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Conduit margin heating and deformation during the AD 1886 basaltic Plinian eruption at Tarawera volcano, New Zealand.

Schauroth, Jenny and Wadsworth, Fabian B. and Kennedy, Ben and von Aulock, Felix W. and Lavallée, Yan and Damby, David E. and Vasseur, Jérémie and Scheu, Bettina and Dingwell, Donald B. (2016) 'Conduit margin heating and deformation during the AD 1886 basaltic Plinian eruption at Tarawera volcano, New Zealand.', Bulletin of volcanology., 78 (2). p. 12.

Abstract

During explosive eruptions, a suspension of gas and pyroclasts rises rapidly within a conduit. Here, we have analysed textures preserved in the walls of a pyroclastic feeder dyke of the AD 1886 Tarawera basaltic Plinian fissure eruption. The samples examined consist of basaltic ash and scoria plastered onto a conduit wall of a coherent rhyolite dome and a welded rhyolitic dome breccia. We examine the textural evidence for the response of the wall material, built of ∼75 vol.% glass and ∼25 vol.% crystals (pore-free equivalent), to mass movement in the adjacent conduit. In the rhyolitic wall material, we quantify the orientation and aspect ratio of biotite crystals as strain markers of simple shear deformation, and interpret juxtaposed regions of vesiculation and vesicle collapse as evidence of conduit wall heating. Systematic changes occur close to the margin: (1) porosity is highly variable, with areas locally vesiculated or densified, (2) biotite crystals are oriented with their long axis parallel to the margin, (3) the biotites have greater aspect ratios close to the margin and (4) the biotite crystals are fractured. We interpret the biotite phenocryst deformation to result from crystal fracture, rotation and cleavage-parallel bookcase translation. These textural observations are inferred to indicate mechanical coupling between the hot gas-ash jet and the conduit wall and reheating of wall rock rhyolite. We couple these observations with a simple 1D conductive heating model to show what minimum temperature the conduit wall needs to reach in order to achieve a temperature above the glass transition throughout the texturally-defined deformed zone. We propose that conduit wall heating and resulting deformation influences conduit margin outgassing and may enhance the intensity of such large basaltic eruptions.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1007/s00445-016-1006-7
Publisher statement:© The Author(s) 2016 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Date accepted:25 January 2016
Date deposited:25 May 2018
Date of first online publication:13 February 2016
Date first made open access:No date available

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