Made available in DSpace on 2014-06-11T19:26:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-10-10Bitstream added on 2014-06-13T19:54:21Z : No. of bitstreams: 1 fabianrosas_c_me_rcla.pdf: 1833154 bytes, checksum: 7f54453e4517cd519f2424843a053a1b (MD5) / A Jazida Fortaleza de Minas de níquel, cobre e cobalto localiza-se cerca de 6 km a sudoeste da cidade de Fortaleza de Minas (MG). Ela está inserida na Seqüência Morro do Niquel, do Greenstone Belt Morro do Ferro, na Faixa Fortaleza de Minas, ocorrendo no Cinturão de Cisalhamento Campo do Meio e apresentando os seguintes litotipos: Anfibólio Xistos, Serpentinitos, Formação Ferrífera Bandada e Talco Xistos. A mina é constituída por um corpo de sulfeto maciço explorado em uma cava de 1600 m de comprimento e 300 m de largura, atingindo a cota 940 no fundo do open pit e possuindo galerias nos subníveis 920, 919, 900, 870, 851, 833, 817, 801, 781 e 761. O corpo do minério ocorre em uma zona de cisalhamento transtensiva, sinistral (Santos 1996), onde o amendoamento dos corpos provoca uma variação na direção e no mergulho da foliação. Realizou-se uma análise dos elementos estruturais observados em superfície e subsuperfície, uma análise de strain e produziu-se um modelo tridimensional do corpo do minério. Os dados estruturais levantados em todos os subníveis, divididos em norte e sul, e excluindo-se os subníveis 900 e 761., mostraram que a foliação mantém o mesmo padrão em profundidade, isto é, elevado mergulho para SW com máximos em torno de 221/78 e padrão amendoado. Os dados de lineação mineral e de estiramento obtidos mostram que a lineação não é direcional, mas concentrada nos máximos de 137/54 e subordinadamente 326/49, isto é, com plunge respectivamente para SE e NW. A direção principal corresponde ao eixo X do elipsóide de deformação, e a segundária ao eixo Y, que também é de estiramento (Y>1), como revelado pela análise da deformação em quatro amostras de minério, que mostrou elipsóides de deformação finita oblatos, isto é, no campo do achatamento geral. Estes dados indicam uma movimentação oblíqua, sinistral, normal para a zona de cisalhamento na qual insere-se a jazida. / The nickel, copper and cobalt Fortaleza of Mines ore deposit is located about six km southwest of Fortaleza of Mines town, Minas Gerais. The mine is constituted of a body of solid sulfites which is explored in a digging of 1600 m of length and 300 m of width along the galleries of level 920, 919, 900, 870, 851, 833, 817, 801, 781 and 761. The mine levels are physically divided in northem and the southern sector by a small gallery, which is originated in the access ramp to the underground. The structural analysis of surface and underground data, strain analysis and a three-dimensional geometric model of the ore deposit confirmed its setting along a ductile sinistral transtensive shear zone, as previously mentioned in Santos (1996). Lenticular ore bodies and anastoming pattern provokes variation in the strike and dip of the foliation around a maximum of 221/78. Stretching and mineral lineations plunge preferentially to SW (maximum around 137/54) and secondarily to NW (326/49), which indicates the strong oblique character of the sinistral shear zone. The strain analysius of four deformed ore samples revealed finite strain ellipsoids of strong oblate shape and deformation in the flattening field, where the X axes is parallel to the main direction of the stretching lineations and Y, also of stretching (Y>1), is parallel to the secondary direction of the lineations.

