Dissertations / Theses on the topic 'Sm-Nd geochronology'

Submitted by Jordan (jordanbiblio@gmail.com) on 2016-10-19T14:49:06Z No. of bitstreams: 1 DISS_2015_Shayenne Fontes Nogueira.pdf: 6085146 bytes, checksum: 0c934cfd81d96aa21aaed95906de3b37 (MD5)
Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2016-10-19T14:50:04Z (GMT) No. of bitstreams: 1 DISS_2015_Shayenne Fontes Nogueira.pdf: 6085146 bytes, checksum: 0c934cfd81d96aa21aaed95906de3b37 (MD5)
Made available in DSpace on 2016-10-19T14:50:04Z (GMT). No. of bitstreams: 1 DISS_2015_Shayenne Fontes Nogueira.pdf: 6085146 bytes, checksum: 0c934cfd81d96aa21aaed95906de3b37 (MD5) Previous issue date: 2015-08-31
CNPq
O Terreno Rio Apa é marcado por uma história evolutiva complexa e ainda contêm problemáticas a serem estudadas e compreendidas. Neste trabalho são apresentados os resultados obtidos a partir da caracterização petrológica do Granito Aquidabã que pertence à Suíte Intrusiva Alumiador inserida no Arco Magmático Amoguijá deste terreno. Em um contexto anterior, as rochas deste granito eram descritas como pertencentes ao Batólito Alumiador, porém, as mesmas apresentam características singulares que levaram à sua individualização. O Granito Aquidabã está representado por rochas plutônicas e efusivas, de natureza ácida. São classificadas como dacitos e riolitos, riolitos/riolitos alcalinos e adamelitos (monzogranitos)/granitos, subdivididos em três fácies petrográficas: Granito Gráfico (fácies 1), Subvulcânicas Dacítica-Riolítica (fácies 2), Microgranito (fácies 3). A primeira é, volumetricamente, dominante no corpo mapeado sustentando as partes mais elevadas, e disposta na porção central da Serra da Alegria; caracteriza-se por rochas maciças e de cor rosa a rosa-acinzentado, leucocráticas, equi- a inequigranulares média a fina. A fácies 2 é caracterizada pela ocorrência de litotipos que variam de dacitos a riolitos.Os dacitos apresentam-se marrom-acinzentado, com textura porfirítica, destacando fenocristais de plagioclásio e quartzo, por vezes com dimensões entre 1 e 7 mm apresentando, comumente, feições de corrosão magmática como golfos e embaiamentos, envoltos por uma matriz felsítica cinza. Os riolitos são rosa-acinzentado, maciços, afaníticos, com variedades porfiríticas, apresentando fenocristais de feldspato alcalino com tamanhos entre 1 e 5 mm envoltos por uma franja esferulítica de composição quartzo+K-feldspato. A fácies Microgranito (fácies 3) é a de menor representatividade, sendo encontrada nas bordas oeste e sudoeste do corpo granítico, caracterizada por rochas maciças cinza-claro, inequigranulares fina a muito fina. Os dados geoquímicos sugerem um magmatismo de composição compatível com a de granitoides tipo A gerados em ambiente de arco magmático, em período pós-tectônico. Através do método geocronológico U-Pb (SHRIMP) em zircão se obteve idade de 1811±6,8 Ma para o Granito Aquidabã, com valores εNd (1,81Ga) de -2,18; -4,37 e -1,50, e idade modelo TDM de 2,35, 2,57 e 2,26 Ga que apontam para participação de uma fonte crustal na origem do magma, possivelmente envolvendo processos de fusão parcial de uma crosta continental neoarqueana a paeloproterozoica na geração do granito. Os resultados obtidos apontam que o Granito Aquidabã corresponde a um magmatismo desenvolvido no final do Orosiriano no Arco Magmático Amoguijá.
The Rio Apa Terrane is marked by a complex evolutionary history and still contain issues to be studied and understood. This paper presents the results obtained from the petrologic characterization of Aquidabã granite belonging to Intrusive Suite Alumiador inserted into the Magmatic Arc Amoguijá. In a previous context, this granite rocks were described as belonging to the Batholith Alumiador, however, they present unique characteristics that led to its individualization. The Aquidabã Granite is represented by plutonic and effusive rocks, acidic in nature. They are classified as dacites and rhyolites, rhyolites / alkaline rhyolites and adamelitos (monzogranites) / granite, divided in three petrographic facies: Graphic Granite (facies 1), Subvolcanic Dacitic-Riolítica (facies 2), Microgranito (facies 3). The first is volumetrically dominant in the body, arranged in the central portion of the Serra da Alegria; It characterized by massive rocks and pink , pink-gray, leucocratic, inequigranular thin.The facies 2 is characterized by the occurrence of rock types ranging from the dacites, dacites/riolitos. Have color grayish to brown, with phenocrysts of quartz and plagioclase, sometimes with dimensions between 1 and 7 mm, presenting features magmatic corrosion as gulfs and embayments, surrounded by a gray matrix felsítica.The rhyolites are pink-gray, massive, afaníticos with porphyritic varieties, with phenocrysts of alkali feldspar with sizes between 1 and 5 mm surrounded by a fringe spherulitic quartz K-feldspar + composition. The Microgranito facies (facies 3) is the smaller representation, found in the western and southwestern edges of the granite body, characterized by light gray massive rocks, thin inequigranular very thin. The geochemical data suggest a composite magmatism compatible with the granitic type A generated in magmatic arc environment in post-tectonic period. Through the method geochronological U-Pb (SHRIMP) was obtained zircon age ± 6.8 1811 Ma to Aquidabã Granite with εNd values (1,81Ga) of -2.18; -4.37 And -1.50, and TDM model age of 2.35, 2.57 and 2.26 Ga pointing to involvement of a crustal magma source in origin, possibly involving partial melting processes of continental crust neoarqueana the paeloproterozoica in granite generation. The results suggest that the Aquidabã Granite corresponds to a magmatism developed in the late Orosirian in Magmatic Arc Amoguijá.

