The Little Minch Sill Complex

Abstract

Prior to 1983, various relationships between the Tertiary alkaline basic sills of the Shiant Isles, north Syke (Trotternish), the islets of the Little Minch and Raasay had been suggested or implied by several authors. Geikie (1897) thought the Trotternish sills “probably continue northwards under the sea . . . for sills of the same type” occur in the Shiant Isles. It is evident from Walker’s papers on the sills of the Shiant Isles (1930), Trotternish (1932) and the “dolerite isles of the north Minch” (1931) that he considered it likely all these “groups” are somehow related. Davidson (1935) likened the picritic/crinanitic sills of Raasay to those of Trotternish but did not suggest any specific connection. In attempting to define the geographical occurrence of “truly alkaline picrites”, Drever and Johnston (1958) were probably the first to imply a connection between the intrusions of all the above areas while Simkin (1965) quite clearly considered the sills of Trotternish, the Shiant Isles and Raasay to be genetically related. However, it was only with the publication of the results of offshore geophysical surveys (Chesher et al. 1983) that the real extent and size of sills in the area (Fig. 1) were fully appreciated. From magnetic, seismic and other data Chesher et al. postulated that the sills are “probably the leaves of one major sill complex” and are “probably continuous at depth over the whole area”. They estimated the aggregate thickness of the leaves to be about 250 m. Detailed petrological and geochemical studies in . . .