Dissertations / Theses on the topic 'Kaapvaal'

Evidence of three glaciations in Paleoproterozoic successions of North America and at least one on three other continents, suggests that these glaciations were of global extent. In common with the Neoproterozoic record, carbonates cap the glacials. However, the relationship between biogeochemical cycling of carbon and ice ages has not been fully appreciated. This research involved the sedimentology and isotope stratigraphy of carbonates and shales in Paleoproterozoic glacially-influenced successions of Wyoming and South Africa. Carbonates of the Vagner Formation cap the middle of three diamictites in the Snowy Pass Supergroup, Medicine Bow Mountains, WY. The Duitschland Formation occurs between two glacial horizons in South Africa. Limestones retain negative d13C values for over 60 m in the Vagner Formation, and for over 100 m in the lower part of the Duitschland Formation. Isotope compositions of TOC from the lower part of the Duitschland Formation reveal pronounced enrichment resulting in significantly lower fractionation between organic and inorganic carbon. This is similar to enrichment noted in Neoproterozoic cap carbonates. Combined with strongly positive carbon isotope compositions in upper Duitschland carbonates, the data from the Vagner Formation underscores strongly positive-to-negative carbon isotope trends bracketing Paleoproterozoic glaciations. These trends mimic those noted in Neoproterozoic glacial successions and possibly indicate a recurrence of global glaciations. The Slaughterhouse and Nash Fork formations significantly postdate the glacial epoch. Both the lower part of the Nash Fork Formation, Medicine Bow Mountains and the Slaughterhouse Formation, Sierra Madre contains carbonates with 13C-enrichment >+6⠰ and locally up to +28%, whereas carbonates higher in the Nash Fork Formation have d13C values between 0 and 2.5%. This dramatic change in the composition of the Paleoproterozoic ocean is constrained at ca. 2.1 Ga (Karhu, 1993). Carbonates in the Rawhide Canyon section of the Whalen Group in the Hartville Uplift (the easternmost exposure of the Wyoming Craton) display δ13C values up to +8.2% suggesting correlation with the Slaughterhouse and Nash Fork formations and their deposition on continuous carbonate platform along the margin of the Wyoming Craton. These data support an open-marine, and therefore a global origin for the ca. 2.2-2.1 Ga carbon isotope excursion.
Ph. D.

Results from two-station surface-wave inversions across the Archean Kaapvaal craton of southern Africa are compared with seismic velocities estimated from approximately 100 mantle xenoliths brought to the surface in kimberlite pipes. As the xenoliths represent a snapshot of the mantle at the time of their eruption, comparison with recently recorded seismic data provides an opportunity to compare and contrast the independently gained results. These cratonic xenoliths from the southern Kaapvaal, all less than 100Ma in age, have been analyzed geothermobarometrically to obtain the equilibrium P-T conditions of the cratonic mantle to about 180km depth [James et al 2004]. Seismic velocity-depth and density-depth profiles calculated on the basis of these P-T data and the mineral modes of the xenoliths are used to produce theoretical surface-wave dispersion curves and to generate roughly the upper 200km of a starting/reference model. A regionally-developed crustal structure [Niu and James 2002] was used for the crust and 300km of mantle values taken from PREM filled in down to 500km depth. This composite model was used as the starting/reference model for a Neighbourhood Algorithm surface-wave inversion using fundamental-mode Rayleigh-wave phase velocities for 16 paths within the Kaapvaal Craton from five events. The velocity structures found by that inversion are consistent with those derived from the xenolith data. Hence the velocity structure (i.e. thermal structure) of the mantle to a depth of 180km beneath the Kaapvaal craton is basically the same today as it was 80-90Ma. Further, synthetics runs show that for this surface-wave dataset, there is no strong low-velocity zone at depths shallower than at least 200km.
Master of Science

Carbonatites are exotic rocks which usually occur in discrete intrusions. Considering the association of carbonatites with rifting environments, this dissertation proposes that: carbonatites occur in extensional tectonic settings and therefore carbonatite occurrence can be used to constrain an extensional setting for related occurrences. In order to give context in which to consider this hypothesis, the formation of carbonatites is reviewed. This work favours the direct mantle melting model as it is most relevant and consistent with observations of Kaapvaal Craton carbonatites. However the liquid immiscibility model cannot be entirely rejected with current knowledge. The hypothesis is applied to the Bushveld Igneous Complex after providing evidence of the rift-carbonatite association. The Bushveld Igneous Complex is considered to have been emplaced in the same tectonic setting as carbonatites. Therefore the Bushveld Igneous Complex was emplaced in an extensional tectonic setting. Finally the carbonatites which are part of the Pilanesberg Alkaline Province are considered in order to test the hypothesis. This work finds that the Pilanesberg carbonatites do occur with other rift related magmatism during the break-up of Nuna (Columbia) and therefore the hypothesis is not rejected. This work offers reviews of basic carbonatite background, formation models and carbonatite occurrences on the Kaapvaal Craton.
Dissertation (MSc)--University of Pretoria, 2013.
lk2014
Geology
MSc
Unrestricted

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006.
Includes bibliographical references.
Continents are an amalgamation of crust and mantle lithosphere assembled over -4 Gyr and are therefore our best record of the early Earth. Exposures of rocks -3.0-3.7 Ga cover -20,000 km2 of eastern S. Africa and Swaziland, and provide a record of the continental assembly and subsequent stabilization of the eastern Kaapvaal craton. This thesis uses structural, geochronological, thermochronological and isotopic constraints to examine the tectonothermal processes responsible for the growth and stabilization of this portion of Mesoarchean lithosphere. Field mapping was focused on terrane-bounding shear zones and syntectonic plutons, and in combination with ID-TIMS U-Pb zircon geochronology and Sm-Nd analysis, places sub-Myr constraints on the timing, distribution, and kinematics of magmatism and deformation during growth and modification of continental lithosphere. Detailed U-Pb apatite and titanite thermochronological datasets are used in combination with finite difference numerical modeling to determine non-linear temperature-time paths for rocks between -650-300 °C from 3.45-3.08 Ga - providing a sensitive indicator of tectonic and magmatic processes in the middle to lower crust.
(cont.) From 3.2 to 3.3 Ga, multiple microcontinental fragments with distinct age and Nd isotopic characteristics were assembled along an oblique subduction zone boundary, with the Barberton Greenstone belt representing a lithospheric suture zone. During continental assembly and orogeny, strain was partitioned into 3236-3220 Ma syntectonic plutons and terrane-bounding transcurrent shear zones bordering the margins of the previously stabilized ca. 3.66-3.45 Ga Ancient Gneiss Complex. Subsequent 3.2-3.1 Ga reactivation of crustal anisotropies within the lithospheric suture zone - represented broadly by the Barberton Greenstone Belt - controlled the thermal and compositional reorganization of the crust through transtensional tectonics, exhumation of deep-crustal gneiss terranes, and upward migration of granitic batholiths. This final period of crustal modification was responsible for juxtaposing low-grade greenstone supracrustal rocks against middle- to lower-crustal gneiss terranes, and ultimately led to crustal stabilization in the greenstone belt and vicinity. These results support a model in which the stabilization of the Kaapvaal craton was a piece-wise transition resulting from lithospheric thickening and crustal thinning over, hundreds of Myr.
by Robert Blair Schoene.
Ph.D.

Includes bibliography.
The Kaapvaal Craton is one of the best preserved of all Archean cratons. It is partially covered by the supracrustal sequences of the Witwatersrand, Ventersdorp and Transvaal Basin (and correlated Griqualand West Basin), which span almost a billion years (~3.1 to 2.2 Ga). This thesis describes and interprets eight newly available seismic reflection profiles, acquired by the vibroseis method to 6 seconds TWT, and totaling ~720 km in length. New stratigraphic and structural features are identified across three main regions: the Kaapvaal Craton's western margin, the northern margin or Bushveld lines (flanking the Thabazimbi-Murchison Lineament and across the western extremity of the Bushveld Igneous Complex) and the Kaapvaal Craton interior. The seismic data was interpreted using Charisma seismic interpretation software, Geoframe version 3.6 (developed by Geoquest, Schlumberger) on a UNIX, SUN workstation.

Kimberlites are igneous rocks that originate by small degrees of melting of the mantle. Notably, kimberlites carry large variety of crustal and mantle xenoliths. Geochemical data on xenoliths can provide insights into the processes occurring in the subcontinental lithosphere (SCLM) and deeper. The Kaapvaal craton in South Africa hosts one of the best-studied kimberlite populations on Earth. In this thesis, a total of 24 thin sections of peridotite xenoliths from Group I Letlhakane, Letseng, Premier and Frank Smith kimberlites were investigated to constrain the pressure, temperature and depth of these mantle xenoliths. To do so, olivine, orthopyroxene, clinopyroxene, garnet and spinel were analyzed for their major element chemistry using electron microprobe analysis (EPMA). P-T calculations were performed using the PTEXL3 spreadsheet program, which contains different geothermobarometers. Depth constraints were fitted to the characteristic Kaapvaal craton geotherm. According to geochemical results and rough modal mineral estimations, the majority of the mantle xenoliths were identified as depleted harzburgites or lherzolites. Mineral major element compositions show trends of depletion, which correlate with the corresponding mantle xenolith sampling depth. Olivine and orthopyroxene have high average Mg# values of 92.1 and 93.0, respectively, at shallower depth ~70–160 Km. Below ~160 km, Mg# starts to drop rapidly and transition towards a more typical asthenospheric composition. The majority of garnet compositions fall into the G9 classification field. Titanium shows a distinct partition trend that correlates with depletion. Garnets have well developed alteration reaction rims, especially at shallower depths. Geothermobarometric calculations for four-phase peridotites are comparable with the results from other studies. However, the temperature estimates obtained by T(BKN90) are slightly overestimated and, in contrast, the pressure estimates from P(BBG08) are slightly underestimated. Other assemblages have considerable calculated pressure and temperature conditions and were best fitted for the regional conductive geotherm. The mantle xenoliths show pressures ranging from 22 to 56 kb and temperatures from 753 to 1344 °C that characterize an extensive sampling depth range from 70 to 190 km. Three of the samples extend into the diamond stability field. The obtained P-T data for mantle xenoliths cluster along a 44.0±2.0 mWm⁻² conductive Kaapvaal craton continental geotherm, being slightly higher than that of the average thermal state estimate for the craton.

>Magister Scientiae - MSc
The Proterozoic Namaqua-Natal Province comprises highly deformed rocks of medium to high grade metamorphism and is bordering the Archean Kaapvaal Craton to the west, south and east in South Africa. The sector to the west of the Craton, namely the Namaqua Sector, is structurally complex and subdivided from west to east into the Bushmanland Subprovince, the Kakamas and Areachap terranes of the Gordonia Subprovince and the Kheis Subprovince. The prominent Neusberg Mountain Range, with exposures to the north and south of the Orange River in the Kakamas Terrane constitutes evidence of crustal shortening as a result of continental collision of the Namaqua Sector block with the Kaapvaal Craton during the Namaquan Orogeny. The Mesoproterozoic Korannaland Group in the Kakamas Terrane is affected by faulting, folding and shearing.

Includes bibliographical references.
Eighteen Jurassic to Cretaceous South African kimberlites representative of group 1, group 11 and transitional varieties that have been emplaced through both the Archean Kaapvall craton (on-craton) and Proterozoic Namaqua-Natal belt (off-craton), have been selected for a comparative study aimed at characterising their geochemistry and source region compositions, as well as understanding the petrogenetic processes that have affected them. The petrography of the analysed kimberlites is similar to typical group 1 and group 11 kimberlites, characterised by deformed and anhedrarl olivine and phlogopite macrocrysts, with more subhedral to euhedral olivine and phlogopite phenocrysts and microphenocrysts, set in a groundmass of mostly serpentine, calcite and phlogopite (group 1 kimberlites), or calcite, serpentine, phlogopite and diopside (group 11 kimberlites). The transitional kimberlites tend to show intermediate characteristics, with the on-and off-craton transitional kimberlites showing more similarity to group 1 and group 11 kimberlites, respectively.

>Magister Scientiae - MSc
The group of granites on the eastern margin of the Mesoproterozoic Namaqua sector of the polydeformed and highly metamorphosed Namaqua-Natal Province of southern Africa is known as the Keimoes Suite. The suite includes mixtures of diverse rock types not belonging to a single intrusive series and so it should be subdivided into more than one intrusive suite. The exact definition, extent, distribution and petrogenesis of these granites have been poorly defined in the past, with various authors defining the suite differently due to the lack of proper geochronology and geochemical data. The exact contact between the Namaqua sector and Kaapvaal Craton together with the role of the suite to the Namaqua tectonic evolution is still unclear. The granites of the Keimoes Suite are thought to mark the contact between the Namaqua sector and the Kaapvaal Craton. This study seeks to address the above mentioned problems by making use of new geochronology, isotope, major and trace element geochemistry together with petrography. The granites of the Keimoes Suite were previously grouped based on their degree of deformation. The geochronology, undertaken as part of this study, has proven that this classification is unfounded. The degree of foliation in these granites appears to be largely controlled by the abundance of platy minerals, such as biotite and muscovite, together with the intrusion mechanism, with deformational processes, such as shearing, playing a secondary role. The geochronology, together with geochemistry has helped to redefine the previously defined Keimoes Suite so that two well defined separate suites are recognized and the third is poorly defined due to lack of more samples of that age group. The new classification or grouping of the granites of the eastern Namaqua sector allows a more detailed examination of the tectonic evolution of this region. A member of the 1225 to 1200 Ma early syn-tectonic granites, the Josling Granite, shows a strongly developed foliation and was derived from a depleted source with a relatively low continental crustal component. This granite intruded during the time of arc accretion, and is associated with, and partly responsible for the D₁ deformation and M₁ metamorphism recognized in most of the rocks of the eastern terranes of the Namaqua sector. In terms of age, the syn-tectonic granites of the Augrabies Suite extend from 1200 to 1120 Ma and were largely derived from depleted sources with variable but more substantial amounts of continental crustal components as compared to the early syn-tectonic granite. The granites of this suite intruded during the period of peak D₂ deformation with peak magmatism between 1180 - 1135 Ma, and particularly around 1150 Ma, during the peak of metamorphism (M₂) caused by, and associated with these voluminous intrusions. The Keimoes Suite can now be defined as comprising granites of late- to post-tectonic age relative to the 1.2 - 1.08 Ga Namaquan Orogeny with magmatism occurring on the western side of the Kaapvaal Craton. The 1116 to 1066 Ma Keimoes Suite intruded during the stage of the Namaquan Orogeny in which there was continued indentation of the Kaapvaal Craton into the Namaqua sector with wrenching and shearing causing the development of rifting into which the granites intruded. The Keimoes Suite granites were derived from continental crustal sources and incorporated varying degrees of depleted source components. The intrusives and extrusives of this age occured after the main collisional event between the Namaqua Sector and the Kaapvaal Craton and are associated with the D₃ deformational event, imparting the thermal conditions leading to the M₃ metamorphic event of the rocks within both the Kakamas and Areachap Terranes. The suites mark the suture between the Archean Kaapvaal Craton and the Proterozoic Namaqua sector. The compositions of the granites of the individual suites were mainly controlled by the source with the degree of partial melting exerting a major control. The proportion of entrained peritectic assemblages and accessory minerals played a major role in controlling the compositions of the granites, particularly those of the trace elements. Variations within the compositions of the same suite are due to source heterogeneities. Generally, fractionation processes played a secondary role in influencing the composition of the granites.
Council for Geoscience and National Research Foundation

Le travail de thèse reporté dans ce manuscrit se focalise sur la reconnaissance ainsi que l'expression des processus de différenciation crustale à l'Archéen. Cet éon représente à lui tout seul 1/3 des temps géologiques, et se caractérise notamment par des lithologies diagnostiques, ainsi que des contextes géodynamiques complexes. La majorité des études sont portées sur l’investigation des phases alumineuses qui permettent de contraindre précisément les événements métamorphiques au-cours d’une géodynamique d’épaississement crustal. Toutefois, ces phases alumineuses représentent rarement plus de 10% des terrains archéens, alors qu’ils sont faits à plus de 75% de gneiss orthodérivés. L'étude qui suit est une caractérisation du complexe de gneiss gris composite de la marge Nord du craton archéen du Kaapvaal en Afrique du Sud. Les résultats produits durant cette investigation ont amené à plusieurs conclusions importantes au regard de la géodynamique archéenne. L'étude isotopique U-Pb/Lu-Hf sur zircon couplée à des analyses pétro-métamorphiques montre que la construction d’un complexe de gneiss gris composite correspond à une géodynamique prolongée dans le temps, accomplie au-travers de processus de différenciations crustales internes à la Zone accrétée, 1.e. le bloc crustal évolue en système thermodynamiquement fermé. Les complexes de gneiss gris ne sont que modérément étudiés toutefois, les informations contenues dans ces lithologies apparaissent complémentaires avec celles obtenues par les études métamorphiques sur les lithologies alumineuses. Il est donc nécessaire d'approfondir ce type d’investigations afin de mieux contraindre les modèles géodynamiques archéens
The PhD work presented in this manuscript focuses on the recognition and the manifestation of Archean crustal differentiation processes. The Archean eon which represents 1/3 of the geological record is featured by both lithologies unrecognized in younger eons and cryptic geodynamics. Most of investigations concentrate on the characterisation of aluminium-rich lithologies that allow an accurate determination of the pressure-temperature evolution underwent by crustal materials during crustal thickening geodynamics. However, aluminium-rich lithologies - mainly represented by metasediments - account for only 10% on average of Archean terranes whereas orthoderived gneisses - which also testify for crustal differentiation processes - form around 75% of these terranes. The following contribution depicts an Archean composite grey gneiss complex located at the northern edge of the Kaapvaal craton is South Africa. Results carried out during this PhD study have major consequences on Archean geodynamics. The zircon U-Pb/Lu-Hf isotope Investigation coupled with strong petro-metamorphic observations show that composite grey gneiss complexes may be built over a protracted time span, achieved through self-refinement of crustal materials, i.e. the crustal block evolved in a thermodynamically closed system. Grey gneiss compiexes are only moderately investigated even though information enclosed in these lithologies is complementary with those from aluminium-rich rocks. Therefore, deeper investigations of these geological objects must be a central scope in order to improve the knowledge of the Archean eon and appears necessary for the building of even more realistic geotectonic models

The MRS/MISS of the Makgabeng Formation encompasses sand cracks, wrinkle marks, mat fragments, mat chips and roll-ups and those of the Magaliesberg formation are wrinkle marks, petees/petee ridges, sand cracks, and multi-directional ripples. The sedimentary process that moderated the formational mechanism of the MISS of the Makgabeng Formation is (descriptively allochthonous) of high energy (inter-dune depositional setting) that eroded, transported and re-deposited mat bound sediments. The genetic mechanism of the MISS of the Magaliesberg Formation is descriptively authochthonous because of enhanced resistance of biostabilized sediments to being reworked. XRF (major and trace) and XRD analysis (qualitative and quantitative) was done on MISS bearing sedimentary rock layers (A) and underlying sedimentary sections (B) of Magaliesberg and Makgabeng samples. Result show high quartz content of all the analyzed samples compared to average sandstones. This premise suggests a relation of microbes (e.g. cyanobacteria) to phototrophy and/photoautotrophy because of the conduction properties of translucent quartz. Also plausible inference is that the intense chemical weathering that produced the quartz arenite was positively influenced by microbes, as noted in some Proterozoic basins. There is higher concentration of Ba in all A samples compared to B (Makgabeng and Magaliesberg) which might be emblematic of biogenicity. The Magaliesberg analyzed samples (MAG 101, 102, 103) exhibit homogeneity by the higher concentration of Al2O3, TiO2, K2O, and P2O5, and lower concentration of SiO2 in the A compared to the B subsamples of a particular sample. Also, Magaliesberg analyzed samples (MAG 101, 102, 103) exhibit homogeneity by the lower concentration of quartz and higher concentration of muscovite in the A compared to the B subsamples. This exact established negative correlation between the duo of SiO2 and quartz, and the quartet of Al2O3, TiO2, K2O, and P2O5, and muscovite as in Magaliesberg samples pertains also to a Makgabeng sample (MKG 102; roll-up). MKG 101 (mat fragment) deviates from this mineralogical and geochemical trend. Each of the A samples of MAG 101, 102, 103, are uniformly of higher concentration in Ce, Cr, Nb, Th, V, Y, Zn, Zr compared to the B version of that sample. MKG 101 and 102 are uniformly of lower concentration of Ce, Cr, Nb, Th, V, Y, Zn, Zr in A compared to the B version of that sample. The A of each of the samples MAG 101, 102, and 103 has higher concentration of Hf and Rb compared to its B; a character that is also exhibit in MKG 102, and MKG 101 is vice versa. Microscopy shows that A of all the samples is of smaller grain size compared to B, espousing affinity of microbes to fine-medium grained sandstones. Microscopy of the Magaliesberg Formation samples show Pseudo petee ridges and pseudo cross lamination which reflect biostabilization, and microscopy of the Makgabeng Formation show roll-ups, mat chips and composite mat chips. The MISS genetic difference of the two formations is related to energy, water residence time (emergence and inundation), Ph, and similarity is related to mutuality in shallow water environment. Mat types are inferred to be biologically, physically and chemically moderated adaptations of microbial communities to specific cum peculiar locally prevailing environmental conditions; factors that are premised on taphonomy and ecology.
Dissertation (MSc)--University of Pretoria, 2014.
tm2015
Geology
MSc
Unrestricted

La composition chimique de la croûte continentale a significativement évolué à la transition Archéen-Protérozoïque (3000-2500 Ma), témoignant de changements géodynamiques majeurs à cette époque. Afin d'étudier l'expression et les origines de ces changements, qui sont encore mal contraints, j'ai étudié une diversité de granitoïdes qui se sont mis en place dans cette gamme d'âges à la marge Nord du craton du Kaapvaal, en Afrique du Sud. Ce travail a permis de préciser la typologie et l'origine des granitoïdes tardi-archéens ; ceux-ci peuvent être classés dans trois grands groupes : (1) Les sanukitoïdes, représentés en Afrique du Sud par le pluton de Bulai, sont des magmas dérivant de l'interaction entre une péridotite mantellique et un composant riche en éléments incompatibles (TTG, liquide issu de la fusion de sédiments, et, plus rarement, fluide aqueux). Les sanukitoïdes peuvent être classés en deux groupes distincts, selon les mécanismes de cette hybridation : les low-Ti sanukitoids proviennent d'une simple hybridation du liquide silicaté avec la péridotite, alors que les high-Ti sanukitoids sont issus de la fusion d'un assemblage métasomatique à amphibole et phlogopite, résultant de ces interactions. Enfin, les mécanismes de différenciation des suites sanukitoïdes au niveau de la croûte sont contrôlées par des mécanismes de cristallisation fractionnée ou (moins vraisemblablement) de fusion partielle. (2) Les sanukitoïdes " marginaux ", représentés dans le craton du Kaapvaal par les plutons de Mashashane, Matlala, Matok et Moletsi, sont des granitoïdes résultant de l'interaction entre des sanukitoïdes et des magmas provenant de la fusion de croûte préexistante. Etant donné la large gamme de sources possibles (TTG, métasédiments, roches mafiques) d'un craton à l'autre, ce groupe est extrêmement diversifié. Leurs mécanismes de différenciation sont contrôlés par la cristallisation fractionnée. (3) Certains granites, tels que le batholite de Turfloop en Afrique du Sud, sont directement issus de la fusion de lithologies crustales (TTG, métasédiments et amphibolites). Au sein du craton du Kaapvaal, l'évolution spatio-temporelle du magmatisme tardi-archéen suit un schéma très caractéristique : les TTG se mettent en place entre ~3300 et ~2800 Ma, puis laissent la place à la genèse de l'ensemble des granitoïdes présentés ci-dessus, qui se déroule entre 2780 et 2590 Ma. Cette séquence d'évènements est reproduite au sein de tous les cratons du monde à la fin de l'Archéen. Elle témoigne de l'avènement des processus de recyclage crustal, puisque, par opposition aux TTG archéennes qui dérivent de métabasaltes juvéniles, les magmas tardi-archéens sont issus à la fois de la différenciation intracrustale et de l'interaction entre une péridotite et du matériel continental introduit dans le manteau. Cette dualité de processus pétrogénétiques est aussi très typique des épisodes magmatiques qui ont lieu à la fin des cycles de subduction-collision post-archéens. Ainsi, l'évolution de la composition des granitoïdes entre 3000 et 2500 Ma traduit vraisemblablement l'initiation d'une forme de tectonique des plaques proche du régime actuel. Celle-ci serait liée au refroidissement planétaire global, qui a probablement entraîné un " effet de seuil " dans l'évolution de l'épaisseur de la croûte océanique ainsi que la rhéologie et le volume de la croûte continentale, permettant ainsi à la subduction et à la collision de ne devenir thermo-mécaniquement stables qu'à partir de la fin de l'Archéen.

