The geochemistry of Lewisian semipelitic schists from the Gairloch District, Wester Ross
- 1 August 1980
- journal article
- Published by Geological Society of London in Scottish Journal of Geology
- Vol. 16 (2-3) , 165-179
- https://doi.org/10.1144/sjg16020165
Abstract
Synopsis: The chemical composition of 63 samples of non-calcareous semipelitic schists from the Lewisian Loch Maree Group at Gairloch, Wester Ross is compared with that of 83 samples of the adjacent acid gneisses. The semipelitic metasediments can be clearly distinguished from the gneisses by their significantly higher Fe 2 O 3 (total), MgO, TiC 2 , Nb, Y, Zr, Zn, Cu, Cr and Ni contents, and lower concentrations of Al 2 O 3 , Na 2 O, Ba and Sr. These chemical differences can be used to distinguish sheared gneisses from sheared metasediments in certain transitional schist belts where the origin was formerly in doubt. Previous views that the semipelitic schists represented predominantly non-volcanogenic, greywacke-type sediments are confirmed, and the presence of two chemically distinct types representing different stratigraphic units is established. These metasediments are distinct from other Lewisian metasediments described in Assynt and Harris.Keywords
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