2.3 Subproject
110
Sub-Project 2.3:
South-East African coast geophysical and
geological program
Participants
* Coordinators
Institutions
Names
Email adresses
Alfred Wegener Institute
(AWI)
W. Jokat*
wjokat@awi-bremerhaven.de
GFZ Potsdam
(GFZ)
M. Weber
O. Ritter
A. Schulze
U. Weckmann
T. Ryberg
V. Haak
S. Sobolev
mhw@gfz-potsdam.de
oritter@gfz-potsdam.de
robert@gfz-potsdam.de
uweck@gfz-potsdam.de
trond@gfz-potsdam.de
vhaak@gfz-potsdam.de
stephan@gfz-potsdam.de
BGR Hannover
C. Reichert*
S. Neben
c.reichert@bgr.de
s.neben@bgr.de
University of Kiel
K. Haase
kh@gpi.uni-kiel.de
Council for Geoscience
E. Stettler
J. Mahanyele
edgars@geoscience.org.za
josphat@geoscience.org.za
Univ. Natal
M. Watkeys*
watkeys@nu.ac.za
Requested Funding:
Total for the 5-year duration beginning in 2004: Euros 2386700
(excluding costs for ship time)
2004
AWI
GFZ
BGR
RSA
Totals
2005
165200
165200
2006
401200
382500
100000
167200
1050900
2007
151200
534500
2008
161200
184500
127200
812900
12000
357700
2.3 Subproject
Summary
This subproject will investigate the deep crustal structures and
composition along the east margin of southern Africa, as well as
the surface expressions of Mesozoic magmatic and tectonic
events related to the break-up of Gondwana. This region is the
most complex of the southern African Gondwana margins, and
the pre-drift fits of Africa, Mozambique and Antarctica are still
controversial. Continental breakup along the eastern coast
involved important elements of shear (Falkland Plateau) as well
as extreme LIP magmatism (Karoo event). The significance of
the Karoo event to the breakup process is still enigmatic because
some characteristic hallmarks of a mantle plume are lacking
despite the huge volumes of magma produced, and the peak of
magmatism appears to pre-date seafloor spreading in the region
by as much as 50 My. To constrain the pre-drift fit between
Africa and Antarctica, the origin of large-scale geological feature
like the Mozambique Ridge and the Mozambique plains are
essential, but these are poorly known at present. This project will
therefore involve an extensive seismic programme offshore,
designed to describe the structure and location of the continentocean boundary/ transition. Additionally, three seismic transects
are planned to cross the continental margin westwards to the
Lebombo monocline. Seismic, magnetic, geodetic and
magnetotelluric methods will be applied to describe the crustal
fabric and the current stress regime. The nature of origin of
mantle-derived magmatism will be addressed with new
geochemical and dating studies of the Jurassic (Karoo) and
younger lavas and dike complexes to better describe the
processes in the mantle which preceded and finally caused the
final break-up. The integrated interpretation of the new
geoscientific data will be complemented by lithospheric-scale
thermo-mechanical modeling to provide a state-of-the-art
assessment of the break-up processes within Gondwana.
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Scientific Background
The break-up of Gondwana was the greatest geological event to have affected the southern
hemisphere. Breakup commenced during late Permian/early Triassic (Karoo) times with
rifting between SE Africa and Antarctica along the Lebombo. The intense volcanism
associated with this event took place at about 180 Ma (Encarnación et al., 1996, Duncan et
al., 1997). It has been proposed that the intersection of the N-S trending Lebombo monocline
with the ENE-trending Sabi monocline and the WNW-trending Okavango dyke swarm is a
triple junction sited in SE Zimbabwe (Burke and Dewey, 1974; Reeves, 1978). The volcanism
of the Karoo Large Igneous Province (LIP) (Erlank 1988) appears centered on this triple
junction, with initial nephelinites and succeeding picrite basalts confined to the triple point
region while the younger tholeiitic flood basalts are far more widespread, being found all over
southern Africa as well as in Antarctica. The Lebombo monocline appears to have many of
the characteristics of a volcanic rifted margin (VRM), being adjacent to a LIP, flexed and
faulted, and having seaward dipping reflectors represented by the basalts, which are capped
by rhyolites (Watkeys, 2002). In addition, at its southern end, there is the MORB-like Rooi
Rand sheeted dykes swarm (Duncan et al., 1990). In the light of this evidence, it seems to be
generally accepted that the Karoo “triple junction” represent the site of a major plume head
and that this plume was responsible for the break-up of Gondwana (viz. White and McKenzie,
1995; Storey, 1995).
