Opening of the S Atlantic
A 'traditional' interpretation of how the development of the Parana (or Tristan) plume, combined with that of the smaller St. Helena plume, gave rise to the splitting of S America from Africa and the opening of the S Atlantic (Wilson, 1992) is shown in Figure 6.22. We have already argued that a plume-head, with a diameter of about 2000 km and a maximum elevation of about 2 km cannot generate the magnitude of lateral stress required to split open a super-continent. A much more powerful mechanism is required.
Figure 6.22 Traditional reconstruction of Africa and S America during the initial stages of opening of the S Atlantic, supposedly generated by plumes (after Wilson, 1992).
In detail, the break-away of S America from Africa was almost certainly a complex process which is not yet fully understood. It has never been our intention to attempt to explain the many historic events involved in plate motions. We are primarily concerned in this text with the various driving mechanisms involved. Consequently, here we shall initially restrict our comments to the opening of the southernmost portion of the S Atlantic, to the south of the Parana-Entendeka flood basalts which, as indicated in Figure 6.22, was situated some 800-900 km north of the current estuary of the Rio Plata.
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