A Reappraisal of the Tectonic Evolution and Structure of the East African Margin, With Specific Reference to the Mozambique Coastal Plains

Abstract

We have carried out a reappraisal of the structural and tectonic evolution of the Mozambique Basin in the wider context of the East African Margin. Detailed interpretation of gravity and magnetic data alongside SRTM, bathymetry and Landsat data enables us to apply the most recent research in passive and transform margin formation to the East African margin. Based on these concepts, we interpret features such as exhumation of the sub-continental lithospheric mantle within broad zones of complex transitional crust, which have generally been previously unrecognised in this region. Southern Mozambique comprises the Mozambique Coastal Plains (MCP), a flat lying area bordered to the west by the Lebombo Monocline and to the north by the Matake-Sabi/Mwenetzi Monocline. The area to the east and south of these major crustal structures has been variably interpreted as continental or oceanic crust within the literature. Interpreting the MCP as continental crust causes problems in rigid plate models; overlap between two regions of known cratonic crust (Kaapvaal and Grunehogna Cratons) implies extension of cratonic crust that is unobserved. The interpretation of a fully continental basement also ignores the continuation of gravity and magnetic anomalies over the Mozambique Ridge, which we interpret as thickened oceanic crust, northwards beneath the Mozambique Coastal Plains. An entirely oceanic basement for the MCP would eradicate problematic overlaps between eastern and western Gondwana. However this is at odds with relatively thick crust (~30 km) shown underlying the area from our geophysical analyses and seismological investigations (Copley et al., 2012). Using potential field data, we define three spreading ridges in the Mozambique Ridge in agreement with Leinweber & Jokat (2012) and show the eastern part of the MCP to be underlain by thickened oceanic crust continuous with the Mozambique Ridge. This is in agreement with the drilled interception of Jurassic volcanics over the eastern part of the MCP, which were previously interpreted as Karoo-age. In the west, the interpretation of early Jurassic (pre-seafloor spreading) grabens (e.g., Salman & Abdulla, 1995) indicates the presence of continental crust; consequently, we interpret the western part of the MCP to be underlain by attenuated continental crust related to the end-Karoo (~182 Ma) formation of the Lebombo and Matake-Sabi Monoclines.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015