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Graphite-bearing peraluminous dacites from the Erlend volcanic complex, Faeroe-Shetland Basin, North Atlantic

Published online by Cambridge University Press:  05 July 2018

Raymond Kanaris-Sotiriou*
Affiliation:
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.

Type
Petrology
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1997

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