With an estimated erupted volume of 300,000 km3 and an areal extent of more than 200,000 km2, the Paleoproterozoic (2.06 Ga) silicic volcanic rocks of the Rooiberg Group (Kaapvaal Craton) in northern South Africa forms one of the largest and to the same time oldest silicic large igneous provinces (SLIPs) known. This large volume of rocks can be sub-divided into four formations: the Dullstroom, Damwal, Kwaggasnek and Schrikkloof Formations. The results of this study show that a clear chemostratigraphy (by using major elements such as TiO2, SiO2, Na2O, K2O, P2O2, MgO, and Fe2O3) can be established in the area north of Loskop Dam, dividing the rocks of the study area into the Damwal, Kwaggasnek and Schrikkloof formations. The studied rocks are characterized by aphanitic lavas bearing amygdales, spherulitic textures and flow-bands with some sedimentary and pyroclastic interbeds. The dacites could mainly be described as high-Mg felsites (HMF), whereas the rhyolites could be described as low-Mg felsites (LMF). The negative Eu anomaly, Nb and Ta values of the upper part of the Rooiberg Group range between 5.38-24.2 and 0.45-1.86 ppm, respectively, similar to crustal compositions. Furthermore, Nb/Ta values range from 10.91-14.83 (also similar to typical crustal compositions) while few samples from the Damwal Formation exhibit higher values of 15.13-16.02, similar to mantle-derived compositions. Tectonic discriminant diagrams show that the rocks used in this study evolved from fractional crystallization of a mafic liquid although all samples plot in fields with crustal signatures. Plot of ƐNd and 87Sr/86Sr show a mantle-derived origin for the upper part of the Rooiberg Group. However, ƐNd values of the upper part of the Rooiberg Group range between ~-10 to ~-6, typical of crustal composition or continental basalts formed in the crust. From the results, the Rooiberg Group exhibit both mantle (as observed in the Dullstroom and lower Damwal formations) and crustal signatures as exhibited by the Kwaggasnek and Schrikkloof formations. This is interprested as a result of the interaction of the thick crust and a shallow mantle source within the Bushveld Province during magmatism. Furthermore, similarities in geochemical signatures between the Rooiberg Group and selected SLIPs around the world suggest a similar origin for SLIPs by fractional crystallization of a mafic melt and melted (or assimilated) crustal material.
Thesis (PhD)--University of Pretoria, 2017.
Geology
PhD
Unrestricted

Cette étude présente de nouvelles données U-Pb et Pb-Pb sur le Central Rand Group du bassin aurifère d'Evander et sur la Murchison greenstone belt, Afrique du Sud. Le bassin aurifère d'Evander, non encore étudié d'un point de vue géochronologie, est localisé à l'est du bassin du Witwatersrand. L'étude des zircons détritiques donne une population essentiellement comprise entre 3050 et 2850 Ma, le plus vieux étant âgé de 3180 Ma. Elle permet aussi la mise en évidence d'une phase de croissance de zircon (ou de remise à zéro du système U-Pb de grains détritiques) reliée à la mise en place des laves de Ventersdorp à ca. 2. 7 Ga. Des pyrites détritiques provenant du mur du Kimberley Reef donnent des âges plus anciens que l'âge minimum du dépôt des sédiments du bassin du Witwatersrand. Les pyrites authigènes ainsi que certaines pyrites détritiques provenant des zones altérées du Kimberley Reef définissent deux événements. Le premier, daté à 2370 Ma, est à relier à la subsidence du bassin liée au dépôt des séquences supérieures du Transvaal et semble associée à la circulation de fluides fortement radiogéniques. Le second, daté aux alentours de 2020 Ma, est contemporain de la mise en place du Bushveld Complex et de l'impact météoritique de Vredefort. , les fluides ayant ici une signature beaucoup moins radiogénique. Cette étude démontre une évolution complexe multi-phase des minéralisations d'or et d'uranium au niveau du bassin du Witwatersrand. La Murchison greenstone belt représente une des régions les plus riches en antimoine. Elle renferme aussi des minéralisations d'or, de Cu-Zn et d'émeraude. Le but de cette étude est de déterminer l'âge de la ceinture ainsi que celui des minéralisations, mais aussi d'estimer le rôle potentiel que les granitoïdes ont pu jouer lors des processus de formation des minéralisations. La mise en place de la ceinture est ainsi datée entre 3. 09 et 2. 97 Ga. Trois phases magmatiques majeures ont pris place à 2. 97, 2. 82 et 2. 68 Ga. Les pyrites associées avec les minéralisations d'Au-SB et de Cu-Zn définissent un âge isochrone de 2. 97 Ga suggérant qu'elles sont à relier à la mise en place du Maranda batholith et des roches volcaniques de la Rubbervale Formation à 2. 97 Ga. Les pyrites associées aux émeraudes au sud de la ceinture reflètent un mélange entre le plomb provenant d'un socle ancien à 3. 23 Ga et celui de l'événement magmatique à 2. 97 Ga. La Rubbervale formation et le Maranda batholith représentent par conséquent une importante métallothèque dont l'importance de ne s’applique pas à la seule région de Murchison, mais aussi à l'importante question de l'origine de l'or dans le Witwatersrand.

Les travaux réalisés durant cette thèse apportent de nouvelles contraintes sur les relations entre déformation, hydratation et percolation de fluides et/ou de magmas dans le manteau subcontinental sous un craton et sous un rift, et leurs implications sur son comportement rhéologique. Il repose sur l'analyse des microstructures, des OPRs et des teneurs en hydrogène de xénolites mantelliques du craton du Kaapvaal, et sur deux séries de xénolites provenant de différentes localités le long du rift Est-Africain (Divergence Nord Tanzanienne et SE de l'Ethiopie). Les microstructures granulaires à gros grains et les OPRs bien définies des péridotites du craton du Kaapvaal sont cohérentes avec un épisode de déformation suivi d'une longue période de quiescence. Les OPRs de l'olivine sont majoritairement à symétrie orthorhombique, mais des symétries axiale-[100] et axiale-[010] sont aussi mesurées. Les péridotites cratoniques enregistrent de multiples épisodes métasomatiques, ayant entraîné une hétérogénéité de compositions à petite échelle ne pouvant être détectée par les études sismiques. Les teneurs en hydrogène mesurées dans l'olivine sont variables, mais ont tendance à augmenter jusqu'à 150 km de profondeur, atteignant alors jusqu'à 50 ppm wt. H2O. En dessous de cette profondeur, les échantillons montrent des teneurs en hydrogène très faibles. Les expériences réalisées en piston-cylindre sur la diffusion de l'hydrogène issue d'un liquide kimberlitique vers de la forstérite suggèrent que la fugacité en eau pourrait fortement être diminuée par la présence de CO2, empêchant l'hydratation de l'olivine durant extraction des xénolites par les kimberlites. Ces résultats expérimentaux suggèrent que les teneurs en hydrogène dans l'olivine des péridotites du craton du Kaapvaal ont été acquises durant un épisode métasomatique en profondeur et non pendant leur extraction par les kimberlites. Ces teneurs n'ont toutefois pas à ce jour entraîné de remobilisation de la racine cratonique. Enfin, le calcul des propriétés sismiques des péridotites cratoniques révèle que les anisotropies générées par les OPRs de ces échantillons sont suffisantes pour expliquer les anisotropies mesurées par les ondes SKS et les ondes de surface.Les xénolites de la Divergence Nord-Tanzanienne, montrent des variations significatives de microstructures et d'OPR de l'olivine entre les péridotites des localités dans l'axe du rift et celles de la chaîne volcanique transverse (Lashaine et Olmani). A Lashaine, les microstructures granulaires à gros grains et les OPRs de type orthorhombique et axial-[010] peuvent être expliquée par une déformation en transpression liée à la formation de la chaîne Mozambique ou par la présence d'une relique d'un domaine cratonique à l'intérieur de la chaîne Mozambique. Dans l'axe du rift, les microstructures porphyroclastiques à mylonitiques suggèrent une déformation plus récente, accompagnée de réactions magma-roche sous des conditions proches du solidus, suivie d'un recuit variable. L'hétérogénéité des microstructures enregistrées par les échantillons du rift suggère de multiples épisodes de déformation localisée, probablement liés à l'injection percolation épisodique de magmas, espacés de périodes d'accalmie. Les OPRs de l'olivine de type axial-[100] et l'orientation des directions de polarisation des ondes SKS suggère que le rift s'est formé en régime de transtension Les péridotites du Sud-Est de l’Éthiopie présentent des microstructures porphyroclastiques à gros grains moins recristallisées qu'en Tanzanie. Les microstructures et les OPRs principalement de type orthorhombique suggèrent une déformation syn- à post-métasomatisme. Les anisotropies de polarisation des ondes S calculées pour ces échantillons sont insuffisantes pour expliquer à elles seules les déphasages des ondes SKS dans cette partie du rift
This study provides additional constraints on the relations between deformation, hydration and percolation of fluids and melts in the subcontinental lithospheric mantle beneath a craton and a rift, as well as their implication on its geodynamical behaviour. I have analysed the microstructures, the CPOs, and the hydrogen content of mantle xenoliths from the Kaapvaal craton, and two sets of xenoliths from different localities along the East African Rift (North Tanzanian Divergence and SE Ethiopia). The coarse-granular microstructures and the well-defined CPOs in Kaapvaal peridotites suggest a deformation followed by a long quiescence time. Orthorhombic olivine CPOs predominates, but axial-[100] and axial-[010] are also measured. Cratonic peridotites record multiple metasomatic episodes, leading to a significant compositional heterogeneity, which cannot be imaged by seismic studies. Olivine hydrogen contents are variable, but tend to increase until 150 km depth, reaching up to 50 ppm wt. H2O. The deeper samples are almost dry. Piston-cylinder experiments on hydrogen diffusion between a volatile-rich kimberlitic melt and forsterite suggest that the presence of CO2 in the system could significantly decrease water fugacity and thus forsterite hydration. These experimental results indicate that the hydrogen contents measured in olivine were acquired during a metasomatic event rather than during xenolith extraction by kimberlites. However, this metasomatism was not followed by remobilization of the cratonic root. In the North Tanzanian Divergence, localities within the rift axis and the volcanic transverse belt (Lashaine and Olmani) show significant differences in microstructures and olivine CPO patterns. In Lashaine, coarse-granular microstructures and orthorhombic to axial-[100] CPO patterns in olivine can be explained by transpressional deformation during the formation of the Mozambique belt, or by the occurrence of a remnant of a cratonic domain embedded within the Mozambique belt. Within the rift axis, porphyroclastic to mylonitic microstructures suggest a recent rift-related deformation accompanied by syn-kinematic melt-rock reactions, and followed by variable annealing. The strong heterogeneity in microstructures and olivine CPO suggests that this deformation was acquired during multiple tectonic events probably linked to episodic magma percolation, separated by quiescence episodes. The axial-[100] patterns in olivine and the oblique fast directions reported by SKS studies are coherent with transtensional deformation within the lithospheric mantle beneath the rift. The peridotites from SE Ethiopia are less recrystallized than the rift-axis Tanzanian peridotites, displaying coarse-porphyroclastic microstructures. Microstructures and orthorhombic CPOs in olivine suggest syn- to post-metasomatic deformation. S-waves polarization anisotropies calculated for these samples cannot explain alone the delay times reported by SKS studies in this part of the East-African Rift

L’altération des roches supracrustales archéennes implique des conditions environnementales encore mal contraintes qu’il est nécessaire de définir afin de mieux comprendre l’évolution des enveloppes externes au Précambrien, ainsi que les conditions d’émergence et de diversification de la vie. Le premier objectif de cette thèse est l’étude des métasomatismes des formations volcano-sédimentaires du Paléoarchéen, la caractérisation des mécanismes à leur origine, ainsi que la quantification des bilans géochimiques associés. Le deuxième objectif est l’étude de la composition isotopique de l’azote dans ces mêmes formations, et sa signification pour le cycle de l’azote au Paléoarchéen. Pour cela, une étude géochimique et isotopique des systèmes volcanosédimentaires Paléoarchéens de Pilbara et de Barberton a été entreprise. Le métasomatisme potassique est issu de l’altération par l’eau de mer du matériel volcanique en un assemblage séricite - feldspath-K - quartz à des pH de 5,5-6,5 en conditions réductrices et à des températures supérieures à 70 °C. Le bilan de masse de cette altération implique un enrichissement de l’eau de mer de l’ordre de 1 mole de Fe2+, Na+, Ca2+, et de 3 moles de Mg par kg de komatiite. Trois moles de H+ et 1 mole de K+ sont incorporées dans la roche en échange. Quatre moles d’oxygène sont ainsi libérées dans l’eau de mer, impliquant au total la neutralisation de 10 moles de H+ par kg de komatiite. La silicification est un processus diagénétique précoce contrôlé par la granulométrie des particules sédimentaires, les plus fines engendrant les plus fort taux de silicification. Les particules volcano-détritiques déposées dans les bassins sédimentaires paléoarchéens adsorbent jusqu’à 5 fois leur volume de silice dissoute, produisant un flux de silice depuis l’eau de mer vers la croûte de l’ordre de plusieurs dizaines de kilomoles par kilogramme de matériel détritique. Les sédiments grossiers ne subissant qu’une silicification partielle sont carbonatisés pendant la diagenèse profonde par la précipitation de dolomite riche en Fe à partir de l’eau de mer piégée dans la porosité résiduelle durant la silicification. La carbonatisation des formations sédimentaires archéennes permet le stockage de 1,8 moles de CO2 par kg de matériel détritique. Les bilans de masse proposés montrent un profond déséquilibre entre l’eau de mer et la croûte au Paléoarchéen, résultant certainement d’une forte pression partielle de CO2 dans l’atmosphère, et de conditions globalement réductrices. Les compositions isotopiques (δ15NATM) de l’azote dans les roches sédimentaires étudiées sont comprises entre 7,1 ± 0,6 et 9,4 ± 0,4 ‰ avec des teneurs en N entre 0,8 et 5 ppm, sous forme d’ions ammonium dans les silicates potassiques. Ces compositions correspondent à des valeurs maximales de l’ammonium incorporé dans les sédiments au paléoarchéen, et témoignent d’un réservoir d’azote enrichi en 15N potentiellement représentatif de la composition de l’océan, il y a 3. 45 Ga.

