Tie points for Gondwana reconstructions from a structural interpretation of the Mozambique Basin, East Africa and the Riiser-Larsen Sea, Antarctica

Abstract

Abstract. Movements within early East Gondwana dispersal are poorly constrained, and there is debate about conjugate geologic structures and the timing and directions of the rifting and earliest seafloor spreading phases. We present a combined structural interpretation of multichannel reflection seismic profiles from offshore of northern Mozambique (East Africa) and the conjugate Riiser-Larsen Sea (Antarctica). We find similar structural styles at the margins of both basins. At certain positions at the foot of the continental slope close to the continent-ocean transition, the basement is intensely deformed and fractured, a structural style very untypical for rifted continental margins. Sediments overlying the fractured basement are deformed and reveal toplap and onlap geometries, indicating a post-breakup deformation phase. We propose this unique deformation zone as a tie point for Gondwana reconstructions. Accordingly, we interpret the western flank of Gunnerus Ridge, Antarctica as a transform margin similar to the Davie Ridge offshore of Madagascar, implying that they are conjugate features. As the continental slope deformation is post-rift, we propose a two-phase opening scenario. A first phase of rifting and early seafloor spreading, likely in NW-SE direction, was subsequently replaced by a N-S-directed transform deformation phase overprinting the continent-ocean transition. From previously identified magnetic chrons and the sediment stratigraphy, this change in the spreading directions from NW-SE to N-S is suggested to have occurred by the late Middle Jurassic. We suggest that the second phase of deformation corresponds to the strikeslip movement of Madagascar and Antarctica and discuss implications for Gondwana breakup.

Crustal variability along the rifted/sheared East African margin: a review

“…Its velocity structure fits well to that of stretched continental crust (Christensen and Mooney 1995), with slightly lower velocities in the upper mantle (Vormann et al 2020). The analysis of seismic reflection data (Mougenot et al 1986;Klimke et al , 2018) also supports the interpretation of the southern part of the DR as a continental fragment. Our data confirm older interpretations made on the basis of continental rock samples dredged between 14°and 16°S along the flanks of the DR (Virlogeux 1987;Bassias 1992).…”

“…The velocity-depth models described in the previous chapter support proposals to split the DR into two structurally different parts (Mascle et al 1987;Klimke et al 2018;Vormann et al 2020;Vormann and Jokat in review). In the northern part of the DR, between 9°S and 13°S, we observe no basement elevation in the seismic data (Fig.…”

African cratonic lithosphere carved by mantle plumes

“…The Central Atlantic Magmatic Province 22 (CAMP) at 200 Ma and Paraná-Etendeka 23 at 135 Ma accompanied or preceded the opening of the central and southern Atlantic Ocean, respectively. The emplacement of the Karroo LIP 24 at 180 Ma pre-dated the onset of seafloor spreading between Africa and Antarctica at 170 Ma 25 . More recently, abundant volcanism has accompanied the development of the East African Rift System (EARS) (30 Ma to present 26 ).

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Publisher’s Note

“…Breakup-related volcanics at the continental margins of the Mozambique Basin, and its conjugates, the Lazarev Sea and the Riiser-Larsen Sea in Antarctica, comprise SDRs and high-velocity lower crustal bodies (Hinz et al, 2004;Leinweber and Jokat, 2012;Mahanjane, 2012;Mueller and Jokat, 2017). However, the volcanics terminate before the Mozambique Strait between Madagascar and Mozambique (Klimke et al, 2018). In the West Somali Basin to the north, there is little evidence for magmatism during the breakup and the basin is thought to be magma-poor (Coffin et al, 1986;Klimke and Franke, 2016;Phethean et al, 2016;Stanton et al, 2016;Stanca et al, 2016).…”