General structure of the Skye Tertiary igneous complex and detailed structure of the Beinn an Dubhaich Granite from magnetic evidence

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Abstract
Synopsis: On the Isle of Skye, a series of Tertiary igneous rocks, including a central layered gabbro and associated granites occurs in an area of basement gneiss overlain by sediments of Cambrian to Cretaceous age. Two-dimensional computer modelling of aeromagnetic data (this paper) agrees reasonably well with the three-dimensional gravity model of Bott and Tuson (1973). Both models indicate that the gabbro pluton is a large, slightly cone-shaped mass, with a width of approximately 12 km at the top and 18 km at the base, penetrating to a depth of about 14 km, and that the granites are a shallow, near-surface phenomenon (less than 2.5 km deep), comprising about five to ten per cent of the total mass of the igneous assemblage. The Beinn an Dubhaich granite is approximately 0.8 km wide and 3.2 km long in outcrop and contains numerous patches of limestone. Ground magnetic measurements and the relationship between the granite-limestone contact and the topography indicates that the granite is a stock which extends to depth and underlies the limestone. Further, the granite surface beneath the limestone is not smooth but rather consists of many lobes which intrude the limestone, possibly along pre-existing fractures.