Abstract
Abstract The break-up of the Gondwana supercontinent resulted in the formation of the Central Mozambique passive margin as Africa and Antarctica were separated during the mid-Jurassic period. Although plate kinematics during the oceanic spreading phase are well constrained, the initial fit of Africa and Antarctica, their earliest relative movements and margin architectures remain active areas of interest. This study uses high quality multi-channel seismic reflection profiles to identify the major crustal domains in the Angoche and Beira regions of the Central Mozambique margin. Our results show that the Central Mozambique passive margin is characterised by intense but localised magmatic activity, evidenced by the existence of seaward dipping reflectors (SDRs) in the Angoche region, and magmatic sills and volcanoclastic material marking the Beira High. The Angoche and Beira regions possess faulted upper-continental crusts, with possible exhumation of lower crustal material forming an extended ocean-continent transition (OCT). The Beira High segment reveals an offshore continental fragment, which is overlain by a faulted pre-rift sedimentary unit likely to belong to the Karoo Group. The combination of our seismic interpretation with existing geophysical and geological data has allowed us to propose a break-up model which supports the idea that the Central Mozambique margin was affected by polyphase rifting. The Beira High basement is formed by a strike-slip deformation along a proposed lithospheric weakness - the Lurio-Pebane shear zone. Northwestern-southeastern oriented extension follows and results in continental break-up and oceanic spreading. Our results suggest a segmentation of the Central Mozambique margin with oceanisation first occurring in the Angoche segment. The formation of the first oceanic crust in the Beira segment followed, likely delayed by the formation and failure of the northern Beira High rift.
Highlights
The Central Mozambique passive margin was formed during an episode of rifting which resulted in the fragmentation of the Gondwana super-continent and the formation of the African and Antarctic continents (Fig. 1)
Our study presents the results of the interpretation of several, multi-channel seismic (MCS) reflection profiles which are described in detail in order to identify important crustal domains and establish a style of rifting which may help to fill gaps in the reconstructive history of the conjugate margins
This study has shown that the Central Mozambique margin is characterised by localised magmatism and possesses architectures which are consistent with depth-dependant pure shear extension as well as intracrustal shear zones and may represent something of a structurally hybrid margin
Summary
The Central Mozambique passive margin was formed during an episode of rifting which resulted in the fragmentation of the Gondwana super-continent and the formation of the African and Antarctic continents (Fig. 1). Leinweber and Jokat (2012) successfully identified chron M33n, indicating that the first oceanic crust formed in the Mozambique Basin at c. Outcropping geological features across the conjugate margins have been used to reconstruct the initial positions of Africa and Antarctica within Gondwana (Du Toit, 1937; Cox, 1992; Reeves, 2000; Thompson, 2017), and these models are complimented by dating of the onshore volcanic episodes and dyke complexes (Jourdan et al, 2006, 2007; Klausen, 2009), potentially related to the rifting event. The existing reconstructive models place Antarctica relative to Africa in various initial configurations (Fig. 1a) and despite the distinct views on initial continental fit, there appears to be a growing consensus that the northsouth separation of Antarctica and Africa was preceded by an initial rotation or translation of the Antarctic plate, relative to the African plate (Cox, 1992; König and Jokat, 2006; Leinweber and Jokat, 2012; Mahanjane, 2012), Madagascar belonging to the Antarctica block at this time (e.g. Gaina et al, 2013; Reeves et al, 2016; Leinweber and Marine and Petroleum Geology 100 (2019) 412–433
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