Submitted by Jordan (jordanbiblio@gmail.com) on 2016-10-21T11:39:58Z No. of bitstreams: 1 DISS_2015_Leticia Alexandre Redes.pdf: 8294298 bytes, checksum: 8db7bb3276d8fbf7eb60e5f07cf9aec7 (MD5)
Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2016-10-21T11:40:54Z (GMT) No. of bitstreams: 1 DISS_2015_Leticia Alexandre Redes.pdf: 8294298 bytes, checksum: 8db7bb3276d8fbf7eb60e5f07cf9aec7 (MD5)
Made available in DSpace on 2016-10-21T11:40:54Z (GMT). No. of bitstreams: 1 DISS_2015_Leticia Alexandre Redes.pdf: 8294298 bytes, checksum: 8db7bb3276d8fbf7eb60e5f07cf9aec7 (MD5) Previous issue date: 2015-02-13
CAPES
O Granito Taquaral possui dimensões batolíticas, localiza-se no sul do Cráton Amazônico, na região de Corumbá, extremo ocidente do estado de Mato Grosso do Sul, próximo ao limite Brasil-Bolívia, sendo parcialmente recoberto pelas rochas sedimentares das formações Urucum, Tamengo, Bocaina e Pantanal e pelas as Aluviões Atuais. Com base no estudo das rochas do Granito Taquaral a partir de granulação, cor e composição, juntamente com o mapeamento geológico de detalhe, foi realizada a identificação de três fácies petrográficas: Fácies Média a Grossa Cinza, Fácies Grossa Rosa e Fácies Fina Rosa. A primeira é, volumetricamente, dominante no corpo mapeado; caracteriza-se por rochas leucocráticas, de cor cinza, textura inequi a equigranular média a grossa, às vezes, mostra-se milonitizada e são classificadas como quartzo-monzodiorito, granodiorito e monzogranito. A segunda é constituída por rochas leucocráticas de cor rosa, inequigranulares, grossas, de composição quartzo-monzonito e monzogranito. Enquanto que a terceira é composta por rochas hololeucocráticas de cor rosa-claro, equi a inequigranulares classificadas como monzo a sienogranítica, de granulação fina e representadas por diques aplíticos. Localmente são encontrados dois tipos de enclaves de natureza e origens diferentes, um de composição máfica, corresponde a xenólito e outro, identificado como Enclave Microgranular Félsico. Na área de estudo são encontrados, também diques de diabásio sempre em contatos abruptos com o granito. Foram identificadas duas fases deformacionais, uma de natureza dúctil (F1) e outra rúptil/rúptil-dúctil (F2). Os dados geoquímicos indicam composição intermediária a ácida para essas rochas e sugerem sua colocação em ambiente de arco, representando um magmatismo cálcio-alcalino de médio a alto-K, metaluminoso a peraluminoso. Através do método geocronológico U-Pb (SHRIMP) em zircão se obteve idade de 1861±5,3 Ma para sua cristalização. Análises Sm-Nd em rocha total fornecem valores de εNd(1,86 Ga) de -1,48 e -1,28 e TDM de 2,32 e 2,25 Ga apontando para uma provável fonte crustal riaciana. Os resultados obtidos apontam que o Granito Taquaral corresponde a um magmatismo desenvolvido no final do Orosiriano no Arco Magmático Amoguijá.
The Taquaral Granite comprises an intrusion of batholithic dimensions, located in the south of the Amazon Craton in Corumbá region - far west of the state of Mato Grosso do Sul, near the border between Brazil and Bolivia -, partially covered by sedimentary rocks of the Urucum, Tamengo, Bocaina and Pantanal formations and the Alluvial Deposits. Based on grain size, color, and composition along with detailed geological mapping, three petrographic facies are attributed to the rocks of Taquaral Granite: Medium to Coarse-grained Grey Facies, Coarse-grained Pink Facies and Fine-grained Pink Facies. The first facies is volumetrically dominant in the mapped body; characterized by leucocratic rocks, grey, inequigranular to equigranular medium-to-coarse grained, sometimes displaying a mylonitized texture and are classified as quartz-monzodiorite, granodiorite and monzogranite. The second facies consists of pink leucocratic rocks, inequigranular, coarse-grained, of quartz monzonite and monzogranite composition. In turn, the third facies consists of light-pink hololeucocratic rocks, equigranular to inequigranular, classified as fine-grained aplite dykes of monzogranitic to syenogranitic composition. Two different types of enclaves are locally found: one corresponds to a mafic xenolith; another is identified as felsic microgranular enclave. In the study area, diabase dikes are also found, always in direct contact with the granite. Two deformation phases are identified, one of ductile behaviour (F1) and another of brittle / ductile brittle behaviour (F2). Geochemical data indicate intermediate to acid composition for these rocks and suggest an arc environment, representing a medium to high-K calc-alkaline magmatism, metaluminous to peraluminous. SHRIMP U-Pb zircon ages of 1861 ± 5.3 Ma are attributed to crystallization. Sm-Nd whole rock analyses provided negative εNd(1.86 Ga) values (-1.48 and -1.28) and TDM model ages from 2.32 to 2.25 Ga indicating a Rhyacian crustal source. The results indicate that Taquaral Granite is an evidence of a magmatism developed in the Amoguijá Magmatic Arc in late Orosirian.

