In 1964, W.Q. Kennedy suggested that the crust of Saharan Africa is different from the rest of Africa. To date, the geologic evolution of this region remains obscure because the age and composition of crystalline basement are unknown across large sectors of the Sahara. Most of Africa comprises Archaean cratons surrounded by Palaeo- to Mesoproterozoic orogenic belts, which together constitute Africa’s three major shields (the Southern, Central and West African Shields), finally assembled along belts of Pan-African rocks. By contrast, central Saharan Africa (5.3x106 km2), an area just over half the size of Europe, is considered either as a Neoproterozoic region constructed of relatively juvenile crust (0.5 to 1.0 Ga), or as an older (North African) shield that was reactivated and re-stabilized during that time, a period commonly referred to as “Pan African”. Here, using U-Pb zircon age determinations and Nd isotopic data, we show that remote areas in Chad, part of the undated Darfur Plateau stretching across ¾ million km2 of the central Sahara, comprise an extensive Neoproterozoic crystalline basement of pre-tectonic gabbro-tonalite-granodiorite and predominantly post-tectonic alkali feldspar granites and syenites that intruded between ca. 550 to 1050 Ma. This basement is flanked along its western margin by a Neoproterozoic continental calc-alkaline magmatic arc coupled to a cryptic suture zone that can be traced for ~2400 km from Tibesti through western Darfur into Cameroon. We refer to this as the Central Saharan Belt. This, in a Gondwana framework, is part of a greater arc structure, which we here term the Great Central Gondwana Arc (GCGA). Inherited zircons and Nd isotopic ratios indicate the Neoproterozoic magmas in the central Sahara were predominantly derived from Mesoproterozoic continental lithosphere. Regional deformation between 613 to 623 Ma marks the onset of late alkaline granite magmatism that was widespread across a much larger area of North Africa until about 550 Ma. During this magmatism, the region was exhumed and eroded, leaving a regional peneplain on which early Palaeozoic (Lower-Middle Cambrian) siliciclastic sediments were subsequently deposited, as part of a thick and widespread cover that stretched across much of North Africa and the Arabian Peninsula. Detrital zircons in these cover sequences provide evidence that a substantial volume of detritus was derived from the central Sahara region, because these sequences include ‘Kibaran-age’ zircons (ca. 1000 Ma) for which a source terrain has hitherto been lacking. We propose that, in preference to calling the central Sahara a “ghost” or “meta” craton, it should be called the Central Sahara Shield.

Contact metamorphism along widespread dolerite sills and dykes, emplaced at 182 to 183 Ma through the sedimentary host rocks of the Karoo Basin, triggered devolatilization of carbon-rich shales of the Lower Ecca Group. Hornfel samples collected from drill cores that intersect dolerite sills were analyzed for mineral phase equilibria, chemistry and porosity to characterize thermal aureoles at various distances from sill intrusions. Andalusite-chiastolite and cordierite porphyroblasts with biotite and muscovite occur within 10 to 20 m of many intrusive contacts. These metamorphic minerals crystallized when host shales attained maximum temperatures ranging between 450 and 600 degrees C. Scanning electron microscopy imaging confirms that the hornfels are compact and that their metamorphic minerals limit porosity along grain boundaries. In few cases intra-mineral porosity occurs within individual crystals such as calcite, andalusite and cordierite. Disequilibrium metamorphic textures such as irregular grain boundaries, and inclusions in andalusite and cordierite reveal that the elevated temperatures were too short-lived to accomplish complete (re)crystallization. Thermal modeling results are consistent with the observed metamorphic mineral assemblages. Gas leakage calculations along a 7 m and a 47 m thick dolerite sill that intrude toward the top of the Whitehill Formation suggest that methane volumes ranging between 8 to 15 Tcf were generated during the sill emplacement. Methane was likely released into the atmosphere through hydrothermal vent complexes that are well preserved in the western Karoo Basin. If such loss was widespread across the entire basin, the implications for paleoclimate change and preserved shale gas reserves in the Karoo Basin of South Africa would be significant.