The plume model is attractive as it explains the observed geographical and geological patterns
and offers an explanation for the massive mantle-melting event that gave rise to the Karoo
LIP. However, there are several major challenges to the plume model as well, and these are
summarized below. The aim of this project is to address these and other outstanding problems
related to Gondwana break-up and evolution of the SE African – Antarctic evolution using
geophysical deep sounding methods combined with field and geochemical investigations of
key rock complexes.
The break-up pattern is inherited from pre-existing structures
The first problem is that the three arms of the triple junction follow trends that existed well
before Gondwana break-up (Watkeys, 2002). The Sabi monocline follows the Achaean
Limpopo Belt, the Lebombo monocline is parallel to the Proterozoic Mozambique Belt, while
the Okavango dyke swarm follows a Pan-African trend developed in the late Proterozoic and
early Paleozoic. In addition, not only did other Karoo dyke swarms also utilize pre-existing
trends (Uken and Watkeys, 1997), but the site of the proposed plume head is at the
intersection of three Precambrian crustal provinces (Kaapvaal craton, Limpopo Belt and
Mozambique Belt). It may be that a plume fortuitously rose into this region or was focused
into the intersection by the effect of topography at the base of the lithosphere (thin spot). In
any case it is clear that the surface pattern of dyking and volcanism was not the result of
stresses caused by the plume on a homogeneous crust. Every trend observed and used to
support the plume theory existed in the Precambrian; there is a clear lithospheric control on
the break-up pattern.
This lithospheric control is not just apparent in structures following pre-existing trends; there
are also significant changes in other break-up related features across crustal domains. For
instance, the Lebombo monocline terminates at its southern end where the Kaapvaal craton
ends, as do the rhyolites and Rooi Rand dyke swarm. Further south, the basement comprises
the Meso-Proterozoic Natal Metamorphic Province where the monoclinal structure, so clearly
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expressed by the linear outcrop of Karoo volcanics along the Lebombo, is replaced by the
complex coastal faulting zone of KwaZulu-Natal. In this region, there are no down-faulted
volcanics along the coast but they do occur about 100 km inland at an elevation of about 1800
m. When the Falklands Plateau separated from the Natal region during opening of the South
Atlantic at about 138 Ma, the boundary between the Achaean and Meso-Proterozoic was used
as the line of break-up. Consequently, this boundary also represents the northern termination
of the Falkland-Agulhas Fracture Zone (FAFZ) which is the major transform fault delineating
the southeastern and southern limits of the African continental crust. A combination of
geological studies and analogue modeling of coastal faulting in southern KwaZulu-Natal
indicates that the FAFZ may have been initiated at about 180 Ma as a sinistral strike-slip fault
prior to its utilization as a dextral strike-slip fault in the Cretaceous (Watkeys and Sokoutis,
1998).
There is no evidence of the formation of oceanic crust during late-Karoo times
(180-170 Ma) between Africa and Antarctica
The extraction of the Falklands Plateau mentioned above represents the oldest known oceanic
crust along the SE margin of Africa (Goodlad et al., 1992); there is no evidence of sea-floor
spreading having taken place during Karoo times. The only MORB-like Karoo magmatism
was the Rooi Rand sheeted dyke swarm that occurs along the southern Lebombo, well away
from the proposed plume head site. Magnetic investigations along the Droning Maud Land
(Antarctica) indicate that the onset of seafloor spreading along the Explora Escarpment and in
the Lazarew Sea was not contemporaneous with the Karoo-aged magmatism onshore. The
oldest magnetic anomaly identified in the Riiser Larsen Sea and its conjugate Mozambique
Basin is almost 155 Myr old (Jokat et al, in press). Towards the west, the margin is younger
than previously expected. Clear magnetic anomalies off the Explora Escarpment are dated to
140 Ma, i.e. about 40 Myr younger than the oldest onshore magmatism in Antarctica (Jokat et
al, in press). In SE Africa, however, there are the Movene basalts which overlie the Lebombo
rhyolites and that might be late Jurassic to Cretaceous in age. Together with the volcanic
Bumbeni Complex of the southern Lebombo (Erlank, 1988), these basalts may be evidence of
onshore magmatism associated with the formation of Cretaceous oceanic crust.
