Plate Kinematic model and horizontal stress history of East Africa

graeme.eagles [ at ]


The East African continental margin and the northwest Indian Ocean have been shaped by complicated boundary relocation, propagating ridges and the independent movement of the Seychelles microplate during the break up of Gondwana. As a result, previous attempts to reconcile the different tectonic components into a coherent model of the evolution of the area have so far been unsatisfactory. A new high resolution plate kinematic model has been produced in an attempt to solve these problems, using seafloor spreading data and rotation parameters generated by a mixture of visual fitting and iterative joint inversion (Nankivell, 1997; Livermore et al. 2005). The model identifies three distinct phases of rifting, from the Jurassic to the Paleogene, with associated plate motion vectors. Intracontinental ‘Karoo’ rifting episodes in the late Carboniferous to late Triassic failed to separate the land masses of Gondwana, but initiated sedimentary basins along the East African and West Madagascan margins. The first phase of rifting involved the separation of Madagascar/India/Antarctica from Africa, with the opening of the West Somali and Mozambique Basins. During the second phase, India rifted from Madagascar, accommodated by spreading on the Mascarene Ridge until its abandonment in the Paleocene. The third phase, which continues today, saw the separation of India from the Seychelles and Mascarene Plateau via the southward propagation of the Carlsberg Ridge to form the Central Indian Ridge. The rotation of the independent Seychelles microplate and the opening of the short-lived Laxmi Basin have been further constrained by the new model. The World Stress Map Project (Heidbach et al., 2008) shows that intraplate stress regimes are predominantly compressional, caused by plate boundary forces and therefore directly related to plate boundary geometries (Zoback et al., 1992). Therefore, after break up, the passive east African margin was subjected to compressional forces transmitted through the lithosphere by ridge-push. The differing activities of ridges in the northwest Indian Ocean caused changes in the orientation of the maximum (SH max) and minimum (Sh min) horizontal stresses during each phase of rifting. The most noticeable change was at the onset of rifting in the Mascarene Basin when SH max became ENE – WSW direction from a previous N – S direction, which produced inversion features in the west Madagascan sedimentary basins.

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Conference (Poster)
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European Geophysical Union, 12 Apr 2015 - 15 Apr 2015, Vienna.
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Tuck-Martin, A. , Adam, J. and Eagles, G. (2015): Plate Kinematic model and horizontal stress history of East Africa , European Geophysical Union, Vienna, 12 April 2015 - 15 April 2015 .

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