Theses and Dissertations (Geology)http://hdl.handle.net/2263/324652024-03-29T15:36:30Z2024-03-29T15:36:30ZPrincipal component analysis of trace element data from the Upper Zone of the Bushveld Complex : constraints on possible tectonic provenancehttp://hdl.handle.net/2263/913452023-11-27T07:45:18Z2023-01-01T00:00:00ZPrincipal component analysis of trace element data from the Upper Zone of the Bushveld Complex : constraints on possible tectonic provenance
The Kaapvaal Craton in South Africa is characterised by ultramafic to mafic complexes, and several mafic intrusions are associated closely with different sections of the craton. The focus of this research is the Transvaal basin in the Kaapvaal Craton that hosts the Bushveld Complex. This complex is the most extensive mafic layered intrusion on Earth, with the magmas ranging from Fe-rich to Si-rich. The extensive body of research on this area is a good foundation for the current study, which focuses on the Upper Zone and upper Main Zone (UUMZ) of the complex. The Bushveld Complex is endowed with rich mineral deposits, lending it robust economic significance, allowing substantial contributions to the global economy through various avenues relating to mineral processing and distribution.
Objectively, this research project seeks to provide tectonic constraints on the origin of the magma emplaced in the UUMZ through geochemical analyses of trace elements and rare earth element (REE) data from Bierkraal boreholes (western limb) and Magnetite Layer 21 (eastern limb), respectively. In this research approach, the geochemistry of basaltic rocks is considered a predictive indicator in determining the likely tectonic setting in which the parental magma originated. A global database of basaltic rock data was employed for this project, namely the GEOROC database, which was subdivided according to tectonic settings (convergent plate margin, oceanic island, submarine ridge, and oceanic plateau) for comparing the geochemical signatures against that of the Bushveld Complex. The overall data were analysed following a multidisciplinary approach, i.e. combining geostatistics and programming. Principal component analysis (PCA) was conducted of the Bierkraal trace element data (sampled in the western limb of the complex) by employing various software applications to generate a probability distribution function of the variables, i.e. the trace elements in this context. Initially, PCA identifies the elements that impart the most significant variation to the dataset. These elements function as indicators and identifiers of specific geological and chemical processes.
Overall, the geochemical data from the Bierkraal area and those from Layer 21 are crucial for narrowing down the potential tectonic settings exhibiting similar signatures. The settings and locations most synonymous to those of the Bushveld appear to be those of the Kaula and Nihau islands of Hawaii. In addition, Hawaii data exhibit more depletions in elements such as Nb and Y relative to those of the UUMZ of the Bushveld Complex. The same data show overlaps with data from the Fiji and Tonga islands. These oceanic island-island arc settings are influenced primarily by mantle hotspots/plumes. On the other hand, the REE apatite data show a more generalised overlap with most identified tectonic settings within arc-related settings. The geochemical signatures showing the most similarity are those from the lower 300 m segment of the Upper Zone, characterised by multiple magnetite layers, and those from the East Scotia Ridge spreading centre, located approximately 1 288 km to the east of the tip of South America. This ridge is a back-arc tectonic environment associated with diverging plate motions and subsequent rifting, allowing molten rock to push upward and build new crust. Both geochemical signatures from the Bierkraal trace element data and REE apatite data can be related to an enriched magmatic source (i.e. E-MORB). Conventionally, an enriched geochemical signature is associated with magma derived from the lower parts of the mantle. However, taking the geological location and age of the Bushveld complex into consideration, the E-MORB geochemical signature identified in the Upper Zone could be created by the melting of Archaean crust during the upwelling of depleted (N-MORB) magma.
Dissertation (MSc (Geology))--University of Pretoria, 2023.
