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Evolution of a silicic magma reservoir in the upper crust: Reyðarártindur pluton, Southeast Iceland
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Centre of Natural Hazards and Disaster Science.ORCID iD: 0000-0002-5006-5596
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Field observations of extinct and exposed magma reservoirs shed light on processes operating in the roots of presently active volcanoes. The Reyðarártindur pluton, Southeast Iceland is an example of a fossil shallow magma reservoir that fed eruptions. The different chapters in this thesis examine the accumulation of magma, and processes occurring during the development and evolution of the magma reservoir from different methodological perspectives. A final model for the evolution of the Reyðarártindur pluton is then presented.

The majority of the pluton consists of one voluminous rock unit, the Main Granite, that formed by rapid magma emplacement. However, a local zone of geochemically distinct, but related further Granite Enclaves and Quartz Monzonite Enclaves attest to variations in the composition of the underlying source reservoir. Space for the ca. 2.5 km3 of magma in the pluton was made by piecemeal floor subsidence, which began with multiple dykes that then propagated laterally to form flat-roofed intrusions at different depths. During the first stages of magma emplacement, shattering, sintering and sanidinite-facies contact metamorphism affected a ca. 10 m thick zone of the basalt host rock at the magma reservoir roof. The resulting hornfels was stronger than the original altered basalt, and contained zero porosity and permeability. It thus formed a ‘cap-rock’ to the magma reservoir, limiting heat, volatile and fluid transfer until fractured and faulted at a later stage. 

The magma reservoir erupted at least once, causing local subsidence of the roof, which would have been observable at the Earth’s surface. Recharge of the magma reservoir by the same Quartz Monzonite and further Granite as exposed in the Reyðará River led to overpressure and eruption. We envisage that cooling and sealing of the piecemeal subsidence network preceded eruption, causing overpressure with magma recharge. The eruptive lifetime of the magma reservoir was limited to ca. 1000 years. This timeframe is much less than the duration of silicic magmatism in a typical Icelandic central volcano, or at other rhyolite-erupting volcanoes worldwide, which is in the order of hundreds of thousands to millions of years. Hence, the Reyðarártindur pluton likely represents a small, ephemeral part of a wider magmatic plumbing system that feeds a central volcano.

The results from these studies can provide volcano-monitoring personnel with scenarios for magma emplacement, and processes leading to eruption, which they can then use as a framework for interpreting detectable signals of magma movement and volcanic unrest.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2022. , p. 67
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2151
Keywords [en]
magma, magma emplacement, magma reservoir, floor subsidence, piecemeal subsidence, granite, pluton, cap-rock, magma mingling, magma plumbing systems, volcanic and igneous plumbing systems, eruption
National Category
Geology
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
URN: urn:nbn:se:uu:diva-472813ISBN: 978-91-513-1505-8 (print)OAI: oai:DiVA.org:uu-472813DiVA, id: diva2:1652268
Public defence
2022-06-09, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2022-05-19 Created: 2022-04-18 Last updated: 2022-06-15
List of papers
1. Rapid Assembly and Eruption of a Shallow Silicic Magma Reservoir, Reyðarártindur Pluton, Southeast Iceland
Open this publication in new window or tab >>Rapid Assembly and Eruption of a Shallow Silicic Magma Reservoir, Reyðarártindur Pluton, Southeast Iceland
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2021 (English)In: Geochemistry Geophysics Geosystems, E-ISSN 1525-2027, Vol. 22, no 11, article id e2021GC009999Article in journal (Refereed) Published
Abstract [en]

Although it is widely accepted that shallow silicic magma reservoirs exist, and can feed eruptions, their dynamics and longevity are a topic of debate. Here, we use field mapping, geochemistry, 3D pluton reconstruction and a thermal model to investigate the assembly and eruptive history of the shallow Reyoarartindur Pluton, southeast Iceland. Primarily, the exposed pluton is constructed of a single rock unit, the Main Granite (69.9-77.7 wt.% SiO2). Two further units are locally exposed as enclaves at the base of the exposure, the Granite Enclaves (67.4-70.2 wt.% SiO2), and the Quartz Monzonite Enclaves (61.8-67.3 wt.% SiO2). Geochemically, the units are related and were likely derived from the same source reservoir. In 3D, the pluton has a shape characterized by flat roof segments that are vertically offset and a volume of >2.5 km(3). The pluton roof is intruded by dikes from the pluton, and in two locations displays depressions associated with large dikes. Within these particular dikes the rock is partially to wholly tuffisitic, and rock compositions range from quartz monzonite to granite. We interpret these zones as eruption-feeding conduits from the pluton. A lack of cooling contacts throughout the pluton indicates rapid magma emplacement and a thermal model calculates the top 75 m would have rheologically locked up within 1,000 years. Hence, we argue that the Reyoarartindur Pluton was an ephemeral part of the wider plumbing system that feeds a volcano, and that timeframes from emplacement to eruption were rapid.

Place, publisher, year, edition, pages
American Geophysical Union (AGU)American Geophysical Union (AGU), 2021
Keywords
volcanic-plutonic connection, magma mixing, magma chamber, eruption trigger, conduit
National Category
Geology Geochemistry
Identifiers
urn:nbn:se:uu:diva-461136 (URN)10.1029/2021GC009999 (DOI)000723103400008 ()
Funder
Knut and Alice Wallenberg Foundation, KAW 2017.0153The Royal Swedish Academy of Sciences, GS2019-0024
Available from: 2021-12-17 Created: 2021-12-17 Last updated: 2024-01-15Bibliographically approved
2. Cap-rock formation above a magma reservoir, Reyðarártindur Pluton, Iceland
Open this publication in new window or tab >>Cap-rock formation above a magma reservoir, Reyðarártindur Pluton, Iceland
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(English)Manuscript (preprint) (Other academic)
National Category
Geology
Identifiers
urn:nbn:se:uu:diva-472812 (URN)
Available from: 2022-04-18 Created: 2022-04-18 Last updated: 2022-04-18
3. Volcanic unrest as seen from the magmatic source- Reyðarártindur pluton, Iceland
Open this publication in new window or tab >>Volcanic unrest as seen from the magmatic source- Reyðarártindur pluton, Iceland
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(English)Manuscript (preprint) (Other academic)
National Category
Geology
Identifiers
urn:nbn:se:uu:diva-472811 (URN)
Available from: 2022-04-18 Created: 2022-04-18 Last updated: 2022-04-18

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