Interpreting and correlating epeiric sea sequences is key to understanding ancient marine environments. As a result, eNd, d13C and Sm/Nd profiles are developed as tools for interpreting epeiric sea carbonates. Previously, eNd and d13C profiles in epeiric sea carbonates have been used to study changes in the Nd isotope balance and C-cycle of adjacent ocean water. Instead, eNd, d13C and Sm/Nd profiles of Ordovician Midcontinent carbonates of North America demonstrate that fluctuations in sea level and depth are driving local changes in the eNd, d13C and Sm/Nd composition of epeiric seawater. <p> Dissolved Nd derived from the Transcontinental Arch, Taconic Highlands and the Iapetus Ocean determine the eNd composition of Midcontinent seawater. As sea level fluctuated, submergence of the Arch and an influx of Iapetus ocean waters adjusted the Nd isotope balance of epeiric seawater. As a result, eNd profiles can be used to track the submergence history of the Late Ordovician Midcontinent. Comparison of stratigraphic variations in carbonate Sm/Nd ratios with sea level curves, conodont paleoecology, and the eNd profiles also suggests that variations in Sm/Nd ratios are related to changes in depth. However, processes effecting Sm/Nd ratios in epeiric seas may be varied and require further investigation. <p> Sea level fluctuations and the waxing and waning of cool, nutrient rich, oxygen poor Iapetus waters onto the craton adjusted productivity and organic carbon burial rates on the Ordovician Midcontinent. Close to the Transcontinental Arch sea level rise caused an increase in organic carbon burial and productivity, while close to the Sebree Trough, and the influx of Iapetus waters, sea level rise caused a decrease in organic carbon burial and productivity. Differences in local C-cycling across a single epeiric sea encourage caution when using d13C profiles from epeiric sea carbonates to track changes in the C-cycle of adjacent oceans. <p> Because of their connection to sea level fluctuations, variations in the eNd, d13C and Sm/Nd profiles can also used to correlate Ordovician Midcontinent carbonates. However, the ability to correlate coeval strata using these profiles is limited by changes in depositional environment across the craton, which cause excursions to be absent, dampened, or magnified.

Interpreting and correlating epeiric sea sequences is key to understanding ancient marine environments. As a result, eNd, d13C and Sm/Nd profiles are developed as tools for interpreting epeiric sea carbonates. Previously, eNd and d13C profiles in epeiric sea carbonates have been used to study changes in the Nd isotope balance and C-cycle of adjacent ocean water. Instead, eNd, d13C and Sm/Nd profiles of Ordovician Midcontinent carbonates of North America demonstrate that fluctuations in sea level and depth are driving local changes in the eNd, d13C and Sm/Nd composition of epeiric seawater. <p> Dissolved Nd derived from the Transcontinental Arch, Taconic Highlands and the Iapetus Ocean determine the eNd composition of Midcontinent seawater. As sea level fluctuated, submergence of the Arch and an influx of Iapetus ocean waters adjusted the Nd isotope balance of epeiric seawater. As a result, eNd profiles can be used to track the submergence history of the Late Ordovician Midcontinent. Comparison of stratigraphic variations in carbonate Sm/Nd ratios with sea level curves, conodont paleoecology, and the eNd profiles also suggests that variations in Sm/Nd ratios are related to changes in depth. However, processes effecting Sm/Nd ratios in epeiric seas may be varied and require further investigation. <p> Sea level fluctuations and the waxing and waning of cool, nutrient rich, oxygen poor Iapetus waters onto the craton adjusted productivity and organic carbon burial rates on the Ordovician Midcontinent. Close to the Transcontinental Arch sea level rise caused an increase in organic carbon burial and productivity, while close to the Sebree Trough, and the influx of Iapetus waters, sea level rise caused a decrease in organic carbon burial and productivity. Differences in local C-cycling across a single epeiric sea encourage caution when using d13C profiles from epeiric sea carbonates to track changes in the C-cycle of adjacent oceans. <p> Because of their connection to sea level fluctuations, variations in the eNd, d13C and Sm/Nd profiles can also used to correlate Ordovician Midcontinent carbonates. However, the ability to correlate coeval strata using these profiles is limited by changes in depositional environment across the craton, which cause excursions to be absent, dampened, or magnified.