New field mapping has discovered numerous sections of pillow lavas with hyaloclastites at the lowest levels of Jurassic Karoo volcanic sequences across Lesotho and South Africa. Vesicularity (content and size) and geochemistry of the ca. 1 to 50 m thick pillow lavas sequences presently preserved at 1 670 to 2 150 m asl reveal they originated below 500 m of water. Most of the initial 87Sr/86Sr ratios of the pillow lavas scatter around ca. 0.708, which is also the value of Jurassic seawater. There is an increase in the δ18O values concomitantly with increasing alteration, a well-known feature at low-temperature when marine basalts alter to high-δ18O bearing minerals, such as clays and zeolites, stripping 18O by mass balance from seawater. This feature, combined with element behavior of the most altered samples, as well as the Sr-isotope signatures, suggest that the Karoo pillow lavas and hyaloclastites most likely altered under low-temperature conditions in seawater. Geochemistry of the major oxides and trace elements of the Karoo pillow lavas reveal they define tholeiitic basalt with minor basaltic andesite. The pillow lavas define Th/Yb-ratios well above the mantle array indicating derivation from subduction-related components, and their Ti-V relations are similar to mid-oceanic ridge basalt (MORB). The Nd-Sr isotope data for the pillow lavas indicate that the primary magma assimilated ca. 10 to 15% of continental crust. This is consistent with knowledge from mapping that sills and dykes cover close to 50% of the surface geology surrounding the sub-horizontal pillow lava sequences, and from drill-cores that these dolerites reached a minimum crustal depth of ca. 6 km below Jurassic sea level. The Karoo pillow lavas erupted between 186 and 184 Ma in relatively deep seawater of a possible rift system linked to fragmented continental lithosphere surrounded by ocean spreading domains, such as at the open-end of the East African rift across the Afar. By 183 Ma, Karoo volcanics extruded above sea level and after 182 Ma the pillow lavas were uplifted by at least 1 700 m. Thereafter, during farther up warping across the Karoo Large Igneous Province (KLIP), lavas across Lesotho reached heights over 3 500 masl by 140 Ma, and then eroded to their near present heights around 120 to 100 Ma as determined through a number of thermo-chronology and offshore sedimentation analyses. Thus, unlike the volcanics of the Ethiopian LIP, which erupted across continental crust at 2 000 masl ca. 30 to 40 million years prior to extensional tectonism across the Afar triple junction, KLIP reached its highest topography ca. 30 to 40 Myrs after early initiation across a triple junction system well-below sea level. This difference in timing between crustal extension and epeirogeny has implications for geodynamic and geochemical models that trace dispersal across southern Gondwana between Africa and Antarctica.

During the final glaciation and following melting across the Carboniferous/Permian boundary, southern Gondwana experienced an icehouse to greenhouse transition at a relatively high palaeolatitude (ca. 60 degrees). Sediments deposited from around 300 to 280 Ma in the southern Karoo Basin are archives of this transition, but the evolution of their links to the flanking oceans is still a matter of debate. The aim here is to detail the deglaciation history by simulating early diagenetic processes both under melt and marine water conditions. For this, black shale core samples from three wells, which were drilled in the 1960s through the Lower Ecca Group into the Dwyka Group, were analysed for TOC contents, mineralogical composition and textural properties. The data allow extrapolations about the depositional mineralogy and early diagenesis that in turn serve as input parameters for hydrogeochemical models. The imaging and modelling results reveal that the organic carbon-lean shales associated with, and directly overlying the diamictite beds of the Dwyka Group (known as the Prince Albert Formation) can be interpreted as rhythmites (varves?) deposited under freshwater conditions in response to the deglaciation across southern Gondwana during the latest Carboniferous (similar to 300 to 280 Ma). Thereafter, in the early Permian (similar to 280 Ma) the first notable marine influence is revealed by the occurrence of Mg-bearing carbonate precipitates in black shales of the Whitehill Formation of the overlying Lower Ecca Group; and from the hydrogeochemical models. Preferential preservation of organic matter in these shales is interpreted to be due to marine water fluctuations from the south that created stratified water columns of dense anoxic cold bottom systems overlain by lighter freshwater. Directly above the Whitehill Formation, Mn-siderite in rhythmites of the Collingham Formation points to a recurring influx of fresh water from the north. Today, the black shales of the Lower Ecca Group are tight, and thermogenic gas accumulated in inter-particle pores, in intra-particle pores in albite, organic matter and dolomite, or adsorbed on organic matter in the Whitehill Formation. The brittleness of this prospective Whitehill Formation is weakened in places by high contents of chlorite and illite, but to a lesser degree elsewhere due to low contents of carbonate and quartz cements.

The morphological, chemical impurities and carbon isotope properties of diamonds may reveal subtle details of their mantle source and growth characteristics, supporting efforts towards identifying their original place of harvesting. Here we investigate the mantle carbon and nitrogen sources and growth patterns from selected diamonds mined from four kimberlites: macro-sized diamonds from River Ranch kimberlite in Zimbabwe and the Swartruggens and Klipspringer kimberlitic deposits from South Africa, and micro-sized diamonds from the Klipspringer and Premier kimberlite intrusions in South Africa. Type IaAB diamonds are found in all the samples: Type IaB diamonds only occur in samples from the Swartruggens, River Ranch and Premier kimberlites. A single Type II diamond (nitrogen below the detection limit) was also observed in the River Ranch and Premier kimberlites. Both the micro- and macro-sized diamonds from Klipspringer have similar nitrogen contents. Based on the % B-defect, the diamonds from Klipspringer are grouped into low- and high-nitrogen aggregates (i.e. % of B-defect <40% and >56%, respectively) that likely represent two different diamond forming episodes. Time averaged mantle storage temperatures for Type IaAB diamonds are calculated to have been: 1060 degrees C for Swartruggens; 1190 degrees C for River Ranch; 1100 degrees C (low aggregated); and 1170 degrees C (highly aggregated) for Klipspringer, and 1210 degrees C for Premier diamonds. The CL-images of the River Ranch, Klipspringer and Premier diamonds reveal multi-oscillatory growth zones. The carbon isotopic analyses on the diamonds reveal an average delta C-13(VPBD) value of: -4.5 parts per thousand for Swartruggens; -4.7 parts per thousand for River Ranch; -4.5 parts per thousand for Klipspringer; and -3 parts per thousand for Premier. With the exception of the diamond from Premier, the average delta C-13 value of the diamonds are similar to the average delta C-13 value of the mantle (-5 parts per thousand), which is similar to the occurrence of diamonds in the other kimberlites. The internal carbon isotopic variation of individual diamonds from Swartruggens, Klipspringer and Premier are less than 4 parts per thousand. which is similar to the variability of most other diamond occurrences reported from elsewhere in the world. Up to 6.7 parts per thousand internal carbon isotopic variation was observed in a single diamond from River Ranch. The internal carbon isotopic studies the diamonds reveal that the primary carbon in the Swartruggens and Klipspringer was derived from an oxidation of CH4-bearing fluid, whereas in the River Ranch the primary carbon was derived from the reduction of carbonate-or CO2-bearing fluids. The Swartruggens diamonds also reveal a secondary carbon sourced from a reduction of CO2-or carbonate-rich fluid or melt. Diamonds from Klipspringer exhibit a cyclic change in delta C-13 values that reflects fluctuation in a complex mantle perturbation system or periodic change in fugacity of the mantle. Based on this study, we conclude that, in principle, a selected range of diamond signatures might be used to fingerprint their origins: especially when linked to their other physical properties such as a low temperature magnetic signature.

The Karoo region of South Africa is an ideal laboratory to use ambient seismic signals to map the shallow subsurface, as it is a quiet and pristine environment with a geology that is relatively well known. Ambient seismic signals were continuously recorded for a ten week period between August and October 2015. The ambient seismic noise network consisted of two groups of 17 temporary, stand-alone seismic stations each. These were installed in the southeastern Cape Karoo region, near the town of Jansenville. I Jere we present data on the retrieval and coherency of Rayleigh surface waves extracted from the vertical component recordings. We reconstruct and show, for the first time in the southeastern Cape Karoo, estimates of Green's function from cross-correlating ambient noise data between stations pairs, which can be successfully used to image the subsurface. The stacked cross-correlations between all station pairs show clear arrivals of the Rayleigh surface waves. The group velocities of the Rayleigh waves in the 3 to 7 seconds period range were picked and inverted to compute the 2-D group velocity maps. The resulting 2-D group velocity maps at different periods resulted in a group velocity model from approximately 2 to 7 km depth. which shows a high velocity anomaly in the north of the study area, most likely imaging the denser, thick sedimentary basin of the Karoo (Carboniferous-Permian). To the south, the low velocity anomaly could correspond to the overlying Jurassic-Cretaceous sedimentary sequences of the younger Algoa Basin (Uitenhage Group).

Thyspunt is located along the southern coastal margin of the Eastern Cape Province, South Africa, between Oyster Bay and Cape St. Francis (similar to 88 km west of Port Elizabeth). Field observations, thin section analysis, interpretation of geophysics, a review of more than 247 boreholes and the creation of a 21/2 D model are used to investigate the bedrock lithology and structure, stratigraphic contacts, palaeotopography of the Ordovician to early Devonian (485 to 419 Ma) Table. Mountain Group (TMG) and thickness of the Miocene to Holocene (<23 Ma) overburden of the Algoa Group. The northwest-southeast striking bedrock forms part of the regional southeast plunging, north verging Cape St. Francis anticline. Locally, folds plunge gently southeastward at shallow angles, with axial planes dipping steeply southwest or northeast. Lineaments previously interpreted as inferred faults, are here re-interpreted as zones of closely spaced jointing (shatter zones), that show little to no recognisable displacement. The 40 km long, northwest-southeast trending Cape St. Francis fault occurring offshore within 17.5 km of Thyspunt does not continue onshore within the study area. Jointing is pervasive and five joint systems are identified. Faults and joints do not extend into the younger cover deposits of the Algoa Group and are therefore older than similar to 23 Myrs. Interpolation of bedrock elevation points and sections across bedrock reveal four previously unknown northwest-southeast trending palaeovalleys at Thyspunt, Tony's Bay, Cape St. Francis and St. Francis, where the bedrock relief beneath overburden is below present day sea-level. Roughly 450 m northwest of Thys Bay, a 1050 m(2) (area below sea-level) palaeovalley, gently sloping southeast to a depth of 15.5 m below msl, is cut into bedrock of the Goudini Formation. Bedrock is covered by aeolian and marine sequences of the Algoa Group reaching 61 m in thickness. Understanding of the bedrock and overburden characteristics allow greater understanding of where additional design requirements will potentially be required at Thyspunt.

