A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements of the Master degree in Science. 2017. / This study presents the combined processing, integration and inverse modelling of magnetic and gravity data for first-order crustal scale structures in southern Mali and northeast of Guinea. Southern Mali and northeast Guinea form part of the Palaeoproterozoic Baoulé-Mossi domain, which is part of the West African craton (WAC). The current understanding of the geology region is limited to exploration camp-scale studies with limited borehole investigations, and regional interpretations of historic geophysical datasets. In this study geophysical modelling is used to attempt to advance the understanding of the geology at depth. The combination of geophysical methods is an optimization that can support geophysical interpretations and contribute to the determination of the geological and structural characteristics that are important in understanding the subsurface geology. Geophysical inversion modelling broadly resolved geology and structures under thick sedimentary cover (850-1100, thick) that is interpreted as comprising basinal sediments of the Taoudenni basin, or Cretaceous ferricrete. Geological constraints reduced the non-uniqueness, but could not control the quality. Nonetheless, the architecture, geometry and form of structures and dykes were predicted when compared with experimental analogue models as being a reasonable predictive tool for the behaviour of structures and dykes at depth. The use of surface physical properties added more information to the inversion modelling, but was very limited. The enhancement of magnetic and gravity data, using filters, defined tip damage zones for firstorder scale Yanfolila and Banifing shear zones that host gold mineralisation for example, at the Morila gold mine, and Kalana, Kodieran mines and Komana prospects. Second-order structures were also defined including in the tip damage zones of the Siguiri, Fatou and Syama shear zones, and the Manakoro fault, Madina-Yanfolila fault and Madina fault. / LG2017

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016. / The northern sector of the Archaean Superior Craton has been a significant region for diamond exploration, hosting numerous alkaline intrusions of Proterozoic age. The focus of this study is on two kimberlite fields that are situated in eastern Canada, 400 km apart. These are the diamond-rich Renard pipes and dykes, and the Wemindji field, consisting of barren sheeted dykes. The nine diamondiferous Renard igneous bodies were emplaced between 655-630 Ma in the eastern sector of Laurentia into Archaean metamorphic rocks. Thin, subhorizontal Wemindji kimberlite sills were emplaced into granitic gneiss terrane of the Superior Province near Wemindji, Quebec, at 629 ± 29 Ma, along the inferred extension of the Kapuskasing Structural Zone. These kimberlite fields are grouped with the extensive Late Neoproterozoic magmatism of ultramafic and volatile-rich character, which is said to be associated with the breakup of Rodinia. Despite overall compositional similarity of the studied magmatic kimberlites, the material from Renard has higher concentrations of SiO2, Al2O3, MgO, and K2O, which reflects higher phlogopite abundances. The Wemindji sills show higher CaO concentrations due to high primary carbonate contents. Renard and Wemindji kimberlite incompatible trace element distributions are similar, with differences in Cs, Rb, and Sr corresponding to variable modal mineralogy. The initial 87Sr/86Sr ratios for the Renard kimberlites range between 0.70241 and 0.70765, while the Wemindji kimberlites have values between 0.70361 and 0.70442. Initial εNd values for the Renard kimberlites lie between +1.2 and +4.6, whereas the Wemindji kimberlite sills range between +0.2 and +4.8. Initial εHf values for the Renard kimberlites lie between +1.7 and +6.3, whereas the Wemindji kimberlite sills yielded values between +1.1 and +6.5. The overlapping Sr-Nd-Hf isotope compositions of these kimberlite suites indicate melt derivation from moderately depleted mantle sources. Osmium isotope compositions fall at the unradiogenic end for global kimberlites, with initial 187Os/188Os ratios ranging between 0.11539 and 0.12620 for Renard kimberlites, and between 0.11078 and 0.11729 for Wemindji kimberlites, with Os concentrations all below 1.3 ppb. These Os values suggest that an additional input from the CLM (i.e., ancient refractory cratonic peridotite), which is not reflected in the Hf and Nd radiogenic isotopes, is ii required. Both kimberlite suites depict mantle δ13C values (ca. -6 to –4 ‰), with evidence of hydrothermal alteration in the δ18O values (between 10 and 20 ‰ relative to SMOW). Production of an isotopically depleted melt occurred during the breakaway of Laurentia from Rodinia. Wemindji sits on the inferred extension of the Kapuskasing Structural Zone, which is suggested to have been a short-lived reactivated translithospheric rift-like feature, promoting CO2-rich melting conditions during the Late Neoproterozoic. The data from this study suggest that this ascending sublithospheric depleted melt component (more CO2-rich beneath Wemindji) interacted with a maximum input volume of 5% of the MARID-enriched CLM beneath the eastern Superior craton, and between 2% and 30% of ancient refractory cratonic peridotite. The lack of significant diamond in the Wemindji kimberlite dykes could be due to the resorption of the potential diamond in the CO2-rich kimberlite melt.