SOARES, Francisca Robênia Ferreira. Estudo Isotópico dos Arenitos da Formação Ipú e Serrote Santana, noroeste do Ceará. 2017. 133 f. Dissertação (Mestrado em Geologia)- Universidade Federal do Ceará, Fortaleza, 2017. / Submitted by JOÃO CAVALCANTI JUNIOR (jbeniciojunior@yahoo.com.br) on 2017-06-19T16:00:03Z No. of bitstreams: 1 Dissertaçao Final.pdf: 41468471 bytes, checksum: 33c3cd2f9c3aa26a24f4477b323e19e8 (MD5) / Approved for entry into archive by Jairo Viana (jairo@ufc.br) on 2017-07-11T18:19:09Z (GMT) No. of bitstreams: 1 Dissertaçao Final.pdf: 41468471 bytes, checksum: 33c3cd2f9c3aa26a24f4477b323e19e8 (MD5) / Made available in DSpace on 2017-07-11T18:19:09Z (GMT). No. of bitstreams: 1 Dissertaçao Final.pdf: 41468471 bytes, checksum: 33c3cd2f9c3aa26a24f4477b323e19e8 (MD5) Previous issue date: 2017 / The Ipú Formation composes the basal portion of the Serra Grande Group, Parnaíba Basin, and consists of sandstones and conglomerates deposited by interlaced fluvial systems during the Silurian. In the state of Ceará, these rocks appear in the Serra da Ibiapaba, presenting great expositions, forming hills and plateaus, on the northeast and east edges of the basin. The Morrote de Santana has an extension of approximately 30 km, is elongated in the NE-SW direction and consists of conglomeratic sandstones and sandstones. This silicystic sequence is aligned in the same direction as the rocks of the Ipú Formation. Although it is frequently correlated with the Ipú Formation, the rocks that make up the Morrote Santana are separated from the same in about 70 km, by expositions of epochal rocks (Jaibaras Group) and pre- Cambrian. In this context, the objective of the present study is to test the hypothesis that the Santana de Acaraú mound represents a testimonial hill of the Ipú Formation. The methodology used in the research involved geological reconnaissance techniques for the description of lithotypes and sample collection and Sm-Nd petrographic and isotopic analysis. The selected areas are located in the vicinity of Santana de Acaraú and Guaraciaba do Norte municipalities, north-west of Ceará, in the transition between the Middle Coreaú and Ceará Central Domains along the Sobral-Pedro II Line. These regions are bordered by rocks of the basement (Ceará Group) and lithotypes of the Jaibaras Basin, in addition to a siliciclastic sequence consisting of conglomerates, sandstone conglomerates, both with polymetallic characteristics, conglomerate sandstones with criss-cross and icnofossils, and medium sandstones Thick with ribbed cross laminations. The collected samples are representative of the more homogeneous portions of the sedimentary rocks recognized in the field, which were analyzed microscopically and isotopically, to determine their isotopic signatures. The petrographic study verified mature rocks and sub - sills, with a framework consisting of quartz grains and matrix occurring in a small amount (between 3-6%), of arenitic and sometimes clayey composition. These characteristics allow to classify these rocks as quatzo-sandstones. The isotopic signatures obtained showed little variation in the amounts of εNd (18.41 - 20.15) and TDM model ages varying between 3.21-2 Ga and 3.43-1.73 Ga, for the sediments present in the regions near Santana de Acaraú and Guaraciaba do North, respectively. The TDM ages indicate paleoproterozoic sources and archives for both areas and the low variation in εNd values reinforce the idea of the same source, evidencing evidence that the arenitic body of Santana de Acaraú represents a testimonial hill of the Ipú Formation. Key Words: Isotopic Geology, Sm-Nd Isotopes, Parnaíba Basin, Serrote Santana, Ipu Formation / A Formação Ipú compõe a porção basal do Grupo Serra Grande, Bacia do