Cette thèse présente le modèle 3D du bassin de la Plaine du Pô en Italie du nord. Les six parties de la thèse conduisent le lecteur à partir du cadre géologique de base aux géométries et à la cinématique de la déformation à travers la région, ainsi qu’aux possibles applications en milieu académique ou industriel. Le modèle a intégré des données éparses et de qualité inégale, tirées exclusivement de la littérature publique. L'ensemble de données utilisées pour la création du modèle se base strictement sur des données en profondeur (i.e. dans leur dimension de profondeur). Les données sismiques disponibles ont été intentionnellement écartées pour les raisons suivantes: a) elles sont mal distribuées à travers le secteur d'étude, b) elles se rapportent à des images de basse qualité, d) leur intégration dans le modèle aurait impliqué un long et difficile travail d’évaluation du meilleur modèle de vitesse de propagation des ondes sismiques dans les sédiments, le mieux à même d’être employé pour une conversion finale temps-profondeur, la variation latérale et verticale des vitesses sismiques à l’échelle régionale étant douteuse ou, au mieux, incertaine. La méthodologie appliquée, la création de modèles et l'analyse des améliorations du modèle 3D fournissent un certain nombre de conclusions sur la géométrie, le style structural et la cinématique de la Plaine du Pô et leur contribution en terme de sismicité du bassin et de son potentiel pétrolier, avec une confirmation mutuelle des, mais aussi par, les résultats locaux et épars obtenus par d’autres auteurs. Le résultat principal du projet est d'avoir prouvé la capacité du modèle à visualiser et analyser la complexité du bassin de la Plaine du Pô dans les 3 dimensions à différentes échelles d'observation, de l’échelle crustal jusqu'au niveau des prospects... / This thesis deals with the 3D model building of the Po Valley foreland basin in northern Italy. The six parts of the thesis lead from the basic geological framework to the deformation geometries and kinematics across the region, to some of the possible model applications, for both academia and industry. The model has integrated sparse and variable quality data, exclusively taken from the public literature. The complete dataset used for the performed model building, strictly relies on depth-data (i.e. in their depth dimension). As such, the few available seismic data have been intentionally left apart because: a) they are poorly distributed across the study-area, b) they definitely refer to low quality images, d) their integration into the model would have implied a long and difficult work about the definition of the most-likely sediment velocities to be used for an ultimate time-depth conversion, uncertain and, at best, questionable. The applied methodology, the related model building and the progressing analysis of 3D model results suggest and discuss a number of conclusions about the Po Valley structural geometries-style-kinematics. From such results can be derived implications on basin seismicity and hydrocarbon potential, while confirming (thus being supported by) the local and sparse results of previous authors. The major result from the project is to have proven the model capability in rendering and analyzing the entire Po Valley basin structural complexity in 3D dimensions, from crustal to field scale. Thanks to this, the model is unique in the literature of the region...

The Atnarko complex located in west-central British Columbia comprises pre-Early Jurassic metavolcanic and metasedimentary rocks, termed the Atnarko assemblage, which is structurally interleaved with Late Triassic to Early Cretaceous orthogneiss. The Atnarko assemblage correlates with continental margin assemblages found within the Coast plutonic complex. Tectonic interaction between the Insular and Intermontane superterranes resulted in several phases of deformation including; 1) poorly preserved Jurassic deformation, 2) Early to mid-Cretaceous, southwest to west directed, compression, 3) mid-Cretaceous, north to northeast directed, compression, 4) mid- to Late Cretaceous dextral and sinistral ductile/brittle shearing, and 5) post latest Cretaceous brittle faulting. Peak metamorphism