Convergent plate boundaries evolve through the dynamic interaction between subducting oceanic lithosphere, overriding lithosphere, and adjacent flow of the convective mantle. These lithospheric plates contain remarkable heterogeneity in thickness, strength, and observable seismic character. I investigate the role of variable thickness of continental lithosphere with respect to mantle flow dynamics and develop a relationship of this subduction configuration with the construction of the Andes Mountains. By inclusion of this geodynamic model into the Andean Orogeny, numerous irreconcilable observations in the Eocene and Oligocene can be related with a comprehensive tectonic model. Lithospheric heterogeneity can be imaged with the inversion of seismic travel time data. I develop an analysis of a potential source of non-unique modeling of seismic velocity structure and then develop a case study of a currently subducting oceanic lithosphere using an iterative ray tracing approach. First, I consider the impact of the assumption of isotropic wave propagation implicit in a common methodology of data inversion. First-order structure is shown to be well resolved, but higher-order structure can be significantly different in regions of observed high-amplitude or null SKS splitting observations. The southern edge of the Juan de Fuca plate is imaged by traditional methods and an iterative ray tracing approach. The inclusion of ray tracing allows modeling of a more realistic velocity model by minimizing the error in source to receiver sensitivity. Compared to the standard imaging procedure, the resolved structure with this updated method contains smaller, more confined anomalies that represent the subducted oceanic lithosphere. Velocity perturbation amplitudes generally are decreased for slow structure and increase for fast structures. These changes in velocity structure provide an explanation for the decreased root mean square residual of the data that remain after inversion. I find that the high amplitude fast velocity of the Juan de Fuca is a robust feature and the currently subducting slab does not penetrate the mantle transition zone. I attribute the locus of very fast Juan de Fuca sub-continental lithosphere to be related to deformation of the plate prior to and during subduction. This dissertation includes previously published co-authored material.

Thesis (Ph.D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 203-223) Also available in print.

Orientadores: Julio Cesar Hadler Neto, Sergio Roberto de Paulo / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-19T06:16:04Z (GMT). No. of bitstreams: 1 Saenz_CarlosAlbertoTello_M.pdf: 1643025 bytes, checksum: ba16993be2b79f093039482f8adb91ea (MD5) Previous issue date: 1994 / Resumo: Neste trabalho utilizou-se o método dos traços de fissão para se estudar a história térmica de amostras de apatitas originadas de três regiões brasileiras (craton do São Francisco, borda oriental da Bacia do Paraná e uma região entre o craton do São Francisco e a Bacia do Paraná). As histórias térmicas foram obtidas através da utilização do modelo "Análise de Traços de Fissão em Apatita" (Apatite Fission Track Analysis) , desenvolvido pela "escola australiana", amplamente utilizado atualmente. Neste trabalho, não se buscou fazer interpretações geológicas acerca das histórias térmicas observadas. Procurou-se mais se investigar se o modelo utilizado produz resultados coerentes e seletivos. Nossos resultados mostram que para se obter interpretações geológicas mais precisas serão necessárias mais amostras e mais informações sobre o gradiente geotérmico dos locais onde as amostras foram coletadas / Abstract: In this work, thermal history of apatites originated from three brazilian regions (craton of São Francisco, region situated between the craton of São Francisco and Paraná Basin and oriental border of the Paraná Basin) were studied by using the fission track method. Thermal histories were obtained applying the theoretical model named "Apatite Fission Track Analysis" into our experimental data. Here, one do not aim to perform the geological interpretation concerning the thermal histories that were obtained. Our effort was driven to investigate the utilized model: the coherency and selectivity of its results. Our results showed that in order to perform accurate geological interpretation additional samples should be provided and, also, the knowledge about the thermal gradient of the collection places should be improved. / Mestrado / Física / Mestre em Física

Thesis (Ph. D.)--University of Oregon, 2000. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 93-100). Also available for download via the World Wide Web; free to University of Oregon users.

Two folded coloured maps and 2 coloured overlays in back cover pocket. / Bibliography: p. 183-142. / x, 182 p. : ill. (some col.), maps (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology, 1998?

Thesis (Ph. D.)--University of Adelaide, Dept. of Geology, 1998? / Two folded coloured maps and 2 coloured overlays in back cover pocket. Includes bibliographical references (p. 183-142).

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

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy