Ce travail de thèse présente des analyses isotopiques Lu-Hf par MC-ICP-MS combinées de zircons ignés et de roches totales d’une importante collection de granitoïdes archéens appartenant à la suite des Tonalite-Trondhjémite-Granodiorite (TTG) afin d’apporter un regard nouveau sur la croissance de la croûte continentale et tout particulièrement dans le début de l’histoire de la Terre. Nos données indiquent un bon accord général entre les zircons ignés, mesurés par ablation-laser et par solution, avec leurs roche-hôtes. Nous démontrons que le rapport Lu/Hf intégré dans le temps de la source mantellique des TTG est près de la valeur chondritique et n’a pas significativement changée au cours des 4 derniers milliards d’années. Par conséquent, les continents se sont formés à partir d’un matériel primitif non fractionné extrait du manteau profond par l’intermédiaire de panaches qui après fusion partielle ont laissés un résidu appauvri dans le manteau supérieur. Les cristaux de zircon extraits des TTG ont des compositions isotopiques en Hf cohérentes au sein d’une même population alors que le système U-Pb, dans les mêmes grains, est souvent perturbé résultant ainsi en l’obtention de valeurs d’εHf initial erronées. Ce problème est endémique aux cristaux de zircon détritiques archéens et en accord avec des résultats expérimentaux sur la mobilité préférentielle de l’Hf en fonction de celle de l’U et du Pb au sein du zircon. Nous suggérons que ce problème biaise l’enregistrement détritique archéen en faveur de valeurs d’εHf initial négatives qui contrastent avec les valeurs obtenues pour les TTG mais peuvent être expliquées par l’utilisation d’âges 207Pb/206Pb non-magmatiques. Si l’on considère les cristaux de zircon de Jack Hills au vu de ces résultats, la source des continents serait restée inchangée depuis 4,3 Ga. / This PhD thesis presents combined whole-rock and single zircon MC-ICP-MS Lu-Hf isotope data for a large collection of Archean granitoids belonging to typical Tonalite-Trondhjemite-Granodiorite (TTG) suites. The data were collected in an attempt to shed new light on early crustal growth. Our data display overall good agreement between Hf isotope compositions of igneous zircons, measured by both laser-ablation and solution chemistry, and their host-rocks. It is shown that the time-integrated Lu/Hf of the mantle source of TTGs is near-chronditic and has not significantly changed over the last 4 Gy. Continents therefore most likely grew from nearly primordial unfractionated material extracted from the deep mantle via rising plumes that left a depleted melt residue in the upper mantle. Zircons extracted from the analyzed TTGs have Hf isotopic compositions broadly consistent within populations, whereas the U-Pb system in the same grains is often disturbed, causing spurious initial εHf values. This problem is endemic to the Archean detrital zircon record and consistent with experimental results bearing on the relative retentivity of Hf vs. U and Pb in zircon. We argue that this behavior biases the Archean zircon record towards negative εHf values, which are at odds with the present TTG data set but can be explained by zircons having non-magmatic 207Pb/206Pb ages. If the Hadean Jack Hills zircons are considered in light of these results, the mantle source of continents has remained unchanged for the last 4.3 Gy.

La croûte de granitoïdes de la Terre Primitive la plus ancienne qui ait été préservée remonte au Paleoarchéen et se compose principalement de granitoïdes sodiques tonalite-trondhjémite-granodiorite (TTG) qui se sont formés par fusion partielle de métabasaltes hydratés. En revanche, les granites (stricto sensu) sont en général postérieurs aux TTG et apparaissent tardivement dans les cratons anciens.Cependant, l’existence de zircons Hadéens préservant des suites d’inclusions minérales qui sont compatibles avec la cristallisation à partir d’un magma granitique peralumineux, indique que les roches granitiques faisaient aussi partie de la croûte felsique de la Terre Primitive; même si nous n’avons pas de preuves directes et que cette dernière n’ait pas conservée. Dans cette thèse, je présente une variété inhabituelle de granites et rhyolites peralumineux qui sont marqués par un forte teneur en K2O et une faible teneur en CaO et qui possèdent du rutile. Ces roches sont situées dans le conglomérat basal du Groupe du Moodies (Afrique du Sud). Elles défient la vision commune que l’on a de l’évolution des cratons Archéens puisqu’elles ont été produites en même temps que des magmas TTG, pendant trois cycles magmatiques qui ont affectés la ceinture de roches vertes de Barberton (CRVB). Ces roches ont été par la suite mises en place, comme galets, dans un conglomérat plus jeune.L’étude des inclusions minérales localisées dans des zircons présents dans les granites et les rhyolites qui font le sujet de cette étude, montre que les inclusions de feldspaths alcalins sont plus abondantes que les inclusions de plagioclases et démontre que les principales caractéristiques de ces granites, c’est à dire qu’ils sont riches en K et pauvres en Ca, ont une signature magmatique. La signature isotopique de l’oxygène de ces zircons révèle que ceux-ci ont conservé la valeur du δ18O du magma à partir duquel les granites se sont formés. De plus ceci montre que la valeur du δ18O de la source des granites etait proche de celle de TTG contemporains. La poursuite de l’étude des zircons montre que leur système isotopique Lu-Hf reflète la signature crustale du magma dans lequel ils ont cru. L’étude Sm-Nd des granites et rhyolites indique que l’âge minimum du protolithe de leur source est de près de 3,9 milliards d’années, ce qui est en accord avec la signature Lu-Hf des zircons. De plus, je montre dans cette thèse que le caractère peralumineux des granites et des rhyolites, avec leur forte teneur en Sr et basse teneur en Ca associés à leurs Eu / Eu * ~ 1, est une conséquence de la fusion partielle de phengite dans