The Karoo Basin of South Africa was explored for conventional oil and gas in the 1960s, and during which 19 boreholes were drilled by SOEKOR-the Southern Oil Exploration Corporation. Ten of these boreholes in the southern part of the basin were deep, c. 2.3 to 5.5 km in depth. Geochemical, petrophysical and petrographic studies on the recovered cores from these drill holes concluded that the lower Karoo sequences were possibly prospective for thermogenic gas across the Karoo region immediately north of the Cape Mountains and south of the main concentration of dolerite intrusions flanking the Karoo Escarpment. Since then, very limited analytical work has been undertaken on these cores to gain new data and to extend the concepts towards potential shale gas plays. In the light of the recent interest in unconventional shale gas potential of the Karoo Basin, we re-examine this SOEKOR data and, together with new petrographic and geochemical analyses on 115 core samples from eight of the deep drill holes, we present new resource estimates of two possible reservoirs with recoverable shale gas of 10 to 50 Tcf (Source Rock 1) and 65 to 400 Tcf (Source Rock 2), respectively.

The Barberton Greenstone Belt (BGB) in South Africa is one of the few well-preserved, albeit deformed and complex volcano-sedimentary remnants from the Paleoarchean, and thus an excellent locality to study the formation and evolution of the early Earth's crust. Due to the significant amounts of resources, especially gold in shear zones, the BGB has been extensively studied by geologists for almost 100 years. While the surface geology is well known, only a few geophysical studies have been conducted to investigate the deeper architecture of the BGB and its granitoid surroundings. Here we describe the results of a Magnetotelluric (MT) survey that was conducted over two field seasons to image the subsurface electrical conductivity distribution of geological units of the southern BGB, and to locate dykes, faults and shear zones that are imprints of subsequent tectonic processes. Specifically, mineralization along the shear zones is predicted to reveal high electrical conductivities, in contrast with highly resistive adjacent mafic to ultramafic rocks. The MT station layout of our survey was planned to allow for 2D and 3D interpretation, although it was expected that the 2D inversion models might not be adequate to reveal the expected complex subsurface geology of the BGB and its surrounding region. However, both 2D and 3D inversion results show electrically conductive structures that appear to correlate well with surface traces of known fault zones such as the Inyoka-Saddleback fault system. High resolution 2D conductivity images along selected profiles suggest that some faults might continue further south into the granitoids of the Mpuluzi batholith, implying that the batholith was emplaced along faults (Inyoka-Saddleback fault system and/or Komati Fault), or that a younger fault cuts across the pre-existing batholith. This is contrasted by 3D models that reveal deep-reaching (>10 km) resistive structures beneath the intrusive bodies within the BGB and surrounding batholiths. These results suggest that the granitoids are not disrupted by shear zones, and may imply that episodes of predominant magmatic emplacement have affected the BGB in large parts. A network of conductive faults, especially in the central part of the BGB, suggests that tectonic processes along shear planes have also shaped the BGB, and may have provided pathways for fluids creating zones of gold mineralization.

Earth systems and landforms are defined by complicated patterns and structures that hold key information for many important naturally-controlled systems (e.g. minerals, energy and natural hazards). A deeper understanding of these systems remains elusive, in part due to the complexity in defining their geometry. Fractal analysis (FA) provides a method of characterising patterns that are seemingly complicated beyond conventional geometry principles. FA has been actively applied to faulted regions in an attempt to resolve multi fracture controlled processes. In this study we apply FA to the Soutpansberg Mountains (SM) to better characterise its extensive fracture network (most notably regional faults) covering many orders of scale, and to test whether the results mimic known geological complexities. In addition, we test whether there is any link between the fractal geometry and the occurrence of Cu-mineralisation and groundwater hot springs. We apply the box-counting technique to determine the fractal dimension (D), lacunarity (LC) to quantify the concentration (density) of fracturing, and test for multifractal (MF) affinity. The results of the FA correspond well with the known complex geology across the SM; areas with higher D-values and an affinity toward MF behaviour correspond to regions of the SM displaying at least two fault orientations with possibly two directions of shear displacement (i.e. normal and transcurrent). In addition, lower LC values correspond to regions of the SM that exhibit a greater degree of faulting. Also, regions with higher fractal complexity relate to areas with the highest concentration of Cu-mineralisation and highest-temperature hot springs. This suggests that principles of fractal geometry play a role in the interconnectivity within the brittle upper crust. We thus confirm that FA can be applied together with regional strain controls to better understand dynamics of natural and induced fracture propagation. and recommend that this be further applied to exploration within the Earth's Critical Zone.