coincides with generation of migmatite in the Early Cretaceous (~117-115 Ma) and is contemporaneous with penetrative ductile fabrics. The Atnarko complex had cooled below 350°C by the Late. Comparison of the Atnarko complex to equivalent portions of the orogen along strike, indicates a post mid-Cretaceous change in structural style. To the northwest the orogen records continued southwest-directed compression which dominates the deformation style; while to the southeast large dextral strike-slip faults dominate. Relative plate motions between ca. 70-60 Ma indicate that dextral transpression occurred between the Kula and North American plates. Strain during this transpressive deformation was partitioned into compressive and translational regions. The Atnarko complex area is situated at the transition between translation and compression. The conditions of the lower and middle crust within the orogen were established by how strain was partitioned across the orogen. The distributed strain also shaped how the orogen responded to Tertiary extension. Continued compression to the northwest of the Atnarko complex led to increased crustal thickness and partial melting of lower and middle crust in the Tertiary. Conversely, the cessation of compression in the southeast lead to a more stable (i.e. cooler) crustal lithosphere. A change in relative plate motions in the early Tertiary triggered full-scale, orogen-perpendicular, collapse in the northwest facilitated by decoupling between the middle and lower crusts along thermally weakened layers. Localized orogen-parallel extension occurred in the southeast which was kinematically linked to large dextral strike-slip faults where the upper crust remained coupled to the middle and lower crust. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

In the Paleoproterozoic Trans-Hudson Orogen, a well exposed section of mid-crust on Hall Peninsula, southeastern Baffin Island, offers an opportunity to improve our understanding of mid-crustal tectonothermal processes in hot, collisional orogens. Additionally, more robust age constraints on the tectonic history of Hall Peninsula are important for plate tectonic reconstructions of the North Atlantic region. Recent mapping shows that the section comprises Archean crystalline basement overlain by Paleoproterozoic supracrustal rocks, which host felsic plutons on the western peninsula. There is a westward increase in peak metamorphic grade, from amphibolite- to granulite-facies, and three regional deformation events are recognized (D1, 2, 3). Equilibrium phase diagram modeling constrained by garnet compositions in pelite indicates peak conditions of ~720–740°C on the eastern peninsula and ~850°C further west, with pressures of ~6.25–7.35 kbar. Modeling and petrographical evidence suggest subsequent cooling, decompression, growth of retrograde biotite and, on the eastern peninsula, retrograde muscovite. In situ U-Pb monazite dating (~450 analyses) and U-Pb zircon depth profiling (~90 analyses) resolve the timing of regional metamorphism and crustal shortening between ca. 1860–1820 Ma, coincident with the accretion of crustal blocks and arc terranes during the amalgamation of the orogenic upper (Churchill) plate. Regionally-occurring ca. 1800–1750 Ma monazite domains and zircon rims are interpreted to result from fluid-assisted dissolution-reprecipitation. They likely record the terminal collision with the lower-plate Superior craton and post-orogenic thermal activity, possibly related to the emplacement of pegmatitic syenogranite dykes. The new data strengthen formerly tentative correlations with southern Baffin Island, West Greenland and northern Labrador. 40Ar/39Ar thermochronology on muscovite, biotite and phlogopite suggests that Hall Peninsula underwent slow cooling at rates of ~1–2.5ºC/Myr after peak metamorphism, remaining hotter than ~400°C until ca. 1670–1660 Ma. Analogous thermochronological ages from elsewhere in the Trans-Hudson Orogen imply orogen-wide slow cooling. Despite significant crustal thickening and elevated paleotemperatures, the Hall Peninsula crustal section does not record evidence of orogenic collapse, implying that it may not be a hallmark of all hot, thickened orogens.

