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

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 immediately adjacent to dyke hard, dark-coloured, recrystallised quartz, plagioclase, and alkali feldspar a low permeability porosity frequent macrofractures. At 1-2 m from dyke, dominantly glassy pervasive perlitic microfractures, has high permeability, but A narrow zone of unlithified clay exists 2 dyke. Beyond this, soft zeolite-rich, fewer intrusion promoted welding, fracturing perlitisation in resulting focussed alteration. study shows how their thermal aureoles create vertical pathways for, horizontal barriers to, geothermal fluid flow.