Le système volcanique de La Réunion est formé de la coalescence des massifs du Piton des Neiges et du Piton de la Fournaise. Son édification, liée à l’activité d’un panache mantellique, est caractérisée par une phase de croissance sous-marine, puis subaérienne, suivie d’une période de dégénérescence, comme proposé classiquement pour les volcans boucliers océaniques d’Hawaii. De précédentes études ont montré que l’activité subaérienne de La Réunion aurait débuté il y a environ 2,2 Ma. Les analyses géochimiques menées jusqu’alors sur les produits associés à cette activité volcanique (subaérienne et sous-marine) ont montré un caractère chimique transitionnel avec une composition isotopique (87Sr/86Sr, 143Nd/144Nd et 176Hf/177Hf) particulièrement homogène pour un volcanisme de point chaud. Dans cette étude, nous montrons que des laves sous-marines récemment identifiées sous la série basique du Piton de la Fournaise (au sein de la sur Rift Zone Nord-Est) ainsi que des laves subaériennes affleurant à la base de canyons incisés dans le massif (Série Différenciée de la Rivière des Remparts), présentent des caractéristiques ne s’inscrivant pas dans le modèle d’évolution proposé précédemment pour ce volcan. Se pose donc la question de la nature et de l’origine de ces laves, ainsi que de leur place et appartenance dans l’édification du système volcanique réunionnais. De nouvelles investigations pétro-géochimiques et géochronologiques ont été menées sur la partie sous-marine de l’édifice de La Réunion. Elles révèlent l’existence d’un groupe de laves exceptionnel. Leur composition se distingue clairement de celle des échantillons communément analysés à La Réunion et montre (1) un enrichissement en éléments incompatibles couplé isotopiquement à (2) un rapprochement vers un pôle mantellique enrichi de type EM. Ces particularités géochimiques démontrent que le panache mantellique possède (1) une source hétérogène affectée par (2) des taux de fusion variables. De plus, deux échantillons de ce nouveau groupe datés à 3,77 (0,08) et à 3,34 (0,07) Ma étendent considérablement la période d’activité connue de l’édifice. Ces âges remarquables font de ces laves les plus anciennes jamais datées à La Réunion. La nature géochimique ainsi que la position stratigraphique des laves de cette étude (échantillons subaériens et sous-marins des massifs du Piton des Neiges et du Piton de la Fournaise) impliquent une réinterprétation du schéma d’évolution global de l’île. Contrairement aux études précédentes, nos résultats sur ces laves montrent que : (1) Les laves différenciées de la Rivière des Remparts, qui sont des laves subaériennes, de part leur position stratigraphique et géographique sous-jacente au Piton de la Fournaise et par analogie avec le Piton des Neiges, ne peuvent être reliées à l’activité de la Fournaise, (2) Le signal isotopique du groupe de laves sous-marines de la Rift Zone Nord-Est de la Fournaise, révèlent l’hétérogénéité de la source du panache mantellique sous La Réunion, source que nous identifions comme des enclaves d’éclogite contenues dans une lherzolite à spinelle, (3) L’âge plus ancien de ces laves sous-marines et leur localisation sous le flanc Est de la Fournaise remet en questions le schéma jusqu’alors admis pour l’édification de l’île de La Réunion reposant sur la construction du Piton des Neiges puis celle, adjacente, du Piton de la Fournaise. En conséquence, nos données géochimiques et géochronologiques sont de nouveaux arguments en faveur de l’élaboration d’un modèle d’évolution plus complexe, suggérant l’existence d’un troisième massif volcanique. Il est en accord avec les précédents travaux de pétrologie et de géophysique suggérant l’existence d’un troisième édifice à l’Est de La Réunion, communément appelé le Volcan des Alizés. / The volcanic system of La Reunion is made of the coalescent Piton des Neiges and Piton de la Fournaise edifices. Its formation, associated with the activity of a mantle plume, is characterized by phases of submarine and subaerial growth, followed by a period of destruction, as described in the classical model proposed for Hawaiian Island volcanoes. Previous studies showed that the subaerial activity of La Reunion would have started around 2.2 Ma ago. Geochemical analyses carried out on the products associated with subaerial and submarine volcanism revealed their transitional chemical nature and their peculiar homogeneous isotopic compositions (87Sr/86Sr, 143Nd/144Nd et 176Hf/177Hf) for a hotspot derived magmatism. In this study, we show that some unusual submarine lavas were recently identified below the basal series of Piton de la Fournaise volcano (dredged on the North-East Rift Zone of la Fournaise) and below the subaerial lavas outcropping at the base of the differentiated series of Rivière des Remparts, indicate that the evolution of La Reunion system is probably more complex than previously suggested. The question of the nature and origin of these lavas, together with their implication on the formation of La Reunion, is an issue of major interest in order to better constrain the global evolution of the volcanic system. As a consequence, new petrological, geochemical and geochronological