The Hebridean terrane
The Hebridean terrane consists of that part of northwest Scotland, lying west of the Moine Thrust Zone, which formed part of the stable foreland of the Caledonian orogenic belt during the Palaeozoic era. The rocks making up this piece of crust comprise a crystalline, mainly gneissose, Archaean to Palaeoproterozoic basement (the Lewisian complex) overlain by an undeformed or gently tilted sedimentary cover of Neoproterozoic (the Torridonian) and Cambro-Ordovician age.
The present eastern margin of the terrane is formed by the Moine Thrust Zone, of Caledonian age, which itself conceals an earlier inferred boundary of Grenvillian age (~1.1 Ga) separating Lewisian crust with only minor Grenvillian effects in the west from gneisses with a high-grade (eclogite/granulite facies) overprint in the east (cf. Sanders et al. 1984). It also constitutes the western margin of the Knoydartian (~800 Ma) ‘orogenic’ event (cf. Vance et al. 1998). The nature of this major, long-lived crustal boundary clearly implies that the Hebridean terrane is at least parautochthonous, and may possibly be allochthonous, with respect to the adjacent Northern Highlands terrane.
The crystalline Lewisian basement of the Hebridean terrane was welded together during the Palaeoproterozoic at ~1.9Ga when it formed part of a large continental assemblage, including much of North America and Scandinavia. Further amalgamation and re-organization of crustal fragments around 1.0 Ga resulted in the supercontinent of Rodinia, which existed during the Neoproterozoic, and during this time the Torridonian deposits formed in intracontinental basins. After the break-up of this sector of Rodinia at the end of
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This 4th edition of The Geology of Scotland is edited by Dr Nigel Trewin of the Department of Geology and Petroleum Geology at the University of Aberdeen. The volume is greatly expanded from the previous edition with 34 authors contributing to 20 chapters.
A new format has been adopted to provide a different perspective on the geology of Scotland. A brief Introduction is followed by a chapter outlining some of the important historical aspects that in the 19th century placed Scottish geologists at the forefront of a new science.
Scotland is constructed from a number of terranes that finally combined in roughly their present positions prior to about 410 million years ago. Thus the geology of each terrane is described up to the time of amalgamation, providing chapters on the Southern Uplands, Midland Valley, Northern Highland, Grampian and Hebridean terranes. At the end of this section, a brief synthesis summarizes the events that resulted in the amalgamation of the various terranes into the present configuration.
Traditional practice is followed in the description of the Old Red Sandstone, Carboniferous, Permo-Trias, Jurassic, Cretaceous, Tertiary and Quaternary strata. A separate chapter covers Tertiary igneous rocks. An attempt is made to tell the story of the geological evolution of Scotland, rather than catalogue all areas and formations. Priority is given to the onshore geology, encouraging the reader to go into the field and visit some of the world-class geology on show in Scotland. The chapters are broadly-based, attempting to integrate the sedimentary and igneous histories, and summarize changes in palaeogeography and palaeoenvironments.
Economic aspects are covered with chapters on Metalliferous Minerals, Bulk Resources, Coal and Hydrocarbons. A new departure is a chapter on aspects of Environmental Geology and sustainability.
Additionally, this publication contains a colour section of 32 plates, illustrating aspects of Scottish Geology, as well as a coloured geological map of Scotland.