Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 194-214) Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 121-130) Also available in print.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2006. / CD-ROM contains digital appendices. Includes bibliographical references. Also available online.

Programa de Pós-Graduação em Evolução Crustal e Recursos Naturais. Departamento de Geologia. Escola de Minas, Universidade Federal de Ouro Preto. / Submitted by Oliveira Flávia (flavia@sisbin.ufop.br) on 2014-08-25T17:11:40Z No. of bitstreams: 2 license_rdf: 20592 bytes, checksum: 0c9b9c579af4cbbcf785ca803bd18d4b (MD5) TESE_MissãoGRACEEstrutura.pdf: 7499039 bytes, checksum: 5226b258734caa16785e6855e0e82d23 (MD5) / Approved for entry into archive by Gracilene Carvalho (gracilene@sisbin.ufop.br) on 2014-08-27T15:42:41Z (GMT) No. of bitstreams: 2 license_rdf: 20592 bytes, checksum: 0c9b9c579af4cbbcf785ca803bd18d4b (MD5) TESE_MissãoGRACEEstrutura.pdf: 7499039 bytes, checksum: 5226b258734caa16785e6855e0e82d23 (MD5) / Made available in DSpace on 2014-08-27T15:42:41Z (GMT). No. of bitstreams: 2 license_rdf: 20592 bytes, checksum: 0c9b9c579af4cbbcf785ca803bd18d4b (MD5) TESE_MissãoGRACEEstrutura.pdf: 7499039 bytes, checksum: 5226b258734caa16785e6855e0e82d23 (MD5) Previous issue date: 2009 / A presente tese de doutorado trata da aplicação do modelo geopotencial GGM02C, derivado da missão espacial GRACE (NASA/GFZ-Potsdam), na obtenção do campo gravitacional na região do Cráton São Francisco, que constitui um importante segmento litosférico da Placa Sul-Americana, constituído por terrenos arqueanos e coberturas proterozóicas e fanerozóicas, limitado por faixas de dobramentos brasilianas. Anomalias gravimétricas Ar-livre, Bouguer e ondulações do geóide foram determinadas com base no referido modelo geopotencial, possibilitando o estudo da estruturação da litosfera na região e a determinação de valores médios de espessura elástica efetiva da mesma, que constituí um importante parâmetro na inferência sobre o estado isostático da área e do estado termal da litosfera. Foi implementado um algoritmo de inversão 3D não-linear envolvendo o uso de anomalias Bouguer e ondulações do geóide, permitindo o conhecimento da geometria e da profundidade da interface crosta-manto e o limite litosfera-astenosfera. Os resultados são compatíveis com os demais obtidos a partir de estudos de função do receptor, tomografia de ondas P e de ondas S. Posteriormente, empregou-se a técnica da função admitância, utilizando as informações gravimétricas disponíveis como anomalias Ar-livre, anomalias Bouguer e ondulações do geóide, visando determinar o mecanismo responsável pelo equilíbrio isostático da região do Cráton São Francisco. Os resultados alcançados podem ser assim sumarizados: i) valores médios entre 40 e 60 km para espessura elástica efetiva na região do Cráton São Francisco, compatíveis com outros trabalhos disponíveis na literatura; ii) influência de cargas localizadas na base da litosfera, possivelmente associadas à algum processo de aquecimento e/ou diminuição de densidades e iii) a atuação expressiva de cargas localizadas na interface crosta-manto, que podem estar relacionadas aos sucessivos eventos de magmatismo que fazem parte da complexa evolução tectônica do cráton. Os resultados obtidos nas etapas anteriores aliados a análise da topografia dinâmica da área, a aplicação do conceito de convecção localizada na borda cratônica (edge-driven convection), às modelagens numéricas da interação cráton x plumas mantélicas e aos outros dados geofísicos como a anisotropia sísmica, a evolução termal do manto e ao fluxo geotérmico forneceram subsídios necessários para a elaboração de um modelo de evolução geodinâmica para o Cráton São Francisco, constituído dos seguintes estágios: i) geração da litosfera continental arqueana; ii) amalgamação e estabilização da litosfera cratônica; iii) ocorrência de eventos modificadores crustais e litosféricos; iv) orogenia proterozóica e v) interação cráton x pluma ocorrida a partir do Cretáceo. ________________________________________________________________________________________ / ABSTRACT: The present Ph.D. Thesis deals with the application of the GGM02C geopotential model, derived from GRACE space mission (NASA/GFZ-Potsdam), to obtain the gravitational field in the São Francisco craton, which is an important lithospheric segment of the South-American plate, constituted by archean terrains and proterozoic and fanerozoic covers, and surrounded by neoproterozoic fold-thrust belts. Free-air and Bouguer gravity anomalies and geoid undulations were computed based on the GGM02C geopotential model, yielding the study of the lithospheric structure and the determination of the averaged values of the effective elastic thickness, which is a important parameter to infer isostatic and thermal states of the lithosphere. A 3D non-linear inversion algorithm involving Bouguer anomalies and geoid undulations was implemented, revealing the geometry and depth of the crust-mantle interface and lithosphere-asthenosphere boundary. The results obtained were in according to other geophysical studies such as receiver function and P and S waves tomography. Afterwards, the admittance function was employed based in the the gravity information (freeair and Bouguer anomalies and geoid undulations), in order to investigate the isostatic mechanism occurring in the studied area. The results may be summarized as: i) averaged values between 40 and 60 km for the effective elastic thickness of the São Francisco craton region (in agreement with literature); ii) loads acting in the base of the lithosphere, possibly related to some heating and/or density decreasing processes and iii) significant loads located in the crust-mantle interface that may be associated with successive magmatic events, which are part of the complex tectonic evolution of the craton. The results obtained previously, together with the dynamic topography analysis, the use of the concept of the edge-driven convection, numerical simulations of the craton x mantle plumes interaction and other geophysical data (seismic anisotropy, thermal evolution of the mantle and geothermal flux) provided information to elaborate a geodynamic evolution model of the São Francisco craton, consisting of the following stages: i) generation of the archean continental lithosphere; ii) assembling and stabilization of the cratonic lithosphere; iii) occurrence of the crust and lithosphere modifiers events; iv) proterozoic orogenies and v) craton x plume interaction in the Cretaceous.