Tese (doutorado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação em Geologia, 2017. / Submitted by Raquel Almeida (raquel.df13@gmail.com) on 2018-03-02T17:47:22Z No. of bitstreams: 1 2017_GuilhermedosSantosTeles.pdf: 18531341 bytes, checksum: ef2d4c53a511a11fdb0c544f636d7ccb (MD5) / Approved for entry into archive by Raquel Viana (raquelviana@bce.unb.br) on 2018-03-08T21:20:40Z (GMT) No. of bitstreams: 1 2017_GuilhermedosSantosTeles.pdf: 18531341 bytes, checksum: ef2d4c53a511a11fdb0c544f636d7ccb (MD5) / Made available in DSpace on 2018-03-08T21:20:40Z (GMT). No. of bitstreams: 1 2017_GuilhermedosSantosTeles.pdf: 18531341 bytes, checksum: ef2d4c53a511a11fdb0c544f636d7ccb (MD5) Previous issue date: 2018-03-08 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). / Desvendar os processos que modelaram a superfície do planeta Terra é um papel fundamental da Geologia. Entretanto, devido à antiguidade do nosso planeta, parte considerável de sua história foi obliterada do registro geológico, ou em diversos casos encontra-se profundamente modificada, ou reduzida a exposições isoladas ao redor do globo. Essa premissa é verdadeira tratando-se do registro da primeira metade da existência do planeta, ao longo da qual ocorreram mudanças significativas, que permitiram dentre outras coisas o surgimento da vida e a melhoria das condições de habitabilidade na superfície. O Estado da Bahia reúne em seu território algumas das rochas mais antigas do continente sul-americano, cuja história geológica se inicia no Paleoarqueano. Essas rochas estão localizadas na porção nordeste do Cráton do São Francisco e compreendem o embasamento Paleoarqueano do Bloco Gavião, o que torna essa unidade tectônica um interessante laboratório natural para avaliação dos processos e condições atuantes no planeta naquele período. Duas importantes sequências supracrustais do Bloco Gavião, o Greenstone Belt Mundo Novo e a Bacia de Jacobina, foram estudadas com o objetivo de investigar as condições paleoambientais vigentes durante a deposição dessas unidades (~ 3.3 Ga). Para tanto, foram utilizadas informações provenientes das análises in-situ dos múltiplos isótopos de enxofre (32S, 33S, 34S e 36S), e de elementos traço em sulfetos. A Bacia de Jacobina hospeda um depósito Au-(U)-pirita em camadas de conglomerados, similares ao da Bacia de Witwatersrand. Observações petrográficas indicam a ocorrência de pirita de origem sedimentar, tanto nos conglomerados (continentais) quanto nas amostras da seção marinha de Jacobina. A composição dos múltiplos isótopos de enxofre, reportados pelos valores de δ34S, Δ33S e Δ36S, sugerem que a atmosfera permaneceu empobrecida em O2 durante a deposição da bacia, apesar das recentes evidências de oxidação no Cráton do São Francisco ao final do Paleoarqueano. Entretanto, as amostras continentais e marinhas estudadas apresentam diferentes rotas para preservação das anomalias isotópicas Δ33S e Δ36S (MIF-S), evidenciando o controle ambiental na transferência dessas anomalias atmosféricas para a superfície. Além disso, os dados de elementos traço, em conjunto com as condições paleoambientais observadas na Bacia de Jacobina, sugerem acumulação singenética de ouro na bacia. O Greenstone Belt Mundo Novo possui mineralizações de metais base associadas a sulfetos maciços vulcanogênicos (VMS), formadas num intervalo de tempo cuja ocorrência desse tipo de mineralização é escassa. Logo, essas ocorrências permitem a avaliação dos sistemas hidrotermais marinhos no Paleoarqueano (3.3 Ga). Os dados dos múltiplos isótopos de enxofre indicam a assimilação de S atmosférico nas células hidrotermais. Entretanto, as fontes de enxofre são distintas entre os segmentos setentrional e meridional do greenstone. Ao norte, os sulfetos possuem composição isotópica similar aos depósitos paleoarqueanos de barita na Australia e África do Sul (Δ33S < 0), o que sugere a circulação de sulfato oceânico em uma bacia restrita; enquanto que ao sul (depósito da Fazenda Coqueiro) os sulfetos apresentam Δ33S > 0, assinatura indicativa de fonte sedimentar para o S. A distribuição dos elementos traço nos sulfetos correlaciona-se bem com cada fase analisada, e se assemelha com a partição conhecida em outros depósitos. Os dados isotópicos obtidos neste estudo são particularmente distintos daqueles publicados em