Preprints
https://doi.org/10.5194/se-2020-209
https://doi.org/10.5194/se-2020-209

  02 Feb 2021

02 Feb 2021

Review status: a revised version of this preprint was accepted for the journal SE and is expected to appear here in due course.

Crustal structure of the East-African Limpopo Margin, a strike-slip rifted corridor along the continental Mozambique Coastal Plain and North-Natal Valley

Mikael Evain1, Philippe Schnürle1, Angélique Leprêtre1,2, Fanny Verrier1, Louise Watremez3, Joseph Offei Thompson1, Philippe de Clarens4, Daniel Aslanian1, and Maryline Moulin1 Mikael Evain et al.
  • 1IFREMER, Geosciences Marines, REM/GM/LGS, Centre de Brest, 29280 Plouzané, France
  • 2LGO, IUEM, Place Nicolas Copernic, 29280 Plouzané, France
  • 3Univ. Lille, CNRS, Univ. Littoral Côte d’Opale, UMR 8187 – LOG – Laboratoire d’Océanologie et de Géosciences, F-59000 Lille, France
  • 4TOTAL, R&D, avenue Larribau, 64000 Pau, France

Abstract. Deep seismic acquisitions and a new kinematic study recently highlighted the presence of continental crust in both the southern Mozambique's Coastal Plain (MCP) and further offshore in the North Natal Valley (NNV). Such findings falsify previous geodynamic scenarios based on the kinematic overlap between Antarctica and Africa plates, thus profoundly impacting our understanding East-Gondwana break-up. Using an updated position of Antarctica with respect to Africa this study reconsider the formation mechanism of East-African margins and most specifically of the Limpopo margin (LM). Coincident wide-angle and multi-channel seismic data acquired within the PAMELA project are processed to image the sedimentary and deep crustal structure along a profile that runs from the northeastern NNV to the Mozambique basin (MB) striking through the LM. This dataset is combined with companion deep seismic profiles and industrial onshore-offshore seismic lines to provide a robust scenario for the formation and evolution of the LM. Our P-wave velocity model consists of an upper sedimentary sequence of weakly compacted sediments including intrusions and lava flows in the NNV while contourites and mass transport deposits dominates the eastern edge of the LM. This sequence covers a thick acoustic basement that terminates as a prominent basement high just west of the contourites and mass transport deposits domain. The acoustic basement has a seismic facies and velocity signature typical of a volcano-sedimentary basin and appears widespread over our study area extending toward the eastern MCP and NNV. Based on industrial well logs that calibrate our tectono-stratigraphic analysis we constrain its age to be pre-Neocomian. We further infer that either strike-slip or trans-tensional deformation occurred at the basement high which sustained uplift up to the Neocomian. At depth, the crystalline basement and uppermost mantle velocity structures show a progressive eastward crustal thinning of continental crust along the edge of the MCP/NNV and up to the location of the basement high. On its eastern side, however, a corridor of anomalous crust depicts the velocity signature of a volcanic basement overlying lower continental crust. We infer that strike-slip rifting along the LM was accommodated at depth by ductile shearing responsible for the thinning of the continental crust and an oceanward flow of lower crustal material. This process was accompanied by intense magmatism that extruded to form the volcanic basement and gave to the corridor its peculiar structure and mixed nature. The whole region remained at a relative high level and a shallow marine environment dominated during this period. Only after break-up in the MB decoupling occurred between the MCP/NNV and the corridor allowing for the latter to subside and being covered by deep marine sediments. We provide new insights into the early evolution and formation of the LM that takes into account both kinematic and geological constraints. This scenario favors strike-slip rifting along the LM meaning that no changes in extensional direction occurred between the rifting and the opening of the MB.

Mikael Evain et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on se-2020-209', Anonymous Referee #1, 16 Mar 2021
    • AC2: 'Reply on RC1', Mikael Evain, 28 Apr 2021
  • CC1: 'Comment on se-2020-209', Christian Olaf Mueller, 21 Mar 2021
    • AC1: 'Reply on CC1', Mikael Evain, 25 Mar 2021
    • CEC1: 'Reply on CC1 and AC1', Susanne Buiter, 31 Mar 2021
  • RC2: 'Comment on se-2020-209', Anonymous Referee #2, 28 Mar 2021
    • AC3: 'Reply on RC2', Mikael Evain, 28 Apr 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on se-2020-209', Anonymous Referee #1, 16 Mar 2021
    • AC2: 'Reply on RC1', Mikael Evain, 28 Apr 2021
  • CC1: 'Comment on se-2020-209', Christian Olaf Mueller, 21 Mar 2021
    • AC1: 'Reply on CC1', Mikael Evain, 25 Mar 2021
    • CEC1: 'Reply on CC1 and AC1', Susanne Buiter, 31 Mar 2021
  • RC2: 'Comment on se-2020-209', Anonymous Referee #2, 28 Mar 2021
    • AC3: 'Reply on RC2', Mikael Evain, 28 Apr 2021

Mikael Evain et al.

Data sets

PAMELA-MOZ05 cruise, RV Pourquoi pas ? Moulin, Maryline and Evain, Mikael https://doi.org/10.17600/16009500

PAMELA-MOZ03 cruise, RV Pourquoi pas ? Moulin, Maryline and Aslanian, Daniel https://doi.org/10.17600/16001600

Mikael Evain et al.

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Short summary
This study analyses recently acquired marine seismic data along the Limpopo passive margin offshore south-east Mozambique. This dataset was collected to better understand the early history and formation of south-eastern African margins. It reveals a crustal structure and a segmentation that suggest the margin was affected by strike-slip rifting. This profoundly impacts the geodynamics of the East-Gondwana break-up since it requires no overlap between the Antarctica and Africa plates.