Parnaíba, e é constituída por arenitos e conglomerados depositados por sistemas fluviais entrelaçados, durante o Siluriano. No estado do Ceará, essas rochas afloram na Serra da Ibiapaba, apresentando grandes exposições, formando serras e chapadas, nas bordas nordeste e leste da bacia. O Morrote de Santana possui extensão de, aproximadamente, 30 km, encontra-se alongado na direção NE-SW e está constituído por arenitos e arenitos conglomeráticos. Essa sequência siliclástica encontra-se alinhada na mesma direção que as rochas da Formação Ipú, Apesar de ser frequentemente correlacionado a Formação Ipú, as rochas que compõe o Morrote Santana encontram-se separadas da mesma em cerca de 70 km, por exposições de rochas eopaleozóicas (Grupo Jaibaras) e pré-cambrianas. Dentro desse contexto, o objetivo do presente estudo consiste em testar a hipótese de que o morrote de Santana de Acaraú representa um morro testemunho da Formação Ipú. A metodologia utilizada na pesquisa, envolveu técnicas de reconhecimento geológico, para descrição dos litotipos e coleta de amostras e análise petrográfica e isotópica Sm-Nd. As áreas selecionadas localizam-se nas proximidades dos municípios de Santana de Acaraú e Guaraciaba do Norte, noroeste do Ceará, na transição entre os Domínios Médio Coreaú e Ceará Central, ao longo do Lineamento Sobral-Pedro II. Essas regiões encontram-se bordejadas por rochas do embasamento (Grupo Ceará) e litotipos da Bacia do Jaibaras, além de uma sequência siliciclástica constituída por conglomerados, conglomerados areníticos, ambos com características polimiticas, arenitos conglomerados com estratificação cruzada acanalada e icnofósseis e arenitos médios a grossos com estratificações cruzadas acanaladas. As amostras coletadas são representativas das porções mais homogêneas das rochas sedimentares reconhecidas em campo, as quais foram analisadas microscopicamente e isotopicamente, para determinação de suas assinaturas isotópicas. O estudo petrográfico constatou rochas maduras e submaduras, com arcabouço constituído por grãos de quartzo e matriz ocorrendo em pouca quantidade (entre 3-6 %), de composição arenítica e, por vezes, argilosa. Tais características permitem classificar essas rochas como quatzo-arenitos. As assinaturas isotópicas obtidas apresentaram pouca variação nas quantidades de εNd (18,41- 20,15) e idades modelo TDM variando entre 3.21 - 2 Ga e 3.43-1.73 Ga, para os sedimentos presentes nas regiões próximas a Santana de Acaraú e Guaraciaba do Norte, respectivamente. As idades TDM indicam fontes paleoproterozóicas e arquenas para ambas as áreas e a baixa variação nos valores de εNd, reforçam a ideia de mesma fonte, constatando indícios de que o corpo arenítico de Santana de Acaraú representa um morro testemunho da Formação Ipú. Palavras

High precision 147Sm-143Nd geochronology of garnet is performed in two localities to solve problems in tectonics. In Chapter 1, the age of the basal amphibolite unit of the Ballantrae Ophiolite complex in Scotland is dated at 477.6 ± 1.9 million years old. This age constrains the duration of Grampian orogenesis to 12.6 ± 3.1 million years and allows us to conclude that classic metamorphism by overthickening of continental crust cannot account for the very short-lived event in this region. In Chapter 2, we report ages from a Variscan relict (318 ± 130 Ma) to a range of Cenozoic ages from 35.5 ± 2.1 Ma to 9 ± 10 Ma in the Betic Cordillera of southern Spain. This alone indicates prolonged orogenesis in the region. These ages are linked directly to a microstructure known as a Foliation Intersection Axis (FIA). Results are inconclusive, but they generally indicate that there may be a relationship between broad scale plate motion and FIA orientations at a regional scale.

