Supercontinent formation processes recorded in the Appalachian-Caledonide Orogen

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Supercontinents have existed at several times in Earth history; the best known is Pangea, which contained most of the Earth's continental crust from about 350 to about 200 million years ago. Pangea was built from several separate continents, themselves derived from earlier supercontinent breakup. The proposed program of research will investigate the convergence and amalgamation of these continents, which came together in a series of collisions, building the Appalachian mountain range of North America and the Caledonides of NW Europe. ***The earliest events leading to the formation of Pangea were the initiation of plate convergence by subduction in the Paleozoic Iapetus and Rheic oceans. Subduction initiation is the most poorly understood part of the "Wilson Cycle" of ocean evolution. With collaborators in Canada and Britain, we have proposed a new model for subduction initiation involving a "Caribbean style" plate boundary that entered the Iapetus/Rheic oceans in the Cambrian Period. This model helps to explain apparently simultaneous deformation on both margins of the Iapetus, and suggests that tectonism on those margins was analogous to the modern margins of the Caribbean. ***To test these predictions we will date zircon grains in sandstones to seek the first arrivals, in smaller terranes (e.g. Avalonia and Ganderia), of sediment from major continents. We will use our detrital zircon database to test and develop objective statistical measures for comparisons between populations. We will carry out field mapping and laboratory investigations of rock structures, and analyze paleomagnetic information, to determine the nature of collisions in the Appalachians, whether oblique or orthogonal, as Pangea was assembled.***During the latest stages of this amalgamation, the Maritimes Sedimentary Basin developed in Atlantic Canada, allowing deposition of >12 km of Carboniferous strata including natural resources: coal, oil, natural gas, gypsum, salt and potash. The crustal thinning and subsidence that accommodated this sediment pile probably resulted from oblique fault movements. However, our recent results have shown that the flow of salt within the sediment pile strongly modified the subsidence history. The Maritimes Basin thus provides a natural laboratory for investigating the poorly understood behaviour of salt in strike-slip and oblique-slip settings. We will determine the role and amount of movement along the major faults that dissect the basin, and determine how they influenced the behaviour of salt and the deposition of sediments.***This research will lead to improved understanding of: the process of subduction initiation; the role of strike-slip and oblique movements in supercontinent formation; the interaction between strike-slip faulting and salt movement; and the distribution of natural resources in Paleozoic rocks of eastern Canada.**