Graphite-Bearing Peraluminous Dacites from the Erlend Volcanic Complex, Faeroe-Shetland Basin, North Atlantic

Raymond Kanaris-Sotiriou
Department of Earth Sciences, University of Sheffield, Dainton Building, Brookhill, Sheffield, S3 7HF, UK

Abstract: Strongly peraluminous, cordierite-bearing anatectic dacites from the offshore Tertiary Erlend volcanic centre, north of the Shetland Isles, are shown to contain graphite which is interpreted as being essentially a restite phase inherited from carbonaceous pelitic source rocks. The form and characteristics of the graphite are documented and graphite geothermometry applied to establish that the graphite records a minimum peak temperature of ∼800°C, confirming that temperatures at which anatexis occurs were attained. The different morphological forms of graphite observed suggest the possibility that minor amounts of fluid-deposited graphite may also be present. The chemistry of the Erlend dacites is compared with that of other known examples of graphite-bearing peraluminous silicic igneous rocks and briefly with experimentally generated peraluminous liquid compositions. The Erlend source rocks were probably subjected to a higher degree of partial melting than has occurred in the petrogenesis of many other anatectic peraluminous silicic rocks.

Keywords: graphite • peraluminous • dacite • anatectic • North Atlantic

Mineralogical Magazine; April 1997 v. 61; no. 405; p. 175-184; DOI: 10.1180/minmag.1997.061.405.02
© 1997, The Mineralogical Society
Mineralogical Society (