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Syn-emplacement fracturing in the Sandfell laccolith, eastern Iceland
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.ORCID iD: 0000-0002-3316-658X
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.ORCID iD: 0000-0002-9385-7614
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
2018 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

Felsic magma commonly pools within mushroom-shaped magma chambers, so-called laccoliths or cryptodomes at shallow crustal levels, which can cause collapse of the volcanic edifice. While deformation of magma in volcanic conduits is an important process for regulating eruptive behaviour (Pistone et al., 2016), the bulk of the deformation associated with laccolith emplacement is considered to occur in the host-rock (Pollard & Johnson, 1973), and the effects of magma deformation on the intrusion emplacement is largely unexplored. Here we describe the deformation associated with the emplacement of the 0.5 km3 rhyolitic Sandfell laccolith in eastern Iceland, which formed in a single intrusive event. By combining field measurements, 3D modelling, anisotropy of magnetic susceptibility, and microstructural analysis, we quantify deformation that occurred in both the host-rock and the magma to investigate its effect on intrusion emplacement. Magmatic and magnetic fabric analyses reveal contact-parallel magma flow during the initial stages of intrusion emplacement. The magma flow fabric is overprinted by strain-localisation bands, which indicate that the magma subsequently became viscously stalled and was deformed by consecutively intruding magma. This change in magma rheology can be attributed to the interaction between the strain-localisation bands and the flow bands, which caused extensive fracture-rich layers in the magma and led to decompression degassing, crystallization, and rapid solidification of half of the magmatic body. Our observations indicate that syn-emplacement rheology change, and associated fracturing of intruding magma not only occur in volcanic conduits, but also play a major role in the emplacement of shallow viscous magma intrusions.

References:

Pistone, M., Cordonnier, B., Ulmer, P. & Caricchi, L. 2016: Rheological flow laws for multiphase magmas: An empirical approach. Journal of Volcanology and Geothermal Research 321, 158–170.

Pollard, D.D. & Johnson, A.M. 1973: Mechanics of growth of some laccolithic intrusions in the Henry mountains, Utah, II: Bending and failure of overburden layers and sill formation. Tectonophysics 18, 311–354.

Place, publisher, year, edition, pages
2018. Vol. Session 1.7
National Category
Geology
Identifiers
URN: urn:nbn:se:uu:diva-339027OAI: oai:DiVA.org:uu-339027DiVA, id: diva2:1174269
Conference
33rd Nordic Geological Winter Meeting, 10-12 January 2018, Lyngby, Danmark
Available from: 2018-01-15 Created: 2018-01-15 Last updated: 2018-10-18

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Mattsson, TobiasBurchardt, SteffiAlmqvist, Bjarne

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