The Lower Ecca Group of the Karoo Basin potentially contains significant unconventional gas, hosted in gas shales, of which the most significant sequence is the organic rich shales of the Whitehill Formation. The Whitehill Formation is directly overlain by clastic and volcaniclastic rocks of the Collingham Formation. Due to the potential for the upward migration of hydrocarbons from the gas-shales it is important to establish the integrity of the overlying formation. Here we report on the mineralogical, geochemical and physical properties of the Collingham Formation to test its ability to act as a cap rock to the underlying carbon-rich, potentially gas-bearing shales of the Whitehill Formation.Fresh core samples from a borehole drilled through the Lower Ecca Group near Jansenville, in the Eastern Cape, South Africa, were analysed for their mineralogical and geochemical content, using thin-section microscopy, XRD, XRF, TOC and SEM. The main rock types of the Collingham Formation contain three pore types (intrapore, interpore and microfractures) that are predominantly nanopores (<1 micron). The small size of pores, low permeability values, and their mineral content suggest that the Collingham Formation formed in a marine environment, subsequently modified through burial and regional metamorphism. Physical properties, determined through mercury porosimetry include porosity, permeability and density. Results show that the large proportion of clay minerals, a low TOC, the fine-grained nature of lithologies, a low porosity, a lack of permeability, a moderate fracturability, average density values, and the laminate nature of the formation, favour it as a suitable cap rock.We conclude that, although the characteristics of the formation favour it as a caprock, and therefore a sealing sequence to the Whitehill Formation, our results apply only to the Collingham Formation affected by the Cape Fold Belt. Further work is needed farther into the basin, to reveal its potential as a regional cap rock.

