3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Integrated strato-tectonic, U-Pb geochronology and metallogenic studies of the Oudalan-Gorouol volcano-sedimentary Belt ( OGB) and the Gorom-Gorom granitoid terrane (GGGT), Burkina Faso and Niger, West Africa(2015-05-06) Tshibubudze, AsinneThe Palaeoproterozoic Baoulé-Mossi domain of the West African Craton in northeastern Burkina Faso hosts numerous gold deposits such as Essakane and Tarpako. Integrated strato-tectonic, geophysical, geochemical, geochronological, regional stratigraphic framework and metallogenic studies of the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane have provided new insight into the geotectonic evolution of the northeastern part of Burkina Faso. This work outlines the structural context and architecture necessary for forming these deposits. In this work, a new strato-tectonic model is proposed for the area by integrating field data and geophysical, geochemical, and geochronological data. The integrated data highlights and characterizes the setting of the Essakane gold mine and gold camp relative to the location of other regional gold deposits, metamorphosed Birimian Supergroup, intrusive rocks and shear zones. Structural, geochemical and geochronological analyses have helped to clarify the geological evolution of the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane during the Tangaean (D1) and Eburnean (D2) orogenies through to the Wabo Tampelse Event (D3). Further to these, zircon U-Pb geochronology data have demonstrated that the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane represent some of the oldest outcropping geology in the Palaeoproterozoic Baoulé-Mossi domain recognised to date. The geochronology and geology suggest that the basement or a pre- Birimian crust to the Birimian Supergroup may be found in the northeast of Burkina Faso. The Eburnean Orogeny in northeastern Burkina Faso is preceded by two phases of deformation (D1-x and D1), and two phases of magmatism. The first, D1-x, is associated with the emplacement of the Dori Batholith at the onset of D1 (2164 – 2141 Ma). D1 ductile-brittle deformation formed F1 folds and discrete high-strain mylonite zones that deformed the Oudalan- Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane during a southwestdirected palaeo-principal compressive stress. The pre-Birimian to Birimian supracrustal rocks and intrusions were regionally metamorphosed during D1 to greenschist to amphibolite facies with development of mineral assemblage of quartz-chlorite-muscovite ± chloritoid to biotite-potash feldspar ± hornblende. D1 is also associated with volcanic arc type calc-alkaline magmatism, producing TTGs enriched in heavy rare earth elements. The Eburnean Orogeny (2130 – 1980 Ma) is characterised by northwest-southeast shortening; it was followed by north-northwest - south-southeast shortening with development of northeast trending sinistral strike-slip faults and shears. D2 brittle-(ductile) deformation is manifested by refolding of F1 by northeast-trending F2, and development of a pervasive northeast-trending S2 to S2-C foliation. Metamorphic grade attained greenschist facies during D2, with development of mineral assemblage of quartz-chlorite-muscovite ± actinolite. The Wabo Tampelse (D3) deformation event is brittle in character and does not significantly affect the regional geological architecture in the study area.Item Geology and geochronology of the Nyl River floodplain sediments, Limpopo province, South Africa(2013-08-01) Colarossi, DebraThe Nyl River floodplain, located in the Limpopo Province, is one of the few active sedimentary basins that exist within the South African interior, providing a unique opportunity to study the effect of climate change on fluvial systems. Progradation of tributary fans into the Nyl/Mogalakwena River has raised the surface by 30 m and forced the course of the river westwards towards the Waterberg. Periods of progradation deposited thick sequences of coarse-grained sediments with sand- to gravel-sized mean grain sizes and coarsely-skewed populations in the distal reaches of the tributary fans. These periods were interspersed with periods of relative non-deposition, when active sedimentation on the fan ceased and shallow lakes (or vleis) developed in the trunk river, resulting in deposition of fine-grained, organic-rich, floodplain sediment layers with silt-sized mean grain sizes and finely-skewed distributions in the extreme outer reaches of the tributary fan. The alternating progradational sequences and non-deposition events produced interlayered floodplain and fan deposits in the furthest reaches of the tributary fans along the banks of the Nyl/Mogalakwena River. Incised river cuts within the Rooisloot tributary fan were dated using OSL and 14C techniques. For OSL samples, the SAR protocol was used to measure the equivalent dose and the burial dose was determined using the CAM and MAM. Emission counting methods, including TSAC, GM-beta counting and HRGS were used to determine the dose-rate. The OSL ages ranged from 99 years to 3884 years, constraining the sampled deposits within the late Holocene. Although the 14C ages agreed with this range, carbon contamination of the samples resulted in inverted and overestimated ages. Based on stratigraphic relationships the non-deposition events have been dated at approximately 750–800 years ago, 600 years ago, 475 years BP and 100–150 years ago and two major periods of aggradation at ~ 800–1000 years ago and ~ 500–700 years ago. The rate of aggradation (0.29 cm/year) calculated implies that the entire 30 m deposit could have been deposited in 9 000 years. However, an independent study by McCarthy et al. (2011) proved that tributary sedimentation began prior to 220 ka. Therefore, in order to deposit 30 m of sediment over 220 ka, either the mid – late Quaternary sedimentation rate was lower than the recent past (Late Holocene) or the system periodically undergoes extensive erosion in order to flush the accumulated sediment from the tributary fan system.