The northern Cascadia subduction zone involves convergence of the Explorer Plate and northern part of the Juan de Fuca Plate with the North American Plate along a margin lying west of Vancouver Island, Canada. A wide accretionary complex which underlies the continental slope and shelf has been formed. Two allochthonous terranes, the Crescent Terrane of Eocene oceanic crustal volcanics and the Pacific Rim Terrane of Mesozoic melange sedimentary rocks and volcanics, lie against the Wrangellia Terrane backstop beneath the west coast of Vancouver Island and outcrop on the southern tip of the island. The intrusive Coast Plutonic Complex underlies the westernmost part of the British Columbia mainland east of Vancouver Island and marks the location of the historic and modern volcanic arcs. An integrated interpretation of geophysical and geological data has been conducted for the northern Cascadia subduction zone. Regionally extensive gravity and magnetic anomaly data have formed the basis of the interpretation, while surface geology, physical properties, and seismic reflection, refraction, heat flow, borehole, magnetotelluric, and seismicity data have provided constraints on structure and composition. Horizontal gradient and vertical derivative maps of the potential field data were calculated to provide additional control on the locations of major faults and lithologic boundaries. Iterative forward modelling of the gravity and magnetic anomaly data was conducted along three offshore multichannel seismic reflection lines and their onshore extensions. The two-and-a-half-dimensional (2.5-D) models extended from the ocean basin across the accretionary complex and Vancouver Island to the mainland along lines perpendicular to the major structural trends of the margin and revealed lateral changes in the location of several structural components along the length of the margin. The interpretations were extended laterally by moving the original models to adjacent parallel positions and perturbing them to satisfy the new anomaly profile data and other constraints. The models thus formed were moved to the next position and the process repeated until a total of eleven models was developed across the margin. A twelfth line across a gravity anomaly high on southern Vancouver Island was independently modelled to examine the source of this feature. An average density model for the southern half of the convergent margin was constructed by averaging the models and profiles for seven lines at 10 km spacings. This process removed anomalies due to small source bodies and concentrated on the larger features. Finally, a regional density structural model was developed by linearly interpolating between all eleven cross-margin lines to construct a block model which could then be 'sliced' open to examine the internal structure of the margin at any location. The final models allow the Pacific Rim and Crescent Terrane positions to be extended along the offshore margin from their mapped locations. The Pacific Rim Terrane appears to be continuous and close to the coastline along the length of Vancouver Island, while the Crescent Terrane either terminates halfway along the margin or is buried at a depth great enough to suppress its magnetic signature. The location of the Westcoast Fault, separating the Pacific Rim and Wrangellia Terranes, has been interpreted to lie west of Barkley Sound at a position 15 km west of its previously interpreted position. Beneath southern Vancouver Island and Juan de Fuca Strait, the Crescent Terrane appears to have been uplifted into an anticlinal structure, bringing high density lower crustal or upper mantle material close to the surface and thereby causing the observed gravity anomaly high. The western part of the Coast Plutonic Complex has been interpreted as a thin lower density layer extending from its surface contact with Wrangellia to a position 20 to 30 km further east where the unit rapidly thickens and represents the main bulk of the batholith. The complexity of the thermal regime and its effects on density in this region allows for other interpretations. Finally, a comparison of the models along the length of the margin reveals that the crust of Vancouver Island appears to thin toward the north above the shallower Explorer Plate and the complex low - high density banding used in the southern Vancouver Island models is replaced with a single high density unit on the northernmost line. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Strong evidence suggests that the Cascadia subduction zone, off the west coast of Canada and the United States, is strongly seismically-coupled and that a possible megathrust earthquake might occur in that area in the near future. A study of tsunami hazards along the Canadian west coast associated with such a hypothetical earthquake is presented in this report. Numerical simulations of tsunami generation and propagation have been carried out using three models based on shallow water wave theory. Three cases of ground motion representing the ruptures of different crustal segments in the area have been examined. Computed results provide information on tsunami arrival times and a general view of the wave height distribution. The outer coast of Vancouver Island was found to be the most strongly affected area. At the head of Alberni Inlet, wave amplitudes reached up to three times the source magnitude. Inside the Strait of Georgia, the wave heights are significant enough to receive closer attention, especially in low-lying areas. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The 1980 Vancouver Island Seismic Project (VISP) was conducted to investigate lithospheric structure associated with the underthrusting oceanic Juan de Fuca plate and the overriding continental America plate. The principal components of the survey were: (l) an onshore-offshore refraction line, which was approximately perpendicular to the continental margin (line 1), and (2) a refraction line which ran along the length of Vancouver Island approximately parallel with the continental margin (line IV). Lines I and IV were originally interpreted by Spence el a.1. (1985) and McMechan and Spence (1983), respectively. However since the original interpretations of these lines, deep multichannel seismic reflection data have been obtained on southern Vancouver Island as part of the 1984 LITHOPROBE project and off the west coast of the island during a marine survey in 1985. This study was undertaken to resolve differences between the subsurface structures proposed in the original interpretations of lines I and IV and those suggested by the more recently acquired deep reflection data. The vertical two-way traveltimes to prominent reflectors, observed in the onshore-offshore deep reflection data, were used as a constraint in constructing velocity models which are consistent with both the reflection and refraction data. The traveltimes and amplitudes observed in the VISP refraction data were modeled using a two-dimensional raytracing and asymptotic ray theory synthetic seismogram routine. The principal difference between the model originally interpreted for line I and the revised model involves the introduction of a twice repeated sequence of a low velocity zone (≈ 6.4 km/s) above a thicker high velocity zone (≈ 7.1 km/s) for the underplated region directly above the subducting Juan de Fuca plate in place of the single high velocity block underlain by a thick low velocity zone. The revised model for line IV is significantly different from the originally interpreted model. The two low-high velocity zones of line 1 are continued along the length of the island at depths between 10 and 35 km. Below this, the structure of the subducted plate is included to maintain consistency with the revised model developed for line 1. Additional features of the revised onshore-offshore model corresponding to line 1 include an oceanic lithosphere that dips approximately 3° beneath the continental slope, then 14° to 16° beneath the continental shelf and Vancouver Island, and an average velocity for the upper oceanic mantle of 8.22 km/s. Two separate two-dimensional models were needed to explain the data collected along line IV as a result of considerable azimuthal coverage due to a 30° change in profile direction. The revised models developed for line IV are consistent with the revised model developed for line 1. The velocity in the upper 10 km ranges from 5.5 km/s to approximately 6.7 km/s. Below 10 km the velocity structure is consistent with that interpreted for line 1 and shows some variations along strike of the subduction zone. Several possible interpretations can be made for the origin of the sequence of layers directly above the subducting plate beneath Vancouver Island. The two favored interpretations are: (1) a. three stage tectonic process consisting of: stage 1 — offscraping of sediment from the top of the subducting plate forms the uppermost low velocity layer in the sequence; stage 2 — an imbricated package of mafic rocks derived by continuous accretion from the top of the subducting oceanic crust forms the first high velocity layer; and stage 3 — stages 1 and 2 repeat themselves with stage 2 currently occurring; or (2) remnant, pieces of oceanic lithosphere left stranded above the current subducting plate during two previous episodes of subduction in which the subduction thrust jumped further westward isolating the remnant. The revised model along line IV indicates that this process of subduction underplating could have been a pervasive feature of this convergent margin. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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.

Orientadores: Elson Paiva de Oliveira, Elton Luis Dantas / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-07T09:32:09Z (GMT). No. of bitstreams: 1 Carvalho_MarceloJuliano_D.pdf: 10664209 bytes, checksum: 0a433fc7eec27e438242f51755d9cd54 (MD5) Previous issue date: 2005 / Resumo: O presente trabalho procurou avançar nos conhecimentos sobre a evolução tectônica da Faixa Sergipana, um cinturão de rochas dobradas que ocorre na porção sul da Província Borborema bordejando o Cráton do São Francisco (CSF), com base na estudo da evolução tectônica de dois de seus domínios: os domínios Marancó e Poço Redondo. Para atingir esse objetivo foi realizado trabalho de campo detalhado que teve como base quatro cartas geológ icas em escala 1:100.000 e imagens de satélite (LANDSAT- TM), buscando observar as relações estruturais entre os diferentes Iitotipos. Sobre essa base geológica foram realizados estudos petrográficos, análises geoquímicas em rocha total (elementos maiores e traços), análises de isótopos de Nd e geocronologia U-Pb (SHRIMP e TIMS) nos principais Iitotipos. Os dados obtidos mostram que os domínios Marancó e Poço Redondo são intimamente correlacionados. Propõe-se aqui a denominação Domínio Marancó¿Poço Redondo para o conjunto de rochas que ocorre a norte da Zona de Cisalhamento Belo Monte-Jeremoabo e a sul da seqüência vulcanossedimentar de Canindé