4. Global Thoughts, 2019
The most recent and complete account in the literature, summarizing the work that has been undertaken over many years, is contained in Reeves (2018). This paper was developed from a presentation to the Geological Society's meeting on the East Africa margin held in London in April 2016. The rotation parameters given in the paper were updated to November 2017 (Model CR17AAHH).
The model is undergoing continuous refinement. The most important source of new data since late 2017 is the publication of Mueller & Jokat (2019) which presents new results from surveying the marine magnetic anomalies in the Africa-Antarctica Corridor. This gives new and high precision to the early motion of Antarctica away from Africa in the interval from 183 Ma (when Gondwana break-up staretd) until 126.1 Ma (when the Cretaceous Magnetgic quiet zone started).
The Reeves (2018) model has been revised in several ways as a result of this new data. First, the timing of the change from NW-SE to N-S in spreading direction has been adjusted from 167 to 157.5 Ma (Oxfordian). The subsequent spreading direction is long-lived, apart from a 6 myr interruption estimated to have taken place between 137 and 131 Ma (largely in the Valanginian). This event, previously called the 'Aptian sidestep' (now a misleading name) is thought to conicde with the outbreak of the Kerguelen and Tristan plumes and the onset of ocean growth between both South America and Africa and (Greater) India and Antarctica-Australia.
Davis et al. (2016) review marine magnetic anomaly data for the area between Madagascar and Africa. While they honour the sparse magnetic anomaly data, they appear to ignore the confinement of SW Madagascar to the trace of the Davie Fracture Zone. We also take note of the work of Phethean et al. (2016) on re-examining this same area of ocean and the recently-released news of the occurrence of Precambrian rocks in the Comoros Isalnds (Bahari Resources, 2017).
Our interpretation now includes an initial, small (100 km) disruption of the position of Madagascar against India as part of the 157.5 Ma direction-change. Their post-157.5 Ma relative position can then be held fixed until beyond the start of the Cretaceous Quiet Zone. East Gondwana thus remains intact until at least the end of the Jurassic. This admits a model of the departure of India-Madagascar from Antarctica-Australia that conforms with magnetic anomaly evidence at all three localities: (1) the Africa-Antarctica Corridor, (2) Madagascar-Africa and (3) off Western Australia. This seems more economical of hypothesis than earlier published models (including our own) that invoked large movements between Madagascar and India at earlier stages. A consequence of this model is the onset of new ocean growth all the way from West Africa to Western Australia during the Valangianian (137-131 Ma in our model).
Most recently, we have been considering what might have happened south of Africa and the initial position of the Maurice Ewing Bank and the Malvinas/Falkland Plateau against southern Africa. This work is at an early phase of development and we particularly invite feedback on this. Pre-publication ideas on all these lines of investigation may be found in the series of Research Updates accessible through the links at the foot of this page. Please get in touch with feedback: email@example.com
2019 May 3
Davis, J.K., Lawver, L.A., Norton I.O. and Gahagan, L., 2016. New Somali basin magnetic anomalies and a plate model for the early Indian Ocean. Gondwana Research 34, p ?-?
Mueller, C.O., and Jokat, W., 2019. The initial Gondwana break-up: A synthesis based on new potential field data of the Africa-Antarctica Corridor. Tectononphysics 750 (2019) 301-328.
Phethean, J.J.J., Kalnins, I.M., van Hunen, J., Davies, R.J., and McCaffrey, K.J.W., 2016. Madagascar's escape escape from Africa: a high resolution plate reconstruction for the western Somali basin and implications for supercontinent dispersal. Geochem, Geophys, Geosystems, 17, 2825-2834,
Reeves, C.V., 2018. The development of the East Africa margin during Jurassic and Lower Cretaceous times: a perspective from global tectonics. Petroleum Geoscience, 24, pp 41-56.
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