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.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A área estudada está inserida na Faixa Ribeira, Segmento Central da Província Mantiqueira (Almeida et al., 1973, 1977, 1981), que representa um cinturão de dobramentos e empurrões gerado no Neo-proterozóico/Cambriano, durante a Orogênese Brasiliana, na borda sul/sudeste do Cráton do São Francisco (Almeida, 1971, 1977; Cordani et al., 1967, 1973; Cordani & Brito Neves, 1982; Teixeira & Figueiredo, 1991). Neste contexto, o Complexo Quirino é o embasamento retrabalhado do Terreno Paraíba do Sul (Heilbron et al., 2004). O Complexo Quirino é formado por extensos corpos de ortognaisses foliados a homogêneos, leuco a mesocráticos, de granulometria média à grossa, composicionalmente variando entre granitóides tonalíticos/granodioríticos a graníticos, e apresentando enclaves de rochas ultramáficas, máficas e cálcio-silicáticas (ricas em tremolita). Os ortognaisses tonalíticos/granodioríticos apresentam porfiroblastos de plagioclásio e a hornblenda como máfico principal, contrastando com os de composição granítica que apresentam porfiroblastos de K-feldspato e biotita predominante. Como acessórios aparecem zircão, titanita, apatita e epidoto. Também estão associados a estes ortognaisses, granitóides neoproterozóicos que formam corpos individualizados ou lentes anatéticas no conjunto paleoproterozóico. Estes são compostos predominantemente por biotita gnaisse e hornblenda-biotita gnaisse. A análise litogeoquímicas dos ortognaisses do Complexo Quirino demonstrou a existência de duas séries magmáticas distintas. A primeira pertencente à série cálcio-alcalina de alto-K apresenta uma composição mais expandida granítica-adamelítica/granodioritica/tonalítica e é correlacionável aos bt-ortognaisses e alguns hb-bt-ortognaisses. Os ortognaisses da série médio-K apresentam composição predominantemente tonalítica, sendo correlacionáveis à maioria dos hornblenda-biotita gnaisses. Enclaves lenticulares de metapiroxeníticos e anfibolíticos ocorrem em muitos afloramentos. Também ocorrem granitóides neoproterozóicos de composição graníticas a quartzo-monzoníticas O estudo isotópico de Sm-Nd e Sr demonstrou que os ortognaisses da série cálcio-alcalina de alto-K e aqueles da série cálcio-alcalina de médio-K possuem idades modelo TDM variando entre paleoproterozóicas a arqueanas, consistentes com dados U-Pb em zircão publicados na literatura. A série cálcio-alcalina de alto-K é mais antiga (2308 9,2 Ma a 2185 8 Ma) do que a série calcio-alcalina de médio-K (2169 3 a 2136 14 Ma) e a existência de zircões herdados com idades mínimas de 2846 Ma e 2981 Ma para série de médio-K e 3388 16 para série de alto-K. Os granitóides brasilianos possuem idades de cristalização neoproterozóica correlacionada a Orogênese Brasiliana (602 a 627 Ma) (Viana, 2008; Valladares et al., 2002)./Com base nos dados de Sr e Sm-Nd foi possível caracterizar 4 grupos distintos. Os grupos 1 e 2 são formados por rochas de idade paleoproterozóica (2,1 a 2,3 Ga) com idades modelo TDM variando de 2,9 e 3,4 Ga, &#949;Nd entre -8,1 e -5,8 e 87Sr/86Sr(t) = 0,694707 (Grupo 1) e TDM variando de 2,5 a 2,7 Ga, &#949;Nd entre -5,8 e -3,1 e 87Sr/86Sr(t) = 0,680824 (Grupo 2), formados no paleoproterozóico com contribuição de uma crosta arqueana. O grupo 3 é formado por rochas juvenis de idade paleoproterozóica, com idades de cristalização variando entre 2,0 e 2,2 Ga e com idades modelo TDM variando de 2,1 a 2,2 Ga e &#949;Nd entre + 1,5 e + 1,2. O grupo 4 é formado durante o neoproterozóico (645 Ma) por rochas possivelmente de idade paleoproterozóico com idades modelo TDM igual a 1,7 Ga e &#949;Nd igual a -8,3. / The study area is part of the Ribeira Belt, Central Segment Mantiqueira Province (Almeida et al., 1973, 1977, 1981), which represents one of fold-thrust belt in neoproterozoic/cambrian generated during the Brasiliano Orogeny, at the edge south / southeast of the São Francisco Craton (Almeida, 1971, 1977, Cordani et al., 1967, 1973, Brito Neves & Cordani, 1982, Teixeira and Figueiredo, 1991). In this context, the