Earth Systems Science in Africa
Safeguarding society from natural disasters, sustaining economic growth without threatening the environment, supplying an ever growing world population with industrial raw materials, food, clean water and energy - these challenges are inextricably linked with the dynamics of planet Earth.
Events such as earthquakes and tsunamis manifest themselves in seconds to hours, but they result from stress built up over thousands and millions of years deep within the Earth and at distant locations. Climate change is a similar story, with complex chains of cause and effect that may that operate globally and at different scales.
Quantifying global changes, identifying the anthropogenic influence thereon, and predicting their impingement on societies throughout the world – these are key goals of Earth Systems Science.
The Helmholtz Association of German Research Centres chose southern Africa as an Earth System Observatory for Global Change because of its uniquely preserved geological record.
Southern Africa is at the centre of dramatic current changes in the Earth’s magnetic field and it is the cradle of human culture. South Africa is the technologically and economically strongest nation in southern Africa and has a wealth of mineral resources. The South Africa - German partnership in Earth sciences is truly symbiotic, with both nations facing the same grand challenges of sustainable, safe and clean sources of energy and raw materials needed for advanced technology, and of training a next generation of innovative, holistic scientists.
All stand to benefit from joining together to unravel the workings of our planet from this special perspective.
A 3-D Model of southern Africa, based on seismic tomography, showing the location of kimberlite pipes that penetrate deep into the southern African lithosphere, bringing to the surface a suit of mantle samples (and diamonds) from as deep as 250 km below surface.
The break-up of Gondwana and the formation of the southern oceans has left a globally unrivalled imprint at surface of a wide range of igneous rocks that provide vital clues to understanding the chemistry and dynamics of the mantle. Inset shows the initial location of Gondwana hotspots: numbers 3 and 4 will be studied by Inkaba ye Africa
Perspective of the southern oceans and surrounding continental margins
of southern Africa-Antarctica that will be investigated in Inkaba yeAfrica
The southern sector of the African Plate is unique in a global perspective in at least 15 different ways:
- South Africa's lithosphere preserves a nearly uninterrupted geological history of more than 3.5 billion years. This is the longest, best-preserved geological record of planet Earth
- South Africa's continental lithosphere has been sampled across depths of over 250 km by natural deep-continental "drill-holes" in the form of more than 1 000 kimberlites and related igneous rocks that have brought to surface samples of the mantle (and crust) in the form of xenoliths and xenocrysts (such as diamonds). South Africa has the world's best and largest collection of "core" from these deep drill holes into the mantle
- Global seismic tomography studies have consistently imaged the existence of a low-velocity anomaly of global proportion beneath the southern African plate. The anomaly implies elevated lower-mantle temperatures over a substantial region below South Africa. In the lower mantle, between 1000 and 2900 km depth, the anomaly is located directly beneath South Africa. This deep mantle anomaly has been interpreted as a large-scale up welling of hot mantle; and since the up welling is most intense in the vicinity of the core-mantle boundary, this is assumed to be its point of its origin. In some models, the cause of this anomalously hot lower mantle lies in greater than average global heat flow from the liquid core below South Africa. Since the liquid core is the powerhouse for the generation of Earth's magnetic field, the higher than average heat-diffusion may be monitored through anomalous magnetic field changes across South Africa
- The strength of the magnetic field of Earth is declining most rapidly across the South Atlantic, and the field measured across South Africa has lost near 20% of its total strength over the last 60 years. There is a prominent growing patch of reverse polarity in Earth's magnetic field beneath South Africa. Distinct patches of reversed magnetic flux at the poles and below South Africa can account for 90% of the present day field decrease. There is scientific "rumour" that this heralds the onset of a new reversal of the geomagnetic field. The changes must be monitored to provide forecasts
- Shielding of high-energy radiation from outer space is severely reduced across a large oval-shaped geographical region of the southern Atlantic. This is related to the continued weakening of the magnetic field. Lethal radiation penetrates this growing South Atlantic magnetic "hole" to altitudes of less than 100 km, and already interferes with low orbit satellite and aircraft communications. The magnetic hole is shifting towards South Africa. Predicting growing radiation hazards of this region is of global relevance
- South Africa is part of the African Superswell, Earth's most extensive elevated region not linked to far-field horizontal compressive stresses. Whereas elevated plateaux of most continents can be related to processes across compressional plate tectonic margins (Bolivian Altiplano, Colorado, Tibet) this is not the case for southern Africa because it is surrounded only by extensional plate margins. It is tempting to speculate that there is a causal relationship between the high elevation of the African Superswell and the low-velocity tomographic anomaly of the deep-mantle beneath South Africa. Yet beneath southern Africa the 410- and 660-km seismic discontinuities are both found at their expected depths, so that the temperature in the upper mantle below the southern African lithosphere is close to the global average mantle temperature at that depth. That leaves two competing models for the high topography of South Africa: (1) vertical stresses at the base of the southern African lithosphere generated by flow in the lower mantle, or (2) positive buoyancy in the mid-lower mantle beneath southern Africa. South Africa is the only sub-continental region in the world, therefore, where a history of the elevation of its paleo-surfaces can be used with confidence to track paleo-mantle dynamics of the lower mantle in isolation from horizontal forces of plate tectonics
- Much of the formation of the South African high plateau occurred during the Cainozoic, a 65 million year period of sustained global cooling following the Cretaceous "hothouse" Earth. Tracking the uplift history of the African Superswell will provide a central key to unlocking the kinematics of this global climate change and the associated onset of glaciation in the southern hemisphere some 40 million years before that recorded in the northern hemisphere
- Africa was born between 200-120 million years ago out of the break-up of the super continent Gondwana over a period of 80 million years. South Africa was part of the heartland of Gondwana and it has the world's best preserved terrestrial-marine linked sequences of volcanic rocks, sediments and fossils with which to track the break-up of this super continent, and its associated long-wavelength global climate and biodiversity changes. South Africa has all the geological evidence with which to answer the questions: why do super continents form and break-up; what are the driving forces, and what are the global consequences?
- South Africa's continent-ocean boundaries offer fundamental insights into the formation of "passive" continental margins and their natural resources. South Africa is surrounded by the two end-members of extensional-type continental margins: one produced during pure-shear perpendicular to the present southern Atlantic margin; the other through simple shear parallel to the margin of the southern Indian Ocean. The records of these processes are stored in the stratigraphic sequences preserved in a number of sedimentary basins that straddle the continental margin of South Africa
- South Africa hosts one of the largest igneous basalt provinces on Earth that can be used to study lateral flow of plume material from a deep-mantle source region, followed by shallower sub-lithospheric decompression melting and sub-crustal transportation of the melts laterally over thousands of kilometres. Widespread Karoo intrusive-extrusive igneous activity at the start of Africa-Antarctica break-up (180 Ma) reached far across into Antarctica and South America. Plume activity flared up again below southern Africa and South America (Parana-Etendeka) at 130 Ma just prior to the opening of the South Atlantic. This was followed by near-continuous small-volume alkaline magmatic activity across South Africa that peaked between ~ 80 and 130 Ma, but that lasted until at least 30 Ma. These rocks represent the longest most-complete mantle information-"bite" stored on any continent
- Southern Africa is the world's only subcontinent entirely surrounded by constructive plate boundaries in the form of spreading ridges whose past positions can be confidently tracked-back directly adjacent to its continental margins. The Southern Atlantic and Indian Oceans that surrounds South Africa thus represents unique growth of oceanic lithosphere increasing in area both perpendicular and parallel to its spreading ridges and fracture zones. In addition, a number of significant hotspots have created oceanic islands that provide windows into to deeper asthenosphere sources and magma-mixing dynamics with those of shallower sources below the spreading ridges. A number of hotspot tracts, of which the Walvis Ridge is the most prominent, link these to continental mantle sources. This laboratory thus records 200 million years of continuous upper and lower mantle melts that have mixed in various way with pure continental and pure oceanic lithosphere. Chemical fingerprints of these different mantle domains in this region provide fundamental information about deep- and shallow- mantle dynamics that is not distorted by destructive plate margin processes. The South Atlantic is unique the world over in hosting a number of compositionally extreme end-members mantle components (EM-1, DUPAL, LOMU). With the exception of EM-1, these chemical anomalies are confined to the southern hemisphere. Resolving these will place fundamental constraints on global models of mantle dynamics
- The South Atlantic is a key area for addressing the fixity of hotspots in the lower mantle. The reliable measurement of the absolute plate motion of Africa key to establishing the role played by global mantle plumes in continental rifting, and to testing the notion that hotspots are fixed in the lower mantle. Recent re-evaluation of the migration rate of volcanism along southern Atlantic ocean hotspot trails have revealed, unexpectedly, that current estimates of this basic parameter are seriously flawed. Resolving these issues has a first order bearing on resolving the absolute motion of all Earth's plates
- South Africa is the only place in the world that generates anthropogenic tectonics. The heartland of South Africa is tectonically stable. It comprises a continental fragment (the Kaapvaal Craton) with all the landmarks of a stable continent over the last 3 billion years. Today its stability is certified by an almost complete absence of any significant natural seismic activity. Yet the region is not aseismic. The center of this stable craton hosts the world's deepest mines that are now the source of near-continuous earth-tremors, making it the world's largest man-made seismic laboratory. Continuous removal of rocks at depths of 2-3 km below surface, causes rock bursts; often along pre-existing faults. As a result, an area (~10000 km2) is seismically active and subjected to earthquakes of magnitude 2-4 on the Richter scale on an almost daily basis. The rock bursts are the cause of the high death toll of the mining operations: on average there is a fatal casualty ratio of ~1person/ton gold extracted from the mines. There is an urgent need to drastically improve this poor record. The existing seismic networks in the mines allow the epicenters of seismic events to be determined within a few meters, and these sites can be visited underground. South Africa thus hosts the most unique natural laboratory within which to study nucleation and growth of cracks and fault propagation under semi-controlled conditions at meso-scales. And, because there is no clear distinction between the mechanisms of natural earthquakes and these man-made events, there is an opportunity to improve predictive models for both natural earthquakes and for rock bursts in the deep African mines in particular. This dovetails with the global need to improve forecasting of earthquakes; and in South Africa to increase safety in deep level mining
- The sediments of the southern oceans and the continental shelves of South Africa and Antarctica hold the richest unexplored and continuous 250 million year climate record of the Mesozoic-Cainozoic eras. Today, many of the key aspects of climate change over this time period, that includes several major global mass extinction events, have come predominantly from studies in the northern hemisphere and the North Atlantic region in particular. But there is growing realisation, worldwide, that there is insufficient data from the southern hemisphere to complement those of the northern hemisphere. Yet there is general consensus that the long-term onset of cooler global climates is rooted in the geographic evolution of the southern oceans, particularly during the final isolation of the Antarctic continent during the break-up of Gondwana. Marine and continental margin data, around southern Africa, the sub Antarctic islands and along conjugate Antarctica, must confirm this. Without this these data from the southern hemisphere, true global models will not materialise. Geochemical and biological stratigraphy studies in southern oceans, particularly in the south Atlantic, the Weddell Sea and the southern Indian Ocean will lead global climate change studies over the next decade. South Africa can act as a springboard for oceanographic cruises to sustain these studies. South Africa also has scientific field stations in Antarctica (SANAE) and on its sub Antarctic islands, like the Prince Edwards Islands, to facilitate these studies. High-resolution data generated by the South African mining and petroleum industry are also available for study
- South Africa is bound by a complex set of ocean currents and climate systems that have evolved over 120 million years during the opening of the seaway connecting the Indian to the Atlantic Ocean. Today the ocean currents in these oceans immediately south of South Africa, mix to create the world's most potent and chaotic oceanic turbulence, known as the "Cape Cauldron". One of the outcomes of this "vigorous mixing of the oceans" is the transfer of warm Indian Ocean water to the Atlantic Ocean from where it is further incorporated into the ocean circulation system of the North Atlantic. This unstable southern ocean circulation system buffers southern African climates and, through complex feedback interactions, its biosphere. The coastal regions around South Africa, and particularly in the Cape, are host to a number of world-class biodiversity hotspots whose species have evolved from Gondwana stems; and perhaps the most mysterious of all: 70 000 years ago the emergence of human culture is now believed to have occurred in this coastal region. Understanding the evolving paleo-geography of the new seaways and shifting ocean currents of the southern oceans during the incremental displacement of Africa from Antarctica and South America will tease out some of the mysteries of biodiversity and human evolution around their margins, as Alfred Wegener and Alex du Toit might have predicted.