une source métagrauwacke à des pressions supérieures a celle de la stabilité du plagioclase. Mon travail montre donc que des granites peralumineux riches en K et pauvres en Ca ont été générés durant le Paléo et Méso-Archéen, aux côtés des TTG sodiques, par la fusion partielle de sédiments, à haute pression. Non seulement ce processus a démontré la capacité de la Terre Primitive à recycler du matériel relativement jeune et ce, dès 3,9 milliards d’années; mais il a également contribué à chaque épisode de croissance crustale à travers le Paleo- et Méso-Archéen dans la CRVB, malgré l’absence de pluton mis en place à des profondeurs identiques à celles des TTG. / Earth’s oldest preserved granitoid crust dates back to the Paleoarchean and consists predominantly of sodic tonalite-trondhjemite-granodiorite (TTG) granitoids that arose through the partial melting of hydrated metabasalts. In contrast, granites (sensu stricto) typically postdate the TTG and appear late in the plutonic record of the old cratons. However, the existence of Hadean zircons with mineral inclusion suites that are consistent with crystallization from peraluminous granitic magmas indicates that granitic rocks formed part of the earliest felsic crust; although we have direct evidence, this earliest felsic crust is not preserved. In this PhD I present an unusual variety of markedly CaO-poor, K2O-rich, rutile-bearing, peraluminous granite and rhyolite that are located in the basal conglomerate of the Moodies Group (South Africa). These rocks challenge the common view of the Archean craton evolution as they were produced concurrently with TTG magmas during three magmatic cycles in the Barberton Greenstone Belt (BGB) and were later emplaced, as clasts, in a younger conglomerate. The study of mineral inclusions located in the zircons present within the granites and rhyolites, shows that alkali feldspar inclusions are abundant relative to plagioclase inclusions and demonstrates that the main characteristics of these granites, i.e. they are K-rich and Ca-poor, are a magmatic signature. The oxygen isotope signature of these zircon grains reveals that the zircons have preserved the δ18O value of the magma from which the granites originated and that the source of the granites had a magmatic oxygen isotope value close to the one of the regional coeval TTG. Further study of the zircons shows that their Lu-Hf isotopic system reflects the crustal signature of the magma into which they grew. Sm-Nd study of the granites and rhyolites whole rock indicates that the minimum age of the source’s protolith of the granites and rhyolites is close to 3.9 billion years, which is in agreement with the zircons’ Lu-Hf signature. Additionally I show in this thesis that the peraluminous character of the granites and rhyolites, along with their high Sr and low Ca content associated to their Eu/ Eu* ~ 1 is a consequence of phengite melting in a metagreywacke source at pressures in excess of plagioclase stability. My work therefore illustrates that K-rich, Ca-poor peraluminous granites were generated in the Paleo and Meso Archean, alongside with the sodic TTG, through partial melting of sediments at high pressures. Not only has this process demonstrated the ability of the early Earth to recycle relatively young material since 3.9 billions years ago, but it has also contributed to each episode of continental crustal growth through the Paleoarchean to Mesoarchean in the BGB, despite leaving no plutonic record at the typical mid-crustal level of exposure that the TTG plutons around the belt represent.

The ¹⁷⁶Lu-¹⁷⁶Hf and ¹⁴⁷Sm-¹⁴³Nd decay systems have been extensively used as geochronological tools to determine ages from garnet (Grt) - whole rock (WR) parent-daughter isotopic ratios; however, the ¹⁷⁶Lu-¹⁷⁶Hf age of garnet is almost always found to be significantly older than the ¹⁴⁷Sm-¹⁴³Nd age determined from the same aliquots. This dissertation presents new experimental diffusion data for Lu and Hf in garnet, and numerical simulations using these data, which explain these age discrepancies and also show that Grt-WR ¹⁷⁶Lu-¹⁷⁶Hf isochrons do not generally yield ages which correspond to an unambiguous temporal event in the evolutionary history of the host rocks. This is a result of (a) partial or complete retention of very slow-diffusing radiogenic ¹⁷⁶HF produced during prograde heating, and (b) the lower closure temperature of Lu relative to Hf; these complexities do not affect the interpretation of Grt-WR isochrons based on the ¹⁴⁷Sm-¹⁴³Nd system. In addition, the diffusion kinetic properties of Hf in clinopyroxene were experimentally determined in order to address the age controversy of the shergottite suite of Martian meteorites (~200 Ma ages determined by ¹⁷⁶Lu-¹⁷⁶Hf, ¹⁴⁷Sm-¹⁴³Nd, and various other decay systems as opposed to a ~4 Ga whole rock Pb-Pb age). This was achieved by calculating the timescales needed to re-equilibrate Hf isotopes in clinopyroxene (the primary host of rare earth elements amongst the minerals used to compose the ¹⁷⁶Lu-¹⁷⁶Hf isochrons) with the surrounding matrix at the peak- and post-shock P-T conditions likely to have been experienced by the shergottites. It is concluded that, contrary to the earlier suggestions, impact heating is highly unlikely to have significantly reset the ¹⁷⁶Lu-¹⁷⁶Hf ages of these Martian samples. These calculations are bolstered by the nature of measured Cr and Fe-Mg concentration profiles across olivine-melt boundaries, and Ti profiles across clinopyroxene-maskelynite interfaces in the shergottite RBT-04262. The lack of any evidence of diffusion in the measured concentration profiles, coupled with the qualitative incompatibility of the measured crystal-melt fractionation at these interfaces with the nature of fractionation expected from equilibrium partitioning, provides strong evidence that no substantial chemical exchange took place between the solid and melt phases during peak-shock P-T conditions.

