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11th SAGA Biennial Technical Meeting and Exhibition
- Conference date: 16 Sep 2009 - 18 Sep 2009
- Location: Swaziland, South Africa
- Published: 16 September 2009
101 - 120 of 157 results
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Jwaneng South Structure, Botswana: a New 1.3 km Diameter Buried Cenozoic Impact Crater Discovered by Airship-mounted Gravity Gradiometer
Authors Sharad Master, Brad Pitts and Marek WendorffDuring regional exploration for diamondiferous kimberlites by De Beers Botswana in 2006, a pronounced circular geophysical anomaly, ~1 km in diameter (now called the Jwaneng South Structure), was discovered at ~24°46’E, 24°42’S, about 15 km S of Jwaneng. The target was generated on bouguer gravity data obtained with an airship-mounted full tensor gravity gradiometer. The circular anomaly also appears on airborne EM, ground gravity and CSAMT, images. The structure was investigated by 9 diamond drill holes, which revealed a sedimentary rock sequence, consisting of evaporitic lacustrine carbonates with plant fossils, overlain by sedimentary breccias and sandstones of the Kalahari Group (maximum thickness ~300m), filling an apparent circular bowl-shaped depression about 1.3 km in diameter. Below the sedimentary rocks is a <60m thick allogenic breccia complex consisting of a series of breccias with granitic fragments, which pass downwards into brecciated mafic rocks (which resemble Karoo dolerites geochemically) and then unbrecciated granites (of the 2785 Ma Gaborone Granite Complex). No kimberlites or any other similar intrusive rocks were encountered in the boreholes. Petrographic studies show that the rocks have suffered intense shock eformation (although impact-diagnostic PDFs have not yet been found). They have been completely shattered into angular fragments in the authigenically brecciated basement, and into subangular to subrounded shapes in the allogenic breccias, which have a sandy matrix. Individual mineral grains show features found in known impact structures- including mosaicism, deformation bands and lamellae in plagioclase and alkali feldspars, and cleavage in quartz. Macroscopic indicators of shock include “gries”-textured breccias, and multiply-striated joint surfaces, formed by intersecting shock waves, analogous to shatter cones. The disposition of fractured basement, allogenic breccias, breccia dykes, and sedimentary fill, as well as the geophysical characteristics, closely resemble those found in other buried impact structures developed on granitic targets (Tswaing, Kgagodi, Brent), and modelling points to the origin of the structure due to hypervelocity impact by a meteorite (or asteroidal fragment), with a diameter, if chondritic, of ~100m. Jwaneng South is the first impact structure on earth to have been discovered using airborne gravity surveys.
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Seismic Hazard in the DRC and Western Rift Valley of Africa
Authors T. Mavonga and R. J. DurrheimA probabilistic approach was used to assess the seismic hazard in Democratic Republic of Congo and surrounding areas. Seismic hazard maps were prepared using a 90-year catalogue compiled for homogeneous Mw magnitudes; the attenuation relations of Mavonga (for the Western Rift Valley of Africa), Atkinson and Boore (for eastern North America) and Jonathan (for eastern and southern Africa); and the EZ-Frisk software package. The highest levels of seismic hazard were found in the Lake Tanganyika Rift seismic zone, where peak ground accelerations (PGA) in excess of 0.32 g, 0.22 g and 0.16 g are expected to occur with 2%, 5% and 10% chance of exceedence in 50 years, respectively. The seismic hazard in the Congo basin diminishes with distance away from the Western Rift Valley until, at a distance of about 450 km, the chance of exceeding 0.05 g (the threshold value of engineering interest) is less than 10% in 50 years.
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Detection of Buried Magnetic Objects by a SQUID Gradiometer System
We present a magnetic detection system based on superconducting gradiometric sensors (SQUID gradiometers). The system provides a unique fast mapping of large areas with a high resolution of the magnetic field gradient as well as the local position. A main part of this work is the localization and classification of magnetic objects in the ground by automatic interpretation of geomagnetic field gradients, measured by the SQUID system. In accordance with specific features the field is decomposed into segments, which allow inferences to possible objects in the ground. The global consideration of object describing properties and their optimization using error minimization methods allows the reconstruction of superimposed features and detection of buried objects. The analysis system of measured geomagnetic fields works fully automatically. By a given surface of area-measured gradients the algorithm determines within numerical limits the absolute position of objects including depth with sub-pixel accuracy and allows an arbitrary position and attitude of sources. Several SQUID gradiometer data sets were used to show the applicability of the analysis algorithm.
