Crustal structure beneath southern Africa and its implications for the formation and evolution of the Kaapvaal and Zimbabwe cratons,

Abstract. The formation of Archean crust appears to involve processes unique to early earth history. Initial results from receiver function analysis of crustal structure beneath 81 broadband stations deployed across southern Africa reveal significant differences in the nature of the crust and the crust-mantle boundary between Archean and post-Archean geologic terranes. With the notable exception of the collisional Limpopo belt, where the crust is thick and the Moho complex, the crust beneath undisturbed Archean craton is typically thin (∼ 35-40 km), unlayered, and characterized by a strong velocity contrast across a relatively sharp Moho. This crustal structure contrasts markedly with that beneath post-Archean terranes and beneath Archean regions affected by large-scale Proterozoic events (the Bushveld complex and the Okwa/Magondi belts), where the crust tends to be relatively thick (∼ 45-50 km) and the Moho is complex

Geology (Fundamental Earth Science A/B): GLG 111

Geology (Fundamental Earth Science A/B): GLG 111, BSc main examinatin June 2011

Geology (Economic Geology, Geophysics): GLG 511

Geology (Economic Geology, Geophysics): GLG 511, BSc (Hons) examination June 2011

Geology (Mining and Exploration Geology, Mineralogy, Petrology): GLG 512

Geology (Mining and Exploration Geology, Mineralogy, Petrology): GLG 512, degree exmianation June 2011

A geophysical and hydro physico-chemical study of the contaminant impact of a solid waste landfill (swl) in King Williams’ Town, Eastern Cape, South Africa

Electrical resistivity imaging (ERI) surveys and physico-chemical analysis were carried out on a solid waste landfill (SWL) in Eastern Cape, South Africa to assess the impact of leachate pollution on groundwater quality. 2-D resistivity imaging was done across three profile lines (A, C and E) on the landfill. Physico-chemical properties of water samples from the leachate pond and boreholes (BH1 and BH2), located between 80 m to 200 m from the edge of the landfill were analysed. The results revealed groundwater contamination to a depth of about 75 m,well within the aquiferous zone. High electrical conductivity (EC) and total dissolve solid (TDS) values observed in the groundwater samples indicate a downward transfer of leachate into the groundwater. The difference in EC and TDS values for BH2 and BH1 (9892 μS/cm/ 4939 mg/L and 6988 μS/cm/ 3497 mg/L respectively), indicated that concentration of contaminants increased towards the centre of the landfill The direction of flow of the leachate is towards the southwestern part of the landfill. In the absence of a leachate recovery system, the uncontrolled accumulation of leachate over time at the landfill will pose a threat to the groundwater quality, hence the need to improve waste management practices in the study area to mitigate the effects of pollutio

Contaminant Delineation of a Landfill Site Using Electrical Resistivity and Induced Polarization Methods in Alice, Eastern Cape, South Africa

A combination of electrical resistivity and induced polarization methods were applied to a solid waste landfill in Alice, Eastern Cape, South Africa to delineate the lithologic layers and locate possible leachate plumes. Resistivity and IP data were collected along six profiles; VES on two and the dipole-dipole configuration was used in the rest four. The result shows a 4-layered earth system with a shallow depth to the top of the bedrock (<10 m). Contaminants ranging from unsaturated waste with high ion content to dense aqueous phase liquid contaminants, characterized by low resistivity (34–80 Ohm-m) and low chargeability values (0.05–5.75 ms). The contamination was interpreted based on resistivity/IP anomalies considering the background geology. The shallow bedrock indicated a low risk to groundwater contamination because of its competent nature from its geology, and characteristic high resistivity values (≥1000 Ohm-m). However, the steep nature of the landfill terrain due to its location at the foot of a vertical slope favours the rapid migration of the contaminants into the immediate vicinity of the landfill. The construction of containment structures such as waste cells will help in enhancing effective waste management practices in the landfill

A magnetotelluric model of the Mana Pools basin, northern Zimbabwe

The Mana Pools sedimentary basin lies within the Zambezi mobile belt in northern Zimbabwe. New and preexisting magnetotelluric data and the available seismic reflection data are used to constrain the basin structure and the depth to the electrical basement. Long-period magnetotelluric (LMT) data were collected at five stations along a 60 km north-south profile across the Mana Pools basin and onto the southern escarpment. These data augment an existing audiofrequency (AMT) data set from 11 sites in the same area. The subsurface apparent resistivities measured at periods sampling the basin are very low (a few Ωm). After processing both data sets, the estimated impedance tensor is decomposed, showing that the resistivity structure of the Mana Pools basin can be modeled two dimensionally. The ρ+ algorithm is used to show that there is no systematic offset in magnitude between the AMT and LMT data sets before they are combined. Minimum structure resistivity models of the Mana Pools basin compare well with the information from reflection seismic data and support its previous description as a half graben basin of ∼7 km depth. The excellent conductor in the Mana Pools basin is quite different to those seen elsewhere in the orogenic belt in that it is a feature of the sedimentary fill rather than the basement. The resistivity of the basement is low but no localized good conductor is observed; these low resistivities may result from a high degree of either chemical or tectonic alteration to the underlying rocks due to metamorphic processes and tectonic disruption during rift formation