Research Article| March 01, 2016 Iphakade is Earth Stewardship Science M.J. de Wit; M.J. de Wit AEON-ESSRI, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa e-mail: Maarten.deWit@nmmu.ac.za Search for other works by this author on: GSW Google Scholar P. Booth P. Booth AEON-ESSRI, and Department of Geosciences, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa e-mail: Peter. Booth@nmmu.ac.za Search for other works by this author on: GSW Google Scholar Author and Article Information M.J. de Wit AEON-ESSRI, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa P. Booth AEON-ESSRI, and Department of Geosciences, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa e-mail: Maarten.deWit@nmmu.ac.za e-mail: Peter. Booth@nmmu.ac.za Publisher: Geological Society of South Africa First Online: 20 Nov 2017 Online Issn: 1996-8590 Print Issn: 1012-0750 © 2016 March Geological Society of South AfricaGeological Society of South Africa South African Journal of Geology (2016) 119 (1): 3–14. https://doi.org/10.2113/gssajg.119.1.3 Article history First Online: 20 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M.J. de Wit, P. Booth; Iphakade is Earth Stewardship Science. South African Journal of Geology 2016;; 119 (1): 3–14. doi: https://doi.org/10.2113/gssajg.119.1.3 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search © 2016 March Geological Society of South Africa Two collaborative bilateral Earth System Science Programmes - Inkaba yeAfrica and !Khure Africa - have been active for 12 and 6 years with Germany and France, respectively, and have been generously supported by DST and NRF throughout this time (see www.inkaba.org). More recently the two programmes merged into one as the bilateral spirits of these programmes started to fade. It is therefore timely to move on and establish a South African Programme that can stand on its own, and attract international collaborations on the basis of its indigenous research excellence in... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Cape Fold Belt (CFB) along the southern coast of South Africa contains several tectonic windows that expose low-grade "basement" rocks as inliers that are inferred to be late Neoproterozoic in age subjected to tectono-metamorphism during the Pan African Saldanian Orogeny (ca. 650 to 550 Ma). Whilst a Saldanian tectonic history along the northwest to southeast trending western branch of the CFB has been well documented, such Neoproterozoic deformation along the east-west trending southern branch of the CFB is not established. This work presents new field observations and SHRIMP U/Pb geochronologic data from the Kleinrivier Sequence within the Gamtoos Inlier exposed along the eastern-most known tectonic window, near Port Elizabeth, and which is here renamed the Gamtoos Complex. The study area includes 3 tectonic sequences from the Gamtoos Complex ("pre-Cape") and 2 sequences from the overlying Table Mountain Group of the Cape Supergroup. The lower sequences of the Gamtoos Complex comprise north-east verging thrust packages within a regional antiform, all of which have a common oriented planar tectonic fabric (S-2) coincident with those in the lower Paleozoic rocks. Phyllites from the Kleinrivier and upper Sardinia Bay sequences (spanning the pre-Cape and Cape boundary) are similarly affected by a slaty cleavage (S-1), crenulation cleavage (S-2) and multiple generations of quartz veins. U/Pb data are from zircons of metasediments and igneous rocks from the Gamtoos Complex and from the overlying rocks of the Table Mountain Group. Meta-greywackes of the Kleinrivier Sequence (youngest zircon: 523 +/- 6 Ma) are probably Cambrian in age. However, some units from the Kleinrivier Sequence are intruded by felsic sills with a Concordia age: 530.2 +/- 4.4 Ma and therefore require further U/Pb detrital zircon analyses. Mafic sills and dykes also intrude the Kleinrivier Sequence and were subsequently deformed and contain S-2. Boulder conglomerates in the Sardinia Bay Sequence (youngest matrix zircon: 521 +/- 6 Ma) are separated from the Kleinrivier Sequence by an angular unconformity. It also contains granite-boulders (Concordia age: 530.2 +/- 4.7 Ma), and is overlain by the feldspathic psammites and quartzites of the Sardinia Bay Sequence with zircons as young as 510 +/- 7 Ma (e.g. middle Cambrian). In total, 75% of the detrital zircons from all sequences date between early-Mesoproterozoic and early-Neoproterozoic (ca. 1455 to 852 Ma) and are likely sourced from the gneisses of the Namaqua-Natal province that are known to underlie the CFB, whilst the Neoproterozoic to mid-Cambrian zircons (ca. 828 to 431 Ma) have been sourced from Pan African mobile belts, possibly the Mozambican and/or Saldanian Belts to the east and west, respectively. Such "Pan African" detrital zircons are more prevalent in the Sardinia Bay Sequence and form the dominant component in the Lower Table Mountain Group, suggesting a lesser source influence from the Namaqua Natal Mobile Belt. The conglomerates at Sardinia Bay possibly represent mid-Cambrian rift sequences, similar to the Klipheuwel Group that overlie the Malmesbury Sequence and Cape granites along the western branch of the CFB. The Sardinia Bay Sequence has zircons equivalent to those of the Peninsula Formation (youngest zircon: 516 +/- 5 Ma), and therefore should be linked to represent the lower Table Mountain Group.

New tools and algorithms for geological femote Sensing are developed and verified at test sites throughout the world in preparation of the German hyperspectral satellite Mission (EnMAP), which is an Environmental Mapping and Analysis Program.The aggeneys Cu-Pb-Zn deposit, situated in the arid north western part of South Africa, represents a unique field laboratory for testing these new tools. Here spaceborne hyperspectral data covering the Swartberg, and hyperspectral spaceborne data can be demonkrated, such as the Iron Feature Depth index (IFD), which has recently been proposed for mine waste mapping in the North West Province of South Africa and for gossan detection at Haib River in South Namibia.The work presented here explores the potential of the IFD for gossan mapping and characterization at Gamsberg and Big Syncline, from EO-1 ALI and Landsat-8 OLI data together with mineral maps from expert systems such as the United States Geological Survey (USGS) Material Identification and Characterization Algorithm (MICA), and first results from EnMAPs EnGeoMAP algorithm. Field spectroscopic measurements and field sampling were carried out to validate and calibrate the results from the expert systems and the IFD. This ground truthing is a necessary complementary step to link the results from the expert systems and the IFD to in-situ field spectroscopy.Future mineral exploration initiatives may benefit from the techniques described here, because they can significantly narrow the expensive, exploration activities such as hyperspectral airborne data, field activities and drilling, by identifying the most promising mineral anomalies in an area from the spaceborne data.