Quirino Complex is the reworked basement of Paraiba do Sul Terrain (Heilbron et al., 2004). Quirino Complex is formed by extensive bodies of foliated orthogneisses the homogeneous, the leuco mesocratic, average particle size of the thick, compositionally ranging from tonalitic granitoids / granodioritic to granitic, and featuring enclaves of ultramafic, mafic and calcium silicate (rich in tremolite). The tonalite orthogneiss / granodioritic present porphyroblasts of plagioclase and hornblende as mafic main, contrasting with those of granitic composition showing porphyroblasts of K-feldspar and biotite predominates. Accessories appear as zircon, titanite, apatite and epidote. Also associated with these orthogneisses, neoproterozoic granitoids that make up individual bodies or lenses in the set anatetics paleoproterozoic. These are composed predominantly of biotite gneiss and hornblende-biotite gneiss. Lithogeochemical analysis of orthogneiss from Quirino Complex suggest the existence of two distinct magmatic series. The first belongs to the high-K calc-alkaline series composition shows a more expanded granitic-adamelític/granodioritic/tonalitic and is correlated to some orthogneisses and bt-hb-bt-orthogneiss. The medium-K orthogneisses series feature predominantly tonalitic composition, and correlated to most of the hornblende-biotite gneiss. Lenses enclaves metapiroxenitics and amphibolites occur in many outcrops. Neoproterozoic granitoids also occur composition of granitic to quartz-monzonitic. The isotopic study of Sm-Nd and Sr showed that the high-K calc-alkaline series orthogneisses and those of medium-K calc-alkaline series, have TDM model ages ranging from Archean to Paleoproterozoic, consistent with U-Pb data zircon from the literature. The high-K calc-alkaline series is older (2308 9.2 Ma to 2185 8 Ma) than medium-K calc-alkaline series (2169 3 to 2136 14 Ma) and occurs the existence of zircons inherited with minimum ages of 2846 Ma and 2981 Ma for medium-K series and 3388 16 for high-K series. The brasiliano granitoids have neoproterozoic crystallization ages correlated to Brasiliano Orogeny (602-627 Ma) (Viana, 2008, Valladares et al., 2002). Based on data of Sr and Sm-Nd was possible to identify four distinct groups. Groups 1 and 2 are formed by rocks of Paleoproterozoic (2.1 to 2.3 Ga) TDM model ages ranging from 2.9 to 3.4 Ga, &#949;Nd between -8.1 and -5.8 and 87Sr / 86Sr ratios (t) = 0.694707 (Group 1) and TDM ranging from 2.5 to 2.7 Ga, &#949;Nd between -5.8 and -3.1 and 87Sr/86Sr (t) = 0.680824 (Group 2), formed with the assistance of a Paleoproterozoic Archean. The third group consists of Paleoproterozoic juvenile rocks with crystallization ages ranging between 2.0 and 2.2 Ga and TDM model ages ranging from + 2.1 to + 2.2 Ga and &#949;Nd between +1.5 and +1.2. Group 4 is formed during the Neoproterozoic (645 Ma) of rocks with Paleoproterozoic age possibly TDM model ages exceeding 1.7 Ga and &#949;Nd= -8.3.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A área estudada está inserida na Faixa Ribeira, Segmento Central da Província Mantiqueira (Almeida et al., 1973, 1977, 1981), que representa um cinturão de dobramentos e empurrões gerado no Neo-proterozóico/Cambriano, durante a Orogênese Brasiliana, na borda sul/sudeste do Cráton do São Francisco (Almeida, 1971, 1977; Cordani et al., 1967, 1973; Cordani & Brito Neves, 1982; Teixeira & Figueiredo, 1991). Neste contexto, o Complexo Quirino é o embasamento retrabalhado do Terreno Paraíba do Sul (Heilbron et al., 2004). O Complexo Quirino é formado por extensos corpos de ortognaisses foliados a homogêneos, leuco a mesocráticos, de granulometria média à grossa, composicionalmente variando entre granitóides tonalíticos/granodioríticos a graníticos, e apresentando enclaves de rochas ultramáficas, máficas e cálcio-silicáticas (ricas em tremolita). Os ortognaisses tonalíticos/granodioríticos apresentam porfiroblastos de plagioclásio e a hornblenda como máfico principal, contrastando com os de composição granítica que apresentam porfiroblastos de K-feldspato e biotita predominante. Como