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Magma flow and palaeo-stress deduced from magnetic fabric analysis of the Álftafjörður dyke swarm: implications for shallow crustal magma transport in Icelandic volcanic systems

By
P. I. Eriksson
P. I. Eriksson
Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, IcelandDivision of Applied Geophysics, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, Sweden
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M. S. Riishuus
M. S. Riishuus
Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Iceland
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S.-Å. Elming
S.-Å. Elming
Division of Applied Geophysics, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, Sweden
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Published:
January 01, 2015

Abstract

Neogene regional mafic dykes extending north of the Álftafjörður central volcano in east Iceland are studied to test models of dyke swarm emplacement at spreading ridges. This is accomplished by using anisotropy of magnetic susceptibility to define fossilized magma flow regimes. The imbrication of the foliation plane, defined by the minor susceptibility axis, is used as an indicator of the flow direction. Contemporaneous shear resolved on the dyke walls may modify a pure flow-induced fabric and such shear regimes are therefore retracted. The magma flow and palaeo-stress resolved on the dykes are determined in 13 of 24 dykes. The magma flow is interpreted as subhorizontal and northwards directed away from the central volcano for nine dykes, and found to be vertical in three cases. The preferentially subhorizontal magma flow in the Álftafjörður swarm suggests that dyke propagation in this type of Icelandic volcanic system originates in shallow crustal magma chambers. The regional tectonic palaeo-stress field is deduced to cause oblique spreading across the Álftafjörður dyke swarm and govern a subhorizontal dextral shear component on the dyke planes during propagation. This interpretation is not in conflict with the left-stepping en echelon trend distribution of individual dykes relative to the trend of the swarm.

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Geological Society, London, Special Publications

The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes

M. H. Ort
M. H. Ort
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M. Porreca
M. Porreca
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J. W. Geissman
J. W. Geissman
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Geological Society of London
Volume
396
ISBN electronic:
9781862396722
Publication date:
January 01, 2015

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