PALEOZOIC PALEOGEOGRAPHY OF LAURENTIA AND ITS MARGINS - A REASSESSMENT OF PALEOMAGNETIC DATA

The recognition of wide-spread remagnetization events during the Palae ozoic has greatly added to the problems of reconstructing the Palaeozo ic drift history of Laurentia and in recent years increasing emphasis has been placed on evaluating the relative reliability of palaeomagnet ic data, in an attempt to overcome some of these difficulties. In the light of these developments a revised apparent polar wander (APW) path has been constructed following a rigorous evaluation of all published Palaeozoic palaeomagnetic data from Laurentia and its Palaeozoic marg ins (i.e. North America, northern Britain, Northern Ireland and Greenl and). The use of data from the Laurentian margins, when corrected for the opening of the North Atlantic, has resulted in a revision of previ ously published Palaeozoic palaeogeographic reconstructions and these new palaeogeographic reconstructions for Laurentia are in good agreeme nt with faunal and lithological data. A comparison of this new APW pat h with other APW paths from Avalonia and Baltica reveals a very close agreement between all three paths from mid-Silurian times onwards, ind icating that the closure of the lapetus ocean and the Tornquist sea wa s essentially complete by this time. Laurentia occupied equatorial lat itudes from Cambrian to early Silurian times and its drift history was dominated by anti-clockwise rotation (up to 0.7-degrees Ma-1) and low latitudinal drift rates (up to 3 cm yr-1). Late Silurian and early De vonian times were characterized by increased rates of anti-clockwise r otation (up to 1.3-degrees Ma-1) and southerly directed latitudinal dr ift (rates up to 13 cm yr-1) of the continent, which place Laurentia i n moderate southerly latitudes (30-40-degrees-S) by the early Devonian . These palaeolatitudes are comparable with those from Avalonia and Ba ltica for this time indicating that the amalgamation of Eurmerica had already taken place. By late Devonian time Laurentia had begun to drif t north (rates up to 5 cm yr-1) towards equatorial latitudes by mid-Ca rboniferous time.