La géométrie actuelle de l'est du plateau Tibétain, constitué par le Songpan Ganze et les Longmen Shan, est probablement dictée par une différence de rhéologie entre le craton du Yangtze à l'est, et le Songpan Ganze à l'ouest, qui vient buter contre la marge du craton en réponse à la collision Inde-Asie. L'histoire géodynamique de la région a été reconstituée depuis le Néoprotérozoïque, afin d'évaluer l'influence des différents cycles orogéniques sur la structure thermique, minéralogique et chimique actuelle. L'étude des massifs cristallins bordant le craton du Yangtze et de l'ophiolite de San Dao Qiao a montré que durant le Néoprotérozoïque, le craton était bordé par une marge active, avec ouverture de bassins marginaux sous l'influence de panaches mantelliques. L'étude pétrologique et structurale du complexe métamorphique de Danba permet de déterminer que lors de l'orogénèse Indosinienne (200-180Ma), l'exhumation des niveaux structuraux profonds se produit par extrusion le long d'un grand chevauchement ductile. La position des granites du Songpan Ganze par rapport aux sutures au sein du plateau Tibétain permet de proposer un double retrait de slab sous le Songpan Ganze à la fin de l'orogénèse Indosinienne qui explique la diversité des granitoïdes. Ce double retrait de slab et la différence de réponse à la contrainte entre le Songpan Ganze et le craton du Yangtze a conduit à un déchirement de slab. La délamination complète de la partie mantellique de la lithosphère du Songpan Ganze à la fin de l'orogénèse Indosinienne peut expliquer l'accolement d'une lithosphère à croûte épaisse et manteau fin contre une lithosphère cratonisée à la bordure est du plateau Tibétain / The present geometry of the Eastern Tibetan plateau, made of the Songpan Ganze terrane and the Longmen Shan range, is probably due to a rheological contrast between the Yangtze craton to the East, and the Songpan Ganze, which bump into the craton margin in response to the India-Asia collision. We reconstituted the geodynamic evolution of the area from Neoproterozoic times to present to evaluate how the different orogenic cycles influence the thermal, mineralogical and chemical structures observed today. Studies of the crystalline massifs of the western margin of the Yangtze craton and of the San Dao Qiao ophiolite show that during the Neoproterozoïc times, the craton margin was a subduction zone with opening of marginal basin due to mantle plumes. Petrologic and structural studies of the Danba metamorphic complex allow determining that during the Indosinian orogeny (200-180 Ma), exhumation mechanism of the deep structural level of the complex is an extrusion along a ductile thrust. Plutons position relative to sutures zones in the Tibetan plateau lead to a model of double slab roll-back under the Songpan Ganze at the end of the Indosinian orogeny which explain the diversity of the granites. The double slab roll-back and the difference in deformation between the Songpan Ganze and the Yangtze craton lead to a slab tear along the craton margin. The complete delamination of the lithospheric mantle under the Songpan Ganze terrane can explain the present juxtaposition of a thick crust and thin mantle lithosphere against a cratonized one.

published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

M.Sc. / Please refer to full text to view abstract

Th. univ.--Géol.--Rennes 1, 1994. / Textes en français ou en anglais. Bibliogr., 26 p. Résumé en français et en anglais.

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