Cette thèse porte sur l'histoire géologique paléoprotérozoique du Craton Ouest Africain au nord du Ghana, pendant l'orogenèse Éburnéenne (2.15-2.07 Ga). La géologie régionale est présentée à l'aide de nouvelles cartes lithologique, métamorphique et structurale, issues de l'interprétation de données géophysiques et de terrain. Le nord du Ghana est constitué de ceintures de roches vertes, de gneisses et de granitoïdes. Ceux-ci ont une affinité calco-alkaline ou sont analogues aux TTG archéens, et se sont formés entre 2.21 et 2.11 Ga. L'isotopie Lu-Hf indique que l'ensemble des magmas est juvénile, avec des temps de résidence crustaux de 2.45-2.30 Ga. Le métamorphisme au nord du Ghana révèle une diversité de régimes thermiques. Des reliques métamorphiques témoignent d'un géotherme apparent froid (BT-HP, 15°C/km). Elles sont sur-imprimées par un épisode métamorphique MP - MT (20°C/km) dans les faciès amphibolite à granulite, à partir de 2145 Ma, puis par une autre phase métamorphique en faciès amphibolite (25-30°C/km) entre 2125 et 2105 Ma. L'évolution métamorphique est interprétée comme la conséquence d'une interaction entre épaississement crustal et fluage gravitaire de la pile orogénique. Il est proposé qu'un événement magmatique produise des fragments d'une croute juvénile précoce, précurseur du Craton Ouest Africain à partir de 2.45 Ga. Le nord du Ghana pourrait représenter une suture entre deux compartiments cratoniques distincts entrés en collision. La géodynamique paléoprotérozoique semble unique dans l'histoire de la Terre et représente un état transitoire de son évolution séculaire, entre un régime " archaïque "' et la tectonique des plaques moderne. / This thesis focuses on the Paleoproterozoic geological evolution of the West African Craton in northern Ghana. New lithological, metamorphic and structural regional maps are built from the interpretation of field and airborne geophysical data. The crust in northern Ghana comprises greenstone belts gneissic terranes, and granitoids. The latter have a calc-alkaline affinity, or are analogue to Archean TTGs, and formed between 2.21 and 2.11 Ga. Lu-Hf isotope analyses show that the magmas are juvenile and derived from a source extracted from the mantle at 2.45-2.30 Ga. The Eburnean metamorphic record of northern Ghana reflects a diversity of thermal regimes. Metamorphic relics record conditions that correspond to a cold apparent geothermal gradient (BT-HP, ~15°C/km). They are overprinted by amphibolite- to high-P granulite-facies metamorphism (MP-MT, 20°C/km) starting at 2145 Ma, followed by another metamorphic phase in the amphibolite facies (25-30°C/km) between 2125 and 2105 Ma. The metamorphic evolution is interpreted to reflect the interplay between crustal thickening and gravitational flow of the orogeny. We suggest that a major magmatic event started at 2.45 Ga and produced fragments of juvenile crust, that formed the protolith of the West African Craton's crust. Northern Ghana may represent a suture zone between two distinct cratonic fragments that collided. Its geological record shares some similarities with modern orogenic belts, although it is not strictly identical. The Paleoproterozoic geodynamic settings may be unique in the history of the Earth, and represent a transitional regime in its secular evolution, between archaic geodynamics and modern plate tectonics.

Na porção W-SW do lobo Guaxupé, pertencente à Nappe Socorro-Guaxupé, nos arredores da cidade de São José do Rio Pardo, é registrado um evento metamórfico e anatético de fácies granulito, sob condições de desidratação da hornblenda, com T >=850ºC. As rochas diatexíticas, que compõem as suítes São José do Rio Pardo (SJRP) e Pinhal, resultam desse evento de alta temperatura, ocorrido há ~625 Ma. As assinaturas geoquímicas e isotópicas sugerem uma geração a partir da anatexia da crosta continental inferior. Além disso, o enriquecimento em potássio da suíte SJRP indica uma afinidade vaugnerítica, a qual é caracterizada por altos conteúdos de Mg, elementos do tipo LILE (large ion lithophile elements), HFSE (high field strenght elements) e ETR-leves, além de valores negativos de \'épsilon\'Nd e razões de Sr iniciais baixas, ~0.706. O magmatismo vaugnerítico implica em um manto litosférico metassomatizado como fonte, o qual foi enriquecido por eventos de subducção precedentes. A presença de pseudomorfos de fusão nesses diatexitos indicam uma evolução quase isotérmica sob presença de líquido anatético. O transporte sin-magmático ocorreu para NE-E. A fonte de calor para esse metamorfismo pode estar associada à delaminação da base do arco magmático. O processo de fusão parcial gerou leucossomas charno-enderbíticos na Unidade Metatexítica, com assinaturas geoquímicas e isotópicas que indicam uma fonte crustal. Dessas rochas, foram separados cristais de zircão que mostraram duas populações distintas. A primeira, tipicamente com cristais prismáticos e bipiramidados, indicam idades em torno de 620 Ma, enquanto que a segunda, com cristais isométricos típicos de alto grau metamórfico, indicam idades em torno de 610 Ma. Em relação ao pico metamórfico de ~625 Ma, as idades mais jovens obtidas sugerem um período de 15 my em que predominaram altas temperaturas. O transporte tectônico para NW, em estado sólido de alta temperatura, é posterior à cinemática sin-magmática para NE, e deve estar associado à compressão da placa superior convergente, dentro desse período de alta temperatura. Esse regime tectônico é compatível com modelos recentes da tectônica Andina onde é descrita uma subducção horizontal (Pampean flat subduction). Dentre as rochas da Unidade Granulítica Basal, também submetida à fusão parcial por desidratação da hornblenda, ocorrem gnaisses com afinidade adakítica, sugerida pelas altas razões Sr/Y = 72.73, La/Yb = 23.07, \'(La/Yb) IND.N\' = 15.56, e teores de #mg = 51.77, Sr = 1062 ppm, Cr = 197 ppm e Ni = 103 ppm. Tal afinidade sugere magmas resultantes da fusão de um slab em subducção. A Nappe Socorro-Guaxupé admite uma evolução que se inicia, cerca de 670-640 Ma, com uma subducção inclinada para a geração de