acessórios aparecem zircão, titanita, apatita e epidoto. Também estão associados a estes ortognaisses, granitóides neoproterozóicos que formam corpos individualizados ou lentes anatéticas no conjunto paleoproterozóico. Estes são compostos predominantemente por biotita gnaisse e hornblenda-biotita gnaisse. A análise litogeoquímicas dos ortognaisses do Complexo Quirino demonstrou a existência de duas séries magmáticas distintas. A primeira pertencente à série cálcio-alcalina de alto-K apresenta uma composição mais expandida granítica-adamelítica/granodioritica/tonalítica e é correlacionável aos bt-ortognaisses e alguns hb-bt-ortognaisses. Os ortognaisses da série médio-K apresentam composição predominantemente tonalítica, sendo correlacionáveis à maioria dos hornblenda-biotita gnaisses. Enclaves lenticulares de metapiroxeníticos e anfibolíticos ocorrem em muitos afloramentos. Também ocorrem granitóides neoproterozóicos de composição graníticas a quartzo-monzoníticas O estudo isotópico de Sm-Nd e Sr demonstrou que os ortognaisses da série cálcio-alcalina de alto-K e aqueles da série cálcio-alcalina de médio-K possuem idades modelo TDM variando entre paleoproterozóicas a arqueanas, consistentes com dados U-Pb em zircão publicados na literatura. A série cálcio-alcalina de alto-K é mais antiga (2308 9,2 Ma a 2185 8 Ma) do que a série calcio-alcalina de médio-K (2169 3 a 2136 14 Ma) e a existência de zircões herdados com idades mínimas de 2846 Ma e 2981 Ma para série de médio-K e 3388 16 para série de alto-K. Os granitóides brasilianos possuem idades de cristalização neoproterozóica correlacionada a Orogênese Brasiliana (602 a 627 Ma) (Viana, 2008; Valladares et al., 2002)./Com base nos dados de Sr e Sm-Nd foi possível caracterizar 4 grupos distintos. Os grupos 1 e 2 são formados por rochas de idade paleoproterozóica (2,1 a 2,3 Ga) com idades modelo TDM variando de 2,9 e 3,4 Ga, &#949;Nd entre -8,1 e -5,8 e 87Sr/86Sr(t) = 0,694707 (Grupo 1) e TDM variando de 2,5 a 2,7 Ga, &#949;Nd entre -5,8 e -3,1 e 87Sr/86Sr(t) = 0,680824 (Grupo 2), formados no paleoproterozóico com contribuição de uma crosta arqueana. O grupo 3 é formado por rochas juvenis de idade paleoproterozóica, com idades de cristalização variando entre 2,0 e 2,2 Ga e com idades modelo TDM variando de 2,1 a 2,2 Ga e &#949;Nd entre + 1,5 e + 1,2. O grupo 4 é formado durante o neoproterozóico (645 Ma) por rochas possivelmente de idade paleoproterozóico com idades modelo TDM igual a 1,7 Ga e &#949;Nd igual a -8,3. / The study area is part of the Ribeira Belt, Central Segment Mantiqueira Province (Almeida et al., 1973, 1977, 1981), which represents one of fold-thrust belt in neoproterozoic/cambrian generated during the Brasiliano Orogeny, at the edge south / southeast of the São Francisco Craton (Almeida, 1971, 1977, Cordani et al., 1967, 1973, Brito Neves & Cordani, 1982, Teixeira and Figueiredo, 1991). In this context, the Quirino Complex is the reworked basement of Paraiba do Sul Terrain (Heilbron et al., 2004). Quirino Complex is formed by extensive bodies of foliated orthogneisses the homogeneous, the leuco mesocratic, average particle size of the thick, compositionally ranging from tonalitic granitoids / granodioritic to granitic, and featuring enclaves of ultramafic, mafic and calcium silicate (rich in tremolite). The tonalite orthogneiss / granodioritic present porphyroblasts of plagioclase and hornblende as mafic main, contrasting with those of granitic composition showing porphyroblasts of K-feldspar and biotite predominates. Accessories appear as zircon, titanite, apatite and epidote. Also associated with these orthogneisses, neoproterozoic granitoids that make up individual bodies or lenses in the set anatetics paleoproterozoic. These are composed predominantly of biotite gneiss and hornblende-biotite gneiss. Lithogeochemical analysis of orthogneiss from Quirino Complex suggest the existence of two distinct magmatic series. The first belongs to the high-K calc-alkaline series composition shows a more expanded granitic-adamelític/granodioritic/tonalitic and is correlated to some orthogneisses