VMS arqueanos, o que pode ter forte implicação no tamanho e potencial econômico desses depósitos. / Unraveling the processes that shaped the Earth’s surface is a fundamental role of Geology. However, due to the antiquity of our planet, a considerable part of its history has been obliterated from the geological record, or in several cases has been deeply modified, or reduced to isolated exposures around the globe. This premise is true regarding to the record of the first half of our planet existence, during which significant changes took place and allowed, among other things, the emergence of life and the improvement of habitability conditions for the surficial environments. Some of the oldest rocks of the South American continent are found in the Bahia State territory, whose geological history begins in the Paleoarchean. These rocks are in the northeast portion of the São Francisco Craton, and comprise the Paleoarchean basement of the Gavião Block, which makes this tectonic unit an interesting natural laboratory for evaluating the processes and conditions on Earth in that period. Two important supracrustal sequences of the Gavião Block, the Greenstone Belt Mundo Novo and the Jacobina Basin, were studied in order to investigate the paleoenvironmental conditions prevailing during the deposition of these units (~ 3.3 Ga). Therefore, we used information from in-situ analysis of multiple sulfur isotopes (32S, 33S, 34S and 36S), and trace elements in sulfides. The Jacobine Basin hosts Au-(U)-pyrite mineralization in conglomerate beds, similarly to the Witwatersrand Basin. Petrographic observations indicate the occurrence of sedimentary pyrite in the continental conglomerates and in samples from the marine section of Jacobina Basin. The multiple sulfur isotopic compositions, reported by the δ34S, Δ33S and Δ36S values, suggest absence of atmospheric O2 during the basin deposition, despite the recent evidence for oxidation at the São Francisco Craton in late Paleoarchean. However, the continental and marine samples present different routes for the preservation of Δ33S and Δ36S isotopic anomalies (MIF-S), evidencing environmental control in the transfer of these atmospheric signals to surface. In addition, the trace elements data, together with the paleoenvironmental conditions observed, suggest syngeneic accumulation of gold in the Jacobina Basin. The Mundo Novo Greenstone Belt has base metal mineralizations associated to volcanogenic massive sulfides (VMS) that were formed in a time interval characterized by the relative scarcity of these deposits. Thus, these occurrences allow the evaluation of Paleoarchean (3.3 Ga) marine hydrothermal systems. The multiple sulfur isotopes data indicate the assimilation of atmospheric sulfur in the hydrothermal cells. However, the S sources are distinct between the northern and southern segments of the greenstone belt. At north, the sulfides yield isotopic compositions similar to the Paleoarchean barite deposits in Australia and South Africa (Δ33S < 0), suggesting the circulation of oceanic sulfate in a restricted basin; while at south (Fazenda Coqueiro deposit) the sulfides present Δ33S > 0, a signature indicative of sedimentary source for S. The trace element distribution in sulfides correlates well with each phase analyzed, and resembles the known partition in other deposits. The isotopic data obtained in this study are particularly distinct from those published in Archean VMS, which may have a strong implication on the size and economic potential in these deposits.

O significado da idade do magmatismo, reconhecimento das séries magmáticas e ambientes tectônicos que controlaram a origem das rochas metavulcânicas do Greenstone Belt da Vila Nova (GBVN), é uma importante ferramenta para entender a evolução do Escudo das Guianas durante o Paleoproterozóico. Este trabalho apresenta novos dados geoquímicos de rochas metavulcânicas e de U/Pb em zircão (LA-MC-ICPMS), que foram suplementados por petrografia, dados estratigráficos e estruturais obtidos através de mapeamento geológico e descrição de furos de sondagem. Na região de Vila Nova, as unidades do GBVN repousam sobre o embasamento Arqueano composto por ortognaisses, metagranitos e anfibolitos do Complexo Tumucumaque. A base do GBVN é composta por metabasaltos e metabasaltos