Thesis (DSc)--Stellenbosch University, 2012
ENGLISH ABSTRACT: This study is an investigation of the anatectic history of high-grade paragneisses from the Ancient Gneiss Complex (AGC) in Swaziland. The work involved an integrated field, metamorphic, geochemical, geochronological and structural study of metasedimentary granulites from three separate, but spatially related areas of outcrop in south-central Swaziland, which were subjected to multiple high-grade partial melting events throughout the Meso- to Neoarchaean. The project has aimed to constrain the age(s) and conditions of metamorphism, so as to contribute to the understanding of geodynamic processes in the Barberton and AGC granite-greenstone terranes, as well as to investigate certain physical and chemical aspects of anatexis in the migmatites. The metamorphic record retained in these rocks, constrained by phase equilibria modelling as well as zircon and monazite SHRIMP and LA-ICP-MS geochronology, informs on the state of the mid- to lower-crust of the southeastern Kaapvaal Craton during key events associated with early lithosphere assembly and crustal differentiation. It also suggests that the region is comprised of more than one high-grade terrane. Two of the areas investigated experienced high-temperature metamorphism at ca. 3.23-3.21 Ga, in addition to a major 830-875º C, 6.5-7.6 kbar anatectic event at ca. 3.11-3.07 Ga. Intermediate and younger high-temperature events are recorded at ca. 3.18 Ga, ca. 3.16 Ga and 2.99 Ga. The timing of these metamorphic events coincided with the amalgamation of the eastern domain of the proto-Craton via subduction and accretion of micro-continental fragments at ca. 3.23 Ga, including the Barberton Greenstone Belt (BGB) and AGC terranes, as well as discrete episodes of crustal differentiation and potassic granitic magmatism between ca. 3.23 and 3.10 Ga. The third area investigated holds no record of Mesoarchaean metamorphism, but instead experienced a 830- 855 ºC, 4.4-6.4 kbar partial melting episode at ca. 2.73 Ga. This broadly coincided with the formation of a large continental flood basalt province, the ca. 2.71 Ga Ventersdorp LIP, and widespread intracratonic granitic magmatism on the Craton towards the end of the Neoarchaean. An explanation for the contrast in metamorphic record in the two terranes may be that the 2.71 Ga granulites represent a much younger sedimentary succession, and that granulites from the older terrane were left too restitic, after substantial partial melting during the Mesoarchaean, to record subsequent high-grade events. Finally, this study documents the details of S-type granitic magma production and extraction from a typical metapelitic source. Using the 2.73 Ga granulites from the AGC as a natural field laboratory, a case is made for the selective entrainment of peritectic garnet to the magma as a mechanism for generating relatively mafic, peraluminous S-type granite compositions. The work demonstrates the evolution of entrained peritectic garnet in such magmas, and is in strong support of a ‘peritectic phase entrainment’ process by which relatively mafic granite magmas are produced from melts which, in theory, should be highly leucocratic.
AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die anatektiese geskiedenis van hoëgraadse metasedimentêre gneise uit die Ancient Gneiss Complex (AGC) in Swaziland. Die werk behels 'n geïntegreerde veld, metamorfiese, geochemiese, geochronologiese en strukturele studie van metasedimentêre granuliete van drie afsonderlike, maar ruimtelik verwante gebiede in suid-sentraal Swaziland, wat aan verskeie hoëgraadse anatektiese gebeure onderworpe was gedurende die Meso-tot Neoargeïese tydsperiode. Die studie is daarop gemik om die ouderdomme en die kondisies van metamorfose vas te stel, om sodoende by te dra tot die begrip van die geodinamiese prosesse in die Barberton en AGC granietgroensteen terrein, asook om sekere fisiese en chemiese aspekte van die anatektiese proses te ondersoek. Die metamorfe rekord, bepaal deur mineraal ewewigsmodellering sowel as sirkoon en monasiet SHRIMP en LA-ICP-MS geochronologie, belig die toestand van die middel-tot laer-kors van die suidoostelike Kaapvaal Kraton tydens vroeë litosfeer samesmelting en differensiasie. Dit stel ook voor dat die streek uit meer as een hoëgraadse terrein bestaan. Twee van die gebiede het hoë-temperatuur metamorfose by 3.23-3.21 Ga ervaar, asook 'n hoof 830-875 ° C, 6.5-7.6 kbar anatektiese gebeurtenis by 3.11-3.07 Ga. Intermediêre en jonger hoë-temperatuur gebeure was ook by 3.18 Ga, 3.16 Ga en 2.99 Ga geregistreer. Die metamorfose van die gebied stem ooreen met die samesmelting van die oos Kaapvaal Kraton domein deur subduksie en aanwas van mikro-kontinente by 3.23 Ga, insluitend die Barberton en AGC terreine, asook diskrete episodes van kors differensiasie en kalium-ryke graniet magmatisme tussen 3.23 en 3.10 Ga. Die derde gebied hou geen rekord van Mesoargeïkum metamorfose nie. In plaas daarvan het dit 'n 830-855 ° C, 4.4-6.4 kbar anatektiese episode by 2.73 Ga ervaar, wat ooreenstem met die vorming van 'n groot kontinentale vloedbasalt provinsie, die 2.71 Ga Ventersdorp Supergroep, en wydverspreide intrakratoniese graniet magmatisme teen die einde van die Neoargeïkum. 'n Moontlike verduideliking vir die kontras in metamorfe rekord in die twee terreine mag wees dat die 2.71 Ga granuliete 'n jonger sedimentêre afsetting verteenwoordig, en dat granuliete van die ouer terrein te restieties gelaat was na aansienlike anateksis in die Mesoargeïkum, om daaropvolgende hoëgraadse gebeure te registreer. Ten slotte, hierdie studie dokumenteer die besonderhede van S-tipe graniet magma produksie en ontginning van 'n tipiese metasedimentêre bron. Die 2.73 Ga granuliete word gebruik as 'n natuurlike veld laboratorium om die selektiewe optel-en-meevoering van peritektiese granaat tot die magma te ondersoek. Die werk toon die evolusie van peritektiese granate in sulke magmas aan, en ondersteun lewering van relatiewe mafiese graniet magmas deur 'n ‘peritektiese fase optel-en-meevoerings’ proses.

Les circulations de fluides dans la croûte sont les vecteurs de mobilités élémentaires dont une des conséquences est la concentration de métaux et la genèse de gisements. Ces fluides circulent dans les zones de déformation où ils modifient la composition des roches encaissantes. Dans la ceinture archéenne de roches vertes de Murchison (Afrique du Sud), l'Antimony Line est une zone déformée qui a été le siège de circulations de fluides minéralisateurs en Sb-Au. Pour caractériser les processus minéralisateurs, des données pétro-géochimiques, en particulier en isotopes stables et inclusions fluides, ont été associées à la datation multi-méthode (U-Th-Pb, Pb-Pb et Ar-Ar) des corps minéralisés et de leur encaissant au cœur et autour de l'Antimony Line. L'étude structurale de la région souligne le caractère distribué de la déformation. La ceinture a ainsi subi une phase majeure de collision d'arc, associée à un magmatisme important vers 2.97 Ga, contemporain d'une minéralisation en Au (±Sb) qui pourrait être responsable d'une phase de pré-enrichissement en Sb. La minéralisation principale en Sb est la conséquence de la circulation d'un fluide métamorphique à H2O-CO2, à 2-3 kbar et 350-450°C. L'albitisation de granitoïdes intrusifs dans l'Antimony Line, datée à 2.8 Ga, est génétiquement liée à cette circulation, laquelle s'inscrit donc dans l'histoire tectono-métamorphique tardive de la ceinture et est contemporaine de la mise en place de leucogranites sur la bordure sud. Ces résultats illustrent la pertinence du couplage pétro-géochimie/géochronologie pour la compréhension globale d'un système métallogénique.

Tte structure of the Kaapvaal Craton of southern Africa invesirgated by means of deep seismic sounding using mine tremors as the energy source, and by deep seismic reflection profiling. Seranoneru "9 ware deployed at 10 km intervals on two profiles stretching between the major mine tremor source regions, 15 stout 250 km in length. Record sections have ocnpiled for both P- and S-waves, and the travel-times and anplitudes interpreted using ray-tracing techniques. Synthetic seismograms have also been oenputed using the reflectivity method. A 16 s two-way-time seismic reflection profile, 112 km in length and traversing the northwestern portion of the Witwatersrand Basin, was surveyed during 1988 under the auspices of the National Geophysics Programme and the Geological Survey of South Africa. The reflection profile, which intersects both the refraction profiles, has been interpreted. The seianic models have been integrated with other geophysical and geological data. This study has shewn that the use of mine tremors for deep seismic sounding has particular advantages. Tremors are rich in shear energy, enabling joint interpretation of P- and S-waves and the estimation of Poisson's ratio. Tremors also have a wide bandwidth, with significant energy at frequencies as low as 3 Hz. Consequently reflections are produced from velocity gradient zones which are invisible to conventional reflection profiling using vibrators as the energy source. The seismic model for the Kaapvaal Craton has the following features: supracrustal strata 0-10 km thick; upper crystalline basement with P-velocities of 6.0-6.2 km/s; the boundary between upper and lower crust at a depth of ca. H km is either a discontinuity giving rise to reflections, or a gradient zone giving rise to a caustic; the lower crust has a uniform seismic velocity in the range 6.4-6.7 km/s; the crust mantle transition takes place over 1-3 km; and Moho at a depth of ca. 35 km. The lower crust was also found to be strongly attenuating, and to have a Poisson' s ratio of ca. 0.28. It is also known to be electrically conductive. These observations are in accord with the presence of hydrated mantle rock at the base of the crust.

