A Geochemical Study of Lewisian Metasedimentary Granulites and Gneisses in the Scourie-Laxford Area of the North-West Scotland

P. O. Okeke, G. D. Borley and J. Watson
Department of Geology, University of Benin, Private Bag 1154, Benin City, Nigeria
Department of Geology, Imperial College, Prince Consort Road, London SW7

Abstract: Major element, trace element, and REE data for metasedimentary granulites and their retrogressed derivatives formed from Archaean parent-rocks at two localities in the Lewisian complex of north-west Scotland are presented.

The metasedimentary rocks are enclosed in and intruded by metatonalites and related calc-alkaline rocks and have been highly deformed and metamorphosed along with these rocks. They are geochemically distinct from this meta-igneous suite and range from highly aluminous to highly siliceous types. Comparisons of major and trace element data with those for unmetamorphosed Archaean and post-Archaean sediments suggest that they are derived from a detrital shale-greywacke assemblage, which may have included a volcaniclastic component. High ΣREE and ΣLREE suggest that the source-rocks included fractionated felsic igneous rocks.

Evidence that depletion in the large ion lithophile elements K, Rb, Th accompanied high-pressure granulite metamorphism supports the view, based on data derived from the associated meta-igneous rocks, that depletion was effected by active fluids rather than by abstraction of a partial melt and suggests that removal of K and Th began only when a considerable reduction of Rb had taken place.

Mineralogical Magazine; March 1983 v. 47; no. 342; p. 1-9; DOI: 10.1180/minmag.1983.047.342.01
© 1983, The Mineralogical Society
Mineralogical Society (www.minersoc.org)