rochas cálcio-alcalinas com alguns membros adakíticos. É seguido um momento de colisão, entre 625 e 610 Ma, com a geração de rochas diatexíticas e metatexíticas de alto potássio, onde o arco migrou primeiramente para o ante-arco (estado subsólido) e depois em direção ao interior da placa superior (estado sólido). A estabilização da nappe se deu quando da colocação dos maciços sieníticos pós-tectônicos, Capituva e Pedra Branca. / The W-SW portion of the Guaxupé Domain, nearby the São José do Rio Pardo city, records a granulite facies anatetic event under hornblende dehydration-melting conditions, i.e. T >=850ºC. The diatexitic rocks that are comprised within the São José do Rio Pardo and Pinhal suites resulted from this high-T metamorphic event, ca. 625 Ma. Geochemical and isotopic signatures suggest derivation from the lower continental crust. The K-rich SJRP suite also show geochemical affinity with vaugneritic rocks, suggested by high contents of Mg, LILE, HFSE and light-REE in addition to negative ?Nd and low Sr initial ratio (~0.706). Vaugneritic magmatism implies on a derivation from a metasomatized lithospheric mantle source enriched before partial melting in a previous subduction setting. Once both suites contain melt pseudomorphs, it is then suggested and isothermic evolution under the presence of melt. A syn-magmatic driven transport occurred towards NE-E, and the heat source for high-T conditions could be assigned to mantle delamination under the margmatic arc. Within the Metatexitic Unit, partial melting resulted in charno-enderbitic leucosomes whose geochemical and isotopic signatures indicate crustal sources. From these leucosomes, two different populations of zircon crystals were separated. The first, comprising bypiramidal-prismatic grains, yield ages around 620 Ma, whereas the second typology of zircons is isometric and soccer-ball type, yielding younger ages around 610 Ma. The latter typology is typical of high-T and melt-bearing rocks. Considering the 625 Ma metamorphic peak, the younger ages suggest a 15 my period when high-T conditions prevailed. Top-to-NW transport, under solid-state high-T conditions, can be associated to the compression of the upper convergent plate within this high-T period. Textural features suggest this transport to have occurred after the crystallization of the syn-magmatic rocks. The compression of the upper plate resembles recent models of the Andean orogenic cycle, where the Pampean flat subduction is described. Among the rocks of the Basal Granulitc Unit, which also underwent hornblende-dehydration partial melting, a gneissic rock shows adakitic affinity, suggested by Sr/Y = 72.73, La/Yb = 23.07, \'(La/Yb) IND.N\' = 15.56, #mg = 51.77, Sr = 1062 ppm, Cr = 197 ppm and Ni = 103 ppm. Adakitic magmas are thought to be slab melts. The Socorro-Guaxupé Nappe was built up between 670 and 640 Ma with a steep subduction and generation of calc-alkaline and subordinate adakitic rocks. A collisional setting, generating high-K diatexites and metatexites, took place between 625 and 610 Ma, where the arc firstly migrated (in subsolidus state) towards the forearc and then migrated (in solid state) towards the interior of the upper plate. Post-tectonic Capituva and Pedra Branca syenitic plutons intruded around 610 Ma, recording the arc migration ceasing.

Magmas graníticos peraluminosos são gerados por meio da anatexia de rochas crustais em cinturões orogênicos continentais. Os granitos do Cinturão Ribeira Central são relacionados a processos orogênicos de convergência de blocos litosféricos, durante o Neoproterozoico. O Batólito Serra das Araras é um corpo granítico, tabular e peraluminoso localizado no Domínio Paraíba do Sul, região sudoeste no estado do Rio de Janeiro - Brasil. O corpo é alongado na direção NE-SW e sua deformação foi gerada pela atividade de zonas de cisalhamento dúcteis de movimentação preferencial destral, que também controlaram o alojamento do magma granítico. O presente trabalho visa a caracterizar o Batólito Serra das Araras com base em dados de petrografia, de geoquímica de rocha total, de química mineral (EPMA) e de geocronologia U-Pb e LuHf (LA-ICP-MS) em grãos de zircão. Três amostras representativas foram analizadas para obtenção das idades U-Pb de cristalização e de metamorfismo. Essas amostras são compostas de granitos com matriz protomilonítica com muscovita, biotita e granada, um dique sienogranítico com 15-30 cm de espessura e um enclade de quartzo diorito. O plagioclásio possui composição entre oligoclásio (An16) e andesina (An38) e possui núcleos mais enriquecidos em anortita. Todas as amostras apresentam fases ricas em almandina com bordas levemente enriquecidas em manganês, produto do metamorfismo de médio a baixo grau. Os dados isotópicos U-Pb em grãos de zircão revelaram que o magmatismo granítico cristalizou-se ca. 595 Ma e foi gerado no mesmo evento tectono-termal Ediacarano que gerou granitos tipo-I e tipo-S de caráter pós-colisional no Domínio Embu/Paraíba do Sul. Os dados isotópicos de Lu-Hf indicam a reciclagem de crosta juvenil do Riaciano-Orosiriano e de crosta continental do Orosiriano como fontes do protólito metassedimentar do Batólito Serra das Araras. A composição contrastante do enclave de quartzo diorito (amostra SA-06), de caráter metaluminoso e com valores menos degativos de \'\'épsilon\'Hf IND.t\' (entre -5,7 and -8,1), sugere o envolvimento marginal de fontes orto-derivadas da crosta inferior. As idades de cristalização e a composição do batólito indicam que seu magmatismo é correlacionável com granitos peraluminosos do Domínio Embu e do Orógeno Araçuaí. / Peraluminous granitic magmas are produced by anatexis of crustal rocks in continental orogenic belts. Orogenic granites of Central Ribeira Belt are correlated with the collision of lithospheric blocks during Neoproterozoic. The Serra das Araras Batholith is a tabular granitic body of peraluminous composition located at Paraíba do Sul Domain, southwestwards of Rio de Janeiro state - Brazil. The body is elongated at NE-SW direction and its deformation was produced by ductile shear zones with