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1-D Velocity Model for use by the SANSN in Earthquake Location
Authors V. Midzi, I. Saunders, M. B. C. Brandt and T. MoleaKnowledge of the velocity model of an area is essential both for earthquake location and tectonic implication. Locating earthquakes using an unreliable model contributes in part to the uncertainties of active fault mapping and unexplained scatter of seismic locations. Given that we strive to continually improve our location abilities, it is necessary to always improve on the model used in the location process. The travel time inversion method was used to estimate a 1 - D velocity model that can be utilised by the South African National Seismic Network (SANSN) in seismic data analysis. It should be noted that the velocities obtained are approximately equal to the average velocity of the 3D structure within the same depth range that has been sampled by the data. In order to test the new model, it was used to relocate a sample of well recorded data from the SANSN database and results compared to previous data analyses. The new model VM1 was found to provide improved locations compared to the previously published CGS locations especially when considering the clustering of events in the mining areas as well as the observed reduction in location errors. Station corrections were calculated and showed strong lateral variations across the region. The velocity model will continue to be improved with time as more seismic stations are installed throughout the country especially in the southern part and thus more data are collected.
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Large-Scale Structural Map of the Cape Fold Belt Derived by Remote Sensing Analysis
Authors Ch. Mielke and M.J. de WitThe presented map shows the geology and structure of the Cape Fold Belt at a scale of 1:600,000. This map was produced to analyze fold structures and fault lineament trends to propose distinct structural domains within the Cape Fold Belt. This map is a first attempt to provide a coherent regional framework into which regional studies could be integrated to link the structures of the Cape Fold Belt to the structures of Gondwanide Fold Belts in South America and Antarctica. Data from Landsat-7, ASTER, SRTM and Air Photos provided the image base for an estimation of fold plunge data (azimuth and dip) and fault lineament data that were correlated with field measurements for accuracy assessment. The map shows that the Cape Fold Belt can be subdivided into six major structural domains. The two structural blocks in the Western Cape Province, separated by the Worcester Fault, show great similarities in fold plunge data. However, more detailed structural data from the field are necessary to characterize the proposed structural domains and to quantify the structural blocks north and south of the Worcester Fault in greater detail.
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Magnetotelluric Study in Northeastern Botswana
The proposed boundaries of geological terranes in northeastern Botswana are mainly based on regional magnetic and gravity data, because there are not many outcrops available due to the thick Phanerozoic cover rocks. The extent of the Zimbabwe craton into Botswana as well as the location of the boundaries to its neighbouring mobile belts (Limpopo Belt, Magondi Mobile Belt and Ghanzi-Chobe Belt) are not very well known. Magnetotelluric (MT) profiles of the Southern African MagnetoTelluric EXperiments (SAMTEX) are present in this area and provide information about lithospheric strike directions and the resistivity distributions as well as possible locations of terrane boundaries, which verify some of the proposed terrane boundaries and suggest modification for others (e.g., Ghanzi-Chobe Belt to Magondi Mobile Belt terrane boundary and the western boundary of the Zimbabwe craton).
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Maximum Flooding Surface; the Ultimate Correlator.