andesíticos, sotoposto por um domínio superior metassedimentar com rochas químico exalativas e metavulcânicas subordinadas. As rochas metavulcânicas incluem anfibolitos e anfibólio xistos, cujos corpos estão alongados segundo a xistosidade regional de direção NW-SE. A geocronologia pelo método U-Pb em zircão mostra uma idade de 2.154 ± 6 Ma para um meta-andesito da porção inferior do GBVN. O evento de metamorfismo orogênico esteve associado a três eventos deformacionais. Os eventos D1 e D2 formaram a xistosidade (S1), preservada como dobras intrafoliais (F2) e a clivagem de crenulação (S2), originadas a partir de movimentos de cavalgamento. O pico metamórfico (M1) está marcado pela assembleia plagioclásio+hornblenda+granada e, plagioclásio+hornblenda+diopsídio, indicando temperaturas entre 450 e 650 °C e pressão entre 4 e 6 kbares. Os metabasitos compreendem Fe-toleítos e Mg-toleítos com afinidade komatitica, composições geoquímicas enriquecidas em LILE e ETR e empobrecidas em HFSE (com anomalias negativas de Nb, Ti e P) e padrões de ETR semelhantes ao MORB. As características observadas indicam um magmatismo toleítico relacionado à bacias de retro-arco e arco de ilhas de 2.15 Ga no Escudo das Guianas. / The significance of the age of magmatism, magma series and tectonic settings that controls the origin of metavolcanic rocks of Vila Nova Greenstone Belt (VNGB) is an important issue in order to understand the evolution of Guiana Shield in Paleoproterozoic times. This work presents new U-Pb LA-ICP-MS geochronological and geochemical analyzes carried out on zircon grains and metavolcanic rocks of the Vila Nova greenstone belt (VNGB) which were supplemented by petrography, and stratigraphic and structural data acquired through description of boreholes and field work. In the Vila Nova region, the VNGB units rest on the Archaean basement composed of orthogneisses of the Tumucumaque Complex. The lower portion of the VNGB is composed of metabasalts and andesitic metabasalts, supported by an upper metasedimentary domain with exhalative chemical rocks and subordinate metavolcanic rocks. The metavolcanic rocks include amphibolites and amphibole schists, whose bodies are elongated according to the regional NW-SE schistosity. U-Pb zircon geochronology data showed an age of 2154 ±6 Ma for a meta-andesite of the lower portion of VNGB. Orogenic metamorphism event followed by three deformation events were recognized. The D1 and D2 events formed the schistosity (S1), preserved as intrafolial folds (F2) and the crenulation cleavage (S2), derived from thrust movements. The assemblages plagioclase + hornblende + garnet and plagioclase + hornblende + diopside define the metamorphic peak (M1-M2) with temperatures from 450-650 °C and lithostatic pressure between 4 and 6 kbars. The metabasites comprise Fe-tholeiites and Mg-tholeiites with komatiitic affinity, geochemical compositions enriched in LILE and REE and depleted in HFSE (with negative Nb, Ti and P anomalies) and MORB-like REE patterns. The observed features indicate an expressive magmatism related to back-arc basins and island arcs at 2.15 Ga in Guiana Shield.

Orientador: Elson Paiva de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-11T16:36:13Z (GMT). No. of bitstreams: 1 Costa_FelipeGrandjeanda_M.pdf: 10447471 bytes, checksum: c27e2dc3f77cf21b0841b3e40d6e57ae (MD5) Previous issue date: 2008 / Resumo: O greenstone belt do Rio Itapicuru é uma seqüência vulcano-sedimentar paleoproterozóica cortada por uma série de corpos plutônicos com idades entre 2160-2070 Ma. O Granodiorito Fazenda Gavião (GFG) é um corpo intrusivo em metabasaltos da porção ocidental do greenstone, próximo ao contato com o embasamento arqueano. Este pluton tem textura fanerítica média e hornblenda como mineral máfico dominante. Uma característica de campo é a presença de enclaves máficos magmáticos e diques máficos sinmagmáticos com evidências da mistura física de magmas (magma mingling). A analise geoquímica classifica o Granodiorito Fazenda Gavião como uma rocha intermediária (SiO2~63 wt%), com composição de granodiorito a quartzo-monzodiorito, da série cálcioalcalina de médio a alto-K, metaluminoso, espectro Terras Raras fracionado (razão (La/Yb)N = 22.81), alto Sr (900-800 ppm), alto Ba (1000-1500 ppm), e alta razão Sr/Y. Comparando com a geoquímica