| Summary: | The Torfajökull central volcano in south-central Iceland contains the largest volume of exposed silicic extrusives in Iceland (∼225 km^3). Within SW-Torfajökull, postglacial mildly alkalic to peralkalic silicic lavas and lava domes (67–74 wt.% SiO_2) 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 (An_(10-40)), Na-rich anorthoclase ( © 1998 Elsevier Science B.V. Received 17 April 1997; accepted 5 January 1998. We are grateful to Ole Stecher and Richard Carlson at the Department of Terrestrial Magnetism, Carnegie Institute for Sr and Nd-isotope analysis on the Torfajökull samples. We much appreciate insightful reviews by Tanya Furman, Sigurdur Steinthorsson, and Fergus Gibb. B.G. would like to thank Maria-Victoria Gunnarsson for her encouragement and valuable help in writing the initial draft of this paper as well as the initial drafting of many of the figures. Funding for this project came from the American Scandinavian Foundation to Bjorn Gunnarsson and the National Science Foundation grants EAR 86-18202, EAR 88-1734, and OPP 9418513 to Bruce Marsh and grants EAR 90-19190 and EAR 93-17036 to Hugh Taylor.
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