MINERALOGICAL ANALYSES OF SAMPLES FROM THE BUCHAN METAMORPHIC SERIES NEAR BANFF, SCOTLAND

The east-central portion of Scotland that borders the North Sea is located in the Grampian Highlands region. The rocks exposed in the region can be found between the Great Glen Fault and the Highland Boundary Fault, both of which dissect Scotland in a SW-NE direction. The Buchan Metamorphic Series in this region consists of metamorphosed sedimentary and igneous rocks. The rocks range from those exhibiting low grades of metamorphism, near Melrose Farms east of MacDuff, to those exhibiting high grades of metamorphism, near Portsoy. The lowest grades of metamorphism are present in metasedimentary rocks. These rocks originated from sandstones and siltstones to mudstones of the Dalradian Group. An andalusite-bearing schist was found located along the coast at White Hills between MacDuff and Portsoy. The schist contains andalusite porphyroblasts with a biotite and quartz matrix as well as some garnets. The schistosity, as indicated by the orientation of biotite crystals, exhibits crenulation indicating multiple metamorphic events. High-grade amphibolite to granulite facies metamorphic rocks are located near Portsoy. In one of the hand samples, the rock looks much like a quartzite with a hard, light-colored, crystalline texture. However, thin sections of that rock revealed high-grade metamorphic mineralization, including the presence of clinopyroxene, amphibole, calcite, and garnet. A second sample from that area appears to be hornblende-biotite-sillimanite bearing gneiss based on initial thin section analyses. The mineralogy from these samples can be used along with metamorphic phase diagrams including both ACF for and AFM diagrams to understand the parent rocks, mineral reactions, and metamorphic conditions.