de outros plutons da área, o GFG apresenta assinatura dos elementos traço similar aos plutons alcalinos, sugerindo uma provável ¿consangüinidade¿ magmática entre estes plutons. A característica geoquímica dos diques máficos (appinitos) associados ao GFG é similar ao granodiorito em questão, porém com uma maior abundancia em Ba, Sr, MgO, Ni, Cr, K2O, e Terras Raras leves, sugerindo que estes diques são originados da fusão parcial de uma fonte mantélica enriquecida. O GFG apresenta semelhanças com rochas adakíticas e plutons TTGs, mas diferente destas rochas, apresenta maior conteúdo em K2O. É possível que o GFG foi originado pela fusão parcial de crosta máfica (crosta inferior?) (com granada e sem plagioclásio no resíduo) em função do acúmulo de magma máfico na base desta crosta (underplating of mafic magmas). O magma félsico gerado, provavelmente se misturou com uma pequena porcentagem do magma máfico, como é sugerido pelas feições de magma mingling observadas em campo. O GFG com idade de 2106 + 6 Ma (U-Pb SHRIMP em zircões) é mais jovem do que o magmatismo TTG/cálcio-alcalino (2163-2127 Ma) e é contemporâneo ao magmatismo potássicoultrapotássico (ca. 2110-2105 Ma) presente no contato embasamento-greenstone. O modelo de evolução geológica desenvolvido nesta dissertação sugere que os plutons ricos-em-K do greenstone belt do Rio Itapicuru são o registro da colisão de um arco oceânico com uma margem continental em ~2110-2105 Ma, precedendo outro evento colisional com retrabalhamento crustal em ~2080-2070 Ma / Abstract: The Rio Itapicuru greenstone belt is a gold-bearing Palaeoproterozoic volcanic-sedimentary sequence intruded by several granitic plutons in the time interval 2160-2070 Ma. The Fazenda Gavião granodiorite (FGG) is one of a set of plutons emplaced along the western boundary of the greenstone belt with the Archaean basement complex. The FGG is largely composed of a homogeneous coarse-grained hornblende granodiorite, occasionally crosscut by appinitic mafic dykes. Minor mafic enclaves and amphibolite xenoliths are common close to the contact with the host metabasalts. The FGG is a metaluminous medium-K to high-K calc-alkaline body with relatively constant silica abundances (SiO2 ~ 63-66 wt %). It shows fractionated REE patterns (LaN/YbN ~22), high Sr (900-800 ppm), high Ba (1000- 1500 ppm), and high Sr/Y ratios. Comparing with the geochemistry of other plutons of the area, the trace elements signature of the FGG suggests a probable magmatic consanguinity between this pluton and the alkaline plutons of the area. Similar geochemical characteristics of the FGG are observed in the associated appinitic dykes, which show relatively higher abundances of Ba, Sr, MgO, Ni, Cr, K2O, and the light rare earth elements, suggesting they derived from partial melts of an enriched mantle source. The FGG shares several geochemical characteristics with adakites and TTG plutons, but unlike these series it shows relatively higher K2O abundance. It is suggested here that the FGG originated from partial melts of the mafic lower crust (with garnet and no plagioclase in the residue) possibly triggered by underplating of mantle-derived, enriched mafic magmas, of which the appinitic mafic dykes may be a representative remnant. The granitic melt mixed with minor amounts of the appinitic magma, as suggest by magma mingling. The 2106 + 6 Ma-old (UPb SHRIMP in zircons) FGG is younger in age than the early (2163-2127 Ma) TTG/calcalkaline arc plutons of the greenstone, and is close-related in time to the young potassicultrapotassic plutons (ca. 2110-2105 Ma) emplaced along the basement-greenstone boundary. We suggest that the K-rich plutons in the Rio Itapicuru greenstone belt are the records of island arc-continent collision at ~2110-2105 Ma, preceding major continental rework and collision at ~2080-2070 Ma / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