investigations were conducted on the submarine part of La Reunion edifice. They revealed the existence of a geochemically exceptional group of lavas. Its composition is clearly different from common samples of La Reunion and presents (1) an enrichment in incompatible elements and (2) tends toward an enriched EM endmember. These chemical specificities reveal that the source of La Reunion magmatic products is (1) an heterogeneous source affected by (2) variable melting degrees. Moreover, two samples of this new group dated at 3.77 (0,08) and 3.34 (0,07) Ma extend considerably the period of activity of the island. These rocks are the oldest samples ever dated at La Reunion. The nature and stratigraphical location of subaerial and submarine samples from Piton des Neiges and Piton de la Fournaise imply a new interpretation of the global evolution of the island. Unlike previous studies, our results indicate that :(1) The differentiated subaerial lavas from Rivière des Remparts, due to their stratigraphical and geographical location underlying Piton de la Fournaise, and by analogy with the Piton des Neiges, cannot be linked to the activity of Piton de la Fournaise. (2) The isotope signature of the submarine lava group from the North-East Rift Zone of Piton de la Fournaise, reveals the heterogeneous character of the mantle source under La Reunion Island, that can be modelled as embedded eclogite in a matrix of spinel lherzolite, (3) The age of this submarine group and its location under the eastern flank of Piton de la Fournaise, imply a more complex model of evolution of La Reunion. Therefore, our geochemical and geochronological data are new arguments suggesting the existence of a third volcanic center on the island. This assumption confirms the previous petrological and geophysical evidence supporting the existence of this volcano at the East of La Reunion, commonly called Les Alizés volcano.

The Cenozoic Ailaoshan – Red River shear zone marks the present day western margin of the South China Block. Along this margin are well preserved late Paleoproterozoic to early Neoproterozoic sedimentary and volcanic successions. This work examines the ages and tectonic environments for the formation of the successions, as well as significance of the regional tectono-magmatic events on the formation of widespread iron oxide-copper deposits. The oldest succession is the Paleoproterozoic Dahongshan Group. A new SHRIMP UPb age of 1675 ± 8 Ma for a tuffaceous schist unit confirms its Paleoproterozoic age. Detrital zircon ages of the Dahongshan Group range between Archean to Paleoproterozoic (ca. 2780 – 1860 Ma). They include a population of ca. 2400 – 2100 Ma grains, which have no known source region on the exposed Yangtze Block. Previous geochemical studies of metavolcanic rocks from the Dahongshan Group have suggested that these rocks were erupted in an oceanic setting. However, this study shows that the metavolcanics are extremely altered and cannot be used for reliable tectonic discrimination. Based on the characteristics of sedimentary rocks in the Dahongshan Group, it is suggested that these rocks were deposited in a continental setting. Overlying the Dahongshan Group is a thick sedimentary sequence which has been variably termed the Kunyang, Dongchuan, Huili or Xide Groups. In the past, these rocks have been considered as a Mesoproterozoic rift succession. However, no precise age constraints were available for the succession. In this study, this sequence is found to contain at least two separate tectonostratigraphic units. The oldest (ca.1140 Ma) is comprised of alkaline basalt with a geochemical and isotopic character similar to that of modern intracontinental rift basalts. The presence of Cathaysia-derived sediments in this unit indicates sedimentary transportation from the southerly Cathaysia Block to the northerly Yangtze Block (in present coordinates) in South China at that time, which suggests an “impactogen” scenario. The thick sedimentary sequence of what has traditionally been defined as the Kunyang Group has been found to have significantly younger depositional age of ca.1000 – 960 Ma. The composition of sedimentary rocks and the provenance of detrital zircons from the Kunyang Group are consistent with a foreland basin setting. The depositional age of this sequence coincides with the timing of Sibao Orogeny as determined elsewhere in the South China Block. Summary Page ii Numerous iron oxide - copper (gold) deposits occur within the rocks of the Dahongshan and Kunyang Groups. Previous studies have classified these deposits into two deposit styles: the Dahongshan-type Paleoproterozoic VMS mineralisation hosted within the Dahongshan Group, and the Dongchuan-type diagenetic carbonate and shale-hosted deposits hosted within the Kunyang Group. However, both deposit types share similarities with the iron oxide – copper (gold) deposit class, such as stratabound disseminated and massive copper ores, abundance of iron oxide occurring mostly as low Ti - magnetite and haematite, and variable enrichments in Au, Ag, Co, F, Mo, P and REE. 40Ar/39Ar data from both deposit types indicate mineralisation ages of ca. 850 – 830 Ma and 780 – 740 Ma.

