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Mahanjane E.S.,Institute National Petroleum INP
Marine and Petroleum Geology | Year: 2014

The interpretation of 2-D seismic reflection data provides a modern structural framework including hydrocarbon potential in the present-day stratigraphic and structural traps of both the Davie Fracture Zone and the adjacent Nacala and Angoche basins. Possible stratigraphic traps were identified in submarine fan and channel depositional environments during Cretaceous to Tertiary times. Structural traps are mostly defined within compressional structures formed by a variety of fault-related folds and rift grabens within the Jurassic and Cretaceous successions.The Nacala and Angoche basins form two depressions separated by the Davie compressional zone. This compressional structure is a prominent interior high running approximately north-south. An event of transpression and contraction characterizes the main tectonic setting commonly hosting several detached compressional structures along the western edge of the transform zone.Both basins are associated with the Late Jurassic/Early Cretaceous rifting during the opening of the Mozambique Channel. The Angoche basin is proposed here to have formed by the earliest stage of break-up in mid-Jurassic time. The basin is bounded landward by the Angoche volcanic zone, a dyke swarm branch oriented N64degE forming part of the Karoo and Dronning Maud Land magmatism at c. 180 Ma.Subsequent rifting and break-up led to the drift of East Gondwana southwards along the dextral strike-slip Davie Fracture Zone. At about 150 Ma (Tithonian), East Gondwana appears to have rotated slightly clockwise about a pivot in the proximity of the Angoche basin leading to extension and rifting in the Rovuma basin to the north of the pivot point and compression west of the Davie Fracture Zone to the south. Consequently, the eastern boundary of the Angoche basin was compressed developing a typical growth wedge of massive thrust imbrication structures while extensional tectonics created several depressions and rift-grabens forming the Nacala and Quirimbas basins.Basin stratigraphy is interpreted along seismic reflection lines and correlated to the regional stratigraphic information and wells from the Zambezi Delta and Rovuma basins. © 2014 Elsevier Ltd.

Mahanjane E.S.,Institute National Petroleum INP
Marine and Petroleum Geology | Year: 2012

The interpretation of a comprehensive two dimensional (2D) seismic reflection data set discloses several rifting events for a typical passive rifted margin. Two major phases have been identified: Rift I phase is in agreement with the initial rifting of Gondwana postulated for the early Jurassic. This rift resulted in break-up stage 1 governed by a north-eastern motion of Antarctica along the reactivated Pebane shear zone. Indications for lava flows were identified in the seismic profiles along the Offshore Zambezi Depression. They form a link between early rifting, the initial break-up and early sea-floor spreading. The nature of these lava flows may be associated with the emplacement of thick volcanic dykes during post-rift magmatism that occurred when the Antarctica Plate (with the Beira High) drifted dextrally from the west to east until the Mid-Jurassic times. It is more likely that the break-up in stage 1 resulted from high tension due to strain relief of Rift I phase. Above all, the extensional deformation occurred in a narrow-rift mode. Therefore, the V-shape of the Offshore Zambezi Depression suggests a possible rift-failure structure. This is best explained by the Reeves and de Wit model (2000). This model postulates that the motion of Antarctica changed to southward direction at around 170 Ma. Consequently a "rift jump" from the Offshore Zambezi Depression in the northwest to the south-eastern edge of the Beira High occurred, and Rift II phase may have started leading to the break-up in stage 2. During this stage (Rift II phase) the extension migrated towards the east, thus thinning the crust, and exhuming the sub-continental mantle in the continental-ocean transition zone. The Rift II phase shows a sequence of half-graben morphologies confining the syn-rift infill that is subdivided in three units: syn-rift I, syn rift-II and rift sag. All three units appear to have developed under minor extensional regimes in the crust evidenced by gently dipping, low-angle detachment faults. With respect to the presence of the two rift phases, it is deduced that break-up and sea-floor spreading are diachronous within Rift I and Rift II segments. © 2012 Elsevier Ltd.

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