Orientador: Elson Paiva de Oliveira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias / Made available in DSpace on 2018-08-12T03:34:56Z (GMT). No. of bitstreams: 1 Ruggiero_Alberto_M.pdf: 5764806 bytes, checksum: cdadd28e98d86c8738fcf5955bd71eea (MD5) Previous issue date: 2008 / Resumo: Novos dados geoquímicos nas rochas vulcânicas andesíticas e dacíticas da Unidade Maria Preta (UMP), Greenstone Belt do Rio Itapicuru, revelaram a presença de dois grupos geoquímicos distintos: um de rochas com afinidade adakítica e outro com caráter cálcio-alcalino. A suíte adakítica (ADK), localizada nas porções oeste da UMP, é caracterizada pelos altos valores de Sr/Y (Sr ~900 ppm, Y~5ppm); Na2O ~ 4,5ppm (K2O/Na2O ~0,3). É caracterizada também pelo enriquecimento de LILE (elementos litófilos de alto raio iônico) relativos aos HFSE (elementos de elevado potencial iônico) e também pelo moderado fracionamento dos elementos terras-raras (La/Yb ~ 12). A suíte cálcio-alcalina (CA) apresenta baixas razões Sr/Y (Sr ~ 170 ppm, Y~ 22 ppm), menor fracionamento de elementos terras-raras (La/Yb ~8) e anomalias negativas de Eu. No entanto apresenta maiores concentrações de elementos incompatíveis (Y ~22ppm, Zr ~142ppm, Th ~6ppm) e também Cr e Ni. Foi revelado, através de modelagem geoquímica que as duas suítes não se relacionam por cristalização fracionada. Contudo a suíte Adk apresenta indícios de cristalização fracionada de hornblenda enquanto que na CA a cristalização fracionada de plagioclásio desempenhou papel importante. O ambiente mais provável para a formação das rochas vulcânicas cálcioalcalinas é fusão em baixas profundidades da cunha do manto metassomatizado por fluídos liberados a partir de uma crosta oceânica subductada, seguida por fracionamento de plagioclásio. A geoquímica dos adakitos requer fusão de meta-basaltos hidratados em pressões elevadas, onde granada+hornblenda são estáveis e constituem o restito da fusão. Em geral, as rochas adakíticas apresentam indícios de pouca interação do magma original com uma coluna de manto peridotitico, como visto em adakitos atuais, dados os baixos valores de Cr e Ni em relação aos adakitos cenozóicos. A suíte cálcio-alcalina apresenta menores valores de fugacidade de oxigênio no sítio de extração do magma (entre -3 e -1 FMQ). Ao contrário, os adakitos apresentam maiores valores (entre -1 e +0,5 FMQ), semelhantes aos valores encontrados em adakitos modernos formados por fusão de crosta oceânica subductada. Dados de isótopos de Sm-Nd forneceram idades modelo TDM para a suíte adakítica de 2.213 a 2.010 Ma, com valores de eNdT de +3,9 a +1,7. A suíte cálcio-alcalina revelou idades modelo mais antigas, entre 2.330 e 2.279 Ma e menores valores de eNdT de +0,7 a + 1,3. Estes valores indicam magmatismo juvenil para ambas as suítes, porém com maior tempo residência crustal para a fonte das rochas cálcio-alcalinas, ou interação do magma com crosta mais antiga. Datação U-P SHRIMP em andesito adakítico revelou idade de cristalização de 2.081 ±9 Ma e a presença de zircões herdados arqueanos (3364, 3017, 3064 Ma), evidenciando que o magma gerado em zona de subducção interagiu com crosta arqueana, provavelmente o embasamento do Greenstone Belt do Rio Itapicuru, sugerindo então um provável arco continental como origem da Unidade Maria Preta. Esses dados sugerem que o vulcanismo intermediário a félsico do Greenstone Belt do Rio Itapicuru foi formado ou teve relação direta com subducção. Esta possivelmente teve uma vergência de leste para oeste, evidenciada pela zonalidade na geoquímica das rochas vulcânicas (adakitos à oeste e cálcio-alcalinas a leste). / Abstract: New geochemical data on andesites and dacites of the Maria Preta Unit, Rio Itapicuru Greenstone Belt, revealed two distinct geochemical groups: one of adakitic affinity and another of typical calc-alkaline. The adakitic suite, localized west in the unit, is characterized by high values of Sr/Y and Ti/YN >1. It shows enrichment in LFSE (Low Field Strength Elements) relative to HFSE (High Field Strength Elements) and a moderate rare earth element fractionation. The calc-alkaline suite (CA) shows low Sr/Y ratios, less rare earth elements fractionation and negative Eu anomalies. On the other hand it shows higher incompatible elements abundances (Y, Zr, Th) and high Cr and Ni concentrations. The two suites cannot be linked by fractional crystallization and are derived from different sources (distinct initial Nd ratios). The most probable setting for the formation of CA is partial melting of mantle peridotite modified by hydrous fluids released from a subducting slab, followed by low pressure plagioclase fractionation. The adakite geochemical features require partial melting of hydrous metabasalts at