Neotectonics of Africa and the Indian Ocean: Development of the geoidal low

Abstract

The western, trans-Africa lobe of the Indian Ocean geoidal low correlates with Neogene tectonic features, such as the east Africa rift system and the Congo river basin. The opposite, eastern flank of the Indocean geoidal low is indented westward by the geoidal high associated with Sundaland (Indonesia), believed to have been displaced westward into its present location since mid-Tertiary times. The Indocean low thus seems to be slowly mobile, and to have acquired its present shape, elbowed at the Equator pointing west, as a result of tectonic processes continuing at present. We have sought lithosphere motion accounting for the large-scale tectonics and for the changes in the geoidal low. The constraints suggest that Africa and the western part of the Indian Ocean basin have been experiencing slow westward drift in Neogene times. This has resulted in the development of the mass-deficiency to the east, expressed as the Indian Ocean geoidal low, in the Africa meridional rifting, and in seafloor spreading as material upwells from the asthenosphere in response to the developing hydrostatic deficiency. The motion is consistent with the seafloor magnetic record, and would explain the dextral displacement at the south boundary of the Eurasian lithosphere segment.