Late Caledonian sinistral displacements in Britain: Implications for a three‐plate collision model

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Abstract
In recent years, most geotectonic syntheses of the North Atlantic Caledonides have adopted a two plate configuration, with a roughly E‐W closure direction between Laurentia and Baltica producing the N‐S striking Scandinavian and East Greenland Caledonides and inducing dextral strike‐slip along the NE‐SW oriented British sector of the Iapetus suture. The North German‐Polish Caledonides are a third arm to the Appalachian‐N. Atlantic Caledonide orogen. Recently, Ziegler has proposed that the mid‐Palaeozoic deformation belts of S. Britain ‐ N. Germany‐Poland and also of central Europe were produced by the northward impact of microcontinental fragments onto the southern margin of the already sutured continental mass of Laurentia‐Baltica. Some ascribe the whole Appalachian orogen to a sequence of terrane accretion events in mid‐Ordovician through mid‐Devonian time. A N‐S collision direction would induce sinistral shear across the British sector of the Iapetus suture. In this paper, we outline the evidence for sinistral displacements within the British Caledonides and for their age. We conclude that the “non‐metamorphic Caledonides” were produced by the northerly accretion of a Cadomian terrane in late Silurian‐early Devonian time, and that this event was entirely separate from the earlier Laurentia‐Baltica collision which produced the post‐Grampian thrust related “metamorphic Caledonides” of Scotland.