depths high enough to stabilize garnet+hornblende as the residual phase. This suite does not reveal significant interactions with the mantle, as shown by its lower Cr and Ni values than Cenozoic adakites. For an assumed 2170 Ma age, the Sm-Nd isotope data show higher eNd(t) for the adakites (+4,8 to +2,5) than for the calc-alkaline suite (+1,9 to +1,4). These data indicate a juvenile source for the UMP volcanic rocks. U-Pb SHRIMP dating indicates a crystallization age of 2,081 ± 9 Ma for the adakitic volcanic. Inherited Archean zircons (3364, 3017, 3064 Ma) evidence a magma generated at a subduction zone followed by interaction with Archean lithosphere, probably the basement of the Rio Itapicuru Greenstone Belt. The calc-alkaline suite shows low oxygen fugacities at the magma extraction site (between -3 e -1 FMQ). On the other side, the adakites shows higher values (between -1 e +0,5 FMQ), similar to modern adakites formed by a subducting slab melt. This results suggests that the UMP volcanism was formed or was directly connected to a subduction. The geographic position of the two suites, i.e. adakites to the west of the calc-alkaline volcanics, suggests subduction of an oceanic plate to the west. / Mestrado / Geologia e Recursos Naturais / Mestre em Geociências

The study area comprises the Archaean Manica Greenstone Belt and the Vumba Granite Gneiss, the Proterozoic Messica Granite Gneiss of the Zimbabwe Craton, the possibly allochthonous metasedimentary sequence of the Frontier Formation, the granitoids of the Mozambique Metamorphic Province, which are subdivided into Vanduzi Migmatite Gneiss, the Chimoio Granodiorite Gneiss, the Nhansipfe Granitic Orthogneiss and the Pan-African Tchinhadzandze Granodiorite Gneiss. The rock sequences in the two provinces are cut by mafic intrusions. The greenstone belt comprises mafic to ultramafic and pelitic schists and serpentinites of the Macequece Formation and metasediments ofthe M'BezaNengo Formation. The mafic to ultramafic schists and the serpentinites have chemical signatures of komatiites. The Vumba Granite Gneiss comprises the northern and southern Vumba granitoids dated at 3885±255 Ma, and 2527±632 Ma respectively. They vary from metaluminous to peraluminous, have normative QAP compositions of granodiorites and monzogranites and chemical signatures of mantle fractionates and volcanic-arc granitoids. The Early Proterozoic Messica Granite Gneiss is 2348±267 Ma old, is metaluminous and has QAP compositions of monzogranites and chemical signatures suggesting a crustal source and a volcanic-arc environment. The Frontier Formation comprises quartzite and pelitic schists. The Vanduzi Migmatite Gneiss comprises stromatic and stictolithic types. Two mineral assemblages are distinguished as they contain either garnet or hornblende. The Mid-Proterozoic Chimoio Granodioritic Gneiss is 1236±201 Ma old. It is granodioritic and metaluminous with a chemical signature of volcanic-arc granitoids. The Late Proterozoic Nhansipfe Granitic Orthogneiss is dated at 981 ±83 Ma and varies from metaluminous to peraluminous. The Rb, Nb and Y contents are typical of within-plate granitoids, whereas Ga, Zr, AI, Ce andY are typical of A-type granitoids. The age of the mafic intrusions falls between ~500 and ~11 00 Ma. The rocks typically contain plagioclase, hornblende and clinopyroxene with or without garnet and orthopyroxene. The chemistry of the rocks is typical of sub-alkaline tholeiites. The Tchinhadzandze Granodiorite Gneiss may be part of a Pan African event which lasted till ~450-~500 Ma. The normative feldspar compositions and Rb, Ba and Sr contents are typical of granodiorites. It is metaluminous and has Rb, Y and Nb contents typical of volcanic arc granitoids. The planar fabrics in the Archaean granite-greenstone belt are characterized by E-W to SW-NE strikes and steep dips to N and S and to NW and SE. The mineral lineations and fold axes plunge 60° and 30° respectively towards the E. Within the Mozambique belt, around the central part and in the extreme east of the study area, the planar fabrics have essentially N-S strikes and steep dips to E and Win contrast with complex deformation observed in the migmatites and megacrystic granitoids. The study area can be subdivided into three metamorphic blocks, namely, one of low-grade greