Margins of Africa

Continental Break-up and Oceanic Gateways


Theme Co-ordinators:
Gabriele Uenzelmann-Neben (AWI), Reginald Domoney (UWC), Michael Weber (GFZ)

Under investigation:

  • Magmatic Processes, Mantle Dynamics and Rifting
  • Gondwana Breakup and Evolution of the Southern Oceans
  • Sedimentary systems and Ocean Gateways

Benefits:

  • Changes in ocean currents – climate driver evolution
  • Generation and accumulation of oil and gas
  • Outpourings of lava - past catastrophic events

Projects:

2.1 Magmatic processes, rifting and continental breakup
2.2a Gondwana Breakup and Evolution of the Southern Oceans - Continent-Ocean transition on the Indian Ocean Margins (MARMOZ)
2.2b Gondwana Breakup and Evolution of the Southern Oceans Madagascar – a key site for Gondwana reconstruction
2.3a Sequence Stratigraphy, chemostratigraphy and petrophysical modelling of the western Atlantic margin of South Africa
2.3b Sedimentary systems and Ocean Gateways Neogene palaeoceanography of the western South African margin
2.3c Sedimentary systems and Ocean Gateways Seismic investigations, ocean currents and offshore sediment systems


Project Descriptions



Project 2.1:

Magmatic processes, rifting and continental breakup

Participants (* indicates project coordinator)

GeoForschungsZentrum (GFZ) Potsdam (Germany) Robert Trumbull*
R.L. Romer
University of Cape Town (UCT), SA David Reid*
Chris Harris
George Smith
University of Johannesburg (UJ), SA Hassina Mouri
Council for Geoscience SA (CGS - Bellville) Coenie de Beer
Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany Soenke Neben
University of KwaZulu-Natal (UKZN), SA Michael Watkeys

Summary

The aim of this subproject is to read and interpret the magmatic “signal” of processes related to Gondwana breakup and dispersal in the Mesozoic, and to the enigmatic development of the south African "superswell" which drove continental uplift into the Tertiary. The diversity of southern Africa's rifted continental margins offers a globally unique chance for comparative studies from different parts of the margins system that experienced variable intensity, composition and duration of magmatism. By studying in detail the composition of magmas produced, we can identify their sources and estimate the temperature and pressure conditions of formation. Combined with age and volume estimates, we can deduce magma flux rates for different parts of the developing margins and relate these to new geophysical and geologic constraints on style and rates of deformation, and on the regional margin architecture from the first phase of the Margins of Africa programme.

Our work will address the following key questions: Where, when and how much heat and mass were delivered into and through the rifting continental lithosphere? What were the controlling factors that determined the location and the degree of mantle melting, how and why did these factors change along the margins and in time as the margin systems evolved from the rift to drift stages. What was the relative importance of shallow-mantle convection vs. deep-mantle plumes in driving and sustaining the breakup process? To what extent is the process controlled or influenced by preexisting structures and properties of the continental lithosphere?

The key feature of this project is an integrative approach towards understanding the magmatic processes as an expression of deep-earth mass and energy transfer, how these relate to lithospheric rifting and breakup and how they influence the subsequent development of the newly formed rifted margins. Our methods are field and laboratory study of igneous complexes in key regions of southern Africa, with joint interpretation of the results using relevant geologic and geophysical data to build an earth system model for the breakup of Gondwana.


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Project 2.2a:

Gondwana Breakup and Evolution of the Southern Oceans - Continent-Ocean transition on the Indian Ocean Margins (MARMOZ)

Participants (* indicates project coordinator)

Alfred-Wegener-Institut (AWI), Germany Soenke Neben*
University of Cape Town (UCT), AEON, SA Maarten De Wit*
University KwaZulu-Natal (UKZN), SA Michael Watkeys*

Summary

The overall goals of this project are:
  • To investigate the architecture and internal structure of the continental margin off Central Mozambique with regard to the distinction between passive-volcanic and passive-non-volcanic types and hence, to investigate the opening mechanism(s) of Gondwana in this area.

  • Were the magmatic processes on the conjugate margins in east Antarctica and off Mozambique symmetric? The existing data in the Antarctica (Lazarev and Riiser- Larsen Sea) indicate a high crustal variability along the margin.

  • The data from Antarctica show at least two distinct phases of excessive volcanism (an older subaerial and a younger subaquatic one). Are those also present off Mozambique?

  • These phases indicate cyclicity and are in conflict to the plume hypothesis but point to decompression melting along the initial rift.

  • Reconstruction of the paleo-oceanography.

  • Estimation of the hydrocarbon potential along the continental margin off Mozambique from the shelf into the abyssal plain or Mozambique Ridge, respectively.


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Project 2.2b:

Gondwana Breakup and Evolution of the Southern Oceans Madagascar – a key site for Gondwana reconstruction

Participants (* indicates project coordinator)

GeoForschungsZentrum Potsdam (GFZ), Germany Oliver Ritter*
Ute Weckmann
Christian Haberland
Jacek Stankiewicz
Samuel Niedermann
BGR (Germany) Soenke Neben*
University of Cape Town, AEON, SA Maarten deWit*
Council for Geoscience (CGS), SA Paul Macey
Eduardo Mondlane University, Mozambique Daud Jamal

Summary

Madagascar plays a key role in the reconstruction of the Gondwana break-up history, with a rock record that spans more than 3000 Ma during which it has been episodically united with, and divorced from, Asian and African connections. However, nothing robust is known about the crustal and lithospheric structure of Madagascar because modern geophysical investigations are lacking. Here we propose an integrated approach, which includes the acquisition of new onshore and offshore geophysical deep sounding data, combined with input from geological and petrological investigations, and geochronology.