The interpretation of magnetic data offshore of Antarctica is supported by two deep seismic
sounding profiles in the Lazarew and Weddell seas. The line across the Explora Escarpment
confirms earlier interpretations on the existence of volcanic seaward dipping reflectors. The
northern termination fits perfectly within the onset of oceanic crust in this region (Ritzmann,
2000). At 6°E the situation is more complicated. Steep and wide-angle seismic data show
again the presence of volcanic seaward dipping reflectors (SDR). However, the onset of
oceanic crust is almost 100 km northward according to the seismic refraction and magnetic
data (Ritzmann, 2000). The area between the northern termination of the SDR's in this region
and the onset of oceanic crust is characterized by very flat lying, most likely volcanic layers.
They have a positive magnetic polarity compared to the negative one of the SDR. It is not
clear yet if the two volcanic phases were created during subaerial and submarine eruptions.
Mapping the landward extent of the SDRs was not been done during the experiment in 1996
and may be difficult to achieve. The current shelf ice edge prevents any detailed research
south of a water depth of 2500 m. Most of the continent-ocean transition in Antarctica is
covered by up to 200 m thick ice shelves.
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There is no conclusive geochemical evidence of a plume signature in the 180 Ma
Karoo LIP
The third problem is that there is no clear plume signature in the composition of Karoo
volcanics. Previous studies have shown significant variations of the magma sources and
asthenospheric, lithospheric and plume sources have all been suggested (viz. Sweeney and
Watkeys, 1990; Sweeney et al., 1991, 1994; White and McKenzie, 1995). For example, the
relatively late-stage high Fe-basalts have been assumed to represent the plume end member
but the existing isotopic data imply some crustal contamination so that the mantle source
cannot be defined properly. The possible impact of a plume should show up in the Sr, Nd, Pb
and He isotopic compositions of primitive basalts because both the Bouvet and the Marion
hotspot lavas have distinct isotopic compositions but there are not sufficient geochemical data
available to evaluate the possible presence of either the Bouvet or the Marion plume beneath
the Karoo LIP. Most Karoo lavas show significant crustal and subcontinental lithospheric
mantle contamination. In order to avoid this problem, the incompatible element compositions
(e.g. Ce/Pb ratios) and the Sr, Nd, and Pb as well as O isotope ratios of the basalts need to be
determined. Uncontaminated lavas should have comparable compositions to their plume
source and show high 3He/4He ratios if their source has an origin in the lower mantle. The
lowest 87Sr/86Sr ratios in the southern Lebombo and Swaziland lavas are 0.7035 to 0.7037,
which are comparable to Bouvet lavas. However, more data are required to investigate their
compositions in terms of Nd and Pb isotopes to rigorously define the mantle sources.
Investigations of the Rooi Rand dyke swarm (RRDS) have revealed that they are very
depleted in terms of most chemical and isotopic characteristics but they display LREE
enrichment (Duncan et al., 1990). There is no evidence of crustal contamination, while
selective contamination is unlikely to produce these effects. More recently, the establishment
of age relationships between different dykes phases has shown that, although they display a
moderate Fe-enrichment trend typical of dolerites produced by fractionation of a gabbroic
magma, the overall trend is not one of simple fractionation with time (Watkeys et al., in prep).
The REE patterns are themselves can be explained by varying degrees of partial melting in
the mantle during the evolution of the RRDS. Isotopic studies, however, indicate that the
compositional differences between the various phases are not the result of a closed-system
process. The early phases, which are within one of the southern Lebombo isotopic groups,
are mixtures of melts from a MORB-like asthenosphere (positive εNd, CeN/YbNd<0.5) and
enriched sub-continental lithospheric mantle (SCLM) (negative εNd, CeN/YbN>3.5). This
contrasts with the final dyke phase, which has the characteristic higher εSr and lower εNd
values of the northern Lebombo and Nwanedzi volcanics. This phase appears to have
sampled a SCLM segment which had been LREE enriched at a much earlier period.
Significantly, all of the RRDS phases have unradiogenic Pb isotopic compositions and thus
they appear to lack the HIMU mantle component characteristic of plume involvement. Thus
the most MORB-like Karoo magmatism does not appear to be the product of a plume, unless
one makes a plea for a LOMU plume.