By Daniel Mikeš‘Sequence stratigraphy’ claims to be a method that describes the 3D/4D basin-fill. However, it comes short in a number of ways: there is no concensus on its concepts and terminology, some of the assumptions are known to be incorrect, there is no general model that fits all environments and locations. The scientific community has been working hard on these issues and the latest joint effort (Catuneanu et al., 2009) gives an excellent overview of the present state of the method. The authors make a wise distinction between model-independent and model-independent features of the technique. Although impressive in its review of existing models and including a range of techniques, areas and environments, it continues to build on the same assumptions and hence leaves the same shortcomings as all previous models, even though it mentions them explicitly. The main assumptions on which sequence stratigraphy seems to be built are the following. (1) The base level curve is cyclical. This is very unlikely the case, the more so since it is known that base level is a combination of tectonic, eustatic, and climatic signals. Added to this is the fact that although the insolation curve can be calculated there is no adequate high-resolution model for the other three signals. It is highly unlikely of any of the individual signals to by cyclic or symmetric, let alone the compound signal. A look at the insolation curve itself shows us its irregular shape. As a result, it is unlikely for the succession of geometric elements to be regular. (2) Length translates directly to time. The behaviour of a sedimentary system is known to be extremely variable in both space and time, and both on larger and smaller space and time scales. It is therefore highly unlikely that a geometric element will be laterally continuous in both facies and time. The natural migration of sedimentary systems makes timelines naturally cut through lithological boundaries and the diachronicity of the same geometric element within a sedimentary system can be substantial. This is even enhanced by the fact that sedimentation and erosion most probably occur in only a fraction of the entire time. As a result a sequence at one place is unlikely to correlate with a similar one some space away. The basic concepts of ‘sequence stratigraphy’ are relatively straightforward and have been proposed as early as 1949 (Sloss et al., 1949), all concepts thereafter have intended to expand and improve the method. However, there is to date no concensus on many of those concepts. This means that either the concepts are not sufficiently general, or that there is disagreement on the assumptions. One thing is sabotaging all attempts and that is the fact that we study the output signal and try to reconstruct the input signal from it. One of the main differences between the alternative models is the choice of main correlative surface. All but one (Galloway, 1989) use the erosional unconformity. The question is: if we don’t know the input-to-output relationship, can we employ the output-to-input interpretation? To answer this question we concentrate our studies on the growth of deltaic systems with and without external forcing. To that end we simulate a deltaic system in a scaled environment for a selection of prototype scenarios and we intend to run numerical models for a large range of scenarios. Our preliminary results show that the erosional unconformity is a strongly diachronous local phenomenon, whereas the maximum flooding surface is a weekly diachronous regional phenomenon. From our findings we recommend the following: the maximum flooding surface as correlator; the shoreline migration to establish purely geometric behaviour like e.g. aggradation, progradation, retrogradation; a combination of geometric behaviour and lithofacies to establish ‘stratotypes’ or elements. We recommend to not use the following: orders of cyclicity (e.g. 4th, 5th, 6th), unless the period is known through age-control; systems tracts or socalled ‘genetic’ elements. Overall we recommend the use of well-established existing techniques like sedimentary structure analysis, facies analysis, basin analysis to establish the areal extent of 3D geometric elements like lithofacies and their bounding surfaces.
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A Structural and Petrographical Study of the Peninsula Formation at Moregrove Quarry, Port Elizabeth
Authors J. A. Moodley, P. W. K. Booth and G. BrunsdonA 100 metre section of quarry face in the Moregrove quarry in Port Elizabeth was mapped with the purpose of carrying out a detailed structural analysis of Peninsula Formation rocks. Along the quarry face primary sedimentary structures and deformation structures (faults, cleavages, joints) were measured in detail with a Brunton compass, and results plotted on an accurately constructed section, with accompanying stereogram data. Rock types are predominantly quartzites with lesser phyllite horizons. The latter occur as lense-shaped pods along faults zones and are highly sheared. Several thrust faults dipping shallowly towards the southwest have in places imbricate faults ramping up to join thrust planes, thus forming duplex structures. Normal faults are also present showing displacements of the order of only a few metres. A fracture cleavage, probably related to thrust development, is prominent in hangingwall blocks. At least two open joint sets are present in the quartzites which enhance the close-spaced fracture patterns in these rocks. In addition there are en echelon quartz filled fractures, which relate to the normal fault development probably during a post- thrusting episode. Structures formed as a result of compressional tectonism are interpreted as having developed during the Cape Orogeny, during the Late Palaeozoic, whereas normal faulting is probably related to the breakup of Gondwana, during the Mesozoic.
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Using 3-D Gravity Gradient Space Plots Instead of 2-D; a Forward Step for Basin Analysis
More LessThe historical works in gradient space had 2-D space plots of almost all possible geological structures. Evaluation of recent work by this method for interpretation of a sedimentary basin showed that error entrance caused by lots of approximations must be eliminated. As a more complete and less approximated geometrical interpretation method, 3-D space plots were offered. These kinds of plots contain more details and also they are suitable to use for not only basin but also all dominant anomaly's shape. There isn't any estimation of density in this method because density estimation doesn't appear in this method procedure at all.