Archean sulfur is recognized by anomalous isotopic signatures where D36S/D33S* = ~0.90. These signatures have been attributed to photolysis of SO2 in a low oxygen atmosphere and disappear from the rock concurrent with the timing of the Great Oxidation Event and the apparent rise in atmospheric oxygen. The main objective of this thesis is to examine the isotopic composition of sulfide minerals from different depositional environments and explore the mechanisms which preserve the anomalous signatures. The South African Witwatersrand and Pongola Supergroups are the primary study areas. Both are Mesoarchean in age and contain well-preserved sedimentary sequences. They were chosen as they contain a wide variety of lithostratigraphic occurrences of pyrite; here samples were collected from diamictites, paleosols and fluvial and marine clastic sedimentary rocks. The texture and morphology of sulfide grains were documented via reflected light microscopy, etching and backscattered electron imaging. This was combined with LA-ICP-MS trace element measurements to determine paragenesis. The sulfur isotope composition was defined through in-situ four isotope analysis using the SHRIMP-SI. Pyrite from diamictites returned mostly negative D33S and D36S values, in the ranges of -0.43 - 0.09 per mil (pm) and -1.95 - 0.15 pm, respectively. The d34S** values showed a range of -6.09 - 11.7 pm. Deviation in D36S from the atmospheric D36S/D33S array and variation in d34S is consistent with microbial sulphate reduction of atmospheric sulphate. The restricted d34S values observed in one sample set may represent input of mass-dependent crustal sulfur. Paleosol-hosted sulfide minerals had negative or near-zero D33S values, with a range of -0.50 - 0.17 pm, and near-zero D36S values, with a range of -0.99 - 0.52 pm. The d34S values showed a range of -8.88 - 6.87 pm. In samples where both D33S and D36S were ~0 pm, the sulfur is likely magmatic sulfur inherited from the igneous parent rocks. Samples with small negative D33S values likely preserve a mixture of atmospheric sulfate and inherited magmatic sulfur. Pyrite from fluvial rocks typically returned negative D33S and D36S values, with the majority of data falling in the ranges of -0.72 - 0.10 pm for D33S and -0.98 - 0.34 pm for D36S. The d34S values typically fell within the range of -3.21 - 9.65 pm. The muted negative D33S values and small d34S values are consistent with a mixture of atmospheric sulfate and mass-dependent crustal sulfur. The consist deviation in D36S from the atmospheric D36S/D33S array suggests microbial sulfate reduction. Shallow marine samples returned variable isotopic signatures. Several samples showed D36S/D33S = ~6.9, consistent with microbial sulfate reduction. These samples showed D33S values of -0.18 - 0.51 pm, D36S values of -2.05 - 0.02 pm and d34S values of -15.8 - 8.53 pm. Other samples showed D36S/D33S = ~-2, with D33S values of 0.11 - 0.80 pm and D36S values of -2.04 - -0.25 pm. The d34S values showed a range of -1.17 - 7.74 pm. Data from individual samples were observed to show consistent D33S but variable D36S, forming steep arrays extending downwards from the atmospheric D36S/D33S array. This was interpreted to represent microbial fractionation of atmospheric elemental sulfur. These results indicate that terrestrial and marine depositional environments preserve different isotopic signatures. Terrestrial environments favour preservation of atmospheric sulfate and marine environments favour preservation of atmospheric elemental sulfur. Within both environments, microbial processes were involved in preservation of the atmospheric sulfur species. Atmospheric signatures in terrestrial environments are muted, which is attributed to mixing of atmospheric and crustal sulfur. Signatures are also muted in marine samples, which may also be due to mixing, or possibly some other localized environmental effect. *D = Capital delta **d = lowercase delta

M.Sc. (Geology)
The south-easternmost Kaapvaal Craton is composed of scattered inliers of Archaean basement granitoid-greenstone terrane exposed through Phanerozoic cover successions. In addition, erosional remnants of the supracrustal Mesoarchaean Pongola Supergroup unconformably overlay this granitoid-greenstone terrane in the same inliers. Into this crust a variety of Precambrian intrusions occur. These are comprised of SE-, ENE- and NE-trending dolerite dykes. Also, the Hlagothi Complex intrudes into Pongola strata in the Nkandla region, particularly the quartzites of the basal Mantonga Formation. The whole area, including Phanerozoic strata, has in turn been intruded by Jurassic sills and dykes related to the Karoo Large Igneous Province. All the rocks of the Archaean inliers, with the exception of the Jurassic sills and dykes have been subjected to greenschist facies metamorphism and deformation, with petrographic, Ar-Ar geochronologic and palaeomagnetic studies attesting to this. This metamorphism and deformation is associated with the Mesoproterozoic orogeny from the nearby Namaqua-Natal Mobile Belt located to the south. This orogeny has a decreasing influence with distance from the cratonic margin, and is highly variable from locality to locality. However, it is generally upper greenschist facies up to a metamorphic isograd 50 km from the craton margin. Overprints directions seen within the palaeomagnetic data confirm directions associated with the post-Pongola granitoids across the region and the Namaqua-Natal Mobile Belt. The dolerite dykes consist of several trends and generations. Up to five different generations within the three Precambrian trends have potentially been recognised. SEtrending dykes represent the oldest dyke swarm in the area, being cross-cut by all the other dyke trends. These dykes consist of two possible generations with similar basaltic to basaltic andesite geochemistry. They provide evidence of a geochemically enriched or contaminated magma having been emplaced into the craton. This is similar to SE-trending dolerite dyke swarms across the Barberton-Badplaas region to the north from literature. In northern KwaZulu-Natal the SE-trending dolerite dyke swarms have been geochronologically, geochemically and paleomagnetically linked to either ca. 2.95 or ca. 2.87 Ga magmatic events across the Kaapvaal Craton. The 2866 ± 2 Ma Hlagothi Complex is composed of a series of layered sills intruding into Nkandla sub-basin quartzites of the Pongola Supergroup. The sills consist of meta-peridotite, pyroxenite and gabbro. At least two distinct pulses of magmatism have been recognised in the sills from their geochemistry. The distinct high-MgO units are compositionally different from the older Dominion Group and Nsuze Group volcanic rocks, as well as younger Ventersdorp volcanic rocks. This resurgence of high-MgO magmatism is similar to komatiitic lithologies seen in the Barberton Greenstone Belt. It is indicative of a more primitive magma source, such as one derived from a mantle plume. A mantle plume would also account for the Hlagothi Complex and the widespread distribution of magmatic events of possible temporal and spatial similarity across the craton. Examples include the layered Thole Complex, gabbroic phases of the ca. 2990 to 2870 Ma Usushwana Complex, and the 2874 ± 2 Ma SE-trending dykes of northern KwaZulu-Natal already described above and dated herein. A generation of NE-trending dolerite dykes in northern KwaZulu-Natal can also be palaeomagnetically linked to this event with either a primary or overprint direction. Flood basalts seen within the upper Witwatersrand and Pongola Supergroups (i.e., Crown, Bird, Tobolsk and Gabela lavas) may also be related. This large, voluminous extent of magmatism allows us to provide evidence for a new Large Igneous Province on the Kaapvaal Craton during the Mesoarchaean. This new Large Igneous Province would encompass all of the above mentioned geological units. It is possible that it could be generated by a shortlived transient mantle plume(s), in several distinct pulses. This plume would also explain the development of unconformities within the Mozaan Group. This is reasoned through thermal uplift from the plume leading to erosion of the underlying strata, culminating in the eruption of flood basalts coeval to the Hlagothi Complex. Marine incursion and sediment deposition would occur during thermal subsidence from the plume into the Witwatersrand-Mozaan basin. This magmatic event also assists in resolving the apparent polar wander path for the Kaapvaal Craton during the Meso- to Neoarchaean. Between existing poles established for the older ca. 2.95 Ga Nsuze event, to poles established for the younger ca. 2.65 Ga Ventersdorp event, a new magnetic component for this ca. 2.87 Ga magmatic event can be shown. This new component has a virtual geographic pole of 23.4° N, 53.4° E and a dp and dm of 8.2° and 11.8° for the Hlagothi Complex, with a similar magnetic direction seen in one generation of NE-trending dolerite dykes in the region. This new ca. 2870 Ma addition to the magmatic barcode of the Kaapvaal Craton allows for comparisons to be made to other coeval magmatic units on cratons from around the world. Specific examples include the Millindinna Complex and the Zebra Hills dykes on the Pilbara Craton. Precise age dating and palaeomagnetism on these magmatic units is needed to confirm a temporal and spatial link between all the events. If substantiated, this link would assist in further validating the existence of the Vaalbara supercraton during the Mesoarchaean. After the Hlagothi Complex event, different pulses of magma can be seen associated with the Neoarchaean Ventersdorp event. A generation of NE-trending dolerite dykes in the region was dated herein at 2652 ± 11 Ma. In addition, a primary Ventersdorp virtual geographic pole established in Lubnina et al. (2010) from ENE-trending dolerite dykes was confirmed in this study. This ENE-trending dolerite dyke has a virtual geographic pole of 31.7° S, 13.6° E and a dp and dm of 7.0° and 7.2°. This date and virtual geographic poles from NE- and ENE-trending dolerite dyke swarms in northern KwaZulu-Natal match up with NE- and E-trending palaeostress fields seen in the Neoarchaean Ventersdorp and proto- Transvaal volcanics by Olsson et al. (2010). Both generations of dolerite dykes also demonstrate variable geochemistry. The NE-trending dolerite dyke swarm is tholeiitic, and the ENE dolerite dyke swarm is calc-alkaline. In addition, some of the tholeiitic NE-trending dolerite dykes have a similar magnetic component to NE-trending dolerite dykes much further to the north in the Black Hills area according to Lubnina et al. (2010). This magnetic component is also similar to the Mazowe dolerite dyke swarm on the Zimbabwe Craton. The NE-trending dolerite dykes in the Black Hills area differ geochemically from those in northern KwaZulu-Natal though, but are also of ca. 1.90 Ga age. The Mazowe dolerite dyke swarm was linked to the dyke swarm of the Black Hills dyke swarm through palaeomagnetic studies. The Mazowe dolerite dyke swarm however is geochemically similar to the NE-trending dolerite dykes of northern KwaZulu-Natal, creating greater complexity in the relationship between the three dyke swarms. It is clear from the complex array of dolerite dyke swarms and other intrusions into these Archaean inliers of northern KwaZulu-Natal, that much more work on the dykes within the south-easternmost Kaapvaal Craton needs to be done. This will resolve these complex patterns and outstanding issues with regard to their palaeo-tectonic framework.

A suite of mafic dykes occurs as a late component in a wellcharacterized trondhjemite–tonalite–diorite–granodiorite assemblage in the Johannesburg Dome of the central Kaapvaal Craton, southern Africa. The dykes have been subdivided into two sets, based on their orientation, and major and trace element geochemistry. Set 1 dykes are characterized by elevated SiO2, Al2O3 and TiO2, and particularly by enriched LILE and HSFE (e.g. Zr > 200 ppm, Nb > 20 ppm, Ba > 300 ppm), higher than in any of the accompanying felsic rocks. REE and trace element values for Set 1 dykes are similar to those for calc-alkaline lamprophyres. The Set 2 dykes have similar trace element distributions, but are significantly less enriched in general, and are broadly tholeiitic in composition, with enriched MgO (>11 wt.%) indicative of an olivine–phyric tholeiitic basaltic protolith. Field relationships and available U–Pb zircon geochronology indicate that the dykes are contemporaneous with components of the trondhjemitic host rocks, and with late granodiorites. The geochemical, geochronological and field petrological setting indicates partial melting of basaltic and eclogitic lithosphere at c. 3120 Myr ago in the basal Kaapvaal Craton, and subsequent emplacement into pre-existing c. 3430 Myr tonalitic to dioritic crust.

Ph.D. (Geology)
Shear zone controlled hydrothermal alteration zones in the northern Kaapvaal craton (NKC) are developed in host rocks of vastly different chemical composition and metamorphic grade. Some carry appreciable Au and base metals and some are barren. Alteration zones in three different distinctive crustal zones were examined in detail to determine the controls of these two types of alteration. 1. The Matok Complex is situated in the southern marginal zone (SMZ) of the Limpopo Belt (LB), close to the zone of rehydration. Two major stages of hydrothermal alteration could be identified in local shear zones, a pervasive propylitization and a subsequent vein controlled quartzalbite alteration. The two-stage alteration occurred sometimes between the emplacement of the Matok Complex (2670 Ma) and the intrusion of unaltered mafic dykes (1900 Ma). Calculated isotopic compositions of the hydrothermal fluids indicate that magmatic ± meteoric waters as well as juvenile C02 were responsible for the establishment of the alteration zones. The fluids most probably were late magmatic fluids associated with the Matok magmatism. The propylitic alteration was accompanied by introduction of small amounts of CU + Au and represents an alteration type identical to that developed in porphyry copper deposits. The subsequent quartz-albite alteration was caused by extremely saline fluids which depleted the rocks of all the major and trace elements with exception of Si, Al, Na and Zr. 2. This chemical alteration pattern' contrasts with those developed in two alteration zones associated with economic gold mineralization in greenstone belts of the NKC (Sutherland and Pietersburg belts). At the Birthday and Eersteling gold mines, a biotite-calcite-quartz alteration is developed. The chemical pattern of the alteration is...

