View source for Geology of the Aberfoyle district: Pre-caledonian amphibolite sheets (Neo-proterozoic Basic Minor Intrusion Suite)

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The oldest igneous intrusions within the district are a series of cleaved amphibolite/metadolerite sheets of Neoproterozoic age. They crop out around the northern end of Loch Lubnaig, and are particularly common on the northern and eastern slopes of Benvane [NN 535 137], locally forming a dense sill complex. The amphibolite sheets are mostly sills, a few metres or tens of metres thick, occurring predominantly within rocks of the Loch Katrine Volcaniclastic Formation or older units. These intrusions belong to a wider suite of mafic rocks, developed around the Argyll–Southern Highland Group boundary throughout the Dalradian of Scotland, and occurring in the northern half of Ireland. Their emplacement is related to the opening of the Iapetus Ocean at about 600&nbsp;Ma (e.g. Stephenson and Gould, 1995<ref name="Stephenson 1995">Stephenson, D, and Gould, D. 1995. The Grampian Highlands (Forth edition). ''British Regional Geology''. (London: HMSO for the British Geological Survey.)</ref>).

The amphibolites are dark green, commonly massive rocks. Often they have a speckled appearance and preserve relict igneous textures. Hornblende and plagioclase feldspar dominate the mineralogy. The margins of the amphibolite sheets are commonly schistose, whilst the interiors are more isotropic; thin sheets may be schistose throughout. Elsewhere in the southern Highlands similar amphibolites sheets at this level record a complex history of fluid–rock interaction, between the fluids generated by the amphibolites and host rocks and the rocks themselves during prograde and retrograde metamorphism (Skelton et al., 1995<ref name="Skelton 1995">Skelton, A D L, Graham, C M, and Bickle, M J. 1995. Lithological and Structural Controls of Regional 3-D Fluid Flow patterns during Greenschist Facies Metamorphism of the Dalradian of the SW Scottish Highlands. ''Journal of Petrology'', Vol.&nbsp;36, 563–586.</ref>; Graham et al., 1997<ref name="Graham 1997">Graham, C M, Skelton, A D L, Bickle, M, and Cole, C. 1997. Lithological, structural and deformation controls on fluid flow during regional metamorphism. 196–226 ''in'' Deformation-enhanced fluid transport in the Earth’s crust and mantle. Holness, M B (editor). ''Mineralogical Society Series'', No.&nbsp;8. (London: Chapman and Hall.)</ref>).

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== Geology of the Aberfoyle district - contents ==
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