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Assessing Source Rock Maturity within the Prince Albert and the Whitehill Formations
Authors Z. Mowzer and R. DomoneyPetroleum plays a pivotal role in society, so much so that petroleum accounts for a huge percentage of the world’s energy consumption. The population boom has made the demand for this commodity increase exponentially. New ventures into the petroleum sector are increasing to keep up with the demand of hydrocarbons. The Karoo in South Africa is an area in which petroleum studies are being reviewed with particular interest, especially within the Tanqua and Laingsburg subbasins of the Karoo. Research in this area is becoming more readily available as the oil industry seeks to gain more knowledge for exploration purposes. Understanding this region can help aid in offshore development that is not as readily accessible as the onshore sediments. Using new modern technologies as well as old geochemical techniques we can expand our knowledge on hydrocarbons within this onshore environment. The particularly formations of interest comprises of the Prince Albert and the Whitehill of the Lower Ecca group, located within the southern tip of the Laingsburg subbasin. The Prince Albert consists of siliceous shale, whereas the Whitehill is made up of very fine grained black shale that has been weathered white. These sedimentary rocks are important for hydrocarbon exploration research due to the fact that it is found onshore and has not been altered by faulting, fracturing and metamorphism. The present research work deals with interpreting and distinguishing the different type of rock lithologies, to identify the source rock zones and organic matter within the Whitehill and Prince Albert formations. This will be achieved by utilizing different geochemical analysis (such as XRD, XRF, rock eval pyrolysis, vitrinite reflectance, TOC and SEM) to assess the maturity and the quality of the source rocks.
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Mineralogy of the Middle Group Chromitite Cumulates at the Tweefontein Chrome Mine Section, Central Critical Zone, Eastern Bushveld Complex
Authors C.T. Mphatse, C.D.K. Gauert, E. Denge and M. Maluma.The understanding of the silicate mineralogy in the Middle Group chromitite section of the central Critical Zone at Tweefontein in the eastern Bushveld Complex south of Steelpoort is essential for the investigation of the genesis of the cumulate rocks; in particular the crystallization history of the cumulus minerals and the development of the interstitial liquid are considered to be key parameters controlling the PGM distribution in those mafic rocks. The detailed ongoing investigation of the textural relationships and the mineral chemistry of the rock forming minerals may therefore assist in explaining the PGE distribution. Vertical geochemical and modal mineral distribution patterns are prime indicators of magmatic system conditions. The investigations will help to better understand the PGE distribution in a dynamic ultramafic to mafic system on the theoretical side, and will characterize the possibly variable PGE patterns of the different Middle Group chromitite sections within the Bushveld Complex. Practical conclusions such as PGE abundances and their occurrence in various minerals, as well as grain sizes and textures relations relevant for liberation are important for economic extraction processes.
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Rapid Mesozoic Thermal and Chemical Modification of the Rehoboth Terrane and Kaapvaal Craton from Broadband Magnetotellurics and Xenolith Geochemistry
Authors Mark R. Muller, Alan G. Jones, Rob L. Evans, Herman S. Grütter, Chris Hatton, Xavier Garcia, Mark P. Hamilton, Marion P. Miensopust, Patrick Cole, Tiyapo Ngwisanyi, Dave Hutchins, C.J.S. Fourie, Hielke A. Jelsma, Shane F. Evans, Theo Aravanis, Wayne Pettit, Susan J. Webb, Jan Wasborg and the SAMTEX TeamA 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.
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Exploring Exploration Play Models with FTG Gravity Data
Authors Colm A. Murphy and Jade L. DickinsonExploration play models are employed by mineral and hydrocarbon exploration companies to establish and help explain the geological setting of their targeted resource. These models vary from salt domes to structural fault blocks, from igneous intrusives such as dykes and sills to kimberlite pipes. Such geological models are based on geological observations that are enhanced through the usage of geophysical data.
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The Proposed Use of Seasonal Forecasts to Improve Maize Production in the Free State
Authors K.M. Nape, A.S. Steyn and S. WalkerClimate variability is one of the major causes of instability in crop production, especially in semi-arid regions where high variability of rainfall results in uncertainty of water availability for rainfed farming. Improvement of rainfall predictions at a 1-3months lead-time can give a benefit in South Africa due to the high contribution from the agricultural economy. If rainfall predictions are available in time, strategic management decisions can be adjusted to reduce impacts and take advantage of favourable conditions. However, this has not been applied to maize in the Free State. The aim is to use the long-term climate data in a locally tested crop simulation model (Agricultural Production Systems Simulator Model (APSIM)) to generate a range of maize yields. The study area is quaternary catchments along Modder-Riet rivers using different arable soils. APSIM will predict maize yield under various management strategies (fertilizer applications, plant density, planting dates, cultivar types, etc) to identify optimal yields. These outputs will be assessed with two 3-month rainfall forecast periods for the maize growing season (6 possible combinations). The comparative advantage of maize production using seasonal rainfall forecasts will be evaluated against standard practices. This information could be incorporated into a decision support system based on the financial benefit of maize production using the seasonal rainfall forecast each year as an input. The success of the crop yield forecasting application strongly depends on the crop simulation model’s ability to quantify the influence of weather, soil and management conditions on crop yield. Wise utilization of the seasonal rainfall-crop model information by farmers, agribusiness and policy makers could contribute substantially towards achieving sustainability in crop production.