dextral movement component, which has also controlled magma emplacement. The aim of this study is to characterize the Serra das Araras Batholith and to provide petrography, whole-rock geochemistry (major and trace elements), mineral chemistry (EPMA) and combined LA-ICP-MS U-Pb and Lu-Hf isotopic analyses in zircon grains. Three representative samples were analyzed for isotopic determination in order to obtain crystallization and metamorphic U-Pb ages. These samples are composed of monzogranite with protomylonitic texture; a 15-30 cm thick syenogranite dyke and a biotite-hornblende quartz diorite enclave. Plagioclase is Andesine and Oligoclase (An16-38). Anorthite contents display a progressive zoning with rims having lower contents than cores. All samples exhibit almandine-rich phases, with slightly Mg-rich cores and Mn-rich rims, produced by metamorphism of medium to low grade. Zircon U-Pb isotopic data reveal that the batholith was emplaced ca. 595 Ma and was generated at the same middle-Ediacaran tectono-thermal event that generated voluminous I-type and S-type granitoids of post-collisional character at Embu/Paraíba do Sul Domain. Lu-Hf isotopic data suggest that late-Rhyacian to Orosian juvenile and continental crust have been sources of metasedimentary protoliths of Serra das Araras Batholith. The contrasting composition of the quartzdiorite enclave (sample SA-06), of metaluminous character and less negative \'\'épsilon\'Hf IND.t\' values (between - 5.7 and -8.1), suggests a marginal involvement of ortho-derived igneous rocks of the lower crust. The crystallization ages of the granites are coeval with peraluminous granites of Embu Domain and of Araçuaí Belt.

Na porção W-SW do lobo Guaxupé, pertencente à Nappe Socorro-Guaxupé, nos arredores da cidade de São José do Rio Pardo, é registrado um evento metamórfico e anatético de fácies granulito, sob condições de desidratação da hornblenda, com T >=850ºC. As rochas diatexíticas, que compõem as suítes São José do Rio Pardo (SJRP) e Pinhal, resultam desse evento de alta temperatura, ocorrido há ~625 Ma. As assinaturas geoquímicas e isotópicas sugerem uma geração a partir da anatexia da crosta continental inferior. Além disso, o enriquecimento em potássio da suíte SJRP indica uma afinidade vaugnerítica, a qual é caracterizada por altos conteúdos de Mg, elementos do tipo LILE (large ion lithophile elements), HFSE (high field strenght elements) e ETR-leves, além de valores negativos de \'épsilon\'Nd e razões de Sr iniciais baixas, ~0.706. O magmatismo vaugnerítico implica em um manto litosférico metassomatizado como fonte, o qual foi enriquecido por eventos de subducção precedentes. A presença de pseudomorfos de fusão nesses diatexitos indicam uma evolução quase isotérmica sob presença de líquido anatético. O transporte sin-magmático ocorreu para NE-E. A fonte de calor para esse metamorfismo pode estar associada à delaminação da base do arco magmático. O processo de fusão parcial gerou leucossomas charno-enderbíticos na Unidade Metatexítica, com assinaturas geoquímicas e isotópicas que indicam uma fonte crustal. Dessas rochas, foram separados cristais de zircão que mostraram duas populações distintas. A primeira, tipicamente com cristais prismáticos e bipiramidados, indicam idades em torno de 620 Ma, enquanto que a segunda, com cristais isométricos típicos de alto grau metamórfico, indicam idades em torno de 610 Ma. Em relação ao pico metamórfico de ~625 Ma, as idades mais jovens obtidas sugerem um período de 15 my em que predominaram altas temperaturas. O transporte tectônico para NW, em estado sólido de alta temperatura, é posterior à cinemática sin-magmática para NE, e deve estar associado à compressão da placa superior convergente, dentro desse período de alta temperatura. Esse regime tectônico é compatível com modelos recentes da tectônica Andina onde é descrita uma subducção horizontal (Pampean flat subduction). Dentre as rochas da Unidade Granulítica Basal, também submetida à fusão parcial por desidratação da hornblenda, ocorrem gnaisses com afinidade adakítica, sugerida pelas altas razões Sr/Y = 72.73, La/Yb = 23.07, \'(La/Yb) IND.N\' = 15.56, e teores de #mg = 51.77, Sr = 1062 ppm, Cr = 197 ppm e Ni = 103 ppm. Tal afinidade sugere magmas resultantes da fusão de um slab em subducção. A Nappe Socorro-Guaxupé admite uma evolução que se inicia, cerca de 670-640 Ma, com uma subducção inclinada para a geração de rochas cálcio-alcalinas com alguns membros adakíticos. É seguido um momento de colisão, entre 625 e 610 Ma, com a geração de rochas diatexíticas e metatexíticas de alto potássio, onde o arco migrou primeiramente para o ante-arco (estado subsólido) e depois em direção ao interior da placa superior (estado sólido). A estabilização da nappe se deu quando da colocação dos maciços sieníticos pós-tectônicos, Capituva e Pedra Branca. / The W-SW portion of the Guaxupé Domain, nearby the São José do Rio Pardo city, records a granulite facies anatetic event under hornblende dehydration-melting conditions, i.e. T >=850ºC. The diatexitic rocks that are comprised within the São José do Rio Pardo and Pinhal suites resulted from this high-T metamorphic event, ca. 625 Ma. Geochemical and isotopic signatures suggest derivation from the lower continental crust. The K-rich SJRP suite also show geochemical affinity with vaugneritic rocks, suggested by high contents of Mg, LILE, HFSE and light-REE in addition to negative ?Nd and low Sr initial ratio (~0.706). Vaugneritic magmatism implies on a derivation from a metasomatized lithospheric mantle source enriched before partial melting in a previous subduction setting. Once both suites contain melt pseudomorphs, it is then suggested and isothermic evolution under the presence of melt. A syn-magmatic driven transport occurred towards NE-E, and the heat source for high-T conditions could be assigned to mantle delamination under the margmatic arc. Within the Metatexitic Unit, partial melting resulted in charno-enderbitic leucosomes whose geochemical and isotopic signatures indicate crustal sources. From these leucosomes, two different populations of zircon crystals were separated. The first, comprising bypiramidal-prismatic grains, yield ages around 620 Ma, whereas the second typology of zircons is isometric and soccer-ball type, yielding younger ages around 610 Ma. The latter typology is typical of high-T and melt-bearing rocks. Considering the 625 Ma metamorphic peak, the younger ages suggest a 15 my period when high-T conditions prevailed. Top-to-NW transport, under solid-state high-T conditions, can be associated to the compression of the upper convergent plate within this high-T period. Textural features suggest this transport to have occurred after the crystallization of the syn-magmatic rocks. The compression of the upper plate resembles recent models of the Andean orogenic cycle, where the Pampean flat subduction is described. Among the rocks of the Basal Granulitc Unit, which also underwent hornblende-dehydration partial melting, a gneissic rock shows adakitic affinity, suggested by Sr/Y = 72.73, La/Yb = 23.07, \'(La/Yb) IND.N\' = 15.56, #mg = 51.77, Sr = 1062 ppm, Cr = 197 ppm and Ni = 103 ppm. Adakitic magmas are thought to be slab melts. The Socorro-Guaxupé Nappe was built up between 670 and 640 Ma with a steep subduction and generation of calc-alkaline and subordinate adakitic rocks. A collisional setting, generating high-K diatexites and metatexites, took place between 625 and 610 Ma, where the arc firstly migrated (in subsolidus state) towards the forearc and then migrated (in solid state) towards the interior of the upper plate. Post-tectonic Capituva and Pedra Branca syenitic plutons intruded around 610 Ma, recording the arc migration ceasing.

Magmas graníticos peraluminosos são gerados por meio da anatexia de rochas crustais em cinturões orogênicos continentais. Os granitos do Cinturão Ribeira Central são relacionados a processos orogênicos de convergência de blocos litosféricos, durante o Neoproterozoico. O Batólito Serra das Araras é um corpo granítico, tabular e peraluminoso localizado no Domínio Paraíba do Sul, região sudoeste no estado do Rio de Janeiro - Brasil. O corpo é alongado na direção NE-SW e sua deformação foi gerada pela atividade de zonas de cisalhamento dúcteis de movimentação preferencial destral, que também controlaram o alojamento do magma granítico. O presente trabalho visa a caracterizar o Batólito Serra das Araras com base em dados de petrografia, de geoquímica de rocha total, de química mineral (EPMA) e de geocronologia U-Pb e LuHf (LA-ICP-MS) em grãos de zircão. Três amostras representativas foram analizadas para obtenção das idades U-Pb de cristalização e de metamorfismo. Essas amostras são compostas de granitos com matriz protomilonítica com muscovita, biotita e granada, um dique sienogranítico com 15-30 cm de espessura e um enclade de quartzo diorito. O plagioclásio possui composição entre oligoclásio (An16) e andesina (An38) e possui núcleos mais enriquecidos em anortita. Todas as amostras apresentam fases ricas em almandina com bordas levemente enriquecidas em manganês, produto do metamorfismo de médio a baixo grau. Os dados isotópicos U-Pb em grãos de zircão revelaram que o magmatismo granítico cristalizou-se ca. 595 Ma e foi gerado no mesmo evento tectono-termal Ediacarano que gerou granitos tipo-I e tipo-S de caráter pós-colisional no Domínio Embu/Paraíba do Sul. Os dados isotópicos de Lu-Hf indicam a reciclagem de crosta juvenil do Riaciano-Orosiriano e de crosta continental do Orosiriano como fontes do protólito metassedimentar do Batólito Serra das Araras. A composição contrastante do enclave de quartzo diorito (amostra SA-06), de caráter metaluminoso e com valores menos degativos de \'\'épsilon\'Hf IND.t\' (entre -5,7 and -8,1), sugere o envolvimento marginal de fontes orto-derivadas da crosta inferior. As idades de cristalização e a composição do batólito indicam que seu magmatismo é correlacionável com granitos peraluminosos do Domínio Embu e do Orógeno Araçuaí. / Peraluminous granitic magmas are produced by anatexis of crustal rocks in continental orogenic belts. Orogenic granites of Central Ribeira Belt are correlated with the collision of lithospheric blocks during Neoproterozoic. The Serra das Araras Batholith is a tabular granitic body of peraluminous composition located at Paraíba do Sul Domain, southwestwards of Rio de Janeiro state - Brazil. The body is elongated at NE-SW direction and its deformation was produced by ductile shear zones with dextral movement component, which has also controlled magma emplacement. The aim of this study is to characterize the Serra das Araras Batholith and to provide petrography, whole-rock geochemistry (major and trace elements), mineral chemistry (EPMA) and combined LA-ICP-MS U-Pb and Lu-Hf isotopic analyses in zircon grains. Three representative samples were analyzed for isotopic determination in order to obtain crystallization and metamorphic U-Pb ages. These samples are composed of monzogranite with protomylonitic texture; a 15-30 cm thick syenogranite dyke and a biotite-hornblende quartz diorite enclave. Plagioclase is Andesine and Oligoclase (An16-38). Anorthite contents display a progressive zoning with rims having lower contents than cores. All samples exhibit almandine-rich phases, with slightly Mg-rich cores and Mn-rich rims, produced by metamorphism of medium to low grade. Zircon U-Pb isotopic data reveal that the batholith was emplaced ca. 595 Ma and was generated at the same middle-Ediacaran tectono-thermal event that generated voluminous I-type and S-type granitoids of post-collisional character at Embu/Paraíba do Sul Domain. Lu-Hf isotopic data suggest that late-Rhyacian to Orosian juvenile and continental crust have been sources of metasedimentary protoliths of Serra das Araras Batholith. The contrasting composition of the quartzdiorite enclave (sample SA-06), of metaluminous character and less negative \'\'épsilon\'Hf IND.t\' values (between - 5.7 and -8.1), suggests a marginal involvement of ortho-derived igneous rocks of the lower crust. The crystallization ages of the granites are coeval with peraluminous granites of Embu Domain and of Araçuaí Belt.

