Precambrian dyke swarms and their geodynamic significance

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A consensus is emerging among geoscientists that the repeated formation of supercontinents and their subsequent dispersal may be a fundamental pattern in the behavior of the Earth's surface for the last 3000 million years. Dynamic modeling of mantle convection suggests that two antipodal super-plumes, which alternately grow and decline may be responsible for continental aggregation and dispersal. In order to place limits on the location of continents at any one time, both high precision U-Pb age dating together with paleomagnetism is required. My research contribution concerns the latter and I describe five projects, both ongoing and new. All of them involve mafic dykes, fissures along which basaltic magma once rose through Earth's crust before solidifying. Dykes are found in enormous swarms and represent times of continental break-up. They are excellent preservers of the geomagnetic field direction at the time of their original cooling and therefore are important geological units to constrain when and how continents have dispersed. Because of their orientation and size,they also provide key units for inter-continental correlation that help restore continental configurations prior to dispersal. All the dyke swarms being studied are Precambrian in age so that their paleomagnetic data are relevant to supercontinents that existed before Pangea. If antipodal plumes re-occur in the same broad location, they would act as sort of geological tennis players in which the continents represent many balls that are being hit back and forth, with complexities in their trajectories being experienced by close encounters with each other! At least two examples are known of plume centres differing in age by 100's of millions of years, that have reappeared in the same location and which give similar paleomagnetic pole positions. A third example is presently being tested and may strengthen the case for continents re-occupying superplume sites in a "concertina"-like fashion.