and bt-hb-bt-orthogneiss. The medium-K orthogneisses series feature predominantly tonalitic composition, and correlated to most of the hornblende-biotite gneiss. Lenses enclaves metapiroxenitics and amphibolites occur in many outcrops. Neoproterozoic granitoids also occur composition of granitic to quartz-monzonitic. The isotopic study of Sm-Nd and Sr showed that the high-K calc-alkaline series orthogneisses and those of medium-K calc-alkaline series, have TDM model ages ranging from Archean to Paleoproterozoic, consistent with U-Pb data zircon from the literature. The high-K calc-alkaline series is older (2308 9.2 Ma to 2185 8 Ma) than medium-K calc-alkaline series (2169 3 to 2136 14 Ma) and occurs the existence of zircons inherited with minimum ages of 2846 Ma and 2981 Ma for medium-K series and 3388 16 for high-K series. The brasiliano granitoids have neoproterozoic crystallization ages correlated to Brasiliano Orogeny (602-627 Ma) (Viana, 2008, Valladares et al., 2002). Based on data of Sr and Sm-Nd was possible to identify four distinct groups. Groups 1 and 2 are formed by rocks of Paleoproterozoic (2.1 to 2.3 Ga) TDM model ages ranging from 2.9 to 3.4 Ga, &#949;Nd between -8.1 and -5.8 and 87Sr / 86Sr ratios (t) = 0.694707 (Group 1) and TDM ranging from 2.5 to 2.7 Ga, &#949;Nd between -5.8 and -3.1 and 87Sr/86Sr (t) = 0.680824 (Group 2), formed with the assistance of a Paleoproterozoic Archean. The third group consists of Paleoproterozoic juvenile rocks with crystallization ages ranging between 2.0 and 2.2 Ga and TDM model ages ranging from + 2.1 to + 2.2 Ga and &#949;Nd between +1.5 and +1.2. Group 4 is formed during the Neoproterozoic (645 Ma) of rocks with Paleoproterozoic age possibly TDM model ages exceeding 1.7 Ga and &#949;Nd= -8.3.

This study incorporates high precision zoned garnet samarium-neodymium geochronology and thermodynamic analysis of garnet forming dehydration reactions to determine the amount of water release during both subduction and mountain building. Garnet grows during rock dehydration, providing both a temporal and geodynamic record of not only its growth, but of associated dehydration. Laboratory experiments and geodynamic models have been used to predict amounts of dehydration during metamorphism based on equilibrium assumptions. If equilibrium is not maintained, or if aspects of the geodynamic modeling are incorrect, these model-based predictions will prove inaccurate. Field-based evidence is necessary to test such model predictions and to elucidate both the timing and duration of dehydration and the role of kinetics during metamorphism. Localities that have undergone dehydration and associated fluid flow provide natural laboratories in which to study these geologic processes. This study focuses on two geologic settings: regional orogenesis (Townshend Dam, Vermont) and subduction zone metamorphism (Sifnos, Greece). Regional metamorphism of the pelitic schists of Townshend Dam occurred during the Acadian orogeny peaking at ~381 Ma. Garnet growth lasted for 4.2 ± 2.4 million years. Thermodynamic forward modeling from this study has shown that an early stage of burial of the rocks without significant heating first occurred, followed then by a period of intense heating at depth, during which, roughly 2 vol.% water was lost from the rock. In contrast, metamorphism, and thus dehydration, during subduction of a continental margin in Sifnos, Greece was found to have occurred in as brief a timespan as tens to hundreds of thousands of years, releasing 2-3 vol.% water during a period of intense heating at ~75 km depth between ~47-44 million years ago. This short time interval represents a discrete pulse of dehydration and heating within the context of the process of subduction, which probably occurred over timescales of 10 to 20 million years in this location. This is the first study to provide a field-based constraint on the magnitude, timing, and rate of dehydration during subduction, a process that causes intermediate-depth earthquakes, mantle melting and volcanism, and large scale changes to the global water cycle.

