Thermal impact of dykes on ignimbrite and implications for fluid flow channelisation in a caldera

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Ben Kennedy
Michael Heap
Steffi Burchardt
Marlène Villeneuve
Hugh Tuffen
H. Albert Gilg
Jonathan Davidson
Neryda Duncan
Elodie Saubin
Einar Bessi Gestsson
Marzieh Anjomrouz
Philip Butler


Ignimbrites within calderas host intrusions with hazardous and/or economically significant hydrothermal systems. The Hvítserkur ignimbrite at Breiðuvík caldera, north-eastern Iceland, is intruded by basaltic dykes. Our data show that the ignimbrite immediately adjacent to the dyke is hard, dark-coloured, recrystallised quartz, plagioclase, and alkali feldspar with a low permeability and porosity and frequent macrofractures. At 1-2 m from the dyke, the ignimbrite is hard, dominantly glassy with pervasive perlitic microfractures, has high permeability, but low porosity and frequent macrofractures. A narrow zone of pervasive unlithified clay exists 2 m from the dyke. Beyond this, the ignimbrite is soft and zeolite-rich, has low permeability, high porosity and fewer macrofractures. The dyke intrusion promoted a narrow zone of welding, fracturing and perlitisation in the ignimbrite resulting in high permeability and focussed alteration. Our study shows how intrusions and their thermal aureoles create vertical pathways for, and horizontal barriers to, geothermal fluid flow.


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Kennedy, B., Heap, M., Burchardt, S., Villeneuve, M., Tuffen, H., Gilg, H. A., Davidson, J., Duncan, N., Saubin, E., Gestsson, . E. B., Anjomrouz, M. and Butler, P. (2022) “Thermal impact of dykes on ignimbrite and implications for fluid flow channelisation in a caldera”, Volcanica, 5(1), pp. 75–93. doi: 10.30909/vol.05.01.7593.
Received 2021-09-06
Accepted 2022-01-17
Published 2022-02-04

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