Submitted by Jordan (jordanbiblio@gmail.com) on 2016-11-03T14:43:40Z No. of bitstreams: 1 DISS_2015_Frankie James Serrano Fachetti.pdf: 2106239 bytes, checksum: 3e47ff5badd6589019a10893b630751b (MD5)
Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2016-12-15T15:37:50Z (GMT) No. of bitstreams: 1 DISS_2015_Frankie James Serrano Fachetti.pdf: 2106239 bytes, checksum: 3e47ff5badd6589019a10893b630751b (MD5)
Made available in DSpace on 2016-12-15T15:37:51Z (GMT). No. of bitstreams: 1 DISS_2015_Frankie James Serrano Fachetti.pdf: 2106239 bytes, checksum: 3e47ff5badd6589019a10893b630751b (MD5) Previous issue date: 2015-07-01
CAPES
O Ortognaisse Taquarussu e o Granodiorito Guadalupe, integrantes do embasamento da Província Rondoniana - San Ignácio, SW do Cráton Amazônico, norte do município de Jauru- MT, correspondem a corpos orientados segundo um trend principal NW/SE. São rochas de composição granodiorítica com ocorrências subordinadas de monzogranitos. Na petrografia, são rochas de granulação fina a grossa, constituídas essencialmente por plagioclásio, quartzo, microclina, ortoclásio e biotita. Os minerais acessórios são: anfibólio, titanita, granada, apatita, epidoto, zircão e opacos. Apresentam evidências de pelo menos três fases de deformação dúcteis onde a principal estrutura relacionada a fase D1 é a foliação S1, representada ora por um bandamento composicional, ora por uma xistosidade. A segunda fase corresponde a uma clivagem de crenulação que transpõe a foliação S1, A terceira fase é exemplificada pela implantação de zonas de cisalhamento que geraram uma foliação/faturamento de escala local. O estudo geoquímico permitiu classificar as rochas como granodioritos e monzogranitos, oriundos de um magmatismo intermediário a ácido, de caráter sub-alcalino, da série cálcio-alcalina a cálcio-alcalina alto K, com índices de alumina que varia de metaluminoso a levemente peraluminoso. Foram classificados como gerados em ambiente de arco de ilhas e os dados U-Pb (Shrimp em zircão) mostram uma idade concórdia de 1575±6Ma. A idade modelo das análises de Sm-Nd (TDM) apontam para 1,63Ga, com εNd (t=1,57Ga) variando entre -1,52 e +0,78. Estes dados permitem caracterizar estas rochas como uma crosta juvenil com uma possível contaminação de rochas crustais.
The Taquarussu orthogneiss and the Guadalupe Granodiorite part of Rondonian-San Ignacio Province basement, southweast of Amazonian Craton, correspond to oriented bodies according to a NW/SE trend. The rocks are granodiorite composition with subordinate monzogranites, fine to coarse grained, consisting essentially of plagioclase, quartz, microcline, orthoclase and biotite. The accessory minerals are amphibole, titanite, garnet, apatite, epidote, zircon and opaque minerals. There is evidence of at least three phases of ductile deformation where the main structure is related to D1 stage (foliation S1), represented by a compositional banding, or by schistosity. The second phase is a crenulation cleavage transposing the foliation S1 and the third phase is exemplified by the deployment of shear zones that generated a foliation/fracturing on a local scale. The geochemical study indicates that the rocks are classify as granodiorites and monzogranites, coming from an intermediate to acid magmatism, sub-alkaline character calc-alkaline to high-K calc-alkaline series, with alumina ratios ranging from metaluminous to lightly peraluminous. The rocks were generate in a volcanic islands arc environment and the UPb data (Shrimp zircon) show a concord age 1575 ± 6Ma. The Sm-Nd model age (TDM) is 1.63Ga with εNd (t = 1.57Ga) ranging between -1.52 and +0.78. These data indicate that these rocks probably are a juvenile crust with a possible contamination of crustal rocks. Keyword: Geology, Gneiss Taquarussu, Granodiorite Guadalupe.

Thesis advisor: Ethan F. Baxter
Spiral garnets are well-documented metamorphic microstructures that have been observed in orogens throughout the world. The preferred orientation of spiral garnet axes has been proposed (Bell and Johnson, 1989) to record and preserve information about the timing, rate, and orientation of the tectonic-scale processes. Using the model of Be Spiral garnets are well-documented metamorphic microstructures that have been observed in orogens throughout the world. The preferred orientation of spiral garnet axes has been proposed (Bell and Johnson, 1989) to record and preserve information about the timing, rate, and orientation of the tectonic-scale processes. Using the model of Bell and Johnson (1989), Aerden et al. (2013) proposed a link between the preferred orientation of spiral garnets and changes in relative plate motion between Iberia and Africa. The goal of this thesis is to this relationship by absolutely dating, eight samples from the Betic-Rif arc with measurable spiral axis orientations were chosen for Sm-Nd garnet geochronology. Chapter one is a detailed literature review of prior work on the formation and interpretation of spiral garnets. In chapter two we present 11 bulk Sm-Nd garnet ages from eight samples, these ages range from 35.6 ± 2.8 to 13.62 ± 0.69 Ma. The results from the obtained bulk garnet ages reveal a more complex relationship between FIA orientations and plate motion that originally hypothesized in Aerden et al. (2013). Large-scale rigid block rotations that postdate garnet growth may have influenced the current orientation of FIA from the western Betic-Rif. In chapter three, zoned geochronology was conducted on a single sample from the Nevado-Filabride Complex. This study revealed spiral garnet formation occurring on a rapid timescale, just 〖0.45〗_(-0.32)^(+0.51) Myr. While other zoned garnet studies have shown similar rapid growth in subduction zone setting (Dragovic et al., 2012), this is the first such documentation of such rapid growth from a garnet hosting spiral inclusion trails in a regional metamorphic setting. We calculated strain rates considering different genetic models for the spiral inclusion trails either by garnet rotation in simple shear, or by episodic overgrowth of suborthogonal crenulation cleavages due to switching stress axes. In both cases a similar fast strain rate of ca. 10-13 s-1 was obtained, which is an order of magnitude faster than typical regional strain rates and faster than previous spiral garnet studies regardless of the method used to calculate strain-rate
Thesis (MS) — Boston College, 2019
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences

Identifying the crustal affinity of Grenville basement rocks in the Dellwood quadrangle, western NC, provides insight into the tectonic evolution of eastern Laurentia during Grenville orogenesis. U-Pb zircon geochronology of orthogneiss, augen gneiss, and mafic xenoliths in orthogneiss reveal magmatic pulses at 1130, 1180, and 1330 Ma and metamorphic episodes at 450 and 1040 Ma. Xenoliths in 1330 Ma orthogneiss are as old as 1382 Ma and represent the oldest component of Blue Ridge basement identified to-date. Feldspar Pb isotope values span a range between juvenile-Laurentian and southern-central Appalachian basement/Amazonia. Most Pb isotope data define an array consistent with crustal mixing between Laurentia and Amazonia, however, one xenolith has a unique Pb isotopic composition interpreted as Laurentian crust. Sm-Nd isotope data yield depleted mantle model ages ranging from 1.52 to 1.79 Ga (200 to 650 Ma older than their crystallization ages) indicating a broadly non-juvenile heritage for Dellwood basement. Three biotite gneiss samples contain detrital zircon grains derived from 1060, 1160, 1330, and 1750 Ma sources. Multiple magmatic zircon age populations, variable depleted mantle modelages, and regionally unique isotopic Pb signatures are evidence of protracted Grenville magmatism in the southern Appalachians involving both Laurentian and Amazonian crustal components.

Thesis advisor: Ethan F. Baxter
Samarium/Neodymium (Sm-Nd) garnet geochronology of eclogites from Syros, Greece provides constraints on timing of peak metamorphism while thermodynamic modeling of the same samples allows a comparison of pressure-temperature (P-T) paths. Sm-Nd geochronology of four eclogite samples give ages of 48.8 ± 3.2 Ma (high 147Sm/144Nd = 0.49, n = 6, MSWD = 0.67), 48.1 ± 2.3 Ma (high 147Sm/144Nd = 1.22, n = 4, MSWD = 2.4), 44.7 ± 1.0 Ma (high 147Sm/144Nd = 3.9, n = 6, MSWD = 1.4), and 43.6 ± 1.6 Ma (high 147Sm/144Nd = 1.39, n = 6,MSWD = 2). These garnet growth ages span several million years and are younger than the only other published garnet eclogite ages from the island which use Lutetium/ Hafnium (Lu-Hf) garnet geochronology to place peak metamorphism at ~52 Ma (Lagos et al, 2007). Another eclogite sample dated less precisely yielded an age of 57.7 ± 6.3 Ma (high 147Sm/144Nd = 0.40, n = 10, MSWD = 1.9), significantly older than the other garnets dated in this study. The garnet ages from eclogites presented here suggest that high pressure-low temperature metamorphism, and related garnet growth and dehydration, on Syros lasted ~9 myr, similar to what has been reported for nearby Sifnos Island (Dragovic et al., 2015). Thermodynamic modeling of three samples reveals similar prograde P-T paths despite differences in tectonic setting and chemistry between samples. Water loss from mineral breakdown during the span of subduction zone garnet growth varies between samples from 1.09 to 5.13 weight percent but is greatest for the most ultramafic sample due to chlorite stability permitting greater capacity for water to be carried to depth. P-T paths reach greater maximum pressures (up to 2.42 GPa) than what is reported for Sifnos island (Dragovic et al., 2015) and greater than most previously published pressure estimates for Syros (ie. Okrusch and Bröcker, 1990; Putlitz et al., 2005)
Thesis (MS) — Boston College, 2016
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences

Idades radiométricas absolutas recentemente publicadas levantaram questões sobre a evolução deposicional da Formação Sete Lagoas (FSL). Esta unidade é composta predominantemente por carbonatos com rochas siliciclásticas subordinadas e constitui a unidade basal do Grupo Bambuí, sobreposta aos depósitos glaciogênicos da Formação Jequitaí no Cráton São Francisco (CSF). Este estudo combina quimioestratigrafia isotópica (C, O e Sr) e geocronologia (U-Pb e Hf em zircão detrítico e Sm-Nd em rocha total) em amostras de cinco seções da FSL na região de Lagoa Santa, MG, sul do CSF, com a finalidade de responder a tais questionamentos. As seções Vespasiano (VS) e Ana Paula (AP) são constituídas por calcários cinzas e dolomitos beges, com altos teores de sedimentos terrígenos e pobres em matéria orgânica. Os valores de \'delta\'\'POT.13C\' mais representativos do ambiente deposicional oscilam em uma estreita faixa ao redor de 0%o. Estes dados permitem posicionar estas seções na primeira sequência deposicional da FSL, acima dos carbonatos de capa Sturtianos (~740 Ma) da base desta unidade. As seções Bairro da Lapinha (BL), Pedra do Baú (BAU) e Parque da Gruta da Lapinha (PGL) são compostas por calcários de coloração cinza escura a negra, pobres em sedimentos detríticos e ricos em matéria orgânica. São caracterizados por valores de \'delta\'\'POT.13\' C bastante positivos (> 6%o) e razões \'87 ANTPOT.Sr\'/\'86 ANTPOT.Sr\' próximas de 0,7075. Estas seções estão posicionadas na segunda sequência deposicional da FSL. Zircões detríticos foram separados de três amostras de marga das seções VS, AP e PGL e datados pelo método U-Pb. Os resultados indicam que os sedimentos siliciclásticos da FSL na área de estudo provêm de fontes de longa residência crustal do Orógeno Araçuaí-Oeste Congo. A população expressiva mais jovem tem 557 Ma e determina a idade máxima de deposição para a segunda sequência da unidade e para a maior parte do Grupo Bambuí. Além disso, grãos de zircão concordantes mais jovens com idades de 537 ± 4 Ma e 506 ± 7 Ma para a primeira e segunda sequência, respectivamente, refutam a existência de um hiato deposicional expressivo entre as duas sequências, como recentemente proposto, e endossam uma idade deposicional do limite Ediacarano/Cambriano para a FSL. Se existe uma discordância, esta está posicionada entre os carbonatos de capa Sturtianos e as seções com valores de \'delta\'\'POT.13\'C\' ao redor de 0%o. Estas idades indicam que grande parte do Grupo Bambuí foi depositada em uma bacia de foreland, após o fechamento do Oceano Adamastor que culminou com a edificação da Faixa Araçuaí a leste do CSF. As razões \'87 ANTPOT.Sr\'/\'86 ANTPOT.Sr\' obtidas nos carbonatos da FSL contrastam com as recentes curvas de evolução de Sr para os oceanos, especialmente no Cambriano, quando razões maiores que 0,7085 são esperadas. É provável que esta unidade tenha sido depositada em um mar epicontinental restrito e a correlação global por meio de isótopos de Sr não é confiável nestes casos.
Recently published geochronological data has arisen questions on the Sete Lagoas Formation (SLF) depositional evolution. This unit is mainly composed by carbonate rocks with subordinated pelitic intercalations and represents the basal unit of the Bambuí Group, which overlies the glacial deposits of the Jequitaí Formation in the São Francisco Craton (SFC). This study combines isotope chemostratigraphy (C, O, Sr) and geochronology (U -Pb and Hf on detrital zircons and Sm-Nd on whole rock samples) in five sections of the SLF in the Lagoa Santa (MG) region, southern part of SFC, in order to answer such questions. Vespasiano (VS) and Ana Paula (AP) sections are composed by gray limestones and beige dolostones, with high contents of detrital sediments and poor in organic matter. The most representative \'delta\'\'POT.13C\' values obtained oscillate within a narrow range around 0%o. These data allow positioning these sections in the first depositional sequence of the SLF, above the basal Sturtian cap carbonates (~740 Ma) of this unit. Bairro da Lapinha (BL), Pedra do Baú (BAU) and Parque da Gruta da Lapinha (PGL) sections comprises dark gray to black limestones, with low detrital sediments contents and rich in organic matter. They are characterized by very positive \'delta\'\'POT.13\'C values (> 6%o) and \'87 ANTPOT.Sr\'/ \'86 ANTPOT.Sr\' ratios close to 0.7075. These sections belong to the second sequence of the SLF. Detrital zircons were retrieved from three marl samples from sections VS, AP and PGL and dated by the U-Pb method. The results indicate that the siliciclastic sediments of the SLF come from sources of long crustal residence time located in the Araçuaí-West Congo Orogen. The youngest population is 557 Ma aged and sets the maximum depositional age for the second sequence of SLF and most of the Bambuí Group. Furthermore, younger concordant zircon grains with ages of 537 ± 4 Ma and 506 ± 7 Ma for the first and second sequence, respectively, refute the hypothesis of a major sedimentation gap between the sequences, as recently proposed, and endorse an Ediacaran/Cambrian age for the SLF. If such gap does exist, it lies between the Sturtian cap carbonates and the sections with \'delta\'\'POT.13\' C around 0%o. These ages also indicate that the deposition of most of the Bambuí Group took place in a foreland basin, after the closure of the Adamastor Ocean which led to the edification of the Araçuaí Belt to the east of the SFC. The \'87 ANTPOT.Sr\'/ \'86 ANTPOT.Sr\' ratios obtained on the SLF carbonates contrast with the recently proposed Sr evolution curves, especially for the Cambrian, from where ratios higher than 0.7085 would be expected. It is possible that the SLF was deposited on a restricted eipiric sea and global correlations based on Sr isotopes are not reliable in such cases.