The provenance of the Neoarchaean Ventersdorp Supergroup and several age-related supracrustal successions was analysed to gain insight into the geotectonic evolution of the Kaapvaal Craton during the transition from the Archaean to Proterozoic Eras. The studied successions include, besides the siliciclastic formations of the Ventersdorp Supergroup, the upper Wolkberg and Buffelsfontein Groups, the Godwan Formation and the Schmidtsdrift Subgroup of the basal Transvaal Supergroup in Griqualand West. Petrographic, whole rock geochemical and Sm-Nd isotopic analyses were combined with SHRIMP U-Pb age dating of detrital zircons. Furthermore, Rb-Sr isotopic studies were carried out on carefully selected suites of samples from surface exposure or, wherever possible, on deep diamond drill core. The Ventersdorp Supergroup is an up to 5 km thick undeformed, only slightly metamorphosed volcano-sedimentary succession deposited on the Kaapvaal Craton between 2714 Ma and 2665 Ma. A lack of major time hiati to the underlying Mesoarchaean Witwatersrand Supergroup and covering Neoarchaean to Palaeoproterozoic Transvaal Supergroup render the Ventersdorp Supergroup very well suited for the investigation of the geotectonic evolution of the Kaapvaal Craton near the Archaean-Proterozoic boundary. This is supported by its excellent preservation, which also allowed detailed studies of sedimentological structures, such as seismites indicating Neoarchaean earthquakes. The provenance analyses carried out on the clastic formations of the Ventersdorp Supergroup point to a gradual change in tectonic evolution from typically Archaean to post-Archaean processes rather than a drastic, unique transition in the case of the Kaapvaal Craton. Texturally immature wackes of the Kameeldoorns Formation, representing the oldest clastic units of the Ventersdorp Supergroup, are derived mainly from Mesoarchaean source rocks, whereas the stratigraphically younger Bothaville Formation displays geochemical signatures comparable with Archaean trondhjemite-tonalite granodiorite-suites (TTGs), thus suggesting crustal addition in the so-called ‘Archaean-style’. The extension of provenance analyses to supracrustal successions that are tentatively correlated with the Bothaville Formation, revealed contributions from granitoid V sources that formed under post-Archaean and Archaean conditions. Furthermore, the geochemical data for all analysed formations support a passive margin setting. Arc settings, as indicated in some samples, are due to the input of less fractionated volcanic material that provides evidence of distal volcanism. Analyses of Nd-isotopic systematics and U-Pb ages of detrital zircons revealed a Mesoarchaean age for the source rocks of the formations. U-Pb age dating of detrital zircons of the Godwan Formation suggests that this formation is of Mesoarchaean age, and therefore not a correlative of the other Neoarchaean successions. Hence, the results suggest that the continental crust of the Kaapvaal Craton was thick enough since the Mesoarchaean (2.8 - 3.1 Ga) to allow long-term crustal recycling, and therefore modern plate tectonic processes could have operated earlier than on other well-studied cratonic blocks. During the Neoarchaean, however, crustal thickening of the Kaapvaal Craton took place by accretion of Archaean-style TTGs along the margins of the craton. Thus, Archaean and post-Archaean tectono-magmatic processes co-existed. Furthermore, the Neoarchaean supracrustal successions represent the first sedimentation events on an entirely stabilised and tectonically quiescent Kaapvaal Craton. Input from distal volcanic sources marks the last sign of volcanic activity prior to the craton-wide deposition of carbonate rocks of the Transvaal Supergroup. Geochronological data also imply a connection of the Neoarchaean Kaapvaal Craton to further cratonic blocks that may hold source rocks for the studied formations, as for some small age populations of older detrital zircons (ca. 3.1 - 3.4 Ga), no suitable source area could be identified on the Kaapvaal Craton itself. However, it seems unlikely that the Zimbabwe Craton was one of these cratonic blocks, because the Rb-Sr whole rock ages of all studied formations yield a model age of 2092 ± 55 Ma, which is thought to correspond to a craton-wide influence of the 2.05 Ga old Bushveld Igneous Complex on the Rb-Sr isotope systematics of all analysed clastic successions. This influence is apparently missing in the Southern and Central Marginal Zones of the Limpopo Belt, suggesting that the collision between the Kaapvaal and Zimbabwe Cratons only took place after the emplacement of the Bushveld Igneous Complex, i.e. after 2.05 Ga.
Dr. U. Zimmermann Prof. J. Gutzmer

A stratigraphic and structural study of the Archaean Pongola Sequence on the southeastern Kaapvaal Craton centred on the area around the Klipwal Gold Mine is described. The lower predominantly volcanic Nsuze Group is overlain with a gradational transition by the upper clastic Mozaan Group in which six formations are recognized. The Sinqeni, Ntombe, Thalu, Hlashana, Odwaleni and the Kulphiso Formations. The Sinqeni and Hlashana Formations are predominantly arenaceous while the Ntombe and Kulphiso Formations are mainly argillaceous. The Odwaleni Formation contains a diamictite which is interpreted as a tillite, and is therefore the oldest glacial rock on record. The stratigraphic position of the Kulphiso Formation is problematic. The Mozaan Group was deposited in a deepening epeiric sea which was invaded periodically by storm generated deposits. Dolerite and ultramafic dykes and sills of various ages are represented. Three phases of deformation are recognized in the Klipwal area. Early compression from the south-southeast initiated a major zone of bedding-parallel shear, the Izermijn shear zone, along the Nsuze-Mozaan contact and an oblique ramp, the Klipwal shear zone, at a higher stratigraphic level. An extensional phase caused reactivation of the Klipwal shear zone and the development of a major low-angle normal fault, the Gu'nsteling fault, above the Sinqeni Formation. The main phase of deformation, related to northeast-southwest compression is the most complex and most widely developed. Early northwest-trending subhorizontal upright folds were disrupted by contemporaneous north-striking dextral or dextral reverse shearing and northwest-striking sinistral or sinistral normal shearing. The obtuse relationship of these shear zones to the compression direction is probably the result of reactivation of basement structures with similar orientations. Northwest-trending folding continued during and after the shearing. The structural styles and orientations observed in the Klipwal area are recognized regionally in the main Pongola basin, highlighting the need for further detailed studies before basin-wide correlations are made.
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1993.

D.Phil.
The western margin of the Archean Kaapvaal Craton, at its contact with the polydeformed and metamorphosed Proterozoic Namaqua Province, is host to four volcanosedimentary successions of Mesoproterozoic age (1.1-1.3 Ga) that occur in close spatial and temporal association to each other. These are the Areachap Group, the Leerkrans Formation of the Wilgenhoutsdrif Group and the two volcanosedimentary successions that comprise the Koras Group. There has been protracted debate as to the exact nature, origin, age and tectonic evolution of these successions, particularly as they occur immediately adjacent to an important crustal suture. A comprehensive whole rock and isotope geochemical study, complemented by zircon-based geochronology where necessary, was thus carried out to characterize and compare the volcanic rocks associated with these four successions. The results are used to assess the role of the four volcanosedimentary successions during the development of the Mesoproterozoic suture between the Kaapvaal Craton and the Namaqua Province during the ~1.2-1.0 Ga Namaquan Orogeny. The geochemical study of the Areachap Group examined a suite of lithologies from different locations along the ~280km long outcrop belt, with the aim of testing the lateral continuity and integrity of this highly metamorphosed and deformed succession. As the bulk of the samples collected were from diamond drill core intersecting volcanogenic massive sulphide (VMS) Zn-Cu deposits it was only appropriate to extend the investigation to assess the metallogenesis and relation of these deposits to their host rock sequences. This included a survey of the sulphur isotope composition of sulphides and sulphates that comprise the Zn-Cu deposits. Furthermore, the architecture and origin of the world-class Copperton deposit, the largest Zn-Cu deposit of the Areachap Group, was examined. For this purpose, available literature data were collated and complemented by new geochemical and geochronological information. Sm-Nd isotopic systematics and U-Pb zircon ages suggest a coeval origin and close genetic link between the metavolcanic rocks of the Leerkrans Formation of the Wilgenhoutsdrif Group and the Areachap Group. Both successions record the establishment of an eastward-directed subduction zone on the western margin of the Kaapvaal Craton. The Areachap Group represents the highly metamorphosed and deformed remnants of a Mesoproterozoic (ca. 1.30-1.24 Ga) volcanic arc that was accreted onto the western margin of the Kaapvaal Craton at ~1.22-1.20 Ga, during the early stages of the Namaquan Orogeny. The igneous protoliths within the Areachap Group are low- to medium-K tholeiitic to calc-alkaline in composition ranging in composition from basaltic through to rhyolitic. Tholeiitic basalts, represented by volumetrically minor amphibolites within the succession have Sm-Nd isotopic characteristics indicative of derivation from a depleted mantle source as denoted by their positive Nd(t) values. The lithogeochemical results highlight the fact that, despite differences in lithological architecture on a local scale, the Areachap Group exhibits coherent geochemical characteristics along its entire strike length.

The Kaapvaal craton of southern Africa and the Pilbara craton of Western Australia, two of the best-preserved Archean cratons in the world, are covered by remarkably similar early Precambrian cover sequences. This has led to the proposal of the so-called Vaalbara hypothesis, which promotes the existence of the two cratons as a single crustal entity, and possibly, Earth’s oldest assembled continent in Neoarchean-early Paleoproterozoic times. Previous studies have failed to prove the existence of Vaalbara conclusively, principally due to a lack of reliable ages or because of uncertainty and gaps in the paleomagnetic record from the Kaapvaal craton. During the present study paleomagnetic samples were collected from selected Neoarchean- Paleoproterozoic cover sequences of the Kaapvaal craton for the establishment of well-defined paleomagnetic poles. In addition, the Hartswater Group of the Ventersdorp Supergroup was sampled for zircon SHRIMP analyses in order to constrain the ages of poles defined from that succession. The paleopoles established here, together with existing paleopoles from the Kaapvaal craton, are used to evaluate the apparent polar wander path of the craton during the Neoarchean-Paleoproterozoic and are compared with poles of similar age from the Pilbara craton as a test of the Vaalbara hypothesis. Regarding the age of the Hartswater Group, zircon SHRIMP ages of 2735 ± 3 Ma and 2724 ± 6 Ma cast doubt on younger ages from the Klipriviersberg Formation, which comprise the base of the Ventersdorp Supergroup. Traditional (younger) age constraints from the Ventersdorp Supergroup do not support the original Vaalbara correlation. A new correlation is suggested here, taking the new ages into account, showing that the Ventersdorp Supergroup overlaps in time with the Fortescue Group of the Pilbara craton. Most importantly, the new ages also provide constraints on the magnetization within the Platberg Group and the Allanridge Formation. Six new paleopoles, of various quality, are added to the existing database from that craton. These poles from the ~2.73 Ga Platberg Group and ~2.7Ga Allanridge Formation of the Ventersdorp Supergroup, the ~2.5Ga lower Transvaal Supergroup, the lower two unconformitybounded sequences of the Waterberg Group (2.05 Ga and ~1.99 Ga) and the upper Soutpansberg Group (~1.76 Ga) have, together with existing poles from the Kaapvaal craton, led to the definition of an APWP for that craton for a period ~2.78 to ~1.76 Ga. Particularly the poles from the Waterberg and Soutpansberg Groups provided the information to identify complexities (looping) in the APWP that have gone unrecognized in the past. The paleomagnetic data gathered and the newly defined APWP could be used in conjunction with geological evidence from the Kaapvaal and Pilbara cratons to evaluate, and validate, the Vaalbara hypothesis. A good match between the APWP’s of the two cratons for the period ~2.78 to ~2.70 Ga and the geological features (lithology and structure) of the two cratons provide the best evidence that Vaalbara existed as a cratonic unit in the late Archean. Paleomagnetic data constrain the position of the Pilbara craton in immediate proximity to the northwest of the Kaapvaal craton (in a Kaapvaal reference frame). The position of the Zimbabwe craton relative to the Pilbara and Kaapvaal cratons is still unresolved, but indications are that it was most likely in a proximal position to the Kaapvaal craton at 2.7 Ga in a configuration not much different from its present day configuration. This would imply that Vaalbara was most probably the Earth’s oldest assembled continent as proposed by earlier workers. The new paleomagnetic data further suggest that Vaalbara did not exist anymore at ~2.0Ga. When evaluated in conjunction with geological evidence a strong argument can be made for the existence of the Vaalbaran continent up until ~2.22 Ga and that the Pilbara and Kaapvaal cratons became separate entities from about ~2.05 Ga.
Prof. NJ Beukes Prof. DAD Evans

