A geotectonic history of the northern Mozambique Basin including the Beira High - A contribution for the understanding of its development

详细信息    查看全文

• 作者：Estev?o Stefane Mahanjane
• 关键词：BeiraHigh ; Break-up stages ; Onset of oceanic crust ; Lava flows ; Offshore Zambezi Depression ; Post-rift magmatism ; Rifting ; Seismic interpretation
• 刊名：Marine and Petroleum Geology
• 出版年：2012
• 出版时间：September, 2012
• 年：2012
• 卷：36
• 期：1
• 页码：1-12
• 全文大小：3967 K

文摘

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.