Quenched Silicic Glass from Well KJ-39 in Krafla, North-Eastern Iceland

Abstract

In the fall of 2008 well KJ-39 was directionally drilled to a depth of 2865 m (2571 m TVD) into the Suðurhliðar field in Krafla geothermal field, north-eastern Iceland. Quenched silicic glass was found among the cuttings retrieved from the bottom of the well suggesting that magma had been encountered and high temperatures of 385.6°C were measured, while drill string was stuck in the well. The silicic glass contained resorbed minerals of plagioclase, clinopyroxene and titanomagnetite and was subalkaline, peraluminious in composition; containing 4-5% corundum in the norm. The composition of the silicic glass resembles magma that has formed by partial melting of hydrated basalt during initial stages of contact metamorphism. The melt was encountered among cuttings from impermeable, coarse basaltic intrusives at a depth, where the well was anticipated to penetrate the Holseldar volcanic fissure. The disclosure of melt at such shallow depths within Krafla geothermal system conform with the existence of a two phase reservoir, where temperature have reached 340350°C at 2000 m depth.