The Kaapvaal Craton hosts a number of large gold deposits (e.g. Witwatersrand Supergroup) which mining companies have exploited at certain stratigraphic positions. It also hosts the largest platinum group element (PGE) deposits (e.g. Bushveld Igneous Complex) which mining companies have exploited in different mineralised layered magmatic zones. In spite of the extensive exploration history in the Kaapvaal Craton, the origin of the Witwatersrand gold deposits and Bushveld Igneous Complex PGE deposits has remained one of the most debated topics in economic geology. The goal of this study was to identify the geochemical characteristics of marine shales in the Barberton, Witwatersrand, and Transvaal supergroups in South Africa in order to make inferences on their sediment provenance and siderophile element endowments. Understanding why some of the Archaean and Proterozoic hinterlands are heavily mineralised, compared to others with similar geological characteristics, will aid in the development of more efficient exploration models. Fresh, unmineralised marine shales from the Barberton (Fig Tree and Moodies groups), Witwatersrand (West Rand and Central Rand groups), and Transvaal (Black Reef Formation and Pretoria Group) supergroups were sampled from drill core and underground mining exposures. Analytical methods, such as X-ray powder diffraction (XRD), optical microscopy, X-ray fluorescence (XRF), inductively coupled plasma optical emission spectroscopy (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), and electron microprobe analysis (EMPA) were applied to comprehensively characterise the shales. All of the Au and PGE assays examined the newly collected shale samples. The Barberton Supergroup shales consist mainly of quartz, illite, chlorite, and albite, with diverse heavy minerals, including sulfides and oxides, representing the minor constituents. The regionally persistent Witwatersrand Supergroup shales consist mainly of quartz, muscovite, and chlorite, and also contain minor constituents of sulfides and oxides. The Transvaal Supergroup shales comprise quartz, chlorite, and carbonaceous material. Major, trace (including rare-earth element) concentrations were determined for shales from the above supergroups to constrain their source and post-depositional evolution. Chemical variations were observed in all the studied marine shales. Results obtained from this study revealed that post-depositional modification of shale chemistry was significant only near contacts with over- and underlying coarser-grained siliciclastic rocks and along cross-cutting faults, veins, and dykes. Away from such zones, the shale composition remained largely unaltered and can be used to draw inferences concerning sediment provenance and palaeoweathering in the source region and/or on intrabasinal erosion surfaces. Evaluation of weathering profiles through sections of the studied supergroups revealed that the shales therein are characterised by high chemical index of alteration (CIA), chemical index of weathering (CIW), and index of compositional variability (ICV), suggesting that the source area was lithologically complex and subject to intense chemical weathering. A progressive change in the chemical composition was identified, from a dominant ultramafic–mafic source for the Fig Tree Group to a progressively felsic–plutonic provenance for the Moodies Group. The West Rand Group of the Witwatersrand Supergroup shows a dominance of tonalite–trondhjemite–granodiorite and calcalkaline granite sources. Compositional profiles through the only major marine shale unit within the Central Rand Group indicate the progressive unroofing of a granitic source in an otherwise greenstone-dominated hinterland during the course of sedimentation. No plausible likely tectonic setting was obtained through geochemical modelling. However, the combination of the systematic shale chemistry, geochronology, and sedimentology in the Witwatersrand Supergroup supports the hypothesised passive margin setting for the >2.98 to 2.91 Ga West Rand Group, and an active continental margin source for the overlying >2.90 to 2.78 Ga Central Rand Group, along with a foreland basin setting for the latter. Ultra-low detection limit analyses of gold and PGE concentrations revealed a variable degree of gold accumulation within pristine unmineralised shales. All the studied shales contain elevated gold and PGE contents relative to the upper continental crust, with marine shales from the Central Rand Group showing the highest Au (±9.85 ppb) enrichment. Based on this variation in the provenance of contemporaneous sediments in different parts of the Kaapvaal Craton, one can infer that the siderophile elements were sourced from a fertile hinterland, but concentrated into the marine shales by a combination of different processes. It is proposed that accumulation of siderophile elements in the studied marine shales was mainly controlled by mechanical coagulation and aggregation. These processes involved suspended sediments, fine gold particles, and other trace elements being trapped in marine environments. Mechanical coagulation and aggregation resulted in gold enrichments by 2–3 orders of magnitude, whereas some of the gold in these marine shales can be reconciled by seawater adsorption into sedimentary pyrite. For the source of gold and PGEs in the studied marine shales in the Kaapvaal Craton, a genetic model is proposed that involves the following: (1) A highly siderophile elements enriched upper mantle domain, herein referred to as “geochemically anomalous mantle domain”, from which the Kaapvaal crust was sourced. This mantle domain enriched in highly siderophile elements was formed either by inhomogeneous mixing with cosmic material that was added during intense meteorite bombardment of the Hadaean to Palaeoarchaean Earth or by plume-like ascent of relics from the core–mantle boundary. In both cases, elevated siderophile elements concentrations would be expected. The geochemically anomalous mantle domain is likely the ultimate source of the Witwatersrand modified palaeoplacer gold deposits and was tapped again ca. 2.054 Ga during the emplacement of the Bushveld Igneous Complex. Therefore, I propose that there is a genetic link (i.e. common geochemically anomalous mantle source) between the Witwatersrand gold deposits and the younger Bushveld Igneous Complex PGE deposits. (2) Scavenging of crustal gold by various surface processes such as trapping of gold from Archaean/Palaeoproterozoic river water on the surface of local photosynthesizing cyanobacterial or microbial mats, and reworking of these mats into erosion channels during flooding events. The above two models complement each other, with model (1) providing a common geological source for the Witwatersrand gold and Bushveld Igneous Complex PGE deposits, and model (2) explaining the processes responsible for Witwatersrand-type gold pre-concentration processes. In sequences such as the Transvaal Supergroup, a less fertile hinterland and/or less reworking of older sediments led to a correspondingly lower gold endowment. These findings indicate temporal distribution of siderophile elements in the upper crust (e.g. marine shales). The overall implications of these findings are that background concentrations of gold and PGEs can be used to target potential exploration areas in other cratons of similar age. This increases the likelihood of finding other Witwatersrand-type gold or Bushveld Igneous Complex-type PGE deposits in other cratons
Der Kaapvaal Kraton beherbergt eine Vielzahl großer Goldlagerstätten (vor allem in der Witwatersrand Hauptgruppe), die von Bergbaugesellschaften in ihrer jeweiligen stratigraphischen Position abgebaut werden. Im diesem Kraton liegen auch die größten Lagerstätten für Platingruppenelemente (vornehmlich im Bushveld Komplex), die aus diversen magmatischen Intrusionskörpern gewonnen werden. Trotz der intensiven und langen Explorationsgeschichte im Bereich des Kaapvaal Kratons ist die Herkunft des Goldes in den Witwatersrand Lagerstätten und die der Platingruppenelemente in den Lagerstätten des Bushveld-Komplex noch ungeklärt und Gegenstand aktueller Diskussionen. Ziel der Arbeit war die geochemische Charakterisierung von Tonschiefern in den Barberton-, Witwatersrand und Transvaal-Hauptgruppen, um Aussagen über deren Provenienz zu treffen und die Gehalte an siderophilen Elementen darin zu ermitteln. Ein verbessertes Verständnis, warum manche archaischen und proterozoischen Einheiten stark mineralisiert sind und andere nicht, sollte bei der Planung zukünftiger Explorationsprojekte dienlich sein. Um dieses Ziel zu erreichen, wurden unalterierte und nicht mineralisierte Proben mariner Tonschiefer aus der Barberton Hauptgruppe (Fig Tree und Moodies Gruppen), der Witwatersrand Hauptgruppe (West Rand und Central Rand Gruppen) und der Transvaal Hauptgruppe (Black Reef Formation und Pretoria Gruppe) aus Untertage Bergbau-Bereichen sowie aus Bohrkernen genommen. Zur Charakterisierung der Tonschiefer kamen verschiedene Methoden zum Einsatz, darunter die Pulverdiffraktometrie (XRD), Durchlichtmikroskopie, Röntgenfluoreszenz (XRF), Optische Emissionsspektroskopie (ICP-OES), Laserablationsmassenspektrometrie (ICP-MS) und Elektronenstrahlmikrosonde (EMPA), sowie Bestimmung der Gold und Platingruppen-Elementkonzentrationen mittels Graphitrohr-AAS nach Voranreicherung mit der Nickelsulfid-Dokimasie. Die untersuchten Tonschiefer verhielten sich seit ihrer Ablagerung als größtenteils geschlossene Systeme. Nur entlang der Kontakte mit unter- und überlagernden grobkörnigeren Metasedimentgesteinen sowie entlang durchkreuzender Störungen, Quarzadern und Gängen konnte lokal nennenswerte Alteration festgestellt werden. Solche Zonen wurden explizit von der Provenienz-Analyse ausgenommen. Systematische Unterschiede in der primären chemischen Zusammensetzung einzelner Tonschiefer-Abfolgen belegen unterschiedliche Sedimentquellen. So wurde in der Barberton Hauptgruppe der Sedimenteintrag der Fig Tree-Gruppe von einer ultramafisch-mafischen Quelle dominiert, während in der Moodies-Gruppe felsische Quellen eine zunehmende Rolle spielten. In der Witwatersrand Hauptgruppe wurde eine Dominanz von Tonalit-Trondhjemit-Granodiorit sowie kalkalkaline Granite im Liefergebiet der West Rand Gruppe festgestellt, während in der Central Rand Gruppe anfänglich mafisch-ultramafische Gesteine im Sedimentliefergebiet vorherrschten, im Lauf der Zeit aber granitische Gesteine mehr und mehr durch Erosion im Hinterland freigelegt worden waren. Die Geochemie der Witwatersrand Tonschiefer unterstützt die Hypothese, dass die Sedimente der West Rand Gruppe an einem passiven Kontinentalrand abgelagert wurden, jene der Central Rand Gruppe in einem Vorlandbecken. Alle untersuchten archaischen Tonschiefer zeigen, verglichen mit dem Durchschnitt der oberen Erdkruste, deutlich erhöhte Gehalte an Gold und Platingruppenelementen, wobei die marinen Tonschiefer aus der Central Rand Gruppe mit durchschnittlich 9,85 ppm Au die höchsten Konzentrationen aufweisen. Die Gehalte an siderophilen Elementen in der palaeoproterozoischen Transvaal Hauptgruppe nähern sich hingegen typischen kontinentalen Krustenwerten an. Der verstärkte Eintrag von Au und PGE in die archaischen marinen tonigen Sedimente wird durch mechanische Koagulation und Aggregation erklärte, wobei feinstkörnige Goldpartikel im suspendierten Sediment weit ins Meer transportiert worden sind. Adsorption von Au aus Meerwasser an syn-sedimentärem Pyrit spielte auch eine Rolle, aber keine ausschlaggebende. Für die Quelle des Goldes und der Platingruppenelemente in den untersuchten Tonschiefern wurde folgendes genetisches Modell entwickelt. (1) Es wird angenommen, dass sich die Kaapvaal-Kruste aus einem Mantelreservoir differenzierte, welches an siderophilen Elementen angereichert war. Diese Anreicherung könnte entweder das Produkt eines nicht vollständig homogenisierten Eintrags kosmischen Materials sein, welches im Hadaikum oder im Paläoarchaikum durch intensives Meteoritenbombardement eingebracht wurde, oder durch den Aufstieg eines Manteldiapirs aus dem Bereich der Kern-Mantel-Grenze. (2) Tiefgründige Verwitterung unter anoxischen Bedingungen ermögliche die Freisetzung großer Mengen von Au, welches in gelöster Form über Oberflächenwässer in den archaischen Ozean transportiert wurde. Hinweise auf solch intensive Verwitterung liefern die geochemischen Daten der hier untersuchten Tonschiefern, insbesondere hohe chemische Alterationsindizes. Fixierung dieses Goldes durch verschiedene Oberflächenprozesse, wie Filterung aus archaischen/paläoproterozoischen Flüssen durch Photosynthese-betreibende Bakterienrasen führte vor allem im Mesoarchaikum in Zeiten der Sedimentation der Central Rand Gruppe zu lokal extremen Goldanreicherungen, die in der Folge durch Erosion und mechanischen Transport großteils weiter umgelagert wurden. Punkt 1 könnte eventuell die räumliche Nähe der weltweit größten bekannten Goldanomalie im Witwatersrand Becken und der größten PGE-Anomalie im Bushveld Komplex erklären. In wie weit die erhöhten Hintergrundkonzentrationen von Gold und Platingruppenelementen im Kaapvaal Kraton einzigartig sind, gilt es in zukünftigen Studien dieser Art auch an marinen Tonschiefern aus dem Archaikum in anderen Kratonen zu testen

M.Sc.
The Kaapvaal craton is one of few regions on earth with an almost continuous record of wellpreserved supracrustal rocks ranging in age from ~3.5 Ga to the late Paleoproterozoic at ~1.75 Ga. In this study diagenetic carbonates from the Paleoarchean Buck Reef Chert and Joe’s Luck Formation of the Swaziland Supergroup, the Mesoarchean Thalu and Promise Formations of the Mozaan/Witwatersrand Supergroups and the Paleoproterozoic Timeball Hill and Silverton Formations of the Transvaal Supergroup were sampled and analyzed. The aim of the study was to determine possible variations in the composition of the carbonates through time and their significance especially with regards to microbial activity in diagenetic systems in early Earth history. Results indicate similar petrographic observations and geochemical signatures in diagenetic carbonates of iron formations in the Buck Reef Chert, Joe’s Luck and Griquatown Iron Formation. The carbonates all tend to be siderites with iron derived from hydrothermal input and all are depleted in 13C relative to Peedee Belemnite standard. It suggested that siderite formed as a result of microbial respiration. Microbes degrade organic matter and reduce iron in this process. This resulted in the depletion in 13C and in the precipitation of siderite. However in order for iron reduction to have occurred the reduced iron first had to be oxidized. This most probably occurred through iron oxidizing chemolithoautotrophs under microaerophilic conditions. Diagenetic carbonate concretions of the Thalu and Promise Formations are manganiferous and are highly depleted in 13C relative to PDB. There is also strong evidence for hydrothermal input of manganese and iron into the system because of positive europium anomalies. The carbonates from both of the formations strongly suggest the presence of some free oxygen. The reasoning behind this conclusion is as follows: The depletion of 13C in the carbonates points to microbial decomposition of organic matter and manganese respiration (the decomposition of organic matter by microbial MnO2 reduction) is shown to be the most reasonable process that led to the formation of the carbonate concretions. The implication is that MnO2 must first have been precipitated and that can only be achieved in the presence of free oxygen with the oxidation reaction often catalyzed by manganese oxidizing chemolithoautotrophs. The carbonates of the Timeball Hill and Silverton Formationsare calcites ad contain little no iron. There is also little or no evidence for hydrothermal input and the basin appears to be a clastic dominated. It is generally accepted that a major rise in oxygen in the oceans and the atmosphere occurred at about 2.32 Ga. This rise in oxygen levels is reflected in the diagenetic calcite concretions of the Silverton Formation. Both iron and manganese reduction where not very effective because of the depletion in the basin water of these two elements, organic carbon taken up in the calcite concretions, indicated by negative δ13CPDB carbonate values, was most probably derived from aerobic and/or nitrate respiration. The most important conclusion from this study is that sufficient free oxygen and hence oxygenic photosynthesis were present to oxidize both Fe and Mn at least as far back as the Paleo-Mesoarchean.