do São Francisco. A geologia de campo mostrou que o domínio é caracterizado por um bloco de rochas migmatíticas intrudido por diversos corpos granitóides e por uma seqüência vulcanossedimentar adjacente. Os migmatitos são orto-derivados, em sua maioria, e são intrudidos por pelo menos três gerações de granitos distintos. A seqüência vulcanossedimentar é dominada pela ocorrência de rochas metassedimentares imaturas. Metagrauvacas, metarritmitos, metapelitos, quartzitos e metaconglomerados ocorrem com freqüência. As rochas sedimentares têm forte contribuição de rochas vulcânicas intermediárias a acidas em sua gênese e são intercaladas a rocha piroclásticas. Lascas de rochas ultramáficas foram tectonicamente colocadas junto as supracrustais, principalmente na porção norte da seqüência. A geoquímica revelou que o paleossoma dos migmatitos Poço Redondo é granodiorítico e apresenta afinidade geoquímica com plútons de arco magmático. Duas idades U-Pb (SHRIMP) obtidas mostram que esses plútons foram gerados entre 980 e 960 Ma, portanto ligados a Orogênese Cariris Velhos. Os isótopos de Nd permitem considerá-los como gerados em arco de margem continental, onde magmas juvenis interagiram com crosta pré-existente. O augen gnaisse Serra Negra intrude os migmatitos e a seqüência vulcanossedimentar. A geoquímica desses granitos é característica de granitos pós-tectônicos ou associados a zonas de cisalhamento transcorrentes profundas. Uma idade obtida posiciona sua geração logo apôs a geração do granodiorito Poço Redondo, também ligada a Orogênese Cariris Velhos. Na seqüência vulcanossedimentar as rochas sedimentares apresentam características geoquímicas semelhantes às rochas geradas em ambientes de arcos modernos. O estudo de proveniência de sedimentos, realizado por datação de zircão detrítico e de análises Sm-Nd, mostra que a seqüência tem fontes muito restritas e predominantemente ligadas a Orogênese Cariris Velhos, provavelmente ao arco continental adjacente. Além desse conjunto de rochas ligadas ao ciclo Cariris Velhos, rochas associadas à Orogênese Brasiliana também ocorrem. O granodiorito Sítios Novos íntrude as demais unidades. Tratam-se de corpos granodioríticos ísotrópicos ricos em enclaves máficos. Esses granitos apresentam afinidade com granitos de arco magmático. Análise U-Pb mostrou idade de 650 Ma e os isótopos de Nd mostram que sofreram forte contaminação em sua gênese. Rochas vulcânicas andesíticas e dacíticas com afinidade com arco continental intrudem a seqüência vulcanossedimentar de Marancó. Idades de 602 Ma (U-Pb, SHRIMP) foram obtidas nessas rochas. Os isótopos de Nd mostram características semelhantes às dos granitos Sítio Novos. Esse conjunto foi provavelmente gerado em arco de margem continental durante a Orogênese Brasiliana. A deformação foi dividida em dois principais ciclos. O primeiro ciclo evoluiu de tectônica compressiva com vergência para SSW para uma fase transcorrente sinistrai. Três fases foram individualizadas. As relações de campo, sobretudo a das estruturas com os corpos graníticos datados, sugerem que essa deformação pode estar ligada a Orogênese Cariris Velhos. Um segundo ciclo deformacional, representado por zonas de cisalhamento transcorrentes que cortam toda a Faixa Sergipana, afeta as rochas do Domínio Marancó-Poço Redondo, porém em menor intensidade que o ciclo anterior. Esse segundo ciclo é relacionado à Orogênese Brasiliana. O Domínio Marancó Poço Redondo deve, portanto, configurar um arco continental e bacia adjacente gerados na margem sul do Maciço PEAL durante a Orogênese Cariris Velho. Esse bloco foi posteriormente descolado de seu local de origem e mais tarde acrescido à margem norte do Cráton do São Francisco durante a Orogênese Brasiliana. O domínio registra evidências dos dois ciclos orogenéticos em questão e o entendimento da relação entre eles pode contribuir para o entendimento das faixas de dobramento pré-cambrianas e, sobretudo, da Faixa Sergipana. / Abstract: This Thesis aims to advance in the geological knowledge of the Sergipano Belt, by studying the tectonic evolution for two within seven lithotectonic domains: the Marancó -Poço Redondo Domain. To reach the objective a detailed field work, that used four geological maps (1:100.000) from the Carira Project (PLGB, DNPM-CPRM, 1988) as base maps and a Landsat image, was carried out, with the aim to determinate the structural relationships between the main lithologies. Petrographic and geochemical analyses were performed and Sm-Nd isotopic and U-Pb (SHRIMP) data were acquired for the main rock types. The data show that the Marancó and Poço Redondo domains are closely related. We propose the denomination of Marancó - Poço Redondo Domain for the group of rocks that occurs to the north of the Belo Monte-Jeremoabo Shear Zone and to the south of the Canindé do São Francisco sequence. Field geology showed that the domain is composed by a migmatitic unit, which is intruded by several granitic bodies, and by a meta-volcano sedimentary sequence. The migmatites are orto-derived and intruded by at least three distinct granitic suites. The meta-volcano sedimentary sequence is characterized by immature sedimentary rocks. The main rock types include meta-greywacke, meta-pelites, quartzites and meta-conglomerades. Intermediate volcanics were probably the main source for the sedimentary sequence. Ultramafic rocks occur as tectonic slices intercalated to the sedimentary rocks. The geochemistry shows that the migmatites paleossome are granodioritic in composition and have