Terrane evolution of the paratectonic Caledonides of northern Britain

Abstract

A stratigraphically constrained re-evaluation of terrane amalgamation in the Caledonides of northern Britain allows the development of a new orogenic scenario which accounts for many of the outstanding problems in the paratectonic Caledonides and includes a new terrane template which correlates well with that proposed for Newfoundland. The Arenig Grampian Orogeny resulted from the accretion of two arc terranes to Laurentia: the Midland Valley (=Notre Dame Arc in Newfoundland) and a terrane of probable Avalonian/Gondwanan origin, here termed ‘Novantia’ (= Annieopsquotch Accretionary Tract partim ), now hidden beneath the Southern Uplands allochthon. The Tyrone and Ballantrae ophiolites mark the northern boundary of Novantia within the composite Midland Valley Terrane. The Popelogan–Victoria Arc–Grangegeeth Terrane accreted to the amalgamated Midland Valley Terrane during the late Ordovician and initiated the Southern Uplands thrust duplex. A brief period of northward subduction during the Silurian followed, is ascribed to the northerly drift of the amalgamated Avalon–Baltica plate, and a final Wenlock (Scandian) collision and caused underplating of the Midland Valley Terrane. Caledonian deformation had ceased by the Emsian, the age of the undeformed Cheviot lavas that overlie the uplifted and peneplaned Southern Uplands.