Thermal impact of dykes on ignimbrite and implications for fluid flow compartmentalisation in calderas

• Published in: Volcanica
• Main Authors: Kennedy, Ben, Heap, Michael, Burchardt, Steffi, Villeneuve, Marlène, Tuffen, Hugh, Gilg, H. Albert, Davidson, Jonathan, Duncan, Neryda, Saubin, Elodie, Gestsson, Einar Bessi, Anjomrouz, Marzieh, Butler, Philip
• Other Authors: Institut Terre Environnement Strasbourg (ITES), École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; Hvítserkur; Iceland
• Online Access: https://hal.science/hal-03725517; https://hal.science/hal-03725517/document; https://hal.science/hal-03725517/file/document-23.pdf; https://doi.org/10.30909/vol.05.01.7593

International audience 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.