Os métodos radiométricos (Rb-Sr e Sm-Nd) têm sido aplicados, com sucesso, em rochas sedimentares visando a obtenção de idades deposicionais e informações sobre proveniência. Em muitos casos, apesar dos resultados geologicamente significativos, ainda persistem dúvidas em relação a extensão e interpretação dos dados obtidos. Isto ocorre porque as rochas sedimentares resultam da mistura de fragmentos detríticos de diversas proveniências com diferentes sistemas isotópicos, conseqüentemente, já contendo um registro isotópico da rocha fonte. No caso do método Rb-Sr, aplicado em rochas sedimentares de granulometria fina, pode-se obter idades absolutas para o evento deposicional. Isto é viável desde que este registro isotópico proveniente das rochas fonte seja apagado no momento da deposição, ou seja, deve ocorrer a homogeneização isotópica do Sr no ambiente sedimentar. Para tanto, devem ser observados alguns pré-requisitos em relação a amostragem, granulometria, ambiente deposicional e composição mineralógica das amostras, entre outros. No entanto, ainda existem questionamentos em relação a esta metodologia especialmente quanto à ocorrência e à extensão do processo de homogeneização isotópica do Sr em ambiente sedimentar.(Continua0 O método Sm-Nd, apesar de ser uma técnica relativamente nova quando aplicada a rochas sedimentares, tem se tornado uma ferramenta fundamental para auxílio na determinação de proveniência de rochas sedimentares. As maiores dificuldades estão na correta interpretação dos valores obtidos e sua associação com um ambiente sedimentar, ou seja, de baixa temperatura. Neste trabalho, foram aplicados os métodos radiométricos Rb-Sr e Sm-Nd em amostras de rochas sedimentares coletadas em diferentes contextos geológicos da Bacia do Paraná. Foram tentativamente testados os diferentes parâmetros que atuam no sentido da homogeneização isotópica do Sr e do comportamento do Nd. Os resultados obtidos permitiram aprimorar a metodologia radiométrica Rb-Sr e Sm-Nd quando aplicada em rochas sedimentares, bem como obter resultados sobre a idade deposicional de diferentes unidades sedimentares e, por vezes, sua proveniência.

Os métodos radiométricos (Rb-Sr e Sm-Nd) têm sido aplicados, com sucesso, em rochas sedimentares visando a obtenção de idades deposicionais e informações sobre proveniência. Em muitos casos, apesar dos resultados geologicamente significativos, ainda persistem dúvidas em relação a extensão e interpretação dos dados obtidos. Isto ocorre porque as rochas sedimentares resultam da mistura de fragmentos detríticos de diversas proveniências com diferentes sistemas isotópicos, conseqüentemente, já contendo um registro isotópico da rocha fonte. No caso do método Rb-Sr, aplicado em rochas sedimentares de granulometria fina, pode-se obter idades absolutas para o evento deposicional. Isto é viável desde que este registro isotópico proveniente das rochas fonte seja apagado no momento da deposição, ou seja, deve ocorrer a homogeneização isotópica do Sr no ambiente sedimentar. Para tanto, devem ser observados alguns pré-requisitos em relação a amostragem, granulometria, ambiente deposicional e composição mineralógica das amostras, entre outros. No entanto, ainda existem questionamentos em relação a esta metodologia especialmente quanto à ocorrência e à extensão do processo de homogeneização isotópica do Sr em ambiente sedimentar.(Continua0 O método Sm-Nd, apesar de ser uma técnica relativamente nova quando aplicada a rochas sedimentares, tem se tornado uma ferramenta fundamental para auxílio na determinação de proveniência de rochas sedimentares. As maiores dificuldades estão na correta interpretação dos valores obtidos e sua associação com um ambiente sedimentar, ou seja, de baixa temperatura. Neste trabalho, foram aplicados os métodos radiométricos Rb-Sr e Sm-Nd em amostras de rochas sedimentares coletadas em diferentes contextos geológicos da Bacia do Paraná. Foram tentativamente testados os diferentes parâmetros que atuam no sentido da homogeneização isotópica do Sr e do comportamento do Nd. Os resultados obtidos permitiram aprimorar a metodologia radiométrica Rb-Sr e Sm-Nd quando aplicada em rochas sedimentares, bem como obter resultados sobre a idade deposicional de diferentes unidades sedimentares e, por vezes, sua proveniência.