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Abstract

The late Caledonian megatectonic framework of the Arctic-North Atlantic area and its borderlands is summarized in Plate 1.

The Caledonian orogenic cycle spanned Late Cambrian to earliest Devonian times. It embraced the Late Cambrian to Early Ordovician Grampian/Finnmarkian, the mid- to Late Ordovician Taconic, and the Late Silurian to early Gedinnian Main Scandinavian or late Caledonian orogenies (Gee and Sturt, 1986; Fig. 1).

The late Caledonian evolution of the Arctic-North Atlantic domain involved the convergence of four plates. The Late Ordovician and Silurian sinistral oblique collision of the continental Laurentia-Greenland and Fennosarmatian plates was preceded by the progressive subduction of the oceanic Iapetus plate and culminated in their Late Silurian-Early Devonian suturing along the Arctic-North Atlantic Caledonides. With this the Laurussian Megacontinent, also referred to as the North Continent, was formed (Wilson, 1966; Phillips et al., 1976; Roberts and Gale 1978; Soper and Hutton, 1984).

At the same time, the oceanic Proto-Tethys plate converged northward with the colliding Laurentia-Greenland and Fennosarmatian plates (Fig. 2). Northward subduction of the Proto-Tethys plate at an arc-trench system marking the southeastern margin of Laurentia and the southwestern margin of Fennosarmatia was accompanied by the northward rafting of a number of continental fragments that were rifted off the northern margin of Gondwana during the Cambro-Ordovician and Early Silurian. Some of these micro-continents (allochthonous terranes) became accreted during the Caledonian orogenic cycle to the southern margin of the newly forming North Continent (Laurussia). These continental fragments are enclosed by the North German-Polish, Mid-European, and Ligerian-Moldanubian Caledonian

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