News: Earthworks in progress
It is now 50 years since Alan Smith and Tony Hallam published in Nature their classic paper on Gondwana reconstruction (Smith & Hallam, 1970). They applied the contour-fitting algorithm used in Bullard, Everett and Smith (1965) to fit the 500 fathom (914 m) bathymetric contours for South America, Africa, Madagascar, India and Australia to each other and to the 1000 m isobath for Antarctica. The result has withstood well the test of time. The figure at the bottom of this piece presents the fit resulting from current research (available on this website) alongside the original Smith & Hallam (1970) fit.
The main difference in the result is that the convex section of the Mozambique coast of Afcrica is now fitted into the concave section of the Antarctic coast occupied by Sri Lanka in the 1970 fit. A slightly more northwesterly position for Madagascar against Africa then allows the remainder of the assembly of India, Australia and Antarctica to fit snugly against Africa and Madagascar. The modern fit uses offshore satellite gravity anomalies ('gravity margins') with persuasively conjugate detail in place of bathymetric contours. The Smith & Hallam (1970) position for Sri Lanka - which they explain as arbitrary - survived into the 1988 geological map of Gondwana (de Wit et al., 1988) and is still reproduced from time to time.
The arcuate Antarctic Peninsula and the somewhat similar southernmost section of South America have long posed a problem for a satisfactory reassembly. In the second part of the figure we show our recent solution (highlighted in yellow) which brings Patagonia back along the Agulhas fault with the 'sole' of the Malvinas Plateau originally in contact with the Coats Land coast of Antarctica. This 1500 km-long line of contact behaved, we believe, as a dextral strike-slip feature in the earliest disruption of East and West Gondwana, conforming to the Euler pole for the first movements of the first two pieces Gondwana broke into in Jurassic times. This model is demonstrated in the animation on the 'Gondwana' page. Small fragments such as the Maurice Ewing Bank, South Georgia and the South Orkney Islands may all have their origins in this shear zone which developed eventually into a broad rift before the onset of ocean growth in the Weddell Sea.
2020 April 15
Bullard, E.C., Everett, J.E. & Smith, A.G., 1965. Phil Trans Roy Soc, A, 258, 41.
Smith, A.G. & Hallam, A.,1970. Nature, 225, 139.
de Wit et al, 1988. Geological map of sectors of Gondwana, AAPG.