Orientador: Yara Kulaif / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-09T00:52:07Z (GMT). No. of bitstreams: 1 Betti_Andre_M.pdf: 29085853 bytes, checksum: 516edd91e6affd7e352eec0cc1b94dd7 (MD5) Previous issue date: 2007 / Resumo: O trabalho relata um estudo de caso envolvendo uma abordagem interdisciplinar de temas geocientíficos em uma disciplina regular de História do III Ciclo - 5º nível do ensino fundamental de uma escola pública. Nele, o professor, atuando também como pesquisador, procurou observar e interpretar, por meio de transcrições de aulas-debates, textos e desenhos produzidos pelos alunos, a construção do conceito de tempo ¿ um conceito-chave e extremamente importante na aproximação entre a disciplina de História e a Geologia. Sendo assim, para este estudo, utilizou-se uma unidade programática daquele nível de ensino, aquela voltada para o conceito de tempo, de modo a enfocar tanto a sua dimensão social e humana, normalmente adotada nesta disciplina, quanto a sua dimensão no tempo geológico. No trabalho com o tempo geológico, a observação e o estudo do entorno da escola, mais especificamente, a Serra dos Cocais (Valinhos, SP, Brasil) foram fundamentais. Duas questões principais nortearam esta pesquisa: Como utilizar a especificidade de paisagens do entorno da escola para a construção de um conceito de tempo estendido até sua dimensão geológica? E, que possibilidades pedagógicas envolvem a abordagem de conceitos típicos das Ciências da Terra para o professor de História do ensino fundamental? Em meio à pesquisa destas possibilidades, optamos por privilegiar a ênfase na elaboração conceitual dos alunos, por meio da mediação do professor/pesquisador no desenvolvimento das atividades, bem como, por evidenciar o relevante papel do entorno, ou seja, do ambiente local, no processo do conhecimento cognitivo das crianças. Assim, entende-se que, ao integrar o conhecimento geológico no estudo da História, propicia-se a compreensão de que o tempo das culturas humanas está contido num tempo ambiental muito mais amplo que não pode ser ignorado pelas ciências sociais / Abstract: The work reveals a case study involving an interdisciplinary teaching approach for treating geosciences¿ subjects in a discipline of History of the 'III Ciclo¿ ¿ 5th level of the fundamental education of a public school. In that, the teacher, also acting as researcher, observes and interprets, by means of transcriptions of class-debates, texts and drawings produced by the students, the construction of the concept of time ¿ an extremely important and a key-concept for the confluence of the discipline of History and Geology. For this study, a programmatic unit of that teaching level was used, the one that treats the concept of time, in a way to focus on both its social and human dimension, usually adopted in this discipline, and its dimension in the geologic time. In the work with the geologic time, the observation and study of the surrounding environment of the school, more specifically, the 'Serra dos Cocais¿ (Valinhos, SP, Brazil) were fundamental. Two main questions guided this research: How to use the surrounding landscape of the school in the construction of an extended concept of time covering up to its geological dimension? And, what pedagogic possibilities do involve the typical concepts of the Earth Sciences for teaching History? In searching for these possibilities we opted for privileging the students¿ conceptual elaboration, through the teacher¿s/researcher¿s mediation in the development of the activities, as well as, emphasizing the fundamental role of the surrounding area, that is to say, of the local environment, in the process of the children¿s cognitive knowledge. Thus, integrating the geological knowledge in the History subject provides a better understanding that the time of the human cultures is contained in a much broader natural time that cannot be ignored by the social sciences / Mestrado / Mestre em Ensino e Historia de Ciencias da Terra

M.Sc. (Geology) / The Cradle of Humankind is a 47 000 hectare demarcated area with over three dozen fossil-bearing cave sites well known for the preservation of fossil evidence of early hominin taxa such as Australopithecus Africanus, Australopithecus Sediba, Paranthropus Robustus and Early Homo. As a result, a database of precise and accurate chronological data for fossil-bearing cave deposits of the Cradle of Humankind (similar to that for East African fossil sites) is very important, but developing one has proven extremely challenging. The main challenge is that the fossil-bearing deposits at the cradle are mainly complex breccias with a chaotic, localized stratigraphy and no association to any volcanic ash beds, unlike the East African deposits which are lacustrine and fluviatile deposits interbedded with volcanic ash layers. However, substantial success has been obtained recently through the combination of U-Pb dating of CaCO₃ speleothems and palaeomagnetic dating (magnetostratigraphy) after many attempts and unconvincing results from techniques such as biostratigraphic correlations, electron spin resonance on teeth and cosmogenic burial dating of the sediments. The problem with U-Pb dating of CaCO₃ speleothems is that this requires samples that are extremely clean (i.e. detrital-free) and have an appreciable U content (close to 1 ppm), and such material is at many sites not available...

