evolved systems, which can be distinguished using short-term surface observations. We use two-dimensional thermal models to provide first-order constraints on the time scales and conditions associated with coalescence of individual magma bodies into large-scale reservoirs. We find that closely spaced intrusions (less than 1 km apart) can develop combined viscoelastic shells over time scales of 10s kyr and form laterally extensive mush systems over time scales of 10–100 kyr. The highest temperatures and melt fractions occur during a period of thermal relaxation after melt injection has ceased, suggesting that caldera-forming eruptions may preferentially occur long after the main intrusive activity. The coalescence of eruptible melt-rich chambers only occurs for the highest melt supply rates and deepest systems. Thus, these models indicate that, in most cases, conductive heat transfer alone is not sufficient for a full coalescence of magma chambers and that other processes involving mechanical ruptures and mush mobilization are necessary; individual melt lenses can remain isolated for long periods within growing mush systems, and will only mix during eruption or other catastrophic events. The long-term history of the magmatic system is therefore critical in determining rheological structure and hence short-term behaviour. This framework for the development of magmatic systems in the continental crust provides a mechanical basis for the interpretation of unrest at the world's largest volcanoes.

          This article is part of the Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics'.

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          Most cited references 97

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          Pressure, gas content and eruption periodicity of a shallow, crystallising magma chamber

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            On the Origin of Crystal-poor Rhyolites: Extracted from Batholithic Crystal Mushes

             O. Bachmann (2004)
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              Volcanological perspectives on Long Valley, Mammoth Mountain, and Mono Craters: several contiguous but discrete systems

               Wes Hildreth (2004)
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                Author and article information

                Journal
                Philos Trans A Math Phys Eng Sci
                Philos Trans A Math Phys Eng Sci
                RSTA
                roypta
                Philosophical transactions. Series A, Mathematical, physical, and engineering sciences
                The Royal Society Publishing
                1364-503X
                1471-2962
                25 February 2019
                7 January 2019
                7 January 2019
                : 377
                : 2139 , Theo Murphy meeting issue ‘Magma reservoir architecture and dynamics’ compiled and edited by Marie Edmonds, Katharine V. Cashman, Marian B. Holness and Matthew D. Jackson
                Affiliations
                [1 ]School of Earth Sciences, University of Bristol , Queen's Road, Bristol, BS8 1RJ, UK
                [2 ]Univ. Grenoble Alpes, Univ. Savoie Mont Blanc , CNRS, IRD, IFSTTAR, ISTerre, 38000 Grenoble, France
                Author notes

                One contribution of 15 to a Theo Murphy meeting issue ‘ Magma reservoir architecture and dynamics’.

                Article
                rsta20180005
                10.1098/rsta.2018.0005
                6335484
                © 2019 The Authors.

                Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

                Product
                Funding
                Funded by: European Union's Horizon 2020 research and innovation programme;
                Award ID: 794594
                Funded by: NERC RiftVolc;
                Award ID: NE/L013932/1
                Categories
                1005
                190
                81
                Articles
                Research Article
                Custom metadata
                February 25, 2019

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