News: Earthworks in progress
The meeting dedicated to the East Afric Margin, held at the Geological Society in London in April 2016, has led to a dedicated volume of the journal Petroleum Geoscience. The contribution by Colin Reeves is entitled The development of the East African margin during Jurassic and Lower Cretaceous times: a perspective from global tectonics. This paper was released recently online under the doi http://doi.org/10.1144/petgeo2017-021.
The paper includes all the Euler rotation parameters for the reconstruction model, including revisions made up to October 2017, model CR17AAHH. This model is illustrated by the animation accessible on the Gondwana page of this website.
The abstract of the paper appears below where it is followed by a single frame from the animation at 90 Ma (Turonian).
2017 December 15
The eastern margin of Africa resulted from the first successful trans-Gondwana rupture which retraced, in part, the earlier unsuccessful Karoo rift system. Widespread volcanism in southern Africa (182 Ma, Toarcian) presaged northwest-southeast-directed extension between East Gondwana and West Gondwana (Africa). Rifting turned progressively north-south in orientation leading quickly to ocean growth off Somalia and off central Mozambique while, elsewhere, strike-slip within the stretched margin came to predominate. East Gondwana, including Madagascar, was demonstrably still intact at 151.4 Ma (M22, Kimmeridgian) but, as the two large continental fragments disengaged from each other, pure north-south movement became possible. After about 140 Ma (Berriasian), East Gondwana itself started to fragment off Western Australia but little separation occurred as far west as Madagascar before Aptian times (126.1 Ma). Nevertheless, the geometry of the Australia-India opening required that, in the interval 140-120 Ma, Madagascar-India pursued a path against Africa different from that of Antarctica. The arcuate Davie fracture zone, 1800 km in length, functioned as a pure strike-slip transform off the Tanzania-Mozambique coast for this fragment until the early Aptian demise of the Somali mid-ocean ridge. The active transform east of the Lebombo in southern Africa, meanwhile, relocated progressively eastwards, finally to outboard of the Mozambique Ridge at 136 Ma (Valanginian), leaving most if not all of the stretched continental crust and its volcano-sedimentary load attached to Precambrian Africa.