La transition Archéen – Protérozoïque (~2,45 Ga) est marquée par des bouleversements environnementaux majeurs dans l’histoire de la Terre (oxygénation de l’atmosphère et glaciations globales). Les séquences sédimentaires qui enregistrent ces événements ont été très étudiées en Amérique du Nord (séquence Huronienne) et en Afrique du Sud (Transvaal). Une séquence analogue sur le craton de Pilbara en Australie Occidentale (groupe de Turee Creek, TCG) contient 3 niveaux de diamictites glaciaires. 3 forages continentaux (Turee Creek Drilling Project, TCDP) ont été réalisés pour étudier la séquence. La géochronologie U-Pb de monazite et zircon dans des échantillons de forage et de surface a daté la première glaciation à 2,45 Ga et la seconde à ~2,34 Ga. Des analyses Re-Os de pyrites de la seconde diamictite ont donné une isochrone à 2,31 Ga. Ces résultats ont permis de proposer un scenario de corrélation des glaciations paléoprotérozoïques enregistrées sur différents continents. Une ‘Snowball Earth’ aurait eu lieu à ~2,45 Ga sur au moins 5 cratons (Pilbara, Kaapvaal, Supérieur, Wyoming, Karélia). Une seconde glaciation aurait pu avoir lieu à ~2,31 Ga sur 4 cratons. L’ensemble des zircons détritiques du TCG ont une distribution d’âge avec des pics à 2,45, 2,54, 2,68, 2,82, 2,95 et 3,2 Ga. Un cristal de zircon Hadéen a été découvert et indique la présence d’une probable croûte différenciée dans le craton de Pilbara à 4,0 Ga. 70% des zircons ont des compositions isotopiques en Hf juvéniles, suggérant que le TCG a incorporé du matériel volcanique provenant de larges provinces ignées continentales à travers l’érosion des groupes sous jacents de Hamersley et Fortescue / The Archean – Proterozoic transition at 2.45 Ga is marked by major environmental changes in Earth’s history (atmosphere oxygenation and global glaciations). The origin and the relationships between these events are debated. Sedimentary sequences that record these events have been widely studied in North America (Huronian sequence) and South Africa (Transvaal). An analog sequence in the Pilbara craton in Western Australia (Turee Creek Group, TCG) contains 3 glacial horizons. 3 continental drill cores (Turee Creek Drilling Project, TCDP) were performed in order to investigate the sequence. U-Pb geochronology of monazite and zircon from drill core and surface samples allows to date the first paleoproterozoic glaciation at 2.45 Ga and a second glacial event at ~2.34 Ga. Re-Os analyses of pyrites from the second diamictite yielded an isochron at 2.31 Ga. These results enable to propose a correlation scenario of the paleoproterozoic glacial events recorded on different continents. A ‘Snowball Earth’ would have occured at 2.45 Ga at least on 5 cratons. A second glaciation could have occured at ~2.31 Ga on 4 cratons. Detrital zircons age spectrum highlights age peaks at 2.45, 2.54, 2.68, 2.82, 2.95 and 3.2 Ga. A crystal of Hadean zircon was discovered and indicate the existence of a probable differentiated crust within the Pilbara craton at 4.0 Ga. 70% of the analyzed zircons have juvenile Hf isotope composition, suggesting that the TCG incorporated volcanic material from continental large igneous provinces through the erosion of the underlying Hamersley and Fortescue groups

A Faixa Araçuaí, localizada na porção setentrional da Província Mantiqueira, pode ser dividida em três domínios estruturais os quais estão envolvidos em um sistema de empurrões com vergência tanto oeste quanto para leste. A porção ocidental corresponde ao Domínio Milonítico constituido por gnaisses miloníticos de alta temperatura ~750ºC, o Domínio Central é caracterizado por intenso magmatismo tonalítico, granodiorítico e granítico de idade aproximada de 580 Ma e o setor oriental, denominado de Domínio Anatético, formado pelo Leucogranito Carlos Chagas (CC), um granito tipo S de idades compreendidas entre 572 ± 4 Ma a 597 ± 3 Ma. O Domínio Central, formado pelas Suítes Galiléia e Aimorés, são constituídas respectivamente pelos tonalitos São Vitor, e Galiléia e pelo Granito Caladão e o Charnockito Padre Paraíso. A Suíte Aimorés e a borda oeste do Leucogranito Carlos Chagas, constituem-se no foco desta dissertação, a qual teve por meta um estudo estrutural, baseado em Anisotropia de Suscetibilidade Magnética (ASM) e datações através dos métodos U/Pb em zircões e monazitas e Lu/Hf em zircões. Petrograficamente o Granito Caladão tem como característica uma textura porfirítica, com matriz de granulação grossa, composta por quartzo, feldspato, hornblenda e biotita, com cristais de feldspatos de 2 a 5 centímetros. O Charnockito Padre Paraíso é um hiperstênio granito, de cor esverdeada, de matriz de granulação grossa composta de quartzo, feldspato, hiperstênio, biotita e hornblenda, com cristais de feldspato de até 6 centímetros. O Leucogranito Carlos Chagas possui granulação media a grossa e apresenta em sua constituição, quartzo, feldspato, biotita sillimanita, cordierita e granada. Um granito tipo S. Os resultados da análise estrutural através da ASM apresentaram orientações variáveis da foliação magnética em setores distintos dos corpos magmáticos, compatível com a orientação espacial do plúton, indicando assim sua colocação, porém a orientações das lineações magnéticas sugerem