2023-01-01T00:00:00ZPetrography and geochemistry of hydrothermal breccias hosted in the Schrikkloof Formation (Rooiberg Group), north of Modimolle, South Africahttp://hdl.handle.net/2263/910102023-12-19T09:32:26Z2023-01-01T00:00:00ZPetrography and geochemistry of hydrothermal breccias hosted in the Schrikkloof Formation (Rooiberg Group), north of Modimolle, South Africa
The Schrikkloof Formation, composed of rhyolites, tuffs and hydrothermal breccias, is the youngest rhyolitic volcanic sequence of the Rooiberg Group of the Bushveld Igneous Complex and is known to host polymetallic Sn-F-REE. The aim and objective of this research is to understand whether the hydrothermal brecciation in the upper Schrikkloof Formation is associated with ore forming processes or not. The study area is located approximately 20 km north of Modimolle and a total of 30 rock samples (7 rhyolites, 10 tuffs, 12 hydrothermal breccias and 1 vein) was collected from outcrops. These samples were sent for petrography, XRF (major element analysis), ICPMS (trace element analysis), SEM-EDX analysis (ore mineralogy).
Geochemical results (REE diagram and Rb vs Nb+Y) suggest that the Schrikkloof Formation was derived from melting of the continental crust and was emplaced in an intra-cratonic (within-plate) tectonic setting. The sparsely porphyritic and glassy textures of both rhyolites and tuffs, respectively, in the Schrikkloof Formation indicate a subaerial environment.
The hydrothermal breccias are particularly hosted within tuffs rather than in rhyolites, perhaps because of competency contrast. Hand-specimen and petrography observations suggested that both tuffs and rhyolites underwent varying degrees of hematitisation and sericitisation alterations.
In addition, results also indicated that hydrothermal breccias are predominantly characterised by silica-rich (SiO2 > 70%) clasts cemented by Fe-rich veins (Fe2O3 > 80%). The clasts are mainly composed of quartz and K-feldspar, whereas the cement consists of hematite associated with anglesite (PbSO4) and monazite ((Ce,Nd,La)PO4). The Gresens’ and Grant’s mass balance approach results suggest that the hematitisation process is associated with the overall gain of Pb-Zn-Ce-Nd-La in hydrothermal breccia and hematitised tuffs. In conclusion, hydrothermal breccias are associated with Pb-Zn mineralisation and this may suggest that there is a concealed Pb deposit.
Thesis (MSc (Geology))--University of Pretoria, 2023.
2023-01-01T00:00:00ZA parametric investigation on the shear strength and bearing capacity of Cenozoic Berea Red Sand with geosynthetic reinforcementshttp://hdl.handle.net/2263/891802023-09-14T10:00:14Z2021-01-01T00:00:00ZA parametric investigation on the shear strength and bearing capacity of Cenozoic Berea Red Sand with geosynthetic reinforcements
The use of Berea Red sands can be seen extensively among civil infrastructure
particularly along the eastern coast of South Africa. These cohesive soils vary in colour,
composition, and strength. Despite the understanding of limited works being published on the
geotechnical properties on Berea Red sands as well as the implementation of reinforcing agents
to improve it, this study was undertaken to investigate the bearing capacity and shear strength
of Berea Red sands with and without reinforcing agents. In addition, the concept of reinforcing
materials was investigated with the probability of improving the Berea Red sands regarding
the abovementioned properties, thereby displaying the novelty of this study. Deformation
behaviour under an increasing compressive load of 100kPa, 200kPa and 300kPa was
implemented through a suite of consolidated undrained triaxial tests. The triaxial tests provided
an appropriate technique to study the effects of stress and strain correlation as well as in
obtaining the parameters needed to calculate bearing capacity and shear strength. The triaxial
tests compared the behaviour of Berea Red sands under reinforced and unreinforced conditions.
The implementation of two different reinforcing parameters were investigated and compared
with each other as well as with the original unreinforced test results. The two reinforcing agents
used resembled that of a diamond mesh and a mosquito net. Different configurations and layers
of reinforcement were implemented in the triaxial tests to better study its contribution and
influence on the bearing capacity and shear strength of Berea Red sands. The Berea Red sand
properties of bearing capacity, shear strength and strength ratio increased by the
implementation of reinforcing agents as well as the increase in reinforcing layers with the 4
layer diamond mesh exhibited the best strength properties when compared to unreinforced
samples and 2 layer reinforced samples, across all confining pressures (100kPa, 200kPa and
300kPa).