Anomalias biogeoquímicas expressivas têm sido reconhecidas em rochas marinhas neoproterozoicas depositadas em todos os continentes, não havendo similares ao longo do Fanerozoico. O interesse nesta Era aumentou nos últimos anos, especialmente em relação ao Ediacarano, período que precede a grande Explosão de Vida Cambriana e que abriga os primeiros organismos macroscópicos, conhecidos como Fauna de Ediacara. Assim, o entendimento das condições paleoambientais e paleoclimáticas, bem como o estabelecimento da cronologia dos eventos, é fundamental no entendimento da evolução da biota no planeta durante este período. As rochas da Faixa Paraguai Norte, na região de estudo, registram a ocorrência de duas glaciações, uma criogeniana e outra ediacarana (formações Puga e Serra Azul), separadas por uma espessa plataforma carbonática (Grupo Araras), que registra anomalias biogeoquímicas na água do mar ediacarano. Estas rochas foram depositadas na margem sudeste do Craton Amazônico, no intervalo de tempo entre a quebra do paleocontinente Rodínia e a colagem do Gondwana. O presente trabalho é apresentado na forma de artigos e apresenta estudos de: i) quimioestratigrafia isotópica (C, O, S e Sr) de detalhe nos carbonatos do Grupo Araras e da Formação Serra Azul; ii) proveniência (Sm-Nd) das rochas terrígenas das formações Puga e Serra Azul, bem como da base da Formação Raizama; e iii) geocronologia (Pb-Pb em carbonatos e K-Ar em clastos vulcânicos) da Formação Serra Azul. Os valores de \'delta\'\'POT.13 C\' evidenciaram duas anomalias negativas (ca. - 6%o) pósglaciais e um gradiente de até 2,5%o ao longo da bacia, no período interglacial. As razões \'ANTPOT.87 Sr\'/\'ANTPOT.86 Sr\' (entre 0.7074 e 0.7087) mostraram uma evolução coerente com a esperada para o oceano ediacarano. Os valores de \'delta\'\'POT.34 S\' obtidos nos sulfatos-traços dos carbonatos variaram de 22 a 61, enquanto que nas piritas variaram de 11 a 43%o, sendo os mais pesados já registrados no tempo geológico (acima de 48%o e 30%o, respectivamente). As idades modelo (\'T IND.DM\') Sm-Nd obtidas em rochas terrígenas das formações Puga, Serra Azul e Raizama encontram-se entre 1,6 e 2,2 Ga, mostrando contribuição variável, ao longo da seção, com predomínio de fontes localizadas a norte e a leste da bacia precursora da Faixa Paraguai. As idades K-Ar obtidas em clastos vulcânicos recuperados da Formação Serra Azul variaram de 730 a 1167 Ma, evidenciando uma fonte jovem, distinta do esperado para o Cráton Amazônico. A idade isocrônica Pb-Pb de 596 ± 26 Ma determinada em carbonatos da Formação Serra Azul corrobora sua correlação com a Glaciação Gaskiers, datada em 580 Ma.
Expressive biogeochemical anomalies have been recognized in Neoproterozoic marine rocks deposited worldwide, with no similar record throughout the Phanerozoic. The interest in this Era have been increased, especially on the Ediacaran time, the period that precedes the great CambrianLife Explosion, and houses the first macroscopic organisms, which are known as the Ediacaran Fauna. Thus, the understanding of paleoclimatic and paleoenvironmental conditions, associated with the establishment of the chronology of the events is crucial in the understanding the evolution of biota on the planet during this period. The rocks of northern Paraguay Belt in the study area record the occurrence of two glaciations, where one is Cryogenian and another is Ediacaran (Puga and Serra Azul formations). These glacial deposits are separated by a thick carbonate platform (Araras Group), which records biogeochemical anomalies in the Ediacaran seawater. These rocks were deposited in the southeastern margin of the Amazonian Craton, in the time interval between the breakup of the Rodinia Paleocontinent and the assemblage of the Gondwana. This work is composed by five articles, whose study scopes are: i) detailed isotope chemostratigraphy (C, O, S and Sr) in carbonates from the Araras Group and the Serra Azul Formation; ii) provenance (Sm-Nd) of the siliclastic rocks from the Puga and the Serra Azul Formations and the base of the Raizama Formation; and iii) geochronology (Pb-Pb in carbonate and K-Ar in volcanic clasts) from the Serra Azul Formation. The \'delta\'\'POT.13 C\' values showed two post-glacial negative anomalies (ca. - 6%o) and a gradient of up to 2.5%o along the basin, during interglacial period. The obtained \'ANTPOT.87 Sr\'/\'ANTPOT.86 Sr\' ratios (between 0.7074 and 0.7087) showed a consistent trend with that expected for the Ediacaran sea water. The trace sulfate extracted from obtained carbonates yielded \'delta\'\'POT.34 S\' values from 22 to 61%o, whereas the pyrites ranged between 11 and 43%o. These \'delta\'\'POT.34 S\' values are the heaviest ever recorded in geologic time (above 48 and 30, respectively). The Sm-Nd model ages (\'T IND.DM\') obtained from siliciclastic rocks from Puga, Serra Azul and Raizama formations range from 1.6 to 2.2 Ga, and indicate a variable contribution along the section, with predominant sources coming from areas at north and east of the precursor basin. Recovered volcanic clasts from the Serra Azul Formation yielded K-Ar ages between 730 and 1167 Ma, revealing a non expected young source for areas on the Amazon Craton. The Pb-Pb isochron age of 596 ± 26 Ma was determined in carbonates from the Serra Azul Formation and corroborates its correlation with Gaskiers Glaciation which was dated at 580 Ma.

