Epidotic calc-silicates of Arnipol Type—a widely distributed minor sedimentary facies of the Moinian assemblage, Scotland

SummaryIn the Moinian rocks of Scotland, epidote-bearing calc-silicates, distinct from the commoner garnet-zoisite-bearing calc-silicates, occur at several widely scattered locations. The major element geochemistry of the two types of calc-silicate is very similar, and their somewhat different petrology and trace element geochemistry may be explained by the preservation of grains of detrital epidote and heavy minerals in the epidotic calc-silicates. These grains were concentrated in the original sediment and remained stable under greenschist and epidote-amphibolite metamorphic facies conditions. While the garnet-zoisite bearing calc-silicates may be derived from calcareous marls, the epidotic calc-silicate bands are probably derived from epidotic grits similar to those recorded in the Torridonian.