The exact refit of SE Africa and Antarctica is uncertain
This refit problem has two main causes. Firstly, the presence of the ice cover in Antarctica
and the Cretaceous and younger cover of the Mozambique plains masks the geology of
critical regions. The nature of the crust beneath the Mozambique plains is unknown. It might
represent oceanic or stretched continental crust. The continent-ocean transition might be close
related with the Lebombo volcanics or with the present coastline depending on which crustal
2.3 Subproject
115
model is applied. Thus the location of this transition can be shifted by more than 300 km,
which has a profound consequence for the refit of Gondwana. Secondly, the sea-floor
anomalies only go back to 155 Ma, and the initial rifting took place at about 180 Ma.
Consequently the refit proposals depend on individual interpretations of the events that took
place between 180-155 Ma. Basically three refits are possible: a loose fit, a tight fit and a
supertight fit. In the loose fit, the Mozambique Ridge is considered to be continental crust so
has to be maintained between SE Africa and Antarctica. In the other two fits, this ridge is
eliminated so that in the tight fit, the continental shelves are juxtaposed, whereas in the
supertight fit, the Explora escarpment is placed against the Lebombo.
New magnetic data obtained offshore of Dronning Maud Land (Jokat et al., in press) place a
different perspective on the interpretation of the structural units along East Antarctica and its
conjugate margin along southeast Africa. The magnetic data in the Lazarew Sea indicate that
the onset of seafloor spreading along the Antarctic margin occurred some time around 130
Ma. whereas the volcanic rocks of the opposite conjugate margin of the Lebombo have an age
of 180 Ma. One possibility is that the Movene basalts of Mozambique, which overlie the
Lebombo rhyolites may represent a younger SDR sequence. However, no deep wide or steep
angle seismic data exist along the SE-African coast to reveal the deeper structure, which
could then be compared to the Antarctic margin. The occurrence of large Karoo dyke swarms
in SE Africa and the lack of such structures in East Antarctica may point to an asymmetric
evolution of both margins in terms of magmatism, extension history and seafloor spreading.
The SE African coast is a critical area for research on these issues because of its accessibility,
but also because some major geologic features offshore, the Mozambique and Madagascar
ridges, have no conjugates in Antarctica. Their deeper fabric (continental/oceanic) and their
formation during break-up remain unknown
Figure 2.3.1. Location of the proposed geophysical profiles planned for the eastern margin.
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Key references
Burke, K. and Dewey, J.F. (1974). Two plates in Africa during the Cretaceous? Nature, 313-316.
Duncan, A.R., Armstrong, R.A., Erlank, A.J., Marsh, J.S. and Watkins, R.T. (1990). MORB-related
dolerites associated with the final phases of Karoo flood basalt volcanism in southern Africa.
In: Parker, Rickwood and Tucker (eds.) Mafic Dykes and Emplacement Mechanisms.
Balkema, Rotterdam. 119-129.
Duncan, R.A., Hooper, P.R., Rehacek, J., Marsh, J.S. and Duncan, A.R. (1997). The timing and
duration of the Karoo igneous event, southern Gondwana. Journal of Geophysical Research,
102, 18127-18138.
Encarnación, J., Flemming, T.H., Elliot, D.H. and Eales, H.V. (1996). Synchronous emplacement of
Ferrar and Karoo dolerites and the early breakup of Gondwana. Geology, 24, 535-538.
Erlank, A.J. (ed.) (1988). Petrogenesis of the volcanic rocks of the Karoo Province. Special
Publication of the Geological Society of South Africa, 13. 395 pp.
Goodlad, Martin, A.K. and Hartnady, C.J. (1982). Mesozoic magnetic anomalies in the southern Natal
Valley. Nature, 295, 686-688.
Jokat, W., Boebel, T. & Meyer, U. Timing and Geometry of Early Gondwana Break-Up,-- J. Geophys.
Res. In press
Lawver, L.A., Sclater, J.G. and L. Meinke (1985): Mesozoic and Cenozoic reconstruction of the South
Atlantic, Tectonophysics, 114, 233-254.
Marks, K.M. and Tikku, A.A. (2001). Cretaceous reconstructions of East Antarctica, Africa and
Madagascar, EPSL, 186, 479-495.
Rabinowitz, P.D., Coffin, M.F. and D.A. Falvey (1983). The separation of Madagascar and Africa,
Science, 220, 67-69.
Raillard, S., 1990. Les marges de L’Afrique de l’est et les zones de fracture associees: chaine Davie et
ride du Mozambique, Ph. D. thesis, Univ. Pierre et Marie Curie, 270 pp.
Reeves, C.V. (1978). A failed Gondwana spreading axis in southern Africa. Nature, 273, 222-223.
Ritter, O., Weckmann, U., Vietor, T. and Haak, V. (2003) A magnetotelluric study of the Damara Belt
in Namibia 1. Regional scale conductivity anomalies, Phys. Earth Planet. Int., in press
Storey, B.C. (1995). The role of mantle plumes in continental break-up: case histories from
Gondwanaland. Nature, 377, 301-308.
Sweeney, R.J., and Watkeys, M.K. (1990). A possible link between Mesozoic lithospheric
architecture and Gondwana flood basalts. Journal of African Earth Sciences, 10, 707-716.
Sweeney, R.J., Falloon, T.J., Green, D.H. and Tatsumi, Y. (1991). The mantle origins of the Karoo
picrites. Earth and Planetary Science Letters, 107, 256-271.
Sweeney, R.J., Duncan, A.R. and Erlank, A.J. (1994). Geochemistry and petrogenesis of central
Lebombo basalts of the Karoo Igneous Province. Journal of Petrology, 35, 95-125.
Tikkui, A.A., Marks, K.M. and Kovacs L.C. (2002). An Early Cretaceous extinct spreading center in
the northern Natal valley, Tectonophysics, 347, 87-108.
Uken, R. and Watkeys, M.K. (1997). An interpretation of dyke swarms of the north-eastern Kaapvaal
craton. South African Journal of Geology, 100, 341-348.
Watkeys, M.K. (2002). Development of the Lebombo rifted volcanic margin of SE Africa. In:
Menzies, M.A., Baker, J., Ebinger, C. and Klemper, S. Magmatic Rifted Margins. Geological
Society of America, Special Paper 362, 27-46.
Watkeys, M.K. and Sokoutis, D. (1998). Transtension in south-east Africa during Gondwana breakup. In: Holdsworth, R.E., Strachan, R. and Dewey, J.F. (eds.) Continental Transpressional and
Transtensional Tectonics. Special Publication of the Geological Society of London, 135, 203214.
Watts, 2001. Gravity anomalies, flexure and crustal structure at the Mozambique rifted margin. Mar.
Pet. Geology 18, 445-455
Ritter, O., Weckmann, U., Vietor, T. and Haak, V. (2003) A magnetotelluric study of the Damara Belt
in Namibia 1. Regional scale conductivity anomalies, Phys. Earth Planet. Inter., 138:71-90,
2003, doi:10.1016/S0031-9201(03)00078-5
White, R. and McKenzie, D.P. (1995). Mantle plumes and flood basalts. Jour. geophys. Res., 100,
17543-17585.
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Key questions
General:





What were the relative roles of active and passive rifting in the break-up between Africa
and Antarctica?
What role did pre-existing structures play in controlling Gondwana break-up and was
there a mantle plume?
What were the similarities and differences in behavior during break-up of region underlain
by Achaean crust and post-Achaean crust?
Can the break-up process be subdivided into two distinct events (the ca. 180 Ma Karoo
event and a later event commencing at about 155 Ma) or was it continuous?
What is the correct refit between SE Africa and Antarctica?
Specific targets:
Lebombo





Do the Lebombo volcanics mark an exhumed continent-ocean transition? If so, is this a
Karoo-aged boundary or a younger boundary? If not where is the boundary and what is its
deeper structure? Do the physical properties of the volcanics change in the boundary
region?
What is the nature of the crust beneath the Cretaceous and younger cover of the
Mozambique plains east of the exposed Lebombo volcanics?
How does the nature of the crust vary along the Lebombo towards the proposed plume
head site?
What was the total preserved volume of magmatism produced along the Lebombo – what
are the mantle source characteristics and why is the Lebombo also one of the the largest
rhyolite province in the World?
Do seaward dipping reflectors exist? Are there two sequences?
Mozambique Ridge



What is the deep structure of the Mozambique ridge? Is the crust continental or oceanic in
origin, or both?
What amount of volcanic material exists beneath the Mozambique ridge and at the
junction of the Mozambique Ridge with the continental margin?
What is the deeper structure of the African continental margin towards the Mozambique
Basin? Here, the transition from sheared margin in the south to a rifted margin in the north
must occur.
Natal Valley and Agulhas Fracture Zone



What is the nature of the sheared crust along the northernmost section of the Agulhas
Fracture Zone where it separates Proterozoic continental crust from Cretaceous oceanic
crust?
Was the Agulhas Fracture Zone initiated in Karoo times (180 Ma) or in the Cretaceous
(155 Ma)?
What is the deeper structure of the Natal Basin and its continental margin, and what is
nature of its contact with the Mozambique Ridge?
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Madagascar Ridge


What is the deeper structure of the Madagascar Ridge?
What is the magnetic signature of Madagascar Ridge and can this be used to calculate
magma production rates?
Scientific Objectives







Establish the best refit between SE Africa and Antarctica, and reconstruct the sequence of
Gondwana break-up events.
Determine the subsurface geometry and properties of major continental structures by the
combination of seismic reflection and magnetotelluric deep sounding.
Use geological and geophysical investigations along the Lebombo volcanic sequences to
better understand their evolution in space and time, their origin and their possible
relationship with a mantle plume
Document neotectonic motions with GPS measurements and monitor modern seismicity
patterns to provide information on present-day surface strain as a basis for understanding
structure and deformation pattern;
Evaluate post-breakup exhumation and landscape evolution of the E.-African margin
using fission-track and geomorphologic studies
Provide detailed ship-borne magnetic data for south of the Mozambique Ridge and in the
Mozambique Basin to constrain the breakup history
Constrain the seafloor spreading anomalies in the Somali Basin and along the Madagascar
Ridge from detailed aeromagnetic surveys north and south of Madagascar.
Methodical approach/Techniques
Geophysical investigations
The scope of this subproject requires an extensive program of geophysical investigations both
on- and offshore (Fig. 2.3.1). These are briefly listed below and details of the three onshoreoffshore transects are then given.






Offshore deep seismic reflection/refraction profiles along strike of the Mozambique Ridge
and deep seismic reflection profiles along the SE African coast
On/offshore deep seismic refraction transects across the continental margin
Onshore near-vertical seismic and magnetotelluric sounding across the eastern end of the
Beattie magnetic anomaly
Ground-based magnetic susceptibility measurements on a transect along the Lebombo
volcanics.
Seismology measurements across the Lebombo monocline to investigate the mantle
structures
Offshore aeromagnetic surveys in the Somali Basin and Madagascar Basin
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On-Offshore Transects
A minimum of three onshore-offshore seismic transects are required to meet the objectives of
this subproject (Fig. 2.3.1). The sites of each were chosen to best address geologically
significant problems and to be logistically reasonable. Each transect is located in an area that
is currently, or has been, the subject of detailed geological studies.
Southern transect:
This SE-trending transect lies in southern KwaZulu-Natal, commencing onshore inland of
Port Shepstone, moving across the southern Natal Valley and then across the southern end of
the Mozambique Ridge. This will provide a seismic section across the contact between the
Meso-Proterozoic crust that was faulted during Gondwana break-up and the Cretaceous
oceanic crust of the Natal Valley, which formed during the pullout of the Falklands Plateau.
These two domains are separated by the Agulhas Fracture Zone (AFZ). Near Port Shepstone,
the southern transect also intersects the eastern end of the trans-continental Beattie magnetic
anomaly, whose origin is enigmatic but likely related to pre-Karoo lithospheric structures.
Central transect:
This E-W transect lies in northern KwaZulu-Natal, commencing in the vicinity of the town of
Piet Retief, moving E across the southern Lebombo, the northern Natal Valley and offshore
onto the northern portion of the Mozambique Ridge. Onshore the area is underlain by
Achaean crust while the Lebombo here includes the Rooi Rand Dyke swarm where recent
detailed studies have been undertaken. East of the Lebombo, the Karoo basalts and rhyolites
are overlain by the Cretaceous (?) Movene basalts which are covered by Cretaceous and
younger sediments of Maputaland, which is a narrow southern extension of the Mozambique
coastal plain. Apart from a number of other features, there is the potential for intersecting two
SDR sequences on this transect.
Northern transect:
This E-W line crosses the northern Lebombo, the Mozambique coastal plain and the
northernmost part of the Mozambique Ridge. West of the Lebombo, the area is comprised of
Achaean crust which is intruded by numerous dykes swarms of various ages, some of which
radiate from the proposed plume head site. This part of the northern Lebombo provides the
most complete section across the Karoo volcanics, from the nephelinites to the rhyolites, and
is currently being studied in detail with work concentrating on the dykes, flexing and
segmentation of the monocline. East of the Lebombo the seismic line will reveal the nature of
the crust beneath the Cretaceous and younger cover of the Mozambique coastal plain. This
line is closest to the site of the proposed plume head and can then be compared to the central
transect which has similar surface geology but, presumably, a different lithospheric structure
and magmatic imprint.
Near-vertical seismic and magnetotelluric profile
This experiment is planned to complement the wide-angle seismic profile on the southern
traverse explained above. Its goal is to image the deep crustal structure and physical
properties of of major crustal boundary zones. This experiment will involve a combined nearvertical seismic reflection and magnetotelluric (MT) profile of 100-150 km length, that
coincides with the onshore part of the wide-angle southern traverse (Fig. 2.3.1). The
experiment will have the same essential design as those planned for Subproject 2.2 (Fig.
2.2.3) and the results of both will complement each other since they cross the same crustal
boundary at different positions.
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Geochemical and petrologic studies
The basic framework of magmatism in the region is well established by existing geologic and
geochemical studies. In this project, we will provide new petrologic and geochemical
constraints on the age and source of key magma types, with the aim to establish the processes
and timing of mantle melting and to resolve the question of plume vs. lithospheric mantle
sources for the magmas. New ages and source constraints for the Movene basalts and
Bumbeni complex (see above) are particularly important because these rocks are geologically
younger than the main Karoo magmatism and may represent magmas emplaced at the time of
continental breakup.
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Physical properities of the Lebombo volcanic rocks from deep drilling holes, to provide
constraints to intepret geophysical results
40
Ar/39Ar dating of the volcanic rocks across the Lebombo
Determination of the major and trace element composition as well as Sr, Nd, Pb and He
isotopic ratios of selected rock samples from drill holes and outcrops
Expected outcomes/deliverables
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Documentation of the architecture of continental margins along the SE African coast
Reconstruction of Mesozoic palaeogeography;
Better understanding of the nature and significance of pre-break-up lithospheric structures
in continental break-up processes
Providing robust constraints for models developed in projects 1 (Heart of Africa) and 3
(Living Africa)
Training of young South African scientists in modern geoscience techniques, both in
South Africa and Germany
Potential links with other international research programs
South African National Antarctic Program
IGCP 482/489 Geodynamics, resource potential and environmental impact of the East African
Rift System
Time frame
The proposed geophysical experiments have a strong marine component and cannot begin
before 2006. Some of the onshore geophysical surveys are dependent on the marine schedule
but other onshore projects can begin immediately.
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2005: Begin onshore seismological/GPS/geochemical studies.
2006: Seismic refraction work offshore. A research proposal was submitted in 2003 for
ship time of RV Sonne to perform this.
2006: Onshore-offshore refraction transects. The southern and central transects have
priority.
2006: Offshore seismic reflection profiles, organized by the BGR.
2007: The onshore near-vertical seismic and MT profile
2.3 Subproject
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121
after 2007: The northern onshore-offshore transect across the Mozambique coastal plains
is the most difficult task within this research program. Beside the high costs, it requires an
exceptional logistical effort and will need significant support by energy companies and the
government of Mozambique.
Logistic/equipment requirements
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Access to suitable research vessel for conducting seismic reflection and refraction
experiments offshore
Access to existing seismic data along the East Coast (Petroleum Agency of SA)
Access to existing seismic data onshore (Council of Geoscience)
Gravity and magnetic data acquisition equipment
Access to the drilling information on and offshore (Petroleum Agency, Council of
Geoscience, mining companies)
Access to analytical facilities for petrological, geochemical and geochronological studies
(EMPA, SHRIMP or equivalent single mineral grain dating facility, XRF, ICP-MS)
Cooperation of the South African National Parks Board and the Mozambique Geological
Survey for the northern transect
Estimated Funding Requirements
Manpower:
All salaries based on the German public service scale (BAT)
1 post-doc for marine deep crustal seismic data processing, modelling and interpretation
Administrative:
AWI
Salary group: BAT IIa (€ 4800/month)
Duration:
01/2006 – 12/2008 € 172,800
1 post-doc for potential field data on-and offshore: processing, modelling and interpretation
Administrative:
AWI
Salary group: BAT IIa (€ 4800/month)
Duration:
01/2006 – 12/2008 € 172,800
1 post-doc for wide-angle reflection/refraction seismic data processing, modelling and
interpretation
Administrative:
GFZ
Salary group: BAT IIa-O (€ 4250/month)
Duration:
01/2006 – 12/2008 € 158,000
1 post-doc for near-vertical reflection seismic data processing, modelling and interpretation
Administrative:
GFZ
Salary group: BAT IIa-O (€ 4250/month)
Duration:
01/2007 – 12/2008 € 102,000
1 post-doc for geophysical data integration and thermo-mechanical modelling of lithospheric
structure and breakup processes
2.3 Subproject
Administrative:
GFZ
Salary group: BAT IIa-O (€ 4250/month)
Duration:
01/2007 – 12/2008
122
€ 102,000
1 PhD student for magnetotelluric survey: data acquisition, processing, modelling
Administrative:
GFZ
Salary group: BAT IIa-O/2 (€ 2125/month)
Duration:
01/2007 – 12/2009 € 76,500
2 PhD students for geochemical and geochronological studies of the Lebombo volcanics and
related rocks onshore.
Administrative:
RSA/Kiel
Salary group: BAT IIa/2 (€ 2400/month)
Duration:
01/2005 – 12/2007 € 172,800
2 PhD students for geologic, geochemical and geophysical studies of the Lebombo volcanics
and related rocks onshore.
Administrative:
RSA
Salary group: BAT IIa/2 (€ 2400/month)
Duration:
01/2005 – 12/2007 € 172,800
========
total staff:
€1,124,700
Field work (excluding ship costs):
Note: For the onshore-offshore northern transect across the Mozambique Plains the costs and
time frame cannot be estimated at the moment and are not included here.
Offshore seismic refraction experiments:
Administration
AWI
Duration
03/2006-06/2006
€ 100,000
Offshore seismic reflection profiling:
Administration
BGR
Duration
2006
€ 100,000
Aeromagnetic surveys off Madagascar
Administration
AWI
Duration
2006
€ 150,000
Onshore part, wide angle seismic survey, southern transect (150 km)
Administrative:
GFZ
Duration:
03/2006 – 06/2006 € 100,000
Onshore part, wide angle seismic survey , central transect (250 km)
Administrative:
GFZ
Duration:
03/2006 – 06/2006 € 200,000
Magnetotelluric survey, southern transect (total 150 km)
Administrative:
GFZ
2.3 Subproject
Duration
123
€ 100,000
02/2007-04/2007
Near-vertical seismic survey, southern transect (150 km profile)
Administrative:
GFZ
Duration:
02/2007 – 03/2007 € 250,000
Petrological, geochemical and geochronological studies
Administrative:
RSA/Kiel
Duration:
2005
2006
subtotal:
total field work:
€ 15,000
€ 15,000
€ 30,000
========
€1,030,000
Travel:
Congresses and workshops
Participation of project scientists at scientific congresses, GFZ
Basis: 2 international (2000 €), 2 national (1000 €) per year
Time frame:
2006-2008
€ 18,000
Participation of project scientists at scientific congresses, AWI
Basis: 2 international (2000 €), 2 national (1000 €) per year
Time frame:
2006-2008
€ 18,000
Participation of project scientists at scientific congresses, RSA/Kiel
Basis: 4 international (2000 €), 4 national (1000 €) per year
Time frame:
2006-2008
€ 36,000
3 annual project workshops, alternately in Germany and South Africa
Basis: 10 participating scientists, 1 week duration
Administration: AWI
Time frame:
2006-2008
€ 100,000
total travel:
========
€ 172,000
Consumables
Laboratory equipment for sample preparation and analyses (RSA+Kiel)
Duration:
07/2005 – 12/2005 € 20,000
Duration:
07/2006 – 12/2006 € 20,000
Costs for Ar-Ar and SHRIMP age dating (RSA)
Duration:
07/2006 – 12/2006
€ 20,000
total consumables:
=========
€ 60,000
2.3 Subproject
124
Work Plan
2004
Month
Geophysics
experiments
Offshore seismic and
magnetic data aquisition
Onshore-offshore seismic
data aquisition
Seismic data processing,
velocity-depth modelling
Aeromagnetic survey,
Madagascar
Potential field data
processing and modelling
Near-vertical seismic and
MT-data aquisition
Near-vertical seismic and
MT processing, modelling
Petrology/geology
Field sampling
Geochemistry and
interpretation
Synergy/integration
Thermo-mechanical
modelling
Workshops
0
6
12
2005
18
24
2006
30
36
2007
42
48
2008
54
60