Este trabalho objetiva a caracterização petrológica, geoquímica, geocronológica e metamórfica das rochas ortoderivadas pertencentes ao Complexo Metamórfico Brusque em duas regiões: Itapema e Botuverá, Santa Catarina, Brasil. Dos litotipos, destacam-se as exposições de rochas metamáficas e metaultramáficas, ocorrentes em ambas regiões. Em Itapema também foram investigados corpos de leucogranitos peraluminosos e na região da cidade de Botuverá foram investigados diques de diabásio e lamprófiro espessartítico. A análise das condições de geração e das fontes dos eventos magmáticos responsáveis pela geração destas rochas foi fundamental para a caracterização e avaliação do significado tectônico destas unidades no CMB, que foram posicionadas durante os períodos pré, sin e pós colisionais de evolução deste. A foliação regional do complexo é representada por uma S2 de baixo ângulo na região de Itapema e por uma superfície de mais alto ângulo na região de Botuverá, basculada por atuação da fase D3. Dados de geotermometria Hb-Pl indicam que a foliação principal dos xistos máficos foi gerada em condições da transição entre as fácies xistos verdes e anfibolito inferior. O magmatismo pré-orogênico do Complexo Metamórfico Brusque é constituído por lentes de rochas máficas-ultramáficas, produtos do metamorfismo de basaltos, gabros, rochas cumuláticas relacionadas e sedimentos vulcanogênicos. Estas rochas possuem afinidade toleítica e um elevado teor de ETR leves e elementos LILE. A análise de razões de elementos incompatíveis, a disposição dos corpos ígneos intercalados aos metassedimentos e a ausência de crosta oceânica sugerem que foram posicionados em ambiente tipo intra-placa continental, síncronos a sedimentação da bacia. Os valores iniciais de εNd entre -2.96 e 5.05 das rochas metavulcânicas de Itapema e entre -0.14 e -6.97 das rochas de Botuverá indicam a participação de crosta paleoproterozóica na gênese destes magmas. Os valores em geral elevados de 87Sr/86Sr justificam o envolvimento da crosta continental, e os valores mais altos encontrados em Botuverá, destacam o maior envolvimento deste componente na região. O magmatismo sin tectônico está representado por corpos de leucogranitos peraluminosos que mostram posicionamento concordante com a foliação S2. Os parâmetros composicionais destas rochas caracterizados pelas baixas razões K2O/Na2O, CaO/Na2O e LaN/YbN, os baixos teores de Rb, Sr, Zr, Y, Yb e Lu, são consistentes com uma evolução associada com magmas gerados a partir da fusão parcial de rochas crustais de composição pelíticas ricas em quartzo, com participação restrita de processos de diferenciação. Na região de Botuverá a ocorrência de diques de lamprófiros e diabásios que cortam as unidades metamórficas indica que seu posicionamento é pós-colisional. Geoquimicamente possuem afinidade entre as séries toleítica e shonshonítica. O padrão de distribuição dos elementos traços e as razões Th/Yb e Ta/Yb indicam que a extração dos diabásios ocorreu a partir de uma fonte mantélica enriquecida, com presença de rutilo e granada no resíduo e fortemente contaminada por crosta. Estas características são semelhantes às encontradas em rochas vulcânicas básicas pós-colisionais no sul do Brasil. Os dispersos valores de єNd(618) para os termos básicos, variando entre -13.74 e +5.52 destacam a heterogeneidade da fonte e reforçam a importância do componente crustal na geração destas rochas. Foi obtida uma idade concordante de 618 ±8.7 Ma (LA-ICP-MS) pelo método U-Pb em zircão, balizando a idade dos primeiros processos magmáticos pós-colisionais da orogênese brasiliana para a região de Botuverá.
This work objective the characterization of the petrology, geochemistry, geochronology and metamorphism of ortoderivate rocks that belong to Brusque Metamorphic Complex BMC) in two regions: Itapema and Botuverá, Santa Catarina, Brazil. Within these, good expositions of mafic and metaultramafic rocks occur in both regions. In Itapema, bodies of peraluminous leucogranites were also investigated. Around Botuverá were investigated diabase dikes and lamprophyres. The analysis of the conditions of generation and sources of magmatic events responsible for the development of these rocks was essential for the characterization and assessment of the significance of these tectonic units in the BMC, and it were placed during the pre-, syn-and post-collisional period of it’s evolution. The regional foliation of the complex is represented by a low angle S2 surface in Itapema region and a higher angle foliation in the region of Botuverá, folded by actuation of the D3 event. Petrography and Hb-Pl geothermometry data indicate that the main foliation of the mafic schists was generated in conditions between the transition of greenschist and lower amphibolite facies. The pre-orogenic magmatism of the Brusque Metamorphic Complex consists of lenses of mafic-ultramafic, products from the metamorphism of basalts, gabbros, related cumulate rocks and volcanogenic sediments. These rocks have a tholeiitic affinity and high contents of LREE and LILE elements. The analysis of incompatible elements ratios, the position of igneous bodies intercalated with the metasediments and the absence of oceanic crust suggest that the basalts were placed in an intra-continental plate environment, synchronous with sedimentation of the basin. The initial εNd values between -2.96 and 5.05 for the metavolcanics of Itapema and between -0.14 and -6.97 for the rocks of Botuverá indicate the involvement of Paleoproterozoic crust on the genesis of these magmas. The generally high 87Sr/86Sr values justify the involvement of crust, and the highest values found in Botuverá, highlight the greater involvement of this component in the region. Syn tectonic magmatism is represented by bodies of peraluminous leucogranite showing emplacement concordant to S2 foliation. Compositional parameters of these rocks characterized by low ratios K2O/Na2O, CaO/Na2O and LaN / YbN, low levels of Rb, Sr, Zr, Y, Yb and Lu, are consistent with magmas generated from partial melting of pelitic rocks, with limited participation of differentiation processes. In the region of Botuverá the occurrence of diabase dykes and lamprophyres cutting the regional metamorphic units indicates that its position is post-collisional. Geochemically show affinity between the tholeiitic and shonshonitic series. The distribution pattern of trace elements and the Th/Yb for Ta/Yb ratios indicate that extraction of diabase occur from an enriched mantle source, with the presence of rutile and garnet in the residue and heavily contaminated by crust. These characteristics are similar to those found in rocks post-collisional basaltic volcanic in south Brazil. The scattered values of єNd (618) in basic terms, ranging between -13.74 and +5.52 highlight the heterogeneity of mantle supply and reinforce the importance of crustal component in the generation of these rocks. A concordant age of 618 ± 8.7 Ma by U-Pb (LA-ICP-MS) zircon method were obtained, marking a early magmatic processes of post-collisional Brasiliano orogeny in the region of Botuverá.

Étude de la lithostratigraphie et des déformations de la région situé au nord-ouest du quadrilatère ferrifère de Minas Gerais. Elle présente deux séries supracrustales d'âge archeen et protérozoïque inférieur. Ce socle a été affecté par la mise en place de granitoïdes. Deux évènements de déformation majeurs sont relevés. Une étude isotopique permet de dater la différenciation crustale et l'orogénèse minas, les conditions pression-température du métamorphisme sont déterminées. Deux hypothèses sont envisagées pour expliquer une altération métasomatique remarquable dans le supergroupe de Rio Das Velhas

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.

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.

