Gondwana: Its shape,size and position from Cambrian toTriassic times

Gondwana and the associated peri-Gondwana fragments cover an area which isabout two-thirds of the area of all continents above the 2000 m bathymetric contour. The Gondwana continents formed by break-up during a geologically short period (Jurassic to Tertiary times), coinciding with the eruption of flood basalts. The uplift caused by associated plumes probably provided the extra stresses necessary for continental separation. It is unclear whether plumes alone were able to fragment Gondwana. By contrast, the smaller, more numerous, peri-Gondwana fragments are generally elongate and their period of formation spans the whole of the Phanerozoic. Their shapes are tentatively attributed to trench suction and associated effects caused by south dipping slabs acting mostly on the northern margin of Gondwana; their migration to retreat of the hinge lines of the subduction zones generally northwards. Gondwana's position during the Cambrian to Triassic interval is uncertain. The most recent apparent polar wander paths (APWPs), based on high quality palaeomagnetic data, are incompatible with the distributions of corals, tillites and the Clarkeia shelly fauna of Silurian age. Somewhat surprisingly, a new APWP based on all available pal˦omagnetic poles is in much better agreement with the fossil and sediment distributions even though many poles have not been magnetically tested. A solution to the ‘Pang˦a problem’ is proposed, in which it is suggested that many of the Gondwana poles for the period 340-200 Ma have been remagnetised. However, all the APWPs give improbable polar positions for some Early Cambrian Moroccan archaeocyathids. Rates of change of pole position for the new modified APWP (‘apparent drift rates’) are similar to post-Triassic rates, implying that plate driving forces have not changed much during the Phanerozoic.