MICROPLATE MODELING OF THE AFAR DEPRESSION USING 4D LITHOSPHERIC MODEL (4DLM) AND SPLATES : IMPLICATIONS FOR DEVELOPMENT OF PLATE BOUNDARIES

Global plate models of the Afar Depression adopt a classic rift-rift-rift triple junction where the Arabian, Somali and Nubian (African) plates are separated by the Red Sea, the Gulf of Aden and the Main Ethiopian Rift. However, at the regional scale the kinematics are more complex due to stepping of the Red Sea (the SE-propagating Red Sea propagator) and the Gulf of Aden (the NW-propagating Gulf of Aden propagator) onto Afar as well as the presence of three “micro-plates” within Afar – the Danakil, Ali Sabieh and East Central Block. In addition, the East Central Block, which is enclosed between the Red Sea and the Gulf propagators, is fragmenting into six horst entities separated by NW-trending grabens. Mostly, the source of deformation within the East Central Block is its clockwise rotation (14 degrees in the last ~2 Ma) due to differential spreading across the Red Sea and the Gulf of Aden propagators. The exact location of the plate boundary between the Arabian and African plates within Afar is not well defined; however it is thought to be within the East Central Block. This boundary contains NW-trending extensional structures forming right-stepping grabens and transfer zones. The Dobe graben within the East Central Block has beta values much higher (~1.66) than those reported from the Red Sea propagator (~1.1) suggesting that extension has transferred from the overlapping propagators to the overlap zone. Poles and angles of rotation from published literature were modified and used to model the separation of Arabian, Somali, and Nubian plates in the 4D Lithospheric Model (4DLM) and SPlates software applications. The relative motions of the Danakil, Ali Sabieh and East Central Blocks, and the horst blocks are constructed, and rotation values based on literature and remote sensing analysis are adopted for the current model. Flow lines from 4DLM are used to establish the spatial and temporal relationship between conjugate plates, micro-plates and horst blocks. The associated age and rate of extension suggest a rather distinct “deformation pathway” through the Data Yager Hanle-Dobe Graben basins that is characterized by oldest onset of rifting as well as the highest rate of extension. It is proposed here that this pathway defines the potential geographic location of the plate boundary between Arabia and Africa within Afar.