This item is only available electronically.
The Coompana Province between the Gawler Craton in South Australia and the Yilgarn Craton in Western Australia is one of the least understood geological regions in Australia. Recent work by Spaggiari and Smithies (2015) suggests that the known crustal precursors in the Coompana Province originated in a new crustal generation event at ca. 1900 Ma. This new juvenile crustal element then evolved through three distinct reworking and magmatic events at ca. 1610 Ma, ca. 1500 Ma, and between ca. 1192 – 1150 Ma (Wade et al., 2007; Spaggiari and Smithies, 2015). Dating of mafic volcanics underlying the Bight Basin in the south-eastern Coompana Province using the Sm-Nd mineral isochron method has revealed a fourth distinctive episode of mafic magmatism at ca. 860 Ma. The geochemical and Nd-isotopic signatures of ca. 860 ma mafic magmatism, including Nb and Ti anomalies, LREE enrichment, K-anomalies, and highly evolved εNd(860Ma) values between -9.9 and -12.7 provide evidence for assimilation and reworking of subduction/arc related Coompana Province crust. Magmatism at ca. 860 Ma in the Coompana Province was most likely coeval with widespread magmatism that occurred over Central and Southern Australia between ca. 800 – 830 Ma. Magmatism during this period was associated with the NE-SW directed intracratonic extension that resulted in the Centralian Superbasin and produced various suites of mafic volcanics and intrusives referred to collectively as the Willouran Basic Province. We suggest that the Willouran Basic Province now be extended to include the ca. 860 Ma mafic volcanics and intrusives in the south-eastern Coompana Province.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2015

This item is only available electronically.
The Chewings Range Quartzite is a meta-sedimentary cover sequence located in the Warumpi Province of the Arunta Region. U-Pb detrital Zircon analysis of the Chewings Range Quartzite indicates a minimum depositional age of ~ 1640Ma, with the main population of zircons residing within a range of 1700 – 1800Ma. Evidence from Sm-Nd isotopic data suggests that a series of Staurolite Garnet Schists, often grouped with the Chewings Range Quartzite, has a significantly more juvenile character. This suggests that it may represent a new unit with a significantly differing provenance to that of the Chewings Range Quartzite. Combined REE, geochemistry and detrital zircon dating suggests that the Chewings Range Quartzite was derived primarily off the Arunta Region and North Australian Craton, while the Stauralite Garnet Schists holds more affinity with juvenile Musgrave Province to the south.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2010

The Arabian-Nubian shield reflects the complex interplay between juvenile oceanic and continental arc fragments accreted during the final stages of Gondwanian super continental assembly. To date, much of the geochronological and geochemical data from the Arabian Shield, Saudi Arabia, is absent or poorly constrained and extrapolated from neighbouring Middle Eastern and African countries. Little attention has been paid to the petrogenesis and tectonic significance of the plutonic rocks pursuant to lithospheric orogenesis. A total of 137 samples from 26 geological units were collected from the Midyan, Hijaz, Asir, Tathlith, Afif, Ad Dawadimi and Ha’il terranes with particular emphasis on accretionary suture zone and within plate setting relationships. Extensive data bases are constructed using zircon U-Pb geochronology and Hf isotopes to evaluate Gondwanian significance and whole rock major and trace element geochemistry, Nd, Sm, Sr isotopes and zircon geochemistry to determine their petrogenetic properties. These parameters provide new insight into changing mantle conditions beneath collisional sutures (Yanbu, Nabitah and Halaban) and within plate asthenospheric upwelling. 19 granitic units are subdivided into metaluminous, peraluminous and peralkaline groups that possess distinguished island arc (~950-730Ma), syncollisional (~<730-636Ma), post tectonic (~<636-600Ma) and anorogenic (<600Ma) U-Pb geochronology. These magmatic phases represent accretionary cycles initiating from the dismantlement of Rodinia, closure of the Mozambique Ocean and final Gondwana amalgamation. Evidence for final assembly is recorded at ~525Ma (Najd fault reactivation) which is now the youngest dated magmatism in the Arabian-Nubian Shield and warrants repositioning of the regional unconformity at ~542Ma. Emplacement of sampled Arabian Shield classic A-type post-tectonic and anorogenic granitoids falls into three categories: 1) Intrude sutures immediately following collision which contain extensive mafic cumulate fractionation and N-MORB affiliation. 2) Plate boundary juxtaposed suites without obvious mafic cumulates, but posses contaminated N-MORB geochemistry. 3) Within plate granitoids isolated from plate boundaries and also without obvious mafic cumulates, but with a distinctive enriched (OIB) like asthenospheric mantle source. All categories produce similar felsic endmembers, but contain isotopically distinct mantle source. These are differentiated using a newly developed geochemical scheme (contaminated and enriched mantle granitoids) that is successfully applied to regional Arabian-Nubian examples. The diachronous Nabitah Orogenic Belt symbolises collision and subduction between western oceanic and eastern continental terranes that was terminated by the appearance of category 1 post-tectonic granitoids. This long lived (~50Ma) granitic magmatism contains mingling textures, discrete crystallisation ages, distinguished zircon morphologies and isotopically less juvenile mafics that geochronologically and geochemically reflect magmatic pulsing from a contaminated lower crustal MASH zone. The transition from N-MORB like mafics to isotopically enriched granitoids (isotopically similar to category 3 suites) reflects subduction magmatism followed by slab tear and asthenospheric influx. Conversely, the appearance of category 3 anorogenic plutons is characterised by widespread, tightly constrained (<10Ma) magmatism that is geochemically enriched, economic and symbolic of lithospheric delamination and asthenospheric (OIB like) upwelling. Differences between category 1, 2 and 3 zircon geochemistry constrain further contaminated and enriched mantle source behaviour that produces similar felsic products from distinguished petrogenetic processes. In summary, the work presented in this thesis establishes clear distinctions between accretionary syncollisional suites and anorogenic suites, but more significantly, post-orogenic plutons confined to suture zones from those confined to within plate settings. This allows new petrogenetic insights into changing juvenile mantle beneath the Arabian Shield.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2014