East African Continental Margin: Mapping Ocean-Continent Transition Structure, Location and Kinematics

Kusznir, Nick¹; Horn, Brian W.²; Granath, James W.²; Alvey, Andy³
¹Geology and Geophysics, University of Liverpool, Liverpool, United Kingdom.
²ION Geophysical / GX Technologies, Houston, TX.
³Badley Geoscience, Hundleby, United Kingdom.

We use a combination of ION-GXT deep long-offset seismic reflection data and 3D gravity inversion to map crustal thickness, ocean-continent transition structure and continent-ocean boundary location for the East African continental margin from Mozambique to northern Somalia. Crustal thickness mapping suggests that the East African continental margin comprises both transform and rift segments consistent with north-south opening and sea-floor spreading within the Somali Basin in the Jurassic and Early Cretaceous. Combined marine and land geophysical mapping suggests that for some rifted margin segments a broad region (~ 250 km wide) of highly thinned continental crust (e.g. beta = 2 - 3) separates the continental margin hinge (necking zone) from the continent-ocean boundary. In contrast on the transform margin segments, there is a narrow ocean-continent transition from thick continental crust to ocean crust. In places (northern Kenya, Somalia) large sediment accumulations onto highly thinned continental crust result in the continent-ocean boundary being located almost at the coast. The location of the East African continental margin hinge and ocean-continent transition structure is probably influenced by Karoo and possibly even earlier rifting. Restoration of crustal thickness maps using plate reconstructions rotation poles have been used to show and test the development of continental breakup and ocean basin connectivity (and deep water isolation) during the Jurassic and Early Cretaceous. We suggest, on the basis of crustal thickness mapping and plate reconstructions, that the alternating transform-rift segmentation of the East African continental margin extended from Mozambique north-eastwards to include the Oman margin prior to the Neogene formation of the Gulf of Aden.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012