Understanding spatial and temporal variations in strain accumulation and release along plate boundaries is a fundamental problem in tectonics. Short-term and long-term slip rates are expected to be equal if the regional stress field remains unchanged over time, yet discrepancies between modern geodetic (decadal time scale) slip rates and long-term geologic (10^3 to 10^6 years) slip rates have been observed on parts of the Pacific-North American plate boundary system. Contemporary geodetic slip rates are observed to be ~2 times greater than late Pleistocene geologic slip rates across the southern Walker Lane. I use a combination of GPS geodesy, detailed field geologic mapping, high-resolution LiDAR geodetic imaging, and terrestrial cosmogenic nuclide geochronology to investigate the observed discrepancy between long- and short-term slip rates. I find that the present day slip rate derived from GPS geodesy across the Walker Lane at ~37.5°N is 10.6 ± 0.5 mm/yr. GPS data suggest that much of the observed discrepancy occurs west of the White Mountains fault zone. New dextral slip rates on the White Mountains fault zone of 1.1 ± 0.1 mm/yr since 755 ka, 1.9 +0.5/-0.4 mm/yr since 75-115 ka, 1.9 +0.5/-0.4 mm/yr since 38.4 ± 9.0 ka, and 1.8 +2.8/-0.7 mm/yr since 6.2 ± 3.8 ka are significantly faster than previous estimates and suggest that slip rates there have remained constant since the middle Pleistocene. On the Lone Mountain fault I calculate slip rates of 0.8 ± 0.1 mm/yr since 14.6 ± 1.0 ka and 0.7 ± 0.1 mm/yr since 8.0 ± 0.5 ka, which suggest that extension in the Silver Peak-Lone Mountain extensional complex has increased dramatically since the late Pleistocene.

O Domínio Macururé, localizado na porção norte da Faixa de Dobramentos Sergipana, é caracterizado por apresentar um grande volume de granitos (s.l.) de idade Neoproterozóica. O Maciço Glória Norte (MGN), que ocorre na porção centronorte do Domínio Macururé, representa uma das mais importantes intrusões que se colocaram após o pico de deformação e metamorfismo no orógeno (630 Ma). Nesse estudo identificou-se a presença de duas fácies petrográficas nesse maciço: quartzomonzonítica porfirítica, quartzo-monzonítica, além de diques leucocráticos. Os enclaves de diversos tipos, são uma feição recorrente em toda a extensão do maciço, assim como texturas evidenciam a existência do processo de misturas entre magmas. Os estudos microscópicos permitiram a identificação de várias texturas de instabilidade, e uma sequência de cristalização marcada pelo aumento de fluídos ao longo da evolução do magma. Os dados geoquímicos revelam uma afinidade com as rochas da série shoshonítica e seus enclaves exibem afinidade ultrapotássica com conteúdos de MgO e K2O sempre maiores que 3%. Nos diagramas ETR percebeuse um enriquecimento de ETR leves em relação aos pesados, além de fortes anomalias negativas de Ta, Nb, Ti, P, Sr e Eu, principalmente nos enclaves. As temperaturas médias calculadas pelo geotermômetro de Zr revelam que o início da cristalização no MGN se deu entre 810°C e 784°C e teve seu fim entre 730°C e 700°C. A idade obtida através do método U/Pb SHRIMP (588 + 5,2 Ma) posiciona o magmatismo que deu origem ao MGN, no Período Ediacarano, marcando a ocorrência de um magmatismo a 588 Ma, que não foi afetado por eventos tectônicos. / The Domain Macururé located in the northern portion of Sergipano Fold Thrust Belt, is characterized by having a large volume of granites (s.l.) of Neoproterozoic age. The Gloria Norte Massif (GNM), which occurs in the north-central portion of the Domain Macururé, represents a major intrusion that arose after the peak of deformation and metamorphism in the orogen (+ 630 Ma). In this study we identified the presence of two petrographic facies in that massif: quartz-monzonitic porphyritic, quartz-monzonitic and leucocratic dykes. The enclaves, varied tipology, are a recurrent feature in the whole extent of the massif, as well as mixtures of texture of mixing and mingling. Microscopic studies allowed the identification of various textures of the mixing and a sequence of crystallization marked by increased fluids during the evolution of the magma. Geochemical data reveal an affinity with shoshonitic series rocks, and their enclaves exhibit ultrapotassic affinity, wich always show MgO and K2O contents greater than 3%. In the diagrams ETR perceives an enrichment of LREE relative to HREE, and strong negative anomalies of Ta, Nb, Ti, P, Sr, and Eu, mostly in enclaves. The average temperature calculated by Zr geothermometer showed that the onset of MGN crystallization occurred between 810°C and 784°C, and its end was between 730°C and 700°C. The ages obtained by U/Pb SHRIMP (588 + 5.2 Ma) positions the magmatism that gave rise to the MGN, in the Ediacaran and this age mark the occurrence of a magmatism (588 Ma), which was not significantly affected by tectonic events.