Abstract Laurentia, core of the North American continent, is surrounded by Neoproterozoic to Cambrian rifted margins. This led to early suggestions that it was located within a Neoproterozoic supercontinent, Rodinia. Recent models of Precambrian palaeogeographical development also point to a ‘Laurentia-centric’ Rodinian 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 subsequently demonstrated that the results were remarkably accurate. Absent in situ Precambrian oceanic crust, the same lines of evidence are employed here to reconstruct Rodinia, together with others unavailable at that time. A strong case can be made for the former juxtaposition of the Pacific margins of Laurentia and East Antarctica–Australia approximately as proposed in the 1990s, even though the precise match remains elusive. The Atlantic margin is likely to have rifted from Baltica, Amazonia and other South American cratons along the Grenvillian orogenic suture in the early Paleozoic, although the suture itself makes accurate reconstruction difficult. A piercing point and ‘tectonic tracer’ 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 even though the exact geometric fit to its surrounding cratons remains to be refined.

Abstract In the first application of the developing plate tectonic theory to the pre-Pangaea world 50 years ago, attempting to explain the origin of the Paleozoic Appalachian–Caledonian orogen, J. Tuzo Wilson asked the question: ‘Did the Atlantic close and then reopen?’. This question formed the basis of the concept of the Wilson cycle: ocean basins opening and closing to form a collisional mountain chain. The accordion-like motion of the continents bordering the Atlantic envisioned by Wilson in the 1960s, with proto-Appalachian Laurentia separating from Europe and Africa during the early Paleozoic in almost exactly the same position that it subsequently returned during the late Paleozoic amalgamation of Pangaea, now seems an unlikely scenario. We integrate the Paleozoic history of the continents bordering the present day basin of the North Atlantic Ocean with that of the southern continents to develop a radically revised picture of the classic Wilson cycle The concept of ocean basins opening and closing is retained, but the process we envisage also involves thousands of kilometres of mainly dextral motion parallel with the margins of the opposing Laurentia and Gondwanaland continents, as well as complex and prolonged tectonic interaction across an often narrow ocean basin, rather than the single collision suggested by Wilson.

Abstract Benjamin Peach, John Horne and their co-workers recognized a century ago that the identical fauna and lithofacies of the lower Palaeozoic strata in the NW Highlands of Scotland and the North American craton could only be explained if they were: ‘part of one and the same geological and zoological province’. In this sense their work provided critical geological underpinning for the subsequent understanding of Mesozoic–Cenozoic seafloor spreading and continental drift. ‘Tectonic tracers’ such as the fragment of Laurentian craton in the NW Highlands of Scotland, provide the strongest evidence available for deciphering pre-Pangaea palaeogeography. The Laurentian craton appears to have left several such tectonic ‘calling cards’ in today's southern continents. Intriguingly, it is the presence in the Andean Precordillera of northwestern Argentina of an early Palaeozoic fauna identical to that of the NW Highlands that provides perhaps the most unequivocal geological clue to pre-Pangaea palaeogeography. Recent work in East Antarctic and Laurentian cratons has provided a positive test of the hypothesis that they were once juxtaposed prior to the Neoproterozoic opening of the Pacific Ocean basin. Geochronology and isotope geochemistry, supported by palaeomagnetic studies indicate that the Coats Land crustal block of East Antarctica at the head of the Weddell Sea is also a fragment of the Laurentian craton. These three ‘tectonic tracers’ permit tracking of the Laurentian craton in relation to the present southern continents from the Neoproterozoic break-up of the Rodinian supercontinent to the late Palaeozoic assembly of Pangaea.

Metamorphic and sedimentary rocks of the South Orkney and South Shetland island groups and the northern tip of the Antarctic Peninsula appear to represent the products of subduction-related accretion and of sedimentation respectively in a forearc environment along the Pacific margin of Antarctica. Some of the rocks are imprecisely dated, but stratigraphic, paleontologic, and radiometric data indicate that the higher temperature part of the subduction complex was formed and all sedimentary strata deposited prior to the initiation of Gondwanaland break up. The remainder of the subduction complex, comprising comparatively high P/T assemblages, may be of late Mesozoic or even Cenozoic age. Lithology indicates that the metamorphic rocks represent pelagic and volcanic material from the ocean floor tectonically interleaved with slices of oceanic lithosphere. The presence of penetrative polyphase tectonite fabrics and the metamorphic assemblages suggest that the deformation and metamorphism occurred under considerable cover. Thus the complex may be, in part, the product of underplating (“subcretion”) to a forearc accretionary wedge. The sedimentary strata consist of graywacke and shale of turbidite facies associated with rare mafic pillow lava containing prehnite and pumpellyite. Bedding and primary structures are ubiquitously recognizable although the rocks are everywhere deformed by one major set of sub-isoclinal to tight asymmetric folds with associated axial planar slaty cleavage. The regional setting, structural style, and an observed transition structurally downward into the metamorphic rocks suggest that the strata were deposited partly in trench-slope basins, that is, within the zone of active deformation in the wedge. The general parallelism between the dominant structural elements of all the sedimentary rocks and the continental margin along the length of the South Shetland Islands and on the adjacent Antarctic Peninsula indicates that the margin may have been established as a site of subduction-related deformation and metamorphism prior to the initiation of Gondwanaland break up, and that accretionary tectonism continued there after break up. The attitude of structures in the metamorphic rocks of the South Orkney Islands suggests that the microcontinental platform on which they are located may have rotated clockwise relative to the Antarctic Peninsula during opening of the intervening oceanic Powell Basin.