East Gondwana break-up in the Early Cretaceous
Break-up of the plates of East Gondwana
A predecessor of the above animation was revealed initially in August 2022. Subsequent refinements of our Gondwana dispersal model in the South Atlantic Ocean and the Africa-Antarctica Corridor have led to time spent in 2024 re-visiting the plate system of East Gondwana in Jurassic and Cretaceous times. The mechanisms proposed initially have been shown to be robust and the geometry has been refined so that numerical details of credible rotation poles conform precisely with the conceptual model. This is shown in the animation above where the latest model is applied to the plate outlines interpreted in 2022.
In our Gondwana reassembly, India and Madagascar are surrounded closely on three sides by Africa, Antarctica and Australia. How can India and Madagascar escape from such a situation without offending basic rules of plate tectonics, such as overlap of fragments, while following the evidence of oceanic fracture zones and magnetic anomalies as well as the relevant geological observations? The process that satisfies these constraints may be described in the following stages:
- East Gondwana (EGO) and West Gondwana (WGO) separate NW-SE from 184.2 to 154.94 Ma (Toarcian to Oxfordian), EGO and WGO both remaining intact.
- At about 154.94 Ma (Kimmeridgean) the separation direction becomes N-S as the long-offset Davie Fracture Zone (DFZ) is initiated.
- At about 142.3 Ma (Berriasian) the DFZ morphs into the arcuate form evident today in satellite altimetry of the oceans.
- Madagascar and India follow this arc consistently until Madagascar comes to rest at about 117.3 Ma (Aptian).
- From about 142.3 Ma (Berriasian) India+Madagascar start rotating away from Antarctica+Australia, following the arc of the Wallaby-Zenith FZ off Australia.
- From about 130.68 Ma (Hauterivian) Antarctica's path against Africa starts to deviate westwards, sliding past the Mozambique Ridge.
- Separation between Antarctica and India+Madagascar becomes virtually identical to that between Antarctica and Africa as Madagascar and India come to rest as fixed parts of the Africa plate about 117.3 Ma. The Wallaby-Zenith FZ follows the same roation poles as the Africa-Antarctica Corridor for another 20 Myr.
The geometrical options for achieving this elegant solution are very limited but two consistent rotation poles, Madagascar vs Africa and India vs Antarctica, when chosen correctly, have proved capable of maintaing a constant plate-circuit closure between India and Madagascar. Interpretation of the matching oceanic fracture zones off Sri Lanka and Antarctica demonstrates that there was still very little separation between India and Madagascar at the time of India's rapid departure NE at about 89 Ma (Cenomanian).
The idea that India was well south of Madagascar by 89 Ma (e.g. Reeves and de Wit, 2000) is now rejected in favour of the Vishnu FZ joining not India and Madagascar but India and the Madagascar Rise. The latter micro-fragment left Madagascar as part of the complexity of joining the mid-ocean ridge in the AAC with the westward-propagating ridges between India, Sri Lanka and Antarctica.
Secondary intra-plate movements complicate the picture as Africa, south of the Mwembishi shear zone, moves SW as the Antarctic plate becomes compressional against the Mozambique Rise about 130 Ma (Hauterviain). Gravity and aeromagnetic interpretation (this author) suggests that the Mwembishi shear zone may be distributed across a zone as wide as 400-500 km below the Selous basin and into northernmost Mozambique. This conforms with geological field observations in Zambia (source lost). The present model reduces coast-to-coast movement distributed across this series of parallel faults considerably.
A Research Update incorporating the numerical values for model CR24BAAL is in preparation.
Last update: 2024 May 29