geochemical affinities with magmatic arc plutonism. Two U-Pb (SHRIMP) ages of 980 and 960 were obtained for the migmatites. Theses ages link the migmatites to the Greenvile/ Cariris Velho Orogeny. The Nd isotopic data allow us to consider them as continental margin arc plutons, were juvenile magmas interacted with continental crust. The Serra Negra augen gneiss intrudes the migmatites and the meta-volcano sedimentary sequence. Its geochemical data shows that it is probably late tectonic and associated with major transcurrent shear zones. A SHRIMP age of 951 Ma. was acquired for this granites, which means that they were generated soon after the migmatites. In the meta-volcano sedimentary sequence, the sedimentary rocks show geochemical affinities with those generated in continental margin arc basins. A provenance study was carried out by dating detrital zircons and by Sm-Nd analyses in the sedimentary rocks. This study showed that the sequence has a very restrict source, strongly dominated by Cariris Velho-aged rocks, probably related to the continental arc. Besides the rocks closely related to the Cariris Velho Orogeny, Brasiliano/Pan-African aged rocks also occur. The Sítios Novos granite occurs as several intrusive, enclave-rich granodioritic bodies, which crosscut all the other rocks. Its geochemistry showed that it is calco-alkalic, metaluminous arc-related granite. A U-Pb (TIMS) analysis yields an age of 650 Ma and the Nd isotopic data shows strong contamination with older continental crust. Volcanic andesitic and dacitic arc- related rocks occur as dikes and sills cutting the metassedimentary sequence. Two samples were analyzed and yield U-Pb (SHRIMP) ages of 602 Ma. The Nd isotopic composition is very similar to that for the Sítios Novos granites. The deformational history for the Marancó - Poço Redondo Domain can be divided in two major cycles. The first one evolved form a compressional tectonics that developed SSW thrust faults, to dominantly sinistral transcurrent within three deformational fazes. Field relationships, chiefly those between the dated granites and structures, allow the interpretation of that this first cycle is related to the Cariris Velhos Orogeny. The second one is represented by regional scale transcurrent shear zones, which affect only the borders the Marancó Poço Redondo Domain. This second cycle is related to the Brasiliano/Pan-African Orogeny. Therefore, the Marancó Poço Redondo Domain represents a fragment of a continental margin arc and its related basin formed during the Greenvile/Cariris Velhos Orogeny at the southern margin of the Pernambuco - Alagoas Massif. The domain was detached from its original tectonic setting and accreted to the northern margin of the São Francisco Craton during the Pan-African / Brasiliano Orogeny. It records features of these two major tectonic cycles and the understanding of their relationships can be very helpful on the understanding of the Precambrian fold belts, in special the Sergipano Belt. / Doutorado / Metalogenese e Geoquimica / Doutor em Geociências

>Magister Scientiae - MSc / A magmatic Ni-Cu (±Co-Zn) sulphide deposit, named the Hondekloof prospect, is present in the Kliprand area at the border between the Northern Cape and Western Cape Provinces of South Africa. The deposit occurs in the central part of the polyphase deformed and highly metamorphosed Garies Terrane, in the Namaqua Sector, along the south-western margin of the Mesoproterozoic Namaqua-Natal Metamorphic Province. Given the sub-economic concentrations yielded from evaluation of three of its known massive-sulphide lenses evaluated, the Hondekloof prospect has received relatively little consideration in terms of ongoing scientific research. Consequently, many aspects related to the genesis, classification and tectonic evolution of the deposit, to date, remain relatively unclear and unknown. The present contribution has therefore been geared to addressing some of those issues in view of the new data obtained on the country rocks and host rocks to the mineralization.Six exploration boreholes were logged, sampled and examined at the deposit site in Kliprand. A total of seven host rocks, namely meta-gabbronorite, biotite gneiss, feldspathic-biotite-garnet gneiss, pink gneiss, meta-syenite as well as enderbite along with a garnetiferous quartzofeldspathic rock occur in association with the sulphide mineralization. The origin, protoliths and tectonic settings of the host lithological units were determined and discussed in terms of modern plate tectonic principles. The meta-gabbronorite (the actual ore host), which had a magmatic protolith and forms part of the pre- to syn-tectonic Oorkraal Suite, displays the chemical characteristics of a depleted mantle origin (source of MORB-like melt), generated within a continental tectonic rift environment. Country rocks with sedimentary protoliths have chemical characteristics indicating a psammitic, felsic to intermediate provenance deposited within a regional subduction-related tectonic setting. A number of geochemical indices, of which the combination of element-ratios (such as Fe2O3/Al2O3 vs. TiO2/Al2O3, as well as Cr vs. Ni, amongst others) created as exploration vectors towards mineralisation, have shown potential for pointing towards the direction of the mineralization. Based on classification schemes of magmatic Ni sulphide deposits, it is has been suggested that the Hondekloof prospect could be classified as a low MgO, conduit-type, disseminated magmatic nickel sulphide deposit.

