The geology of part of Buchan
The research embodied in this thesis arose from a contract to remap Sheet 87W of the 1:50,000 geological map for the Geological Survey. The rocks investigated include late Precambrian to early Cambrian metasediments of the Dalradian Supergroup, and Caledonian intrusive igneous rocks. The range of sedimentary facies present within the Methlick Formation (Southern Highland Group) is described within the framework of current deep marine clastic facies classifications, and an inner to middle submarine fan facies model erected. Framework petrography, palaeocurrents, geochemistry and facies variation of the Methlick Formation indicate a provenance within the Laurentian shield to the north-west. Analysis of the stream sediment geochemistry dataset acquired by the Geological Survey is used as an aid to stratigraphic correlation in the Dalradian of north-east Scotland. The Ellon Division has middle Argyll Group characteristics, while the Aberdeen Division includes both middle and upper Argyll Group. Rocks with Appin Group geochemistry probably do not crop out in Buchan. Combinations of low-level anomalies for several chalcophile elements may be useful in mineral exploration. Igneous rocks in the Stuartfield area include a wide range of petrographic types of Ordovician age, including previously undescribed Younger Basic cumulates. The area is underlain by a concealed basic intrusion. Contact metamorphic isograds are defined for rocks ranging from andalusite schists to garnet-cordierite gneisses. P and T range up to about 720°C at 4.5kb PH20 falls from near PTOTAL at the K-feldspar isograd to about 0.5 PTOTAL at the garnet-cordierite isograd. A divariant field for coexistence of andalusite and sillimanite is defined, and new occurrences of sapphirine are described. A characteristic upper Argyll Group lithological assemblage in north-east Scotland includes quartzitic and calcareous lithologies, and corundum-bearing pelites with high K and Mg/Fe. Pelites of this assemblage are chemically distinct from those of the Southern Highland Group. The migmatitic gneisses of north-east Scotland, interpreted by some as basement, are in structural, stratigraphic and metamorphic continuity with the Dalradian, and include Argyll Group rocks.