Generation of Icelandic rhyolites: silicic lavas from the Torfajökull central volcano

The Torfajökull central volcano in south-central Iceland contains the largest volume of exposed silicic extrusives in Iceland (∼225 km3). Within SW-Torfajökull, postglacial mildly alkalic to peralkalic silicic lavas and lava domes (67–74 wt.% SiO2) have erupted from a family of fissures 1–2.5 km apart within or just outside a large caldera (12×18 km). The silicic lavas show a fissure-dependent variation in composition, and form five chemically distinct units. The lavas are of low crystallinity (0–7 vol.%) and contain phenocrysts in the following order of decreasing abundance: plagioclase (An10-40), Na-rich anorthoclase (