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Why should SEG members and all other geoscientists be concerned with the topic of education in geosciences? It's the future, not only of our professional society, but also the world. We should all be aware by now of the big crew change, which is already under way. How do we inspire and attract more students to pursue a degree or two in the geosciences to fill the positions vacated by a large portion of the geosciences workforce (the baby boomers) who will be retiring over the next decade? Education in the geosciences is the answer. [Figure: see text]

A roughly 70 km diameter circular feature buried beneath the Kalahari sands in South Africa is revealed on regional aeromagnetic maps. Boreholes drilled into the centre of the structure intercept a ∼ 250 m thick sheet of quartz norite, interpreted as an impact melt, which overlies brecciated and shock metamorphosed basement granite. Zircons recovered from the quartz norite, yield U-Pb ages of 145 ± 0.8 Ma, and biotites provide Ar-Ar ages of 144 ± 4 Ma. These data provide strong evidence for the occurrence of a Late Jurassic impact crater (the Morokweng impact structure) ∼ 100 m beneath the surface.

Silhouette and North Islands in the Seychelles represent an alkaline plutonic–volcanic complex, dated at 63 to 63.5 Ma by U–Pb zircon and 40Ar/39Ar methods. This magmatism coincides with the final stages of the cataclysmic Deccan Traps continental flood volcanism in India (67 to 63 Ma), and thus a causal link has been suggested. Recent reconstructions have placed the Seychelles islands adjacent to the Laxmi Ridge and at the western margin of the Reunion mantle plume at the time of formation of the complex. Here we present geochemical evidence in support of the notion that the Seychelles alkaline magmatism was initiated by the peripheral activity of the Reunion mantle plume and is thus part of the Deccan magmatic event. Positive eNd (0.59 to 3.76) and eHf (0.82 to 6.79) and initial Sr of 0.703507 to 0.705643 at 65 Ma indicate derivation of the Seychelles alkaline magmas from a Reunion-like mantle source with an additional minor enriched component, suggesting entrainment of sub-continental lithospheric mantle. The similarity in trace element composition between the Seychelles suite and Deccan alkaline felsic and mafic rocks provides additional evidence for a common mantle source for the Seychelles and Deccan magmatism. Furthermore, we demonstrate the role of fractional crystallisation in the evolution of the alkaline suite. Modelling using major elements suggests that fractional crystallisation and varying degrees of accumulation of olivine, plagioclase, ilmenite, clinopyroxene, alkali feldspar and apatite can describe the spectrum of rock types, from gabbro, through syenite, to granite.

There has been a lot of puzzled debate and equally puzzling explanations regarding the following question: Will the International Showcase at the upcoming 2004 Annual Meeting in Denver be its 10th anniversary? Well, let's see … the first IS was at the 1995 Annual Meeting in Houston. So, counting on our fingers, … the 2004 showcase is the 10th! Oh, but cooler heads realized that the official, unarguable anniversary will be in 2005.

Summary Using an electrical resistivity array we mapped variations in the weathered subsurface at Dayspring Children’s Village and tentatively identify several significant fractures. The weathered zone is significantly thicker to the west. Time-lapse electrical resistivity data were used to map out variations in moisture between the end of the rainy (April) and end of the dry (September) season. In all the time-lapse difference plots, there is a near surface zone between 8-15 m thick that has consistently lost moisture during the dry season. We interpret a significant increase in resistivity in the deeper zone on the line closest to the trees as being due to depletion of moisture along a fracture from which trees are extracting water.

Evans, Rob L.et al.--16 páginas, 6 figuras, A regional-scale magnetotelluric (MT) experiment across the southern African Kaapvaal craton and surrounding terranes, called the Southern African Magnetotelluric Experiment (SAMTEX), has revealed complex structure in the lithospheric mantle. Large variations in maximum resistivity at depths to 200–250 km relate directly to age and tectonic provenance of surface structures. Within the central portions of the Kaapvaal craton are regions of resistive lithosphere about 230 km thick, in agreement with estimates from xenolith thermobarometry and seismic surface wave tomography, but thinner than inferred from seismic body wave tomography. The MT data are unable to discriminate between a completely dry or slightly “damp” (a few hundred parts per million of water) structure within the transitional region at the base of the lithosphere. However, the structure of the uppermost ∼150 km of lithosphere is consistent with enhanced, but still low, conductivities reported for hydrous olivine and orthopyroxene at levels of water reported for Kaapvaal xenoliths. The electrical lithosphere around the Kimberley and Premier diamond mines is thinner than the maximum craton thickness found between Kimberley and Johannesburg/Pretoria. The mantle beneath the Bushveld Complex is highly conducting at depths around 60 km. Possible explanations for these high conductivities include graphite or sulphide and/or iron metals associated with the Bushveld magmatic event. We suggest that one of these conductive phases (most likely melt-related sulphides) could electrically connect iron-rich garnets in a garnet-rich eclogitic composition associated with a relict subduction slab., Three institutions and one company came together to initiate SAMTEX in 2002: the Dublin Institute for Advanced Studies (academia),Woods Hole Oceanographic Institution (academia), the Council for Geoscience (government), and De Beers Group Services (industry). Seven others joined SAMTEX during the four phases of acquisition. In chronological order: the University of the Witwatersrand (academia), Geological Survey of Namibia (government), Geological Survey of Botswana (government), Rio Tinto Mining and Exploration (industry), BHP Billiton (industry), Council for Scientific and Industrial Research of South Africa (government), and ABB Sweden (industry) for the Namibian Power Corporation (government). Other members of the SAMTEX team include: L. Collins, C. Hogg, C. Horan, G. Wallace, M. Miensopust (DIAS), A. D. Chave (WHOI), J. Cole, P. Cole, R. Stettler (CGS), T. Ngwisanyi, G. Tshoso (GSB), D. Hutchins, T. Katjiuongua (GSN), E. Cunion, A. Mountford, T. Aravanis (RTME), W. Pettit, D. Khoza (BHPB), H. Jelsma (De Beers), P.‐E. Share (CSIR), and J. Wasborg (ABB). We gratefully acknowledge the tremendous contribution made to this work by a large number of people involved in several phases of data acquisition across southern Africa. Many, but not all, are employed by SAMTEX consortium members. We also thank Phoenix Geophysics, the Geological Survey of Canada, and the U.S. EMSOC for providing instrumentation. In addition to the funding and logistical support provided by SAMTEX consortium members, this work is also supported by research grants from the National Science Foundation (EAR‐0309584 and EAR‐0455242 through the Continental Dynamics Program), the Department of Science and Technology, South Africa, and Science Foundation of Ireland (grant 05/RFP/ GEO001).

Diamond formation occurs in high-pressure conditions more than 150 kilometres deep in the Earth's mantle. The diamonds make it to the surface in vertical pipe-like structures made up of volcanic rocks called kimberlites. Several thousand such kimberlite pipes have been mapped so far, but research has focused on very old cratons, the areas of oldest continental crust, as this is where most economically viable diamonds are found. Trond Torsvik and colleagues use a plate-tectonic reconstruction for the past 540 million years to locate the positions of these cratons relative to the deep mantle at times when kimberlites were erupted. The kimberlites are shown to have been associated with the edges of large-scale heterogeneities in the deepest mantle, which the authors infer were zones at the core–mantle boundary where magma upwelling generated the mantle plumes that led to the formation of the kimberlites. These plumes may have controlled the distribution of almost all kimberlites that have erupted in the past 540 million years. Diamonds are formed under high pressure more than 150 kilometres deep in the Earth's mantle, and are brought to the surface mainly by volcanic rocks called kimberlites. Here, plate reconstructions and tomographic images have been used to show that the edges of the largest heterogeneities in the deepest mantle, stable for at least 200 million years and possibly for 540 million years, seem to have controlled the eruption of most Phanerozoic kimberlites. This has implications for future exploration for kimberlites. Diamonds are formed under high pressure more than 150 kilometres deep in the Earth’s mantle and are brought to the surface mainly by volcanic rocks called kimberlites. Several thousand kimberlites have been mapped on various scales1,2,3,4, but it is the distribution of kimberlites in the very old cratons (stable areas of the continental lithosphere that are more than 2.5 billion years old and 300 kilometres thick or more5) that have generated the most interest, because kimberlites from those areas are the major carriers of economically viable diamond resources. Kimberlites, which are themselves derived from depths of more than 150 kilometres, provide invaluable information on the composition of the deep subcontinental mantle lithosphere, and on melting and metasomatic processes at or near the interface with the underlying flowing mantle. Here we use plate reconstructions and tomographic images to show that the edges of the largest heterogeneities in the deepest mantle, stable for at least 200 million years and possibly for 540 million years, seem to have controlled the eruption of most Phanerozoic kimberlites. We infer that future exploration for kimberlites and their included diamonds should therefore be concentrated in continents with old cratons that once overlay these plume-generation zones at the core–mantle boundary.

11th South African Geophysical Association Biennial Conference and Exhibition, Swaziland, 16-18 September 2009

A 1400 km-long, 2-D magnetotelluric (MT) profile across the Archaean Kaapvaal Craton, the Proterozoic Rehoboth Terrane and the Late Proterozoic/Early Phanerozoic Ghanzi-Chobe/Damara Belt reveals significant lateral heterogeneity in the electrical resistivity structure of the southern African lithosphere. The profile indicates the following present-day average lithospheric thicknesses, to a precision of about ± 20 km, for each of the terranes traversed (inferred conductive geotherms in brackets): Eastern Kimberley Block of the Kaapvaal Craton 220 km (41 mWm-2), Western Kimberley Block 190 km (44 mWm-2), Rehoboth Terrane 180 km (45 mWm-2) and Ghanzi-Chobe/Damara Belt 160 km (48 mWm-2). Previously published mantle xenolith pressure-temperature (P-T) arrays from the Gibeon, Gordonia and Kimberley fields, however, suggest that the Rehoboth Terrane had equilibrated to a cooler conductive palaeo-geotherm (40 – 42 mWm-2 ) very similar to that of Eastern Kimberley Block of the Kaapvaal Craton, at some (unconstrained) time prior to the Mesozoic eruption of the kimberlites. A model consisting of the penetration of heat transporting magmas into the lithosphere, with associated chemical refertilisation, at an early stage of Mesozoic thermalism appears to be the most plausible model at present to account for both the present-day lithospheric structure of the Rehoboth Terrane and an earlier, cooler palaeo-geotherm. Some problems, however, remain unresolved in terms of the isostatic response of the model. Based on a compilation of xenocryst Cr/Ca-in-pyrope barometry observations, the extent of depleted mantle in the Rehoboth Terrane is found to be significantly reduced with respect to the Eastern Kimberley Block: 117 km versus 138 – 167 km. It appears most likely that the chemical depletion depth in both terranes, at least in the vicinity of kimberlite eruption, is accounted for by refertilisation of the lower lithospheric mantle.

Campaign GPS observations made from 2000 to 2006 at the rhyolitic Torfajokull caldera in south Iceland have been processed, using GIPSY-OASIS software, and analysed in an attempt to create a 3-D elastic half-space model of the interior of the volcano. Current seismicity, resistivity and tilt data for the volcano point towards a cooling magma chamber at 8 km depth below the western part of the caldera, and a shallower magma source in the southeast. The horizontal site velocities show a large effect due to the spreading eastern branch of the Mid-Atlantic ridge that passes through Torfajokull. Hekla volcano approximately 20 km to the northwest of Torfajokull, has been inflating since its last eruption in 2000 and is also influencing the site velocities to a small extent. The spreading ridge and inflation of Hekla volcano could be masking any smaller deformation due to the Torfajokull magma sources. Vertical velocity data shows an average uplift of around 15 mm/yr in the caldera. This uplift is most likely due to postglacial rebound, as well as high-temperature geothermal activity within the caldera.

The international Kaapvaal Craton project was used to provide extensive training and human resource capacity building within the South African geoscience research community. This report discusses the mechanisms of recruitment, success rates and outcomes of the southern African students specifically, as well as the positive aspects and shortcomings of the protocol that was followed. Suggestions are offered to improve future programmes of this nature.

[Extract] AfricaArray(http://www.AfricaArray.org) is a 20-year initiative in the geosciences to meet the African Union’s New Partnership for Africa’s Development (NEPAD) requirements for continent-wide cooperation in human resources development and capacity building. The name AfricaArray refers to arrays of scientists working on linked projects across the continent, arrays of shared training programs and recording stations, and, above all, a shared vision that Africa will retain capacity in an array of technical and scientific fields vital to its sustainable development. AfricaArray officially launched in January 2005 and, with support from many public and private partners, has become multifaceted, promoting a broad range of educational and research activities and supporting a multiuser sensor network (Figure 1). Though fostering geophysics education and research in South Africa was its initial focus, AfricaArray has expanded to 17 countries and is now branching out into all areas of the geosciences (Earth, atmosphere, and space).

A network of fifty-four broad-band seismometers that forms part of the international Kaapvaal Craton programme (Carison et al, 1996) was deployed at over eighty separate locations across southern Africa from April 1997 until April 1999. The seismology group at the University of the Witwatersrand was responsible for operating and maintaining part of the network, and has developed new facilities and research initiatives in applying broadband seismology to the study of earth structure and regional seismicity.

By using a recent compilation of African alkaline igneous rocks and carbonatites, we show that nearly 90 % (28 of 32 occurrences) of nepheline syenite gneisses and deformed carbonatites are concentrated within known or inferred Proterozoic suture zones. Given the well-established intracontinental rift setting for these rocks and the likely continental collisional setting for their subsequent deformation, we suggest that deformed alkaline rocks and carbonatites (DARCs) represent the products of two well-defined parts of the Wilson cycle. DARCs mark the places where vanished oceans have opened and then closed. We further postulate that DARCs taken into the mantle lithosphere to ∼100 km depths at collision could provide source material for later alkaline magmatism. This possibility could account for the observation of recurrent alkaline magmatic activity over hundreds of million years in provinces such as that of southern Malawi.

Invasive alien tree species are known to use significantly more water than local indigenous trees; however, quantifying the effect of these trees on groundwater resources is a challenging task. We are currently investigating aquifers and recharge at the Dayspring Children’s Village. There is a large stand of mature invasive alien trees which is proposed to be depleting a shallow groundwater aquifer. We have collected gravity, magnetic, resistivity, refraction seismic and TEM data to map out the subsurface and determine temporal variations in the groundwater. Structural controls, such as fractures, appear to host the groundwater, as the diabase sills and metamorphosed shales are not porous enough to host groundwater. Two aquifers have been identified at the school, an aquifer at ~50 m depth with a shallow circulation system age of ~49 years and a deeper aquifer at ~162 m with a closed circulation system hosting water older than 60 years. It is possible that the syenite dyke to the west of the school may compartmentalize the aquifer system. Preliminary resistivity and gravity data collected in 2009, 2010 and 2011 demonstrate significant variations between the end of the dry season and the end of the rainy season.