The petrochemistry of the epidiorites of the Tayvallich Peninsula, North Knapdale, Argyllshire.

Abstract

The geology of the Dalradian rocks near Tayvallich is described with a detailed geological map. 78 new chemical analyses of metamorphic rocks, each for 30 elements, are given including intrusive epidiorites, basic pillow lavas, agglomerates, grits, slates, limestones and calcareous slates. Basic volcanic glasses have been locally showered into the sediments. The epidiorites are albite-chlorite-calcite-quartz-sphene (epidote) rocks with actinolite being confined to rocks with mg in excess of 0.44. Metasomatic movement occurred between the margins and centres of the pillow lavas and is also believed to have affected the volcanic glasses. The sedimentary rocks can be distinguished from the epidiorites by a number of chemical characteristics including the high P, Ti and Nb of the epidiorites and their differing trends of variation such as Cr against Niggli mg. The Loch Awe epidiorites are characterised by high Zr and P and are less tholeiitic than epidiorites higher in the Dalradian sequence. They may be shallow intrusions and extrusions of a magma that had undergone substantial intratelluric differentiation.