We report on geochemical and petrophysical properties of shales from the Prince Albert, Whitehill and Collingham Formations of the Lower Karoo Supergroup, near Jansenville in the Eastern Cape, close to the tectonic front of the Cape Fold Belt. Results are based on two boreholes sited on a southerly dipping limb of a shallowly plunging syncline. Structural, sedimentological, lithological, mineralogical, geochemical and petrophysical analyses provide detailed characteristics that have become the focus of interest for potential shale gas occurrences.The black shales of the Whitehill Formation are composed of quartz, illite, muscovite and chlorite, with lesser plagioclase and accessary pyrite. The Collingham Formation rocks have the largest proportion of quartz, which gives this formation a higher brittleness factor than that of the Prince Albert and Whitehill formations. Mercury porosimetry analyses yield average meso- and macroporosity values of 0.83% for black shales of the Whitehill Formation, confirming that these sediments are tightly packed. Layers of dolomite within the shales have porosities of 2.9%, and pores measuring 1.5 mu m wide.The black shales of the Whitehill Formation have an average total organic carbon (TOC) content of 4.5 weight % whereas the TOC content of shales in the Collingham and Prince Albert Formations is <1 weight %. The elemental composition and relatively higher delta C-13 and delta N-15 stable isotope values suggest that the Whitehill Formation was deposited under anoxic conditions, which led to the preservation of the mixed marine and terrestrial organic matter, whereas the Prince Albert and the Collingham Formations were deposited under oxidizing conditions.High maximum temperature values (Tmax average: 528 degrees C), low overall hydrogen and oxygen index values (all from Rock Eval analyses) and high reflectance measurements on bitumen (BRo= 4%) characterise these sedimentary rocks as over mature. As a consequence, they display few hydrocarbon yields in pyrolysis and thermovaporization experiments, and offer a minor late-gas potential.The main characteristics of black shales in the study area indicate that their overmaturity with respect to hosting gas deposits is attributed to the tectono-metamorphic overprinting during the Cape Orogeny (ca. 250 Ma, Halbich, 1993; Hansma et al., 2013).Rocks of the lower Karoo Supergroup outcropping within the area flanking the northern tectonic margin of the Cape Fold Belt therefore have limited potential for hosting shale gas deposits. This finding has implications for estimates of potential shale gas resources of the Karoo Basin.

Southern Africa displays a high topography but paradoxically exhibits tectonic stability and low denudation rates. Here the present controls on denudation in southern Africa are investigated by comparing maximum denudation rates for Karoo dolerite surfaces in the region, determined from the abundances of cosmogenic noble gas nuclides (3He, 21Ne and 38Ar) in pyroxenes, with the predictions of a climate-dependent weathering rate model. In general, we find an excellent agreement in the value ranges of both datasets (<4m/Myr), and interpret this as evidence that present denudation in southern Africa is weathering-limited and climatically influenced due to an apparent absence of significant regional neotectonic uplift. The onset of this geodynamic coupling is unknown but may be of considerable antiquity, thus allowing for the prolonged tenure of southern Africa's inherited Cretaceous topography.

The basis of this study comprises 540 geochemically analysed samples collected systematically from eighteen stratigraphic sections (2257 m in total length) through the submarine volcanic rocks of the tectonically separated Hooggenoeg, Kromberg and Mendon Complexes in the southwestern part of the Paleoarchean Barberton Greenstone Belt. The lavas are predominantly high- to low-Mg tholeiitic basalts but include minor komatiite and komatiitic basalt. They are non-deformed and preserve delicate igneous textures, but have been allochemically altered and regionally metamorphosed. Comparison of pillow cores and rims, samples from massive flows and interelement correlations demonstrate that Ti, Al, Cr, V, Nb, Ta, Zr, Hf, Y, Pb, Th and the REE were relatively immobile during alteration and hence preserve geochemical evidence bearing on the origin and tectonic setting of the lavas.Chondrite-normalized REE patterns are slightly LREE depleted in komatiite to slightly LREE enriched in basalts. MORB-normalized values of non-conservative elements (Cs, Ba, Pb, Th) are high relative to conservative elements (Ta, Nb, Zr, Hf, Y, HREE) in all of the volcanic rocks, particularly those of the Hooggenoeg Complex. Most of the samples exhibit enrichment of Cs and Ba, Pb anomalies and depletion in Nb and Ta, consistent with a subduction-related oceanic environment. With the exception of the lavas of the Hooggenoeg Complex, using primordial mantle (PM) values for normalisation generally subdues the enrichments of the non-conservative elements seen in MORB-normalised multi-element diagrams. However, negative Nb and Ta anomalies relative to La remain significant. High Ba/Th ratios indicate relatively shallow level enrichment of the magma source in large ion lithophile elements by aqueous fluids, whilst enhanced Th concentrations reflect deeper partial melting. Estimated subduction related contributions to Th vary in the ca. 2700 m thick section of the Hooggenoeg Complex and suggest changes in the depth to the subducting slab, which may relate to variation in the subduction angle in the course of ca. 10 million years. epsilon(Nd(T)) values suggest earlier melt extraction and possible incorporation of older crustal material, probably subducted elastic sediments.Our inferred model for the formation of the Upper Onverwacht Suite, based on the lithological and structural development of the lavas and their geochemistry invokes eruption in intra-oceanic back-arc basins and volcanic island arcs. Magmas were generated by variable degrees of partial melting at different depths and temperatures of metasomatised mantle above subducting and dehydrating oceanic lithosphere, and were subsequently modified by fractional crystallization and hybridization. In terms of MORB- and PM-normalised multi-element patterns, as well as Nd-isotope ratios, the volcanic rocks of the Onverwacht Suite are comparable with the west Pacific-Indonesian arc systems.

