The Green Beds of the Scottish Dalradian Series: Geochemistry, Origin, and Metamorphism of Mafic Sediments

The Green Beds of the Scottish Dalradian Series are greenschists and amphibolites of metasedimentary origin. Field relations, petrography, and chemical data are used to demonstrate that these rocks, approximately of basaltic composition, were derived by metamorphism of basic tuffs deposited in an area of pelite sedimentation. The Dalradian Epidiprites, a series of orthoamphibolites associated with the Green Beds are less siliceous and less magnesian, in general, than the metasediments. Pelitic material is more abundant in the Green Beds of the Southwest Highlands than to the northeast. Amphibole occurrence and abundance are related to calcium content of the rocks. Fifty-eight metasediments and three Epidiorites were analyzed for thirty elements each, by X-ray fluorescence methods.