Field evidence for the lateral emplacement of igneous dykes

Implications for 3D mechanical models and the plumbing beneath fissure eruptions

David Healy, Roberto Rizzo, Marcus Duffy, Natalie J. C. Farrell, Malcolm J. Hole, David Muirhead

Research output: Contribution to journalArticle

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Abstract

Seismological and geodetic data from modern volcanic systems strongly suggest that magma is transported significant distance (tens of kilometres) in the subsurface away from central volcanic vents. Geological evidence for lateral emplacement preserved within exposed dykes, sills and inclined sheets includes aligned fabrics of vesicles and phenocrysts, striations on wall rocks, measurements of anisotropic magnetic susceptibility and geometrical features such as steps and bridges. In this paper, we present geometrical evidence for the lateral emplacement of segmented dykes restricted to a narrow depth range (few tens of metres) in the crust. Near-total exposure of three dykes on wave cut platforms around Birsay (Orkney, UK) are used to map out floor and roof contacts of neighbouring dyke segments in relay zones. The field evidence suggests emplacement from the WSW towards the ENE, and that the dykes are segmented over their entire vertical extent. Geometrical evidence for the lateral emplacement of segmented dykes is likely more robust than inferences drawn from flow-related fabrics, due to the occurrence of ubiquitous ‘drainback’ events (i.e. magmatic flow reversals) observed in modern systems.
Original languageEnglish
Pages (from-to)85-105
Number of pages21
JournalVolcanica
Publication statusPublished - 22 Aug 2018

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fissure
emplacement
volcanic eruption
wave-cut platform
striation
geodetic datum
wall rock
vesicle
magnetic susceptibility
sill
roof
dike
magma
crust
fabric

Keywords

  • magma
  • relay
  • bridge
  • segment
  • igneous
  • volcanic

Cite this

Field evidence for the lateral emplacement of igneous dykes : Implications for 3D mechanical models and the plumbing beneath fissure eruptions. / Healy, David; Rizzo, Roberto; Duffy, Marcus; Farrell, Natalie J. C.; Hole, Malcolm J.; Muirhead, David.

In: Volcanica, 22.08.2018, p. 85-105.

Research output: Contribution to journalArticle

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abstract = "Seismological and geodetic data from modern volcanic systems strongly suggest that magma is transported significant distance (tens of kilometres) in the subsurface away from central volcanic vents. Geological evidence for lateral emplacement preserved within exposed dykes, sills and inclined sheets includes aligned fabrics of vesicles and phenocrysts, striations on wall rocks, measurements of anisotropic magnetic susceptibility and geometrical features such as steps and bridges. In this paper, we present geometrical evidence for the lateral emplacement of segmented dykes restricted to a narrow depth range (few tens of metres) in the crust. Near-total exposure of three dykes on wave cut platforms around Birsay (Orkney, UK) are used to map out floor and roof contacts of neighbouring dyke segments in relay zones. The field evidence suggests emplacement from the WSW towards the ENE, and that the dykes are segmented over their entire vertical extent. Geometrical evidence for the lateral emplacement of segmented dykes is likely more robust than inferences drawn from flow-related fabrics, due to the occurrence of ubiquitous ‘drainback’ events (i.e. magmatic flow reversals) observed in modern systems.",
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author = "David Healy and Roberto Rizzo and Marcus Duffy and Farrell, {Natalie J. C.} and Hole, {Malcolm J.} and David Muirhead",
note = "We thank the USGS Hawaiian Volcano Observatory for help with accessing Kilauea seismicity data, Steven Andrews at Camborne School of Mines for help with the sedimentology and John Howell (Aberdeen) for the lend of a drone. John Still is thanked for help with the SEM at Aberdeen. DH and NF thank Katie and Dave Farrell for ‘baby-sitting’ services while the fieldwork was completed. We thank Craig Magee, Meredith Townsend and Dave Pollard for detailed and thoughtful reviews that helped us improve the manuscript. High-resolution orthomosaics can be found at https://doi.org/10.6084/m9.figshare.6849827.v2",
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