Soil erosion has been considered a major problem in South Africa since the early 20th Century, yet the degree to which rates of soil erosion may exceed rates of soil production has not been well constrained by previous studies. Here we present 22 cosmogenic He-3-based maximum denudation rates of Karoo dolerite bedrock surfaces, and interpret these values as local rates of soil production. These generally low soil production rates (<4 m/Myr measured over a 10(5) yr timescale) are in all instances lower than various literature estimates for the corresponding rates of soil erosion in the same catchments, by up to two orders of magnitude. This significant contrast between long term rates of soil production and short term rates of soil erosion suggests that current agricultural practices are unsustainable under prevailing geological conditions.

Two geophysical onshore-offshore lines on the southern margin of Africa form the Agulhas-Karoo Geophysical Transect (AKGT) and cross prominent geological features such as the Karoo Basin, Cape Fold Belt (CFB) and the Beattie Magnetic Anomaly (BMA). Geophysical data acquired along this AKGTransect between 2004 and 2007 within the Inkaba yeAfrica (IyA) framework, provide the platform for constructing a deep crustal section (IyA-200501) for the centre 100 km of the western AKG'r-transect in order to resolve these features at depth. We present a detailed deep crustal model constructed from the joint interpretation of:i. archive data comprising surface geology, aeromagnetic data, nearby deep boreholes, teleseismic receiver functions and regional seismic reflection profiles, andii. line coincident newly acquired high-resolution geophysical data consisting of near vertical seismic reflection data, shallow P- and S-wave velocity data, wide-angle refraction data, high resolution magnetotelluric data and impedance spectroscopy measurements on borehole samples.Our model differentiates four components in the up to 45 km thick crust:1. a similar to 2 to 5 km thick folded Karoo Supergroup, disrupted by low-angle thrust faults rooted in a zone of local decollements in the lower Ecca Group and resting paraconformably on2. a continuous undeformed sub-horizontal similar to 1.5 to 10 km thick wedge of the Cape Supergroup (CSG). This CSG wedge stretches from the Escarpment in the north to the tectonic front of the CFB in the south, and rests on an unconformity that dips about three degrees to the south. The angular unconformity is interpreted as an erosional peneplain that separates the CSG wedge from component3. the similar to 13 to 21 km mid-crust basement below. The mid-crust contains a distinct north-clipping seismic fabric, here interpreted as similar to 1.4 to 1.0 Ga Mesoproterozoic Namaqua-Natal Metamorphic Belt (NNMB) crust. A south-dipping mid-crustal detachment, interpreted as a ductile thrust zone, separates the mid-crust from component4. a highly reflective similar to 10 to 24 km thick lower crust. The latter is interpreted as an older Palaeoproterozoic section of the NNMB (or even Archean cratonic basement), and bounded by a similar to 2 to 5 km thick, highly reflective bottom layer below that lies sub-parallel to a clear Moho. This bottom layer is interpreted as a mafic underplate, metasomatic reaction zone, or lower-crust to mantle transition zone.Collectively the seismic reflection and wide-angle refraction data support an interpretation that the NNIMB mid-crustal layer contains the BMA source, possibly connected to two zones of strong reflectivity: a similar to 10 to 12 km wide northern zone and a similar to 5 to 7 km wide southern zone, both about 5 km thick and 7 to 8 km below surface. We interpret the BMA source to be at least in part, a Namaqua-like massive to disseminated, deformed/metamorphosed stratiform sulphide-magnetite ore body with metasomatic overprint.The seismic reflection and -refraction data support an interpretation that a Pan-African suture zone at the BMA is absent and that instead, the NNMB continues below the CFB tectonic front, probably up to the continental margin and the Agulhas Fracture Zone. The seismic reflection data also supports a thin-skinned tectonic thrust model for the evolution of the CFB without significant fore-deep stratigraphic thickening of the Karoo Basin strata. A compatible tectonic model implies a Palaeozoic collision orogen setting, coupled to a south verging subduction zone much farther south of the CFB. Similarly, the geophysical data support a south clipping subduction zone during the amalgamation of the NNMB in the Mesoproterozoic.Current reconstructions of the Rodinia supercontinent link the NNMB and the Grenville Province of North America across the Grenville-Kibaran orogen. Our seismic section tests this reconstruction through a direct comparison with seismic profiles on the opposite flank of the orogen. Although the once adjacent continental blocks are now 1000s of kilometres apart, the seismic images show a good correlation and support the reconstruction.