The Cairnsmore of Fleet Granite and its Metamorphic Aureole

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Abstract
The Cairnsmore of Fleet granite, the second largest of the four major intrusions of the Southern Uplands of Scotland, is a roughly oval mass, measuring eleven miles by seven, with the long axis trending north-east and south-west: that is, parallel to the strike of the sediments, mainly Silurian, into which it is intruded. It is the most acid of the four intrusions and consists entirely of granite: an incomplete ring of biotite-granite, with an average specific gravity of 2·64, surrounds a larger area of biotite-muscovite-granite, with an average specific gravity of 2·61. The rocks vary very little, and the authors consider that they are the product of two successive intrusions separated by no great interval of time, the biotite-granite being the earlier. An intrusion, about 250 yards long, of a dioritic rock bearing nickel and cobalt penetrates the sediments near the western margin of the granite and is the only mass in any way comparable with the marginal basic intrusions of the Loch Doon area. Dykes of any kind are very scarce, not only in the granite, but in the immediately surrounding metamorphosed sediments. They are mostly quartz-biotite-hornfelses, cordierite being less plentiful than in the Loch Doon area. The metamorphism is sometimes very conspicuous, as at Knocknairling Hill near New Galloway. While at the north-eastern and south-western ends the granite cuts across the sediments, along the north-western and south-eastern margins the latter dip off the granite, which may be regarded as an intrusion essentially laccolithic in character.

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