Dissertation (MSc (Engineering Geology))--University of Pretoria, 2021.
2021-01-01T00:00:00ZSedimentology, palaeoenvironment and structural interpretation of the Cretaceous SW Anambra Basin, Nigeriahttp://hdl.handle.net/2263/882162023-09-14T09:24:23Z2022-08-01T00:00:00ZSedimentology, palaeoenvironment and structural interpretation of the Cretaceous SW Anambra Basin, Nigeria
The Inland Anambra Basin of Nigeria, formed on the western segment of the Lower Benue Trough, represents the sag phase of the Trough. Its basin infill comprises shallow to marginal marine and freshwater sedimentary clastic deposits of the Cretaceous to Paleogene age. The basin forms part of the larger rift systems of sedimentary basins of the West and Central African Rift Systems (WCARS), a geological chain of faulted and rifted structures that are genetically related. An important part of this study is to investigate the paleosedimentary history of the basin, paleoclimatic implications, paleowater depth, subsurface structures, formation of source beds, petroleum potentials, and evidence for the genetic link between the Anambra Basin and the Benue Trough and other WCARS basins. In order to address this scientific contribution, an integration of multi-proxy tools involving sedimentary geochemistry, mineralogy, organic petrography, rock evaluation, and satellite gravity survey was used in this thesis to provide robust data and new insights.
Satellite-derived gravity data based on the total horizontal derivative technique records anomalous Bouguer values ranging from -58 and +28 mGal in generic directions of NE-SW and NW-SE, and the CRUST 1.0 model reports a Moho depth of 37 km. Seven high-anomaly zones (HR1-HR7) and four low-anomaly areas were identified in the research area (HL1-HL4). Additionally, the sedimentary basin depth ranged from 3.5 to 5.0 km, indicating adequate depths for source rock formation and hydrocarbon accumulation. Furthermore, all Cretaceous and Paleogene Formations were influenced by the primary structural trends that dominated the basin's formation history.
The transgressive units of the Nkporo, Mamu and Imo Formations in the western segment of the basin from subsurface data revealed dominantly warm, humid tropical paleoclimates with high rainfall in the Late Cretaceous-Paleogene epoch, which corresponds to geologic events in WCARS Cretaceous basins in West Africa. Thus, the geologic record in West Africa indicates intense precipitation and high temperatures during the Cretaceous. The paleoenvironment was reconstructed as predominantly brackish to shallow-marine with some freshwater incursions. Deposition under an oxic environment is detected using a combination of paleoredox markers. On the other hand, anoxic conditions only occurred infrequently in the study area. The presence of wavy laminations in the mudrocks reveals receding seawater and strong paleohydrodynamic conditions. In addition, poor to medium primary productivity was recorded due to terrestrial clastic
influx and hydrodynamic settings. Ultimately, the southwestern Anambra Basin is characterized by shallow sea deposits influenced by strong hydroenergy circulation.
Furthermore, a high-resolution petroleum investigation suggests that the source rocks have a high potential for conventional gaseous hydrocarbons. An integrated approach based on palynofacies, maceral data, and rock eval interpretations supports type III kerogen in a marginal thermal stress stage. The results of this study contrasted favorably with other Cretaceous WCARS basins and showed that type III kerogen predominated. The basin's northern portion shows good shale gas potential. Finally, shallow marine to marginal marine transgressive, maximum flooding surface, and highstand deposits were detected in this study. The Anambra Basin and the other WCARS basins are genetically linked, as evidenced by similarities in paleoweathering, paleoclimate, paleowater depth, paleosalinity, paleoredox conditions, palynofacies assemblage, and structural trends, despite differences in sediment origin, paleogeographic positions, and the exposure of some WCARS basins to thermal fracture and crustal upheaval.
Thesis (PhD (Geology))--University of Pretoria, 2022.
2022-08-01T00:00:00Z