The new onshore data will advance our knowledge on structure and composition of the deep roots of continental scale shear zones, major building blocks of modern plate tectonics. Based on new magnetotelluric, seismic and onshore geologic studies we will derive a high resolution image of the crust of Southern Madagascar to establish geophysical models for the development of the deep roots of major shear zones, investigate their interaction with crustal evolution, and their impact on crust/mantle interaction. We will also investigate if present local seismicity is associated with these shear zones.

Off-shore, we will investigate the architecture and internal structure of the Madagascar Ridge, to decide if it is underlain by continental or oceanic crust and if the crustal structure is comparable to the conjugate Gunnerus Ridge in Eastern Antarctica. We also propose acquisition of modern geophysical data to investigate architecture and internal structure of the Davie Ridge and the northern continental margin of Madagascar in order to distinguish between passive-volcanic and passive-non-volcanic margin development and to investigate if the Davie Ridge could be a crustal remnant or an old plate boundary resulting from the separation of Madagascar from Eastern Africa.


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Project 2.3a:

Sequence Stratigraphy, chemostratigraphy and petrophysical modelling of the western Atlantic margin of South Africa

Participants (* indicates project coordinator)

GeoForschungsZentrum (GFZ) Potsdam (Germany) Marlene Scheck-Wenderoth*
Katja Hirsch
Gesa Kuhlmann
Ronaldo Di Primio
University of Cape Town, AEON (UCT), SA Maarten de Wit
George Smith
University of the Western Cape (UWC), SA Reginald Domoney*/Paul Carey
PetroSA Jeff Aldrich
F. Poquioma

Summary

The objectives of this research work shall be to subdivide and interprete the stratigraphic columns of sediments penetrated by the wells into depositional sequences and system tract. To propose a sequence stratigraphic framework for the field. To also, compare geochemistry of the core and side wall samples with the stratigraphic column to establish possible correlations. This is expected to unfold the subsurface geology as it relates to sequences and system tract, assisting in the determination of geometry of potential sands, while suggesting additional appraisal opportunities and development location. Also, to produce a model for future interpretation in well exploration. The project will employ the best geoscience methodology that will reveal accurate deepening of the basins and also, showing several cycles related to eustatic flunctuation in the study area. The depositonal models that will be generated will help in the exploration of the origin of genetically related sedimentary packages during the sea level cycles. Petrophysics will also be used to delineate additional basin parameters, and all the stratigraphic, chemical (geochemical) and petrophysical data will be used to evaluate the evolution of the continental margin.


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Project 2.3b:

Sedimentary systems and Ocean Gateways Neogene palaeoceanography of the western South African margin

Participants (* indicates project coordinator)

University of Cape Town (UCT) (Geological Sciences, Botany), SA John Compton*
Alfred Wegener Institute (AWI), Germany Gabriele Uenzelmann-Neben*
Christian-Albrechts-Universität zu Kiel (Germany) Ralph Schneider

Summary

Multiple geochemical proxies will be used to infer the evolution of the continental margin of South Africa since the Neogene (roughly the last 25 million years). Strontium isotope stratigraphy will be combined with biostratigraphy to develop an improved age model of deposition and diagenesis on the margin. Neodymium (Nd) isotopic changes will be related to changes in oceanic circulation and upwelled waters along the margin. Seismic stratigraphy will be integrated with geochemistry, litho- and biostratigraphy in order to determine the relation among climate, tectonic uplift, upwelling intensity, ocean currents (erosional events) and sea-level fluctuations. The improved age model will allow us to correlate events on the western margin with global tectonism (e.g., opening of oceanic gateways), climate (glaciation of Antarctica and the Northern Hemisphere), eustacy and ocean circulation (e.g., intensity of North Atlantic Deep Water formation). The age of Quaternary successions will be determined using oxygen isotope stratigraphy and AMS radiocarbon ages of the Holocene mud belt. High-resolution Quaternary records will be compared to continental climate proxy (including ice core) records and Northern Hemisphere records.


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Project 2.3c:

Sedimentary systems and Ocean Gateways Seismic investigations, ocean currents and offshore sediment systems

Participants (* indicates project coordinator)

Alfred-Wegener-Institut (AWI), Germany Gabrielle Uenzelmann-Neben*
Universität Bremen (Germany) Katrin Huhn
University of Cape Town (UCT), SA John Compton*
J. Lutjeharms
University KwaZulu-Natal (UKZN), SA Michael Watkeys

Summary

The goals of this project are to achieve a better understanding for the effects (i) oceanic currents have on sediment mobilization and transport and (ii) topographic highs have on paths and intensities of oceanic currents. We will test our conception of the build-up of the Agulhas Drift by different water masses via a numerical simulation of the oceanic current and sediment transport patterns. Different settings for the seafloor topography and climatology will provide information on different time slices representing the LGM and subsidence history of the Agulhas Plateau. Furthermore, we will investigate the impact of the emplacement of magmas and tectonic events both on oceanic currents and the climate. In this way we will achieve a better understanding of the sensitivity of the oceanic circulation with respect to those processes and the evolution of the current systems in the gateway south of South Africa as well as climate variations resulting from modification in current paths and tectono-magmatic events.

 

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