The geology of the Arnage district (Aberdeen-Shire) : a reinterpretation

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Abstract
Summary: In 1923, Read considered that in the Arnage district an initial gabbroic magma had been contaminated by country-rock material to produce on consolidation quartz-biotite-oligoclase-cordierite rocks (Arnage Type), pseudo-dioritic rocks (Kinharrachie Type) and finally granitic rocks (Ardlethen Type). Detailed field investigation leads to a new interpretation. The continuous magmatic series proposed by Read has been broken into two parts :— 1. An older part, consisting of the Arnage-Kinharrachie-Ardlethen types, produced by migmatization and comparable with migmatitic complexes of “ Older Granite ” age developed elsewhere in Aberdeenshire. 2. A newer part, gabbroic in character and belonging to the basic phase of the “ Newer Granite ” igneous activity of North-East Scotland. The “ Older Granite ” migmatites of Arnage have characters, such as the hornfelsic nature of their enclaves and their richness in cordierite, that are appropriate to their setting in the metamorphic zones of North-East Scotland. They present a contrast to the Cromar type of migmatites set in the Barrovian metamorphic zones of the South-East Highlands.