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    Rights statement: This is the author’s version of a work that was accepted for publication in Journal of Volcanology and Geothermal Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Volcanology and Geothermal Research, 388, 2019 DOI: 10.1016/j.volgeores.2019.106691

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Comparative field study of shallow rhyolite intrusions in Iceland: emplacement mechanisms and impact on country rocks

Research output: Contribution to journalJournal article

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  • Elodie Saubin
  • Ben M. Kennedy
  • Hugh Tuffen
  • Marlene Villeneuve
  • Jonathan Davidson
  • Steffi Burchardt
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Article number106691
<mark>Journal publication date</mark>15/12/2019
<mark>Journal</mark>Journal of Volcanology and Geothermal Research
Volume388
Number of pages18
Publication statusPublished
Early online date28/10/19
Original languageEnglish

Abstract

Shallow silicic intrusions are known to exist in many active volcanoes and can fuel both eruptions and hydrothermal fields. However, our knowledge of magma intrusions remains far from complete, and processes occurring at intrusion margins are poorly understood. In this field-based study, we characterise four shallows, dissected rhyolitic intrusions at three sites in Iceland (Njarðvík-Dyrfjöll, Krafla and Húsafell central volcanoes). We focus on the relationship between intrusion emplacement mechanisms and country rock response, employing scanline mapping of fractures and in-situ rock property measurements (hardness and permeability) along transects from the intrusion margins to damaged and undamaged country rocks.We identify various scenarios of shallow intrusion emplacement style, based upon their diverse geometry and lithofacies architecture. Additional information from rock properties and characteristics of fractures and vesicles, indicates that initial country rock properties strongly influence the emplacement style. We identify two discrete types of country rock response to magma injection. The matrix permeability of weak, porous and permeable lithologies (conglomerate and hyaloclastite) is reduced by >1 order of magnitude adjacent to intrusions due to pore occlusion. Stronger and denser, low-permeability lithologies (basalt and welded ignimbrite) undergo a decrease in hardness by a factor >2 related to an up to fivefold increase in fracture density, with no significant change in matrix permeability.Our observations highlight the importance of robust characterisation of the mechanical properties of caldera-filling or geothermal reservoir formations, for appropriate forecasting of magma mobility, geophysical data interpretation, and geothermal resources characterisation.

Bibliographic note

This is the author’s version of a work that was accepted for publication in Journal of Volcanology and Geothermal Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Volcanology and Geothermal Research, 388, 2019 DOI: 10.1016/j.volgeores.2019.106691