Despite over thirty years of plate tectonic theory, the reasons why supercontinents like Gondwana disintegrate into smaller continents and disperse remain enigmatic. Current ideas mostly involve changes in plate-boundary driving forces (passive mantle hypothesis) in preference to an active plume mechanism, even though mantle plumes were present at most stages of Gondwana breakup. The role of these plumes in the breakup process is uncertain, and ideas vary from the chance unroofing of a pre-existing plume, which only contributed in the production of extensive flood basalts, to plumes that controlled the position of breakup. The magmatic and tectonic record along the proto-Pacific margin of Gondwana indicates that there were important changes in subduction zone forces during the initial stages of Gondwana breakup. However, the absence of subduction along the Neotethyan margin at the time of breakup, together with the fact that the initial rift formed almost at right angles to the active subducting margin, suggest a potential active role for a mantle plume in the initial separation. An active mantle mechanism, involving a very large thermal disturbance or megaplume, may, in contrast to a passive mantle hypothesis, more readily explain the formation and rotation of microplates in the South Atlantic region. It accounts also for the production of unusually large igneous provinces (Chon Aike province in Patagonia, Karoo province in southern Africa, and Ferrar province in Antarctica) just prior to breakup.
Authors: Storey, B.C., Kyle, P.R.
1 January, 1997
South African Journal of Geology / 100