The Southeastern US is an ideal location to explore the interactions between mountain-building, rifting, magmatism and intraplate deformation. It experienced the formation of the Southern Appalachians over multiple episodes of orogenesis, continental rifting that formed the South Georgia Rift Basin, and widespread magmatism associated with the Central Atlantic Magmatic Province (CAMP). CAMP was followed by the breakup of Pangea, but the suture between Laurentia and Gondwana from the Appalachian orogeny is preserved in the crust of the Southeastern US. Intraplate seismicity indicates ongoing deformation in the Southeastern US today, but the mechanisms controlling this seismicity are poorly understood. This thesis uses seismic constraints to examine the tectonic history of the Southeastern United States (US). We use new wide-angle refraction seismic data to model crustal and upper mantle velocities in order to investigate the structures formed by mountain-building, rifting, and magmatism. Broadband seismic data are then used to detect and characterize earthquakes in the central Georgia-South Carolina region. Wide-angle seismic data were collected on three profiles crossing major geological features in Georgia to investigate the tectonic history of the Southeastern United States as a part of the SUwanee Suture and GA Rift basin experiment (SUGAR) project. We model VP and VS of the crust and upper mantle on SUGAR Line 2, which extends from the Inner Piedmont to the Georgia coast. We identify a north to south decrease in upper crustal VP/VS at the Higgins-Zietz magnetic boundary, which other recent studies have identified as the location of the suture between Laurentia and Gondwana. This boundary also lies near the northwestern edge of the South Georgia Rift Basin, the southeastern termination of the low velocity zone interpreted as the Appalachian detachment, and localized crustal thinning. Together, these results provide new evidence in support of the Alleghanian suture being located at the Higgins-Zietz magnetic boundary, and suggest that this orogenic boundary influenced the location of subsequent rifting. We compare the VP structures of two SUGAR wide-angle transects that cross western and eastern segments of the South Georgia Rift, respectively. Elevated (>7.0 km/s) lower crustal velocities are observed where the rift basin sedimentary fill is thickest and the crust is most thinned. The quantities of mafic magmatic intrusions are consistent with decompression melting at modestly elevated mantle potential temperatures, such as those estimated for CAMP intrusions. These results suggest that, in contrast with the widespread CAMP-aged magmatism at the Earth’s surface, lower crustal magmatic intrusions in the Southeastern US are limited and localized in areas that experienced extension. These new constraints on the velocity structure and tectonic history of the Southeastern United States are then applied to understand earthquakes in the region today. Using broadband seismic data, we find that earthquakes southeast of the Eastern Tennessee Seismic Zone are concentrated within the Carolina Terrane, a particularly heterogeneous accreted terrane of the Southern Appalachians. Within this terrane, seismicity concentrates near rivers and reservoirs, including a sequence of earthquakes in 2013 associated with an increase in water levels at Thurmond Lake on the Georgia-South Carolina border. Focal mechanisms suggest that the earthquakes are occurring on structures that are oblique to the trend of the Appalachians that are more optimally oriented in the modern stress regime.