D.Phil.
The tectonic history of the Kheis Terrane and its relationship with the Namaqua-Natal Metamorphic Province (NNMP) along the western margin of the Kaapvaal Craton were the focus of this study. Major issues addressed in this study are the origin and timing of formation of the Kheis Terrane and the recognition and definition of terrane boundaries in the area. Results of detailed measured sections across the Kheis Terrane, heavy mineral provenance studies, 40Ar/39Ar analyses of metamorphic muscovite, U-Pb SHRIMP dating of detrital zircon grains from 12 samples from the Kheis- and Kakamas Terranes and one igneous body from the Kakamas Terrane are presented. A new stratigraphic unit, the Keis Supergroup, comprising the Olifantshoek-, Groblershoop- and Wilgenhoutsdrif Groups, is defined. The base of the Keis Supergroup is taken at the basal conglomerate of the Neylan Formation. The Mapedi- and Lucknow Formations, previously considered part of the Olifantshoek Group, are now incorporated into the underlying Transvaal Supergroup. The Dabep Fault was found not to represent a terrane boundary. Rather, the Blackridge Thrust represents the boundary between the rocks of the Kheis Terrane and the Kaapvaal Craton. Provenance studies indicate that the rocks of the Keis Supergroup were deposited along a passive continental margin on the western side of the Kaapvaal-Zimbabwe Craton with the detritus derived from a cratonic interior. Detrital zircon grains from the rocks of the Keis Supergroup of the Kheis Terrane all gave similar detrital zircon age populations of ~1800Ma to ~2300Ma and ~2500Ma to ~2700Ma. The Kaapvaal Craton most probably never acted as a major source area for the rocks of the Keis Supergroup because of the lack of Paleo- to Mesoarchean zircon populations in the Keis Supergroup. Most of the detrital zircon grains incorporated into the Keis Supergroup were derived from the Magondi- and Limpopo Belts and the Zimbabwe Craton to the northeast of the Keis basin. The rock of the Kakamas Terrane was derived from a totally different source area with ages of ~1100Ma to ~1500Ma and ~1700Ma to ~1900Ma which were derived from the Richtersveld- and Bushmanland Terranes as well as the ~1166Ma old granitic gneisses ofthe Kakamas Terrane. Therefore the rocks of the Kheis- and Kakamas Terranes were separated from each other during their deposition. Detrital zircon populations from the Sprigg Formation indicate that it this unit was deposited after the amalgamation of the Kheis- and Kakamas Terranes and therefore does not belong to the Areachap Group. Results provide clear evidence for a tectonic model characterised by the presence of at least two Wilson cycles that affeected the western margin of the Kaapvaal Craton in the interval between the extrusion of the Hartley lavas at 1.93Ga and the collision with the Richtersveld tectonic domain at ~1.13Ga. According to the revised plate tectonic model for the western margin of the Kaapvaal- Zimbabwe Craton, the Neylan Formation represents the initiation of the first Wilson Cycle, with rifting at ~1927Ma ago, on the western margin of the Kaapvaal-Zimbabwe Craton. The metasedimentary rocks of the Olifantshoek Group were deposited in a braided river environment which gradually changed into a shallow marine environment towards the top of the Olifantshoek Group in the Top Dog Formation. The metasedimentary rocks of the Groblershoop Group were deposited in a shallow, passive or trailing continental margin on the western side of the Kaapvaal-Zimbabwe Craton. The rocks of the Wilgenhoutsdrif Group overlie the Groblershoop Group unconformably. This unconformity is related to crustal warping as a volcanic arc, represented by the metavolcanics of the Areachap Group, approached the Kaapvaal-Zimbabwe Craton from the west. The rocks of the Keis Supergroup were deformed into the Kheis Terrane during the collision of the Kaapvaal-Zimbabwe Craton, Areachap Arc and the Kgalagadi Terrane to form the Kaapvaal-Zimbabwe-Kgalagadi Craton. This event took place sometime between 1290Ma, the age of deformed granites in the Kheis Terrane and 1172Ma, the initiation of rifting represented by the Koras Group. This is supported by 40Ar/39Ar analyses of metamorphic muscovite from the Kheis Terrane that did not provide any evidence for a ~1.8Ga old Kheis orogeny (an age commonly suggested in the past for this orogeny). This collisional event resulted in the deformation of the rocks of the Keis Supergroup into the Kheis Terrane sometime between 1290Ma and 1172Ma.The second Wilson cycle was initiated during rifting along the Koras-Sinclair-Ghanzi rift on the Kaapvaal-Zimbabwe-Kgalagadi Craton at ~1172Ma. It was followed soon after by the initiation of subduction underneath the Richtersveld cratonic fragment at ~1166Ma after which the rocks of the Korannaland Group were deposited. The closure of the oceanic basin between the Kaapvaal-Zimbabwe-Kgalagadi Craton and the Richtersveld cratonic fragment occurred about 50Ma later (~1113Ma, the age of neomorphic muscovite in the metasedimentary rocks of the Kakamas Terrane) and resulted in the large open folds characterising the Kheis terrane and NNMP. Detrital zircon populations in the Sprigg Formation show that this formation does not belong to the Areachap Group and that it was deposited after the closure of the oceanic basin between the Kaapvaal-Zimbabwe-Kgalagadi Craton and the Richtersveld cratonic fragment at ~1113Ma. The Areachap Group can be extended towards the north and into Botswana along the Kalahari line where it forms the boundary between the Kaapvaal-Zimbabwe Craton to its east and the Kgalagadi Terrane to its west. The Areachap Terrane is thus related to the collision of the Kaapvaal-Zimbabwe Craton and Kgalagadi Terrane and was deformed a second time during the oblique collision of the Richtersveld cratonic fragment with the combined Kaapvaal-Zimbabwe-Kgalagadi Craton. The extension of the Areachap Group to the north along the Kalahari line opens up new exploration prospects for Coppertontype massive sulphide deposits underneath the Kalahari sand.

The redox state of the cratonic lithosphere and its impact on metasomatism have been examined using garnet peridotite xenoliths from two kimberlite pipes (Wesselton and Kimberley) in the Kaapvaal Craton, South Africa. Conventional petrologic techniques, along with electron probe microanalysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), were used to characterise the samples and identify metasomatic events. Evidence of at least one such event was found in the Wesselton samples. Iron K-edge X-ray absorption near-edge structure (XANES) spectroscopy was used to determine the Fe3+/∑Fe of garnet from both suites, and then calculate the oxygen fugacity (fO2). The Wesselton samples were found to show a decrease in fO2 (relative to the fayalite-magnetite-quartz buffer) with increasing pressure, which was overprinted by an oxidation event in zoned garnet crystals, which were observed in one sample. The fO2 of the core of the zoned crystals was consistent with equilibrium with a carbonated silicate melt, and is possible that the oxidised nature of this melt is related to formation of the metasomatised rim observed, which is more oxidised than the garnet core. XANES spectroscopy was used to produce the first fully quantitative map of the distribution of Fe3+/∑Fe in garnet for one of these crystals, which confirmed the variation in fO2 between the core and rim, strengthening the relationship between oxidation and metasomatism. The interface between the two compositional zones showed a very short profile and this was examined using both electron probe microanalysis and NanoSIMS. The compositional profile at this interface was modelled as a diffusive process and it was found that the zonation formed in 2 - 10 years. The diffusion coefficients (relative to Ca) of Na, Cr, Ti and Y in mantle garnet were also determined for the first time.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy, 2020
An attempt was made to place the proposed tectono-sedimentary evolution of the Free State Goldfield and the Witwatersrand Basin into the context of the geodynamic evolution of the Kaapvaal Craton, including the Zimbabwe Craton and Limpopo Central Zone Terrane, as all share a common and linked geodynamic evolution since the Neoarchaean. This was achieved through a comprehensive compilation and synthesis of a large published and unpublished geoscientific dataset. The outcome is a plate-tectonic reconstruction of the geodynamic evolution of the Kaapvaal and Zimbabwe cratons(and the southern African lithosphere in general) in time and relative space, since their stabilisation as protocratons in the Neoarchaean at ~3.1 Ga until present time, is summarised pictorially in a series of palaeogeographic and palaeogeologic reconstruction ‘time-slice’ maps to provide a perspective not previously available (Appendices 20-A –20-Z). For each time period of the reconstructed sequential geodynamic evolution, these ‘time-slice’ maps show: (1) Archaean continental/cratonic crust, (2) the main structures that were active, (3) the lithostratigraphic units that were deposited, and (4) areas of juvenile crust formation within regions of magmatic-arc/back-arc basin development. Gaps indicate areas, of unknown extent, inferred to have been occupied by either oceanic crust or lost fragments of continental crust that separated the continental crust at the time. Note: Given their illegibility, all time-slice maps presented in A3 format as Appendices 20-A –20-Z are available digitally in PDF file format on the supplementary CD.A summary of geochronological ages used for the plate-tectonic reconstruction is divided into various epochs and/or orogenic cycles (i.e. Archaean, Palaeoproterozoic, Kibaran, etc.) for the Kaapvaal and Zimbabwe cratons, and the Limpopo Central Zone Terrane separately, and is presented in tabular format in Appendices 21-A –21-C respectively. A proposed correlation of Palaeoproterozoic-Mesoproterozoic (~2.6-1.45 Ga) stratigraphic units and tectonic events within the Kaapvaal, Rehoboth, Zimbabwe, Pilbara, Yilgarn, Singhbhum, Bastar and Dharwar cratons, as well as the Limpopo Central Zone Terrane, is provided in Appendix 22.Summariesof Palaeoproterozoic (syn-Transvaal Supergroup; ~2.49-2.41 Ga) formation and resetting ages reported from the Kaapvaal and Zimbabwe cratons and Limpopo Central Zone Terraneare presented in Appendices23-A and 23-B, respectively. A summary of Palaeo-to Mesoproterozoic (post-Transvaal Supergroup; ~2.1-1.0 Ga) deformation events reported from the area of the Witwatersrand Basin and Bushveld Complex (i.e., central Kaapvaal Craton) and their correlation with far field stress related to the Magondi and Okwa orogenies, Bushveld Complex emplacement, and Vredefort meteorite impact, as well as Kheis, Kibaran and Lomanian (Namaqua-Natal) orogeniesis presented in Appendix 24. Summaries of Palaeo-to Mesoproterozoic (post-Transvaal Supergroup; ~2.1-1.0 Ga) formation and resetting ages reported from the Kaapvaal Craton are presented in Appendices25-A and 25-B, respectively. A tectono-structural and terrane interpretation summary map for the Kaapvaal Craton, Limpopo Central Zone Terrane and Zimbabwe Craton, covering the countries of Botswana, Zimbabwe, South Africa, and parts of Mozambique, is presented in Appendix 26
CK2021

Thesis (Ph. D.)--University of Alberta, 2009.
Title from PDF file main screen (viewed on Oct. 16, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geology, Department of Earth and Atmospheric Sciences, University of Alberta." Includes bibliographical references.