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Sequence Stratigraphic Characterization of Petroleum Reservoirs in Block 3013, Deep Water Orange Basin, South Africa
Authors Emmanuel N. Nformi and Reginald Domoney“What’s next” for hydrocarbon exploration in South Africa’s Frontier Basin- the Orange Basin? Remaining one of the largest under explored basins in the world, (Pickford, 2001), exploration has concentrated on the shelf, in water depths of under 500m with numerous gas/condensate discoveries and one oil discovery. The potential of the deep water is so far untested, with clear indications that suitable reservoirs, source rocks and traps exist. This research in an attempt to show that the lowstand reservoir components (often developed in down dip deepwater and slope paleoenvironments) of the Orange Basin should hold unexplored/untapped massive hydrocarbon resources. It is geared at exploration Play Analysis of the deepwater Orange Basin of South Africa from a Sequence Stratigraphic Perspective. A modus operandi is developed which uses the integration of a range of tools and techniques including sequence stratigraphy and seismic reflection analysis. These are in turn linked with core and outcrop study/analyses of the exceptionally exposed Permian submarine fans (3 and 4) of the Tanqua sub basin (Karoo Basin) to constrain the range of possible fan types, reservoir architecture and pinch out which are very valuable in appraisal, development and production.
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Measurement of Electrical Properties of Bushveld Complex Rocks for Assessment of Radar Performance
Authors B. Ngwenya, M.T. Mafiri and P.G. SefaraA vector impedance meter was used to measure the complex impedance of samples from Bushveld complex (BC) Mines for frequencies between 1 MHz and 64 MHz. The samples were obtained from Rustenburg and Boschfontein Platinum Mines. The obtained impedance magnitude and phase angle data were imported into the Winpro computer program, resistivity and relative dielectric constant values were then computed for each frequency setting. The frequency range within which the measurements were done is very low for GPR, but ideal for borehole radar (BHR). From the recently done electrical property studies, there is sufficient dielectric contrast between chromitite and Merensky reef, and host rocks such as norites and anorthosite, which was predicted to lead to good radar reflection signals. The hosts have high resistivity values, implying low radar signal attenuation or a longer radar range.
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Investigation of Techniques to Determine Astronomical Aeeing Conditions at Matjiesfontein
Authors M. Nickola, R. Botha and W.L. CombrinckA new fundamental space geodetic observatory for South Africa has been proposed. Matjiesfontein in the Karoo has been identified as a suitable site for locating the proposed new fundamental space geodetic observatory. Lunar Laser Ranging (LLR) is one of the space geodetic techniques to be hosted on-site. LLR requires optical seeing conditions of ~ 1 arc-sec resolution level for a site to be considered suitable. Seeing quality for various locations on the Matjiesfontein site has to be measured to determine the most suitable location for the LLR. Investigation revealed that the following are feasible techniques to determine seeing quality at the Matjiesfontein site: double star separation, Light Detection and Ranging (LiDAR) and automated seeing monitor. Atmospheric turbulence in the boundary layer contributes significantly to the degradation of seeing quality. Atmospheric boundary-layer structure and behaviour may be simulated by a turbulence-resolving numerical model, such as the Large Eddy Simulation (LESNIC) model. The model’s predictions will be compared with the quantitative seeing measurements to determine whether LESNIC is suitable for modelling seeing conditions as well as to fine-tune the model to deliver more accurate seeing predictions.
