Rodinia paleogeography: Laurentia as the geological 'Key' - Ian Dalziel

Rodinia paleogeography: Laurentia as the geological 'Key' Ian Dalziel The University of Texas at Austin Laurentia, core of the North American continent, is surrounded by late Precambrian-early Palaeozoic rifted margins. This led to early suggestions that it was located within a Neoproterozoic supercontinent, Rodinia. Recent models of Precambrian palaeogeographic development also point to a 'Laurentia-centric' supercontinent. Before plate tectonics, the geometry of continental margins, comparison of cratonic interiors and sedimentary covers, and orogenic piercing points were employed to postulate the geography of Phanerozoic Pangaea. Marine studies have demonstrated the results were remarkably accurate. Absent in situ Precambrian oceanic crust, the same lines of evidence are employed to reconstruct Rodinia. A strong case can be made for former juxtaposition of the Pacific margins of Laurentia and East Antarctica-Australia approximately as proposed in the 1990s. The Atlantic margin is likely to have rifted from Baltica, Amazonia and other South American cratons along the Grenvillian orogenic suture in the early Palaeozoic, but the suture itself makes accurate reconstruction difficult. Piercing points can be used to position the Kalahari craton and Coats Land crustal block of Antarctica off the present southern margin of Laurentia and contemporaneous large igneous provinces point to Siberia being located off the Arctic margin. Hence Laurentia does appear to be the 'Key' to Rodinian palaeogeography.