uma direção predominantemente NNE-SSW, aventando um fluxo magmático nessa direção. Investigações sobre a mineralogia magnética através de curvas termomagnéticas evidenciaram ocorrências de óxidos de ferro, magnetita e hematita, tanto no Granito Caladão como no Charnockito Padre Paraíso. Os baixos valores de suscetibilidade magnética, da ordem de 10-4 a 10-5 SI sugerem que a ASM, para esses corpos ígneos, é controlada essencialmente pelos minerais paramagnéticos. Os elipsoides de ASM são dominantemente oblatos, caracterizando uma forte deformação por achatamento, apenas localmente foram identificados elipsoides prolato. As análises isotópicas forneceram idades de 500.7 ± 1.5 Ma a 512.1 ± 1.5 Ma (zircão) e 445.0 ± 9.5 Ma (monazita) para o Granito Caladão e de 498 ± 2.4 Ma a 502.7 ± 1.9 Ma (zircão) para o Charnockito Padre Paraíso. Idades obtidas como sendo mais antigas para o Granito Caladão e o Charnockito Padre Paraíso, respectivamente de 556.8 ± 3.7 Ma (zircão) e 576.0 ± 2.2 Ma (zircão) foram interpretadas como zircões herdados das rochas encaixantes quando do emplacement dos plutons. A idade de 570.1 ± 1.7 Ma para o CC na porção norte é compatível com as idades obtidas na literatura, entretanto na porção sul, as idades obtidas são da ordem de 510.8 ± 1.7 Ma e 520.5 ± 2.5 Ma para o CC, indicando pulsos magmáticos diacronicos. As determinações Lu/Hf revelaram valores de ?Hf negativos para todos os plutons estudados, mostrando que são provenientes de retrabalhamento crustal, de uma crosta arqueana e paleoproterozoica. / The Araçuaí Orogen corresponds the northern part of the Mantiqueira Province, which can be divided into three different structural domains. These areas are involved in thrust systems towards the west and east. The western part corresponds to the Mylonites Domain, constituted by high temperature mylonitic gneisses, the Central Domain is characterized by a huge tonalitic, granodioritic and granitic magmatism dated around 580 Ma, and, the eastern area, described as Anatexis Domain where the Carlos Chagas Leucogranite (CC) is the predominant lithology. The Galiléia Suite constituting by the St. Vitor and Galiléia tonalites, Aimorés Suites, by the Caladão Granite and the Padre Paraíso Charnockite, all theses suites belong to the Central Domain. The Aimorés Suite and the western border of the Carlos Chagas Leucogranite are the focus of this Master thesis, which the goals are a structural study based on Anisotropy of Magnetic Susceptibility (AMS) and a geochronological analysis using U/Pb in zircon and monazite and Lu/Hf in zircon methodologies. The petrographic analysis shows the Caladão Granite as porphyritic granite, with a thick granulation matrix composed of quartz, feldspar, hornblende and biotite. The feldspar crystals can reach 2 to 5 centimeters in size. The Padre Paraíso Charnockite is hypersthene granite; greenish-colored matrix with a coarse granulation composed of quartz, feldspar, hypersthene, biotite and hornblende, the feldspar crystals size can be bigger than 5 centimeters. The Carlos Chagas Leucogranite has medium to coarse granulation that is constituted by quartz, feldspar, biotite, sillimanite, cordierite and garnet, the mineralogy typical of type S granite. Structural analysis using the AMS showed variable magnetic foliation orientations in distinct sectors of the magmatic bodies, compatible with the spatial trend of the pluton, your emplacement, but the orientations of the magnetic lines suggest a predominantly NNE-SSW direction, suggesting a magmatic flow in this direction. Investigations on magnetic mineralogy through thermomagnetic curves showed evidence of iron magnetite and hematite oxides in both the Caladão Granite and the Padre Paraíso Charnockite. The low values of magnetic susceptibility, on the order of 10-4 to 10-5 SI, suggest that paramagnetic minerals essentially control the ASM for these igneous bodies. The AMS ellipsoids are predominantly oblate, characterizing a strong flattening deformation; only locally prolate ellipsoids have been identified. Isotopic analyzes performed at Caladão Granite provided ages ranging from 500.7 ± 1.5 Ma to 512.1 ± 1.5 Ma (zircon) and 445.0 ± 9.5 Ma (monazite), and zircon ages from 498 ± 2.4 Ma to 502.7 ± 1.9 Ma obtained in the Padre Paraíso Charnockite. Older zircon ages determined in the Caladão Granite and Padre Paraíso Charnockite are, respectively, 556.8 ± 3.7 Ma and 576.0 ± 2.2Ma, whose ages were interpreted as inherited zircons that were captured from the host rocks during the plutons emplacement. In the northern sector of the studied area, the CC age of 570.1 ± 1.7 Ma is compatible with the ages that were obtained in the literature, ranging from 572 ± 4 Ma to 597 ± 3 Ma, however in the south of the area some surprisingly younger ages (510.8 ± 1.7 Ma and 520.5 ± 2.5 Ma) in the CC, suggesting diachronic magmatic pulses. The Lu/Hf determinations revealed negative ?Hf values for all studied plutons, showing that they are derived from crustal reworking, from an Archaean and Paleoproterozoic crust. The most Hf model age are 2,0 Ga, however there are some Archean ages ranging from 3.0 to 3.8 Ga. The presence of highly negative values of -20 and -30 for the Caladão Granite are interpreted as largely crustal-derived melts.