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The Mount Cameroon Volcano, West Africa: an Active Link Between Recent Eruptives and Mantle Signatures of the Deep Past Beneath the Margins of Africa
Authors M.S. Njome, C.E. Suh and M.J. de WitMount Cameroon, a 4095 m high stratovolcano is arguably the most active volcano in Equatorial West Africa, with seven eruptions during the last century. It is the only active member of the 1600 km long volcanic belt – “Cameroon Volcanic Line (CVL)” - with a history going back ~ 80 Ma at the initial opening of the Central Atlantic Ocean during the Cretaceous. In order to decipher recent petrogenetic and geotectonic evolution of the CVL at this volcano, Lava samples of unknown ages but older than all 20th century lavas are investigated for their mineral chemistry and whole rock geochemistry and compared with the 20th century lavas that have been the only focus of petrological investigations for the past three decades. The data show all lavas as within plate and lava types (basalt, basanite/trachy-basalt, hawaiite and basaltic trachy-andesite) indicating these historical eruptions involved even more evolved magmas than those of the 20th century. The lavas are nepheline normative and show an alkaline affinity associated with rift-graben structures, fed from fissures and central vents. Most samples are olivine, clinopyroxene and plagioclase feldspar phyric with additional Fe-Ti oxide phenocrysts. Mineral chemistry data show the compositional range of olivine for older lava samples to be very wide (Fo58%-84%) and a broader plagioclase composition extending to intermediate andesine, a composition which has not been reported for any 20th century lavas. Despite these differences, primitive mantle normalized trace element spidergrams show similar pattern for these older lavas as the 20th century lavas, similar to OIB, confirming they all have a common mantle source of HIMU type. Thus, whilst the precise origin of the CVL is still disputed, it is clear that its mantle source area is not a transient plume. This has major implications for understanding mantle processes marginal to evolving passive Atlantic margins.
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Magnetotelluric Measurements Across the Southern Barberton Greenstone Belt: Data Analysis
Authors A. Nube, U. Weckmann, O. Ritter, X. Chen, J. Deacon, S. MacLennan, L. Moodley, M. DeWit, G. Willkommen, R. Barth, R. Streich and K. TietzeThe Kaapvaal Craton of South Africa is one of the oldest well-preserved continental fragments on our planet and thus is a key area for studies of geodynamic processes of the early Earth. One major controversy concerns the importance of plate tectonic processes in Archean times and the time when this may have been first initiated. Several potential ancient suture zones have been identified at the surface within the Barberton greenstone Belt, and these provide an ideal natural laboratory to test for possible subsurface remnants of mid-Archean plate tectonic processes on lithospheric scale. Within the framework of the German-South African geo-scientific research initiative Inkaba yeAfrica, a high resolution magnetotelluric (MT) field experiment, ELIBABA, was carried out in April/May 2009 in the Barberton/Badplaas area, eastern Mpumalanga, RSA. A 120 km long profile and two complimentary shorter 60 km long profiles with nearly 100 MT sites provide a good areal coverage of the Barberton suture and its complex geology. Strong cultural electromagnetic noise, possibly originating from nearby mines and the DC railway system, is present in the entire area of investigation. As this man-made noise is much larger than the natural electromagnetic signal, which we use to calculate the magnetotelluric transfer functions, advanced data processing schemes have to be used to obtain the cleanest possible sounding curves. This is of major importance for all later analysis steps as we have to make sure that our impedance tensor represents the conductivity structure of the subsuface and does not mirror the electromagnetic noise. We present first results of a standard data analysis in comparison with the remote reference technique and give an outlook on other approaches aiming to improve the data quality
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Oil Sands Exploration in Ijebu-Imushin using Magnetic and Electrical Resistivity Methods
Authors R.K. Odunaike, G. C.Ijeoma, R. O. Edigbe and A. H. BabatopeThere has been tremendous interest in the exploration and production activities of readily available alternatives to conventional oil. Oil seeps observed in Ijebu-Imushin, Ogun State, south-western Nigeria, served as an indication of the occurrence of oil sands – a non-conventional hydrocarbon resource – in the area. Electrical and ground magnetic geophysical survey techniques were thus employed to map the occurrence of the oil sand deposits in the study area as well as to determine the depth to the basement in order to obtain information on the subsurface for exploitation activities. Three vertical electrical soundings and 2-D electrical imaging along a single profile were carried out using the Schlumberger and Werner configurations, respectively. Modelling the likely subsurface structures from the measured magnetic profiles indicates a likely maximum depth to basement of 300m across the study area. The constructed strata from the electrical methods revealed that oil sands deposit are likely to be present and substantial in the south-western part of the study area. The deposit appears to commence from a depth of about 2 m, extending to a depth of approximately 40 m in this part of the study area.
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