The East African Rift (EAR) is a type locale for investigating the processes that drive continental rifting and breakup. The current kinematics of this ∼5000 km long divergent plate boundary between the Nubia and Somalia plates is starting to be unraveled thanks to a recent augmentation of space geodetic data in Africa. Here we use a new data set combining episodic GPS measurements with continuous measurements on the Nubian, Somalian, and Antarctic plates, together with earthquake slip vector directions and geologic indicators along the Southwest Indian Ridge to update the present-day kinematics of the EAR. We use geological and seismological data to determine the main rift faults and solve for rigid block rotations while accounting for elastic strain accumulation on locked active faults. We find that the data are best fit with a model that includes three microplates embedded within the EAR, between Nubia and Somalia (Victoria, Rovuma, and Lwandle), consistent with previous findings but with slower extension rates. We find that earthquake slip vectors provide information that is consistent with the GPS velocities and helps to significantly reduce uncertainties of plate angular velocity estimates. We also find that 3.16 Myr MORVEL average spreading rates along the Southwest Indian Ridge are systematically faster than prediction from GPS data alone. This likely indicates that outward displacement along the SWIR is larger than the default value used in the MORVEL plate motion model.

[1] The kinematics of the East African Rift (EAR) is the least well-known of all major plate boundaries. Here, we show that present-day data (a GPS+DORIS geodetic solution and earthquake slip vectors) are consistent with 3.2 Myr-average spreading rates and transform-fault azimuths along the Southwest Indian Ridge and support a kinematic model that includes three subplates (Victoria, Rovuma, and Lwandle) between Nubia and Somalia. Continental rifting in the EAR appears to involve localized strain along narrow rift structures that isolate large lithospheric blocks.

A revised sequence of reconstructions for East Antarctica relative to Africa is generated from published seafloor spreading and fracture zone anomalies. These date from the Cretaceous/Tertiary boundary to the Late Jurassic and lead to a revised predrift reconstruction for east and west Gondwanaland: Euler pole 1.67°S, 35.99°E, rotation angle 53.43°. This reconstruction derived wholly from marine data places East Antarctica adjacent to the Lebombo Mountains and south of and subparallel to the Sabi acid volcanic suite, supporting the postulate that these rocks represent Mesozoic plate boundaries. This refit implies that part of the coastal plain of Mozambique is underlain by oceanic or very highly extended continental crust. The reconstruction is supported by the alignment of (1) the Cape Fold Belt with its Antarctic equivalents and (2) the western limit of Pan‐African reactivation of the Mozambique Mobile Belt with the western limit of the Sverdrupfjella metamorphic suite. Antarctica initially moved along a transform fault lying immediately east of and subparallel to the Lebombo Mountains, the eastern face of the Tugela Cone, the southeastern face of the Falkland Plateau in its reconstructed position, and the eastern flank of the Agulhas Plateau in its reconstructed position. At M10 time a triple junction formed near the tip of the Falkland Plateau implying that the oldest lineated magnetic anomalies in the eastern Weddell Sea associated with this triple junction cannot predate M10. At M2 time the Mozambique Ridge rifted from the Astrid Ridge in a ridge jump episode. Such an event may also explain the presence of magnetic anomalies in the southern Mozambique Basin. Gunnerus Ridge, Conrad Rise, and Del Cano Rise are all tectonically associated with the Madagascar Ridge.

Geological Society, London, Special Publications, v. 259, p. 9-22, in Part 1: Plate kinematic and geodynamic framework of the Afar volcanic province, 2006. http://dx.doi.org/10.1144/GSL.SP.2006.259.01.03International audienc

No abstract