1.3 Subproject
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Sub-Project 1.3
Epeirogenic history of Southern Africa: tracking 200 Ma of uplift,
exhumation, erosion and influence on climate
Participants
* Coordinator(s)
Institution
Name
Email address
University of Cape Town
(UCT)
G. Viola *
M. de Wit
A. Kounov
gviola@geology.uct.ac.za
maarten@cigces.uct.ac.za
Nuclear Waste Systems
(NECSA)
M. Andreoli
marco@necsa.co.za
GFZ Potsdom
(GFZ)
J. Erzinger
S. Niedermann *
erz@gfz-potsdam.de
nied@gfz-potsdam.de
Requested Funding
Total for the 5-year duration project beginning in 2004: Euros 371.000
Year
UCT and
GFZ
2004
99000
2005
78000
2006
98000
2007
58000
2008
38000
1.3 Subproject
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Summary
Africa's topography is unique in a global perspective in two ways. Whereas
elevated topography of most continents can be related to horizontal forces
across compressional plate tectonic margins (e.g. Andes, Cordilleras,
Himalayas, Tibet), this is not so for Africa. Africa is surrounded mostly by
extensional plate margins in the form of spreading ridges. Yet Africa is
host to some of the world's greatest elevated regions; these are thus truely
epeiorogenic in origin, most likely related to vertical dynamic forces in the
underlying mantle. There is, however, considerable debate about the local
origin of these highlands, including that of South Africa.
By balancing erosion and deposition on and around South Africa since
Gondwana break-up, key questions about the geodynamic uplift history of
South Africa, its connection to mantle convection and its effect on climate
change can be monitored.
By combining low-T geochronological methods (apatite fission track
analysis, apatite U-Th/He analysis, cosmogenic isotopes and exposure
dating) with detailed field investigations we aim at addressing key question
such as when South Africa first underwent significant epeiorogenic uplift
and what the uplift rates were thereafter; a series of related subquestions
are:
 Can we quantify rates of erosion and deposition in southern Africa?
 Where, how and when did erosional products transported in river
systems end up on the continental shelves around southern Africa?
 How did the paleo-drainage system evolve?
 How did climate-change influence southern Africa's geomorphological
evolution (or vice versa)?
The proposed research will to link onshore and offshore processes with
rates of erosion, sediment transport and deposition. Precise dating of paloeupliftments and base-level changes around southern Africa will be
integrated by the detailed analysis of the sedimentary record of the
continental shelves (and beyond) of southern Africa. Understanding how,
where and when sediment is transported offshore hinges on a detailed
seismic and sequence stratigraphic study of selected transects around the
South African coast. The ultimate aim will be to quantify sediment erosion
and depositional fluxes and thus link the terrestrial with marine
environment over the last 200 million years. This project can make an
important contribution to the exploration for oil and alluvial diamonds.
1.3 Subproject
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Scientific motivation and State of the Art
The importance of tectonic factors in influencing modes of long-term landscape development
both in passive margin settings and associated intraplate environments has been increasingly
recognized (e.g. Summerfield, 1985; Bishop, 1988; Gilchrist and Summerfield, 1994). Also,
there is a wider appreciation among geophysicists and geologists that the morphological
evolution of passive margins, in addition to their thermal, structural and stratigraphic
development, must be accounted for if a comprehensive understanding of their tectonic
evolution is to be achieved (Gilchrist et al., 1994; Kooi and Beaumont, 1994; van der Beek et
al., 1995; Brown et al., 2000). Elevated topography of most continents can be directly related
to crustal shortening linked to destructive processes across active plate margins (e.g. Andes,
Cordilleras, Alps, Himalayas). In a global tectonic framework the African continent stands out
remarkably, for it is mostly surrounded (> 90%) by extensional plate margins in the form of
spreading ridges and no high topography should thus shape the African plate. Yet Africa is
host to some of the world's greatest elevated regions. Southern Africa in particular, being very
distant from the elevation of the Atlas Mountains, Africa’s only exception that can be linked
directly to active processes in the diffuse convergent margin between it and Europe, is
remarkable for the very high average topographic elevation. The highlands of Southern Africa
are thus truly epeirogenic in origin, most likely related to dynamic forces in the underlying
mantle (e.g. Lithgow-Bertelloni and Silver, 1998; Gurnis et al., 2000). A further complication
is due to the fact that the relationship between rifting/drifting processes and relief evolution
along passive margin shoulders is still poorly known. High-elevation passive margins and their
associated major escarpments are indeed the most prominent landforms resulting from
continental break-up in Southern Africa.
In spite of a recent strong interest in understanding these morphotectonic features (e.g. Brown
et al., 2002 and references therein), there is still a lack of adequate answers to some of the
basic phenomena observed in southern Africa. A considerable debate about the local origin and
even age of these prominent highlands and physiographic features is still ongoing. Some
believe the highlands of South Africa to be mainly Cenozoic in age (possibly as young as 30
Ma, e.g. Burke, 1996), specifically related to the present-day tomographically imaged
Superswell in the mantle below the region. Present-day topography would thus be a dynamic
feature formed in response to vertical stresses at the base of the southern African lithosphere
generated by flow in the lower mantle or positive buoyancy in the mid-lower mantle beneath
southern Africa. However, others are convinced that much of the topography is at least in part
inherited from pre-Cretaceous times, possibly associated with geodynamic processes
accompanying the birth of Africa during the break-up of Gondwana between 120-200 Ma
(King, 1962; de Wit et al., 1988; Brown et al., 1990, 2000; Doucoure and de Wit, 2003). Some
of the elevation may even be related to earlier events such as isostatic uplift following rapid
deglaciation of the great continental ice sheets that covered much of central and southern
Africa between about 300 and 350 Ma (du Toit, 1936; King, 1962; Crowell, 1999) and even to
the earlier widespread Pan-African orogenesis (ca. 500-700 Ma) during which major cratons
were welded together to form Gondwana (e.g. de Wit et al., 2001).
It is clear that a holistic approach is needed in order to address these basic questions. Only by
balancing erosion and deposition on and around southern Africa since Gondwana break-up,
key questions about the geodynamic uplift history of southern Africa, its connection to mantle
convection and its effect on climate change can be monitored.
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Scientific Goals
The ultimate aim of the research will be to date and quantify the epeirogenic uplift of southern
Africa, to quantify sediment erosion and depositional fluxes and thus link the terrestrial with
the marine environment over the last 200 million years. We will be able to answer questions
such as:





How have tectonic, climatic and oceanographic processes affected the geomorphological
evolution of southern Africa from the Cretaceous to the present?
How have these processes sculptured our present landscape?
How have they influenced the concentrated natural resources like oil, gas, diamonds and
heavy minerals around southern Africa's continental margins?
How does mantle upwelling couple to the lithosphere uplift and exhumation?
How does mantle upwelling tie in with climate changes?
The scientific goals of this ambitious research proposal can be summarized in a series of
interlinked activities that, if fully and holistically addressed, will help clarify some of the
debated scientific issues.

When did South Africa first undergo significant epeirogenic uplift and what were the
uplift rates thereafter? Was uplift episodic or linear?
The initiation of the phase of epeirogenic uplift and its rate through time are to be
precisely determined. Without precise temporal constraints no further investigations and
meaningful interpretations are possible.

Can we quantify rates of erosion and deposition in southern Africa?
By balancing erosion and deposition in and around South Africa since Gondwana breakup, key questions about the geodynamic uplift history of South Africa, its connection to
mantle convection and its effect on climate change can be monitored. We need to link
onshore and offshore processes and rates of erosion, sediment transport and deposition.
Below southern Africa, seismic tomography has identified the “African Superswell”, a
region in the lower mantle that some believe represents a bulge of the core-mantle
boundary (e.g. Nyblade and Robinson, 1994; Lithgow-Bertelloni and Silver, 1998; Gurnis
et al., 2000). The only other comparable lower mantle upwelling is found at Hawaii.
Southern Africa therefore is the only region in the world where a real link between mantle
upwelling (and downwelling) and lithospheric topography can be observed. The proposed
scientific approach would investigate a unique natural laboratory.

How did the paleo-drainage system of southern Africa evolve in response to uplift?
A clear understanding of this aspect is crucial in linking the onshore evolution to the
offshore processes and the origin of southern Africa’s diamond and ore deposits.

How did southern Africa’s geomorphological evolution influence climate-changes and
what are the feed-back processes?
Work Plan
The above questions relate to unravelling the rates of erosion and fluxes of sediments from
the southern African continent. They can be constrained by two scientific methods:
1.3 Subproject
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Precise dating of paleo-upliftments and base-level changes around southern
Africa
Dating of uplift and subsequent exhumation will involve localised mapping of onshore river
systems and paleo-river terraces, together with careful sampling and application of
cosmogenic nuclide, Ar-Ar, U-Pb, and U/Th-He dating as well as fission track analysis.
Sedimentary record of the continental shelves (and beyond) of southern Africa.
Understanding how, where and when sediment is transported offshore hinges on a detailed
seismic and sequence stratigraphic study of selected transects around the South African coast.
The ultimate aim will be to date and quantify the epeirogenic uplift of southern Africa,
quantify sediment erosion and depositional fluxes and thus link the terrestrial with the marine
environment over the last 200 million years.
Manpower
In order to carry out the outlined research in an integrated and holistic study (and within a
reasonable time framework), we plan 2 PhD students and a post-doctoral scientist to be
directly involved in the research.
Because it is important that the project starts as soon as possible and benefits from the
participation of a large number of scientists, UCT has initiated the funding for the salary of a
second post-doctoral student. Dr Kounov, the appointed scientist, will begin his research
activity at UCT in January 2004. The requested funding is also meant to cover part of his
research activity that is integrating closely for the present proposal.
Analytical Methods
To understand how the topography, drainage patterns and sediment source areas of the
subaerial parts of continental margins have changed over geological time scales we clearly
need information on variations in rates of denudation over time spans of 106-108 years. Our
understanding of landscape evolution is compromised by a lack of data on rates of landscape
change over appropriate geologic time scales. Traditional approaches to establishing longterm denudational histories for passive margins and adjacent intraplate terrains relied on the
landward extrapolation off offshore chronosequence boundaries to erosion surface remnants,
and the use of (rarely well-) dated sedimentary deposits inland in the rare instances where
these are present (King, 1967). More recently these have been supplemented by the
employment of weathering deposits and duricrusts to characterize land surfaces interpreted to
be of a particular age (Partridge and Maud, 1987). Problems with dating control inherent in
these models, especially where correlation criteria are limited (since erosional residuals lack
dated coeval deposits) coupled with the growing availability of information on offshore
sedimentary sequences have led to attempts to derive denudational histories from offshore
sediment volumes deposited within known time intervals.
Thermochronologic techniques provide a robust, independent and location-specific means of
quantifying histories of crustal stripping, and in doing so establish denudational histories. The
following section provides a brief description of the thermochronological analytical methods
that we will be using to date paleo-uplifments and base level changes.
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Fission Track and (U/Th)-He analyses
Fission track analysis is based upon the natural, slow, but statistically constant, spontaneous
radioactive fission decay of the more abundant isotope of uranium, 238U. Tracks are damage
trails in the apatite atomic lattice due to the explosive process of fission in which two highly
charged fragments fly apart from each other, stripping electrons from atoms lying in their path.
Tracks accumulate within the crystal over time and, under suitable conditions, they may be
revealed and counted. The number of tracks per unit area depends on the rate at which fission
occurs, the length of time during which tracks have been accumulating and the uranium
content of the crystal. For fission-track systems, there are no discrete “closure” temperatures
beyond which tracks are either preserved or destroyed as in other radiogenic systems. A
transition zone where tracks are essentially unstable is instead recognised – this is termed the
partial annealing zone and is defined by upper and lower temperature limits. The effective
closure of the system lies within these bounds, and is dependent on cooling rates. The partial
annealing zone for apatite lies between 60 to 120° C (Green and Duddy, 1989; Corrigan, 1993)
with a mean effective closure temperature constrained at 100 ± 10°C. Hence, apatite fissiontrack analysis is particularly useful for evaluating low temperature thermal histories, i.e. those
affecting the upper 3-4 km of the crust.
Since tracks are produced continuously, each track in a sample will have been exposed to a
different portion of the time and temperature history of its host rock and the distribution
pattern of confined fission-track lengths is an integrated cooling history. The time taken for a
rock to pass through the partial annealing zone is reflected in the track- length distribution.
Further, if a sequence undergoes burial and/or heating, pre-existing tracks are shortened to a
length determined by the maximum temperature and the duration of burial. At temperatures
greater than the upper limit of the partial annealing zone, all tracks are erased and the ¨clock¨
is reset when the rock cools again through the partial annealing zone. Using the random
Monte Carlo and Genetic Algorithm approach (Gallagher, 1995), the sample age and the
track-length parameters are compared to those determined through experimental annealing in
order to assess some possible T-t paths.
Break-up in the South Atlantic occurred at about 120 Ma, preceded by a period of continental
rifting starting at about 160 Ma (Brown et al., 2000). As the South American and African
plates drifted apart, the rifted continental margins were subjected to a phase of major
denudation immediately following breakup. The results of some fission-track studies as well
as preliminary studies of some offshore basins indicate that the bulk of the denudation of the
south west African margin occurred during the early post-rift phase (Brown et al., 1990, 2000;
Rust and Summerfield, 1990). The total amount of denudation generally decreases from 3 to 5
km in the coastal sector to less than 1 in the continental interior.
As with apatite fission-track dating, U/Th-He dating has been used to study tectonic processes
that cause rock cooling. However, the lower apatite He closure temperature (ca. 60 C) makes
it possible to detect and quantify degrees of tectonically induced cooling that are too small to
be recorded by higher temperature systems. Apatite He ages are thus strongly influenced by
perturbations in the thermal field of the shallow crust and their sensitivity is such that they can
be used to reconstruct the evolution of topography in the past. U/Th-He analysis studies on
passive margins are still very scarce and published material is not yet available for the African
margin. However, preliminary results by Viola et al. (in prep) across the Namibian sector of
the margin confirm very early denudation even as for the U/Th-He system is concerned.
1.3 Subproject
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Cosmogenic isotopes and exposure dating
Cosmogenic nuclides (e.g. 3He, 10Be, 21Ne, 26Al) are generated by nuclear interactions of
high-energetic cosmic-ray particles with target elements (such as O, Mg, Al, Si) in the
uppermost layer of the Earth’s surface (e.g. Gosse and Phillips, 2001; Niedermann, 2002). As
the cosmic ray flux and, hence, production rates decrease rapidly and approximately
exponentially with depth (half depth ~0.4 m), the concentration of a cosmogenic nuclide in a
rock provides a measure for the duration of its surface residence. Over the last decade a
wealth of applications of this dating tool have been developed, providing novel insights into
various fields of geosciences, such as geomorphology, glaciology, neotectonics, climate
change research, etc.
Due to the rapid decrease of production rates with depth, the concentrations of cosmogenic
nuclides do not only depend on the age of a geomorphic surface, but also on the rate at which
it erodes. For very old surfaces they reach an equilibrium value that is directly related to the
erosion rate. On the other hand, the cosmogenic nuclides contained in river sediment can be
used to derive basin-wide mean erosion rates (e.g. Schaller et al., 2001).
Rates of tectonic uplift can also be quantified using cosmogenic nuclides. For example, the
surface exposure ages of fluvial terraces, in combination with their elevations above the active
riverbed, provide a measure for the uplift rate assuming that river incision keeps pace with
uplift (e.g. Hetzel et al., 2002).
The feasibility of cosmogenic nuclides as a tool to unravel the denudation history of southern
Africa has been demonstrated in earlier investigations (Fleming et al., 1999; Cockburn et al.,
2000; Van der Wateren and Dunai, 2001), which have shown that the rates of escarpment
retreat at both the south-west African margin and the Drakensberg are 1-2 orders of
magnitude lower than previously suggested based on the assumption that the escarpments
originated at the continental margin during Gondwana break-up.
Research implementation and time framework
The 2 PhD students will concentrate on two main transects stretching from the coast to the
continent interior (Figure 1). Samples for FT and (U/Th)-He analyses will be collected at
regular intervals along the sections. In order to cover southern Africa geographically and to
integrate this new work with some already ongoing projects (Justine Tinker: PhD project at
UCT), a first transect will be sampled from the West Coast of South Africa, across the main
escarpment to Namaqualand and Griqualand on the Archean craton at Kimberley. The second
will instead cover a transect stretching from coastal Mozambique via Barberton and then
across the escarpment to Johannesburg on the Archean craton. Sampling and dating along the
proposed transects will significantly increase the already existing dataset (especially in
eastern southern Africa) and, even more importantly, will offer for the first time the
possibility of a multiple integrated geochronological approach, whereby different dating
techniques will be applied to the same samples. A number of land- and offshore seismic-lines
are available and will be used to link these transects. Moreover, a vast number of borehole
samples are available and will be used to construct true, vertical crustal cooling profiles.
Selected samples along the transects will be collected for cosmogenic nuclide exposure
dating. Integration of these results with the other low-T geochronological data will provide an
extremely solid basis for a proper interpretation in a regional scheme.
1.3 Subproject
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Figure 1 - Apatite Fission-Track Age-Map of Southern Africa (from Brown, 2002) and location of
suggested transects for fission-track and (U-Th)/He dating. The transect from Mossel Bay to Upington
is currently being investigated by Justine Tinker for her PhD project at UCT.
1.3 Subproject
57
The following table summarizes a suggested time framework for the research activity.
Postdoctoral
student
2004
2005
2006
Mapping of morphotectonic features
along selected
transects. Sampling
of material for
cosmogenic,
exposure dating.
Focus on specific
problems such as
erosional rates at
different sites to
evaluate the influence
of tectonic and
climatic factors.
Analytical work at GFZ
for exposure ages
Write up results in
publication format
Literature review.
Familiarization with FT
technique.
Field work and sampling
along a transect
Mozambique-BarbertonJohannesburg.
Collection of borehole
samples from the Council
for Geosciene.
Sample preparation and
mineral separation for FT
and (U/Th)-He dating. FT
analyses in Cape Town.
(U/Th)-He and selected
cosmogenic dating at
GFZ
Results
analysis and
interpretation.
Writing of the
thesis
Literature review.
Familiarization with FT
technique.
Field work and
sampling along a
transect West coastNamaqualandKimberley. Collection
of borehole samples
from the Council for
Geosciene.
Sample preparation and
mineral separation for
FT and (U/Th)-He
dating. FT analyses in
Cape Town.
(U/Th)-He
and selected
cosmogenic
dating at GFZ
PhD
student 1
PhD
student 2
Funds Requested
Student support:
2 PhD students scholarships:
Salary for living in SA, 2 years: 17.000 € p.a. each
Salary for living in Potsdam, 1 year: 20.000 € p.a. each
1 Post-Doctoral student:
Subtotal: 228.000 €
Salary: 40.000 € p.a.
2007
2008
Results
analysis and
interpretation.
Writing of the
thesis
1.3 Subproject
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Equipment:
Refurbishment of an existing fume hood for heavy-liquid use: 2000 €
Upgrading of the FT laboratory in Cape Town: New microscope: 35.000 €
Hot Plate: 1.000 €
Subtotal: 38.000 €
Research expenses (at UCT):
Irradiation fees for FT: about 110 samples: 5000 €
Heavy liquids, hot plates, glass sections and micas, standard glasses: 8.000 €
General consumables (paper, printer toners, postage expenses, sample bags, markers, etc.),
Basic running expenses: 11.000 €
Computers and printers for the students: 11.000 €
Sampling of 10-15 boreholes for FT and (U-Th)/He analysis: 10.000 €
Subtotal: 45.000 €
Travel and Subsistence:
Field work for 2 PhD students and supervisors (including vehicle rental, petrol,
accommodation and food): 13.000 €
Field work for Post-doc (s): 10.000 €
Introductory field trip for GFZ scientists: 9.000 €
Two international conferences for students, post-doc and supervisors: 28.000 €
Subtotal: 60.000 €
Manpower
Investments
Running
costs
Travel
Subtotal
2004
2005
2006
2007
2008
40.000
38.000
9.000
57.000
0
9.000
77.000
0
9.000
37.000
0
9.000
17.000
0
9.000
12.000
99.000 €
12.000
78.000 €
12.000
98.000 €
12.000
58.000 €
12.000
38.000 €
Existing Infrastructure:
Sample preparation will be carried out both at the University of Cape Town and at the GFZ.
Fission track analysis will be carried out in Cape Town, where Dr. Viola set up a laboratory in
2001. U/Th-He and surface exposure dating will be carried out at GFZ Potsdam, where a
thermal ionization mass spectrometry (TIMS) and a noble gas laboratory are available for
these analyses. In addition, depending on the results obtained from cosmogenic He and Ne it
may be necessary to determine cosmogenic radionuclides (10Be, 26Al) in a few samples, which
will be done in collaboration with Dr. P. Kubik at ETH Zurich.
1.3 Subproject
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Co-operation with other INKABA ye AFRICA projects:
The proposed research program represents a natural integration to several others proposals of
INKABA ye AFRICA:



It links very tightly with the studies aimed at a better understanding of the present mode of
mantle dynamics beneath southern Africa. The present-day lithospheric response to the
mantle dynamics, which is the goal of other projects and will be investigated using long
term geodetic and vertical GPS measurements, is a natural integration of our research. The
answer to the question posed in turn may aid better understanding of the core/mantle heat
flux and its possible feedback on geomagnetism.
This project will make an important contribution to the exploration for oil and alluvial
diamonds on the continental shelf and offshore sedimentary basins around southern
Africa.
The project will integrate closely with the proposed seismic studies across the West and
East coasts of southern Africa.
Potential Impact on HR Development
First, the project will be important for student training. Two PhD students and a post-doctoral
student will be directly involved in the research. Every possible effort will be made to
guarantee that at least one of the students will be a non-white South African. The application
and perfection of modern geochronological techniques and tools (as those employed to carry
out the research for this project) is recognized as being the necessary key to unravel any
complex tectonic evolution. The cutting-edge training component the students would benefit
from during this project (at UCT and during exchange periods overseas at GFZ) is such that
they will have more chances of obtaining a position to continue research in this field at other
universities or industries.
Active cooperation is being established at the moment with the University of Western Cape,
in the hope of exposing, attracting and involving even more students from previously
disadvantaged backgrounds in the project.
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Nyblade, A.A., Robinson, S.W., 1994. The African superswell. Geophysical Research Letters 21,
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