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Resumo: Foram usados estudos de mobilidade de elementos geoquímicos, isotópicos e petrológicos para investigar o comportamento dos isótopos radiogênicos Rb/Sr, Sm/Nd e U/Pb na formação de, migmatitos estromáticos e diatexiticos em três ambientes geotectônicos distintos. Os estudos foram realizados em migmatitos derivados de rochas metassedimentares do Grupo Seridó que teve deposição e metamorfismo no Neopreterozóico, em ortognaisses migmatíticos de composição granítica e tonalítica do Complexo Caicó de idade Paleoproterozóica e em ortognaisses migmatíticos de composição tonalítica do Complexo Presidente Juscelino no Maciço São José de Campestre de idade Arqueana. Os resultados nos micaxistos do Grupo Seridó mostraram que os leucossomas foram gerados por exsudações de quartzo e feldspatos formados a partir dos elementos Na, Ca e Si liberados do paleossoma pela fusão parcial que se individualizaram como veios. O Rb permaneceu imóvel no sistema e Sr perdeu massa, enquanto Sm e Nd permaneceram imóveis. As sistemáticas isotópicas Rb/Sr e Sm/Nd foram fortemente afetadas durante o processo de migmatização, fornecendo idades sem significado geológico. / Abstract: Studies of chemical elements mobility, isotopics and petrologic were used to investigate the behavior of the radiogenic isotope Rb/Sr, Sm/Nd and U/Pb in the formation of, estromatics migmatites and diatexites in three different tectonic setting. The studies were accomplished in derived migmatites of metasedimentary rocks of the Seridó Grup Seridó that had deposition and metamorphism in Neopreterozóico, in migmatitics orthogneisses of granitic and tonalitic composition of the Caicó Complex of Paleoproterozoic age and in migmatitics orthogneisses of tonalitic composition of the President Juscelino Complex in São José de Campestre Massif of Archaean age. The results in mica-schist's Seridó Grup showed that the leucosome was generated by exsudation of quartz and feldspars formed starting from the elements In the Ca and Si liberated of the paleosome for the melting partial that were individualized as veins. The Rb stayed immobile in the system and Sr lost mass, while Sm and Nd stayed immobile. The isotopics systematics Rb/Sr and Sm/Nd were strongly affected during the process migmatization, supplying ages without geological meaning. / Orientador: Jean Michel Legrand / Coorientador: Elton Luiz Dantas / Banca: Luiz Sérgio Amarante Simões / Banca: Antenor Zanardo / Banca: Jaziel Martin Sá / Banca: Elson Paiva Oliveira / Doutor

La chronologie de la formation de la croûte continentale est débattue mais la plupart des modèles convergent sur le fait qu'une bonne partie de la croûte continentale présente à la surface de la Terre aujourd'hui est présente depuis le Protérozoïque (2,5 - 0, 54 Ga) et qu'elle a essentiellement subit un remaniement au cours d'orogénèses. L'uranium, qui est un élément incompatible, est un traceur de cette évolution depuis son fractionnement initial par fusion partielle du manteau jusqu'à son remaniement dans les niveaux crustaux supérieurs. La ceinture orogénique Néoprotérozoïque Pan-africaine (0,5 ± 0,1 Ga) du Damara en Namibie constitue une cible géologique pour tester les relations entre croissance / évolution crustale et métallogénie de l'uranium. Elle s'est formée suite à la collision des cratons archéens du Congo et du Kalahari (plaque subductante). Ce travail de thèse montre que l'évolution de la croute continentale de la ceinture du Damara durant l'orogènese Pan-africaine au Néoprotérozoïque se fait par remaniement de roches ayant été extraites du manteau depuis l'Archéen et que leur fusion partielle est le mécanisme prépondérant pour la minéralisation uranifère primaire associée à la cristallisation de granites intrusifs. Les granites in-situ issus de la fusion partielle des sédiments dans les niveaux crustaux supérieurs sont peu ou pas propices à de fortes concentrations d'uranium du fait 1) de la faible préconcentration de leur protolithes et 2) de leur migration relativement limitée. Les granites intrusifs minéralisés correspondent à des injections tardi- à post-collision (ca. 520 - 480 Ma dans la zone centrale) et sont liés aux phases de relaxation thermique et d'effondrement gravitaire subséquentes à l'épaississement crustal de l'orogène dans un contexte de convergence de plaques / The chronology of continental crust formation is debated but most models converge on the fact that much of the continental crust on the surface of the Earth is present since the Proterozoic (2.5 - 0, 54 Ga) and has essentially undergoes reworking during orogenesises. Uranium which is an incompatible element is a tracer of this crustal evolution, since its initial fractionation by partial melting of the mantle to its reworking in higher crustal levels. Neoproterozoic Pan-African (0.5 ± 0.1 Ga) orogenic belt of the Damara in Namibia is a good geological target to test the relationship between crustal growth and evolution and metallogeny of uranium. It was formed after the collision of the Archean cratons of Congo and Kalahari (subducting plate). This thesis shows that the evolution of the continental crust during the Neoproterozoic Damara Orogen is by reworking of Archaean to Neoproterozoic crustal domains and partial melting of rocks is the predominant mechanism for primary uranium mineralization associated with crystallization of intrusive granites derived from anatexis of paleo- to mesoproterozoic basement fragments. The intrusive granites issued from partial melting of sediments in the upper crustal levels are low or not favorable to high concentrations of uranium because of 1) the low preconcentration of their protoliths and 2) their relatively limited migration. The mineralized intrusive granites correspond to late- to post-collision injections (ca. 520-480 Ma in the central area) and are related to thermal relaxation phases and gravitational collapse subsequent to thickening in crustal orogen in a context of plates convergence

Depuis au moins 540 Ma deux grands systèmes de subduction coexistent sur Terre : d'une part, les systèmes de subduction-collision (chaînes Hercynienne, Himalayenne ou Alpine) et d'autre part, les systèmes de subduction de type péri-pacifique. Pour ces derniers, l'avant-arc constitue une zone clef pour retracer l'évolution de la subduction au cours du temps. En effet ces zones au contact avec le slab peuvent enregistrer des événements tectoniques et/ou des conditions métamorphiques variées (e.g. formation de « paired metamorphic belts »), qui sont autant d'indicateurs du contexte géodynamique. Le massif métamorphique de El Oro en Equateur est un exemple exeptionnel où une section complète et basculée de l'avant-arc Triasique est préservée. L'ensemble est constitué d'une série métasédimentaire de bas à haut grade métamorphique intrudée par des granitoïdes de type S, juxtaposé avec un laccolithe gabbroïque et des schistes bleus. Ce travail de thèse s'est concentré sur l'étude du métamorphisme de haute-température basse-pression et ses relations les schistes bleu. Afin de contraindre l'événement tectono-métamorphique affectant l'avant-arc Equatorien au Trias et la formation d'une "paired metamorphic belt", nous avons utilisé des outils structuraux, métamorphiques, géochimiques, géochronologiques et de modélisation thermique. Nos résultats montrent que durant cette période l'avant-arc Equatorien connait un intense épisode de fusion partielle en régime extensif. La base de la croûte est migmatisée sur une épaisseur de 10km. Les estimations Pression-Température indiquent que les conditions de fusion partielle varient de 4.5 kbar et 650°C pour la partie supérieure métaxitique et jusqu'à 7.5 kbar et 720°C pour la partie inférieure diatexitique. La gradient géothermique inféré est divisé en deux segments : un segment supérieur caractérisé par un gradient de 40°C/km et un segment inférieur caractérisé par un gradient quasi-isothermique. L'absence de paragénèse de ultra-haute température est attribuée à la grande fertilité du protolithe métasédimentaire. Les résultats géochimiques montrent que les plutons granodioritiques sont issus d'un mélange entre : (1) les liquides de fusion partielle produit par la réaction de deshydration de la muscovite des métasédiments et (2) un magma basique. Les âges U-Pb sur zircons et monazites révèlent que l'événement anatectique fût bref entre 229 et 225 Ma. La source de chaleur à l'origine de l'événement thermique est attribuée à la mise en place d'un pluton gabbroïque à ~ 230 Ma en base de croûte. Successivement, se sous-plaque les schistes-bleu refroidissant rapidement l'avant-arc. L'événement anatectique observé dans le massif de El Oro au Trias s'insrit à plus grande échelle au sein d'une large anomalie thermique affectant l'ensemble du continent sud Américain entre 260 et 220 Ma. Durant cette période la marge est un soumise à un régime extensif accompagné d'un important magmatisme d'origine crustal, principalement en position d'arc et d'avant-arc. Nous attribuons cette anomalie thermique d'ampleur continental à une "avalanche mantellique". A la lumière du contexte géodynamique globale nous inteprétons la formation de la paired metamorphic belt de El Oro à la rupture du slab. / Since about 540 Ma, two subductions systems co-exist on Earth: the subduction-collision systems (Hercynian, Himalayan or Alpin belts) and the circum-pacific subduction system. For the last the forearc region constitutes a key zone to understand the dynamic of the subduction. Indeed the forearc region in contact with the slab may records various tectonics events and/or metamorphic conditions (e.g. formation of paired metamorphic belt). Theses geological records are direct evidences of the linked geodynamical context. The El Oro metamorphic complex in Ecuador is a unique example where a whole Triassic forearc section is tilted and well preserved. The complex is made of low to high grade metasedimentary rocks intruded by S-type granitoids, juxtaposed with gabbroic rocks and blueschists. This study is focused on the high-temperature metamorphism and its retionaships with the high-pressure metamorphism. In order to constrain the tectono-metamorphic affecting the forearc region and the formation of a paired metamorphic belt we used strutural, metamorphic, geochemical, geochronological and themal modeling studies. Our results show that during Triassic times the Ecuadorian forearc underwent a strong episode of partial melting in extentional context. The migmatized part of crust is 10 km thick. Pressure-Temperature estimates indicate that partial melting started at 4.5 kbar and 650°C for the upper metatexitic part until 7.5 kbar and 720 °C for the lower diatexitic part. The resulting geothermal gradient exhibits two parts: an upper part caracteristed by a thermal gradient of 40°C/km and a lower part caractérized by a near-adiabatic gradient. The absence of ultra-high tempetature paragenesis is attributed to the high fertility of the metasedimentary protolith. Geochemical results show that granodiorite made of a miwing between: (1) the melt extacted under muscovite dehydration melting and (2) a basic magma. U-Pb ages on zircon and monazite reveal that the anatectic event was short, between 229 and 225 Ma. The origin of the thermal anomaly is attributed to the emplacement of the gabbroic plutonic unit at ~230 at root level. Successively, the blueschites are underplating triggering a strong coolng of the forearc region. The anatectic recorded in the El Oro metamorphic complex at Triassic times is part of a larger thermal anomaly affecting the whole south american margin between 260 and 220 Ma. During this period the margin is under extentional conditions and exhibit a strong S-type magmatic activity. This magmatism is mainly located in arc and forearc position. We attribute this large-scale thermal anomaly to slab fall in the lower mantle. In the light of the geodynamical context, we suggest that the formation of the El Oro paired metamorphic belt is related to slab breakoff.

Orientador: Marcos Aurélio Farias de Oliveira / Banca: Colombo Celso Gaeta Tassinari / Banca: Norbeto Morales / Resumo: A evolução de rochas migmatíticas e granulíticas da porção de baixa-média pressão do Complexo Guaxupé, na região de São João da Boa Vista, foi investigada a partir de estudos petrográficos, geoquímicos, isotópicos e geotermobarométricos. Os dados de campo, em conjunto com a geoquímica, permitem reconhecer pelo menos três fases de anatexia, e agrupar os litotipos em quatro suítes geoquímicas distintas onde os paleossomas têm assinatura de crosta inferior e foram formados em um arco magmático, com colisão continental, diferenciando-se das demais, que apresentam assinatura de crosta superior. As análises isotópicas sugerem longa residência crustal com valor mínimo da razão 86Sr/87Sr de 0,707199 e valores de εNd sempre negativos (-6,17 a -16,46). Os valores de TDM variam entre 1,34 e 1,77Ga. A idade do pico metamórfico é sugerida em 639.6+3.7Ma e foi obtido pela datação de U/Pb em zircões granulíticos. Cálculos geotermobarométricos sugerem trajetória metamórfica aberta com sentido horário, e pico metamórfico em 11,5kbar e 820°C, seguido por descompressão isotérmica até 8kbar. Esses dados permitem abrir a discussão para um modelo evolutivo onde os protólitos foram formados na crosta inferior em um arco magmático muito anterior aos eventos de pico metamórfico e migmatização, que ocorreram no Neoproterozóico, quando essas rochas foram arrancadas dessas porções profundas e colocadas em ambiente de crosta superior. A evolução parece ter ocorrido com uma fase de fusão parcial, nos estágios iniciais, e pelo menos mais duas durante a ascensão e exumação dessas rochas / Abstract: The evolution of migmatitic and granulitic rocks of the middle to high pressure portion of Guaxupé Complex are investigated by petrografic, isotopic, geochemical and geothermobarometric studies. Field data together with geochemistry indicate at least three phases of anatexis making possible to group the lithologies into four suits in which the paleossome shows a lower crust signature and evolved in a magmatic arc environment, by continental collision. The other three groups show upper crust signatures. Isotopic analysis suggest a long crustal residence with a minimum value of 0,707199 for the 86Sr/87Sr ratio and with εNd values always negative (-6,17 to -16,46). The TDM ages for the protolith are between 1,34 and 1,77 Ga. The metamorphic peak occurred at 639.6 ± 3.7 Ma, obtained by U/Pb in zircon crystals of granulites. Geothermobarometric calculations suggest an open metamorphic clockwise P-T path, with metamorphic peak in 11,5 kbar and 820 oC followed by isothermal decompression until 8 kbar. These data conduct to a model for the evolution of that region where the protolith were formed at the lower crust in a magmatic arc older than the metamorphic peak that occurred in the Neoproterozoic, when the rocks were dislocated from lower to upper portions of the crust. The evolution started with a partial melting phase in the initial stages and proceeded with at least two more phases of partial melting during the rising and exhumation of these rocks / Mestre

Apesar da existência de vários estudos geológicos detalhados no segmento norte do Andes, muitos aspectos estão ainda por serem resolvidos, principalmente aqueles concernentes ao tipo, grau e evolução metamórfica, ambiente tectônico de formação e correlação com margem paleozóica do continente Gondwana e com os terrenos mesozóicos oceânicos. A Cordilheira Central dos Andes Colombianos, é representada por um complexo polimetamórfico com magmatismo associado e uma fina pilha de sedimentos suprajacente em algumas partes da cordilheira. O embasamento desta cordilheira é principalmente composto por rochas metamórficas e por isto a sua compreensão deve ser feita a partir do entendimento dos processos de metamorfismo que afetaram a área. Na Cordilheira Central, a caracterização dos distintos processos geológicos, tem sido interpretada em termos de eventos orogênicos em escala regional, pelo que muitas incongruências são percebidas na aplicação dos diferentes modelos e o análise detalhado da evolução metamórfica permitiria separar os diferentes eventos e a possibilidade de reconstruir as condições de pressão e temperatura (P-T) da crosta, podendo definir a natureza do ambiente tectônico assim como a relação entre as unidades. Nos arredores da cidade de Medellín (municípios de Caldas e El Retiro) afloram rochas metamórficas com protólitos básicos e pelíticos (Anfibólio Xistos de Caldas e Xistos de Ancón), com alguns aportes de material granítico, às vezes metamorfisado (Gnaisse de La Miel). Outro conjunto de rochas metabásicas e metapelíticas associadas apresenta-se ao oriente destas unidades. Este conjunto de rochas é nomeado Anfibolitos, Migmatitos e Granulitos de El Retiro. A termobarometria nos Anfibólio Xistos de Caldas indicam condições de pressão e temperatura próprias da facies anfibolito e descrevem uma trajetória em sentido antihorário sem ficar claro o caminho de regresso das condições de retrometamorfismo. As pressões nestas rochas variam entre ~6.3 e 13.5 Kb com variações relativamente estreitas da temperatura, com valores que estão entre ~550 e 630ºC. No caso dos Xistos de Ancón, a trajetória resultante é em sentido anti-horário e reflete aumentos de temperatura evidenciados na petrografia pela presença de sillimanita e o regresso da trajetória é pela zona da cianita. As temperaturas neste conjunto variam entre ~400 e 555ºC para pressões constantes de 5 e 6Kb en condições de metamorfismo progressivo. O retrometamorfismo apresenta pressões entre ~7.6 e 7.2Kb com temperaturas ~645 e 635ºC, além de temperaturas entre ~500 e 600ºC com pressão constante de 6Kb. No conjunto de rochas de El Retiro, apresenta-se uma forte descompressão com variações estreitas no campo da temperatura, apresentando valores de pressão entre ~8.7 e 2.7Kb com variação na temperatura de ~740 e 633ºC. As unidades conhecidas como Anfibólio Xistos de Caldas, Xistos de Ancón e Gnaisse de La Miel, evidenciam uma historia metamórfica comum de processos de tipo colisional. Os Anfibólio Xistos de Caldas e os Xistos de Ancón poderiam representam fragmentos de crosta oceânica com sedimentos pelíticos intercalados, a qual foi exumada, além de ter um corpo metagranítico relacionado (Gnaisse de La Miel) cuja geoquímica evidencia seu caráter colisional. Este corpo granítico pode ser o resultado do metamorfismo ou do processo de exumação que afetou a região e gerou o pacote de xistos ou pelo menos começou fazer parte da história geológica da área logo depois da formação dos xistos. As rochas de El Retiro (Anfibolitos, Migmatitos e Granulitos de El Retiro) sugerem que seja um bloco que colidiu com as de Caldas (Anfibólio Xistos de Caldas, Xistos de Ancón e Gnaisse de La Miel) e a partir de então têm uma história conjunta, no mínimo, a partir do Triássico, como é indicado pela geocronologia e pela ausência de estruturas regionais entre estas unidades. Finalmente um possível processo de rifteamento que da origem a pontos restritos de calor e que geram as rochas em facies granulito, assim como estruturas de cisalhamento mais marcadas em alguns litotipos. / In spite of the existence of several detailed geological studies in the northern segment of the Andes Cordillera, many aspects are still to be resolved, mainly those concerning the type, grade and metamorphic evolution, tectonic setting formation and correlation with the Palaeozoic margin of Gondwana and with Mesozoic oceanic terranes. The Central Cordillera is represented by a polimetamorphic complex with associated magmatism, and a thin pile of cover sediments in some parts of the mountain range. The basement of the Central Cordillera is mainly constituted by metamorphic rocks and for that its comprehension should be done from the understanding of the metamorphism that affected the area. In the Central Cordillera, the characterization of the different geological processes has been interpreted in terms of orogenic events in regional scale, however, a lot of incongruities are perceived in the application of the different models, and the detailed analysis from the metamorphic evolution would permit the separation distinct events and the reconstruction possibility of the crusts pressure and temperature (P-T) conditions, being able to define the nature of the tectonic setting, as well as the relation among the units. In the surroundings of the city of Medellín (Caldas and El Retiro cities) occur metamorphic rocks with basic and pelitic protolites (Amphibole Schist of Caldas and Schists of Ancón), with some contributions of granitic material, sometimes affected by metamorphic processes (Gneiss of La Miel). Another group of metabasic and metapelitic rocks associated is observed to the east of these units. This group is named Amphibolites, Migmatites and Granulites of El Retiro. The group Amphibole Schist of Caldas and Schists of Ancón could be formed in an distal environment and under reduct conditions and later inserted to the continent by a possible subduction zone. El Retiro rocks could be correspond to the continental basement of the area and it leaves of them it can correspond to impure sediments, of continental margin, formed under high grade metamorphic conditions. The metamorphism in these last rocks was more intense, originating the rocks in the granulite facies in portions of the crust in which the partial pressure of H2O was relatively lowers, as well as of migmatites, result of the anatexis of quartz-feldspatic composition rocks, in places which the partial pressure of H2O was higher. This metamorphism was accompanied of intense deformation, which to have juxtaposed both migmatites and granulites blocks. Therefore later there was intense interaction fluid-rock, as well as restricted points of heat caused by igneous intrusions and that are responsible for the variations in the size of grain of the minerals and especially by the fortress retrometamorphic reequilibrium and by the fluids transport. Thermobarometric data in Amphibole Schist of Caldas indicate pressure and temperature conditions of the amphibolite facies and they describe a counterclockwise path, with no precise retrometamorphic P-T-t trajectory. The pressures in these rocks vary between 6.3 and 13.5Kb with narrow variations of the temperature, with values between ~550 and 630ºC. In the case of the Schists of Ancón, the result is a counterclockwise path and it reflects increases of temperature evidenced by the occurence of sillimanite and the return of the path to the kyanite zone (amphibolite facies). The temperatures in this group vary between ~400 and 555ºC for constant pressures of 5 and 6Kb in prograde metamorphic conditions. The retrometamorphism presents pressures between ~7.6 and 7.2Kb with temperatures aproximately between ~645 and 635ºC, besides temperatures between ~500 and 600ºC with constant pressure of 6Kb. The El Retiro set presents a strong decompression with narrow variations in the temperature field, showing pressure values between ~8.7 and 2.7Kb with temperatures of ~740 and 633ºC.

Svalbard represents the uplifted and exhumed northwest corner of the Barents Sea Shelf. Pre-Carboniferous rocks of Svalbard are divided into the Eastern, Northwestern and Southwestern Terranes, were amalgamated during the Caledonian Orogen and are separated by north-south-trending strike-slip faults. Even though our knowledge of Svalbard’s pre-Carboniferous history has increased dramatically during the last two decades, a major issue remains: Where did the different tectonostratigraphic terranes of Svalbard originate? The answer to this question has profound significance for the entire eastern Laurentian margin, which spans two supercontinent cycles, from the amalgamation and breakup of Rodinia to the amalgamation of Pangea. This thesis constrains the tectonothermal evolution of Svalbard’s Northwestern Terrane (NWT) using ion microprobe and LA-ICP-MS U-Pb zircon geochronology and electron microprobe thermobarometry on metasediments, clastic rocks and granitoids. Detrital zircon age populations of metasediments from the NWT suggests that they (e.g. the Krossfjorden Group) were deposited at c. 1000 Ma in a remnant ocean basin setting outboard the Eastern Grenville Province and were subsequently deformed and intruded by Late Grenvillian granitoids during the final suturing of Rodinia. Thus, a northern branch of the Grenvillian/Sveconorwegian orogeny is not present. This older history of the NWT is extensively overprinted by Late Caledonian deformation and metamorphism, with peak metamorphic conditions of 850 °C at >6 kbars, and subsequent migmatization of the Krossfjorden Group at c. 420 Ma. Based on these data, together with the detrital zircon age population from overlying Late Silurian-Early Devonian clastic rocks, a unifying model is proposed involving fragments from the Grampian orogen and Avalonian crust originally accreted to the Laurentian margin, subsequently transported northwards along sinistral strike-slip faults during Scandian deformation. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: In press.

Description pétrographique des grands ensembles de la chaine des Maures .

Made available in DSpace on 2014-06-11T19:26:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-04-27 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A evolução de rochas migmatíticas e granulíticas da porção de baixa-média pressão do Complexo Guaxupé, na região de São João da Boa Vista, foi investigada a partir de estudos petrográficos, geoquímicos, isotópicos e geotermobarométricos. Os dados de campo, em conjunto com a geoquímica, permitem reconhecer pelo menos três fases de anatexia, e agrupar os litotipos em quatro suítes geoquímicas distintas onde os paleossomas têm assinatura de crosta inferior e foram formados em um arco magmático, com colisão continental, diferenciando-se das demais, que apresentam assinatura de crosta superior. As análises isotópicas sugerem longa residência crustal com valor mínimo da razão 86Sr/87Sr de 0,707199 e valores de εNd sempre negativos (-6,17 a -16,46). Os valores de TDM variam entre 1,34 e 1,77Ga. A idade do pico metamórfico é sugerida em 639.6+3.7Ma e foi obtido pela datação de U/Pb em zircões granulíticos. Cálculos geotermobarométricos sugerem trajetória metamórfica aberta com sentido horário, e pico metamórfico em 11,5kbar e 820°C, seguido por descompressão isotérmica até 8kbar. Esses dados permitem abrir a discussão para um modelo evolutivo onde os protólitos foram formados na crosta inferior em um arco magmático muito anterior aos eventos de pico metamórfico e migmatização, que ocorreram no Neoproterozóico, quando essas rochas foram arrancadas dessas porções profundas e colocadas em ambiente de crosta superior. A evolução parece ter ocorrido com uma fase de fusão parcial, nos estágios iniciais, e pelo menos mais duas durante a ascensão e exumação dessas rochas / The evolution of migmatitic and granulitic rocks of the middle to high pressure portion of Guaxupé Complex are investigated by petrografic, isotopic, geochemical and geothermobarometric studies. Field data together with geochemistry indicate at least three phases of anatexis making possible to group the lithologies into four suits in which the paleossome shows a lower crust signature and evolved in a magmatic arc environment, by continental collision. The other three groups show upper crust signatures. Isotopic analysis suggest a long crustal residence with a minimum value of 0,707199 for the 86Sr/87Sr ratio and with εNd values always negative (-6,17 to -16,46). The TDM ages for the protolith are between 1,34 and 1,77 Ga. The metamorphic peak occurred at 639.6 ± 3.7 Ma, obtained by U/Pb in zircon crystals of granulites. Geothermobarometric calculations suggest an open metamorphic clockwise P-T path, with metamorphic peak in 11,5 kbar and 820 oC followed by isothermal decompression until 8 kbar. These data conduct to a model for the evolution of that region where the protolith were formed at the lower crust in a magmatic arc older than the metamorphic peak that occurred in the Neoproterozoic, when the rocks were dislocated from lower to upper portions of the crust. The evolution started with a partial melting phase in the initial stages and proceeded with at least two more phases of partial melting during the rising and exhumation of these rocks

Made available in DSpace on 2014-06-11T19:32:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-04-04Bitstream added on 2014-06-13T19:42:59Z : No. of bitstreams: 1 trindade_ir_dr_rcla.pdf: 3348728 bytes, checksum: e5ef235a8ad9a2230bec13d0bfbd1659 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Foram usados estudos de mobilidade de elementos geoquímicos, isotópicos e petrológicos para investigar o comportamento dos isótopos radiogênicos Rb/Sr, Sm/Nd e U/Pb na formação de, migmatitos estromáticos e diatexiticos em três ambientes geotectônicos distintos. Os estudos foram realizados em migmatitos derivados de rochas metassedimentares do Grupo Seridó que teve deposição e metamorfismo no Neopreterozóico, em ortognaisses migmatíticos de composição granítica e tonalítica do Complexo Caicó de idade Paleoproterozóica e em ortognaisses migmatíticos de composição tonalítica do Complexo Presidente Juscelino no Maciço São José de Campestre de idade Arqueana. Os resultados nos micaxistos do Grupo Seridó mostraram que os leucossomas foram gerados por exsudações de quartzo e feldspatos formados a partir dos elementos Na, Ca e Si liberados do paleossoma pela fusão parcial que se individualizaram como veios. O Rb permaneceu imóvel no sistema e Sr perdeu massa, enquanto Sm e Nd permaneceram imóveis. As sistemáticas isotópicas Rb/Sr e Sm/Nd foram fortemente afetadas durante o processo de migmatização, fornecendo idades sem significado geológico. / Studies of chemical elements mobility, isotopics and petrologic were used to investigate the behavior of the radiogenic isotope Rb/Sr, Sm/Nd and U/Pb in the formation of, estromatics migmatites and diatexites in three different tectonic setting. The studies were accomplished in derived migmatites of metasedimentary rocks of the Seridó Grup Seridó that had deposition and metamorphism in Neopreterozóico, in migmatitics orthogneisses of granitic and tonalitic composition of the Caicó Complex of Paleoproterozoic age and in migmatitics orthogneisses of tonalitic composition of the President Juscelino Complex in São José de Campestre Massif of Archaean age. The results in mica-schist`s Seridó Grup showed that the leucosome was generated by exsudation of quartz and feldspars formed starting from the elements In the Ca and Si liberated of the paleosome for the melting partial that were individualized as veins. The Rb stayed immobile in the system and Sr lost mass, while Sm and Nd stayed immobile. The isotopics systematics Rb/Sr and Sm/Nd were strongly affected during the process migmatization, supplying ages without geological meaning.