Picritic Basalts from the Palaeocene Lava Field of West-Central Skye, Scotland: Evidence for Parental Magma Compositions

Brian R. Bell and Ian T. Williamson
Department of Geology and Applied Geology, University of Glasgow, Glasgow G12 8QQ, Scotland
British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, England

Abstract: Mineral chemistry and whole-rock compositional data are reported for two lavas of picritic basalt from the Palaeocene lava field of west-central Skye, Scotland. Whole-rock compositions for both flows plot on Thompson's (1982) 9 kbar cotectic for olivine + plagioclase + clinopyroxene + liquid. Both flows contain highly forsteritic olivine phenocrysts (c. Fo89), which enclose early-precipitated crystals of chrome-spinel (Al2O3: c. 25 wt.%; Cr2O3: c. 36 wt.%; FeO + Fe2O3: c. 20 wt.%; MgO: c. 15 wt.%). The olivine compositions indicate equilibrium with picritic basalt magma compositions, as represented by the whole-rock compositions of both lavas. A high-pressure origin for the chrome-spinels is suspected on the basis of their textural association and aluminous composition. Compositional comparisons between the whole-rock and mineral chemistry characteristics of both flows and a picritic basalt chill facies of the temporally- and spatially-associated Rum Igneous Complex suggests that similar parental magmas were involved.

Keywords: basalt • picrite • magma composition • Skye • Scotland

Mineralogical Magazine; September 1994 v. 58; no. 392; p. 347-356; DOI: 10.1180/minmag.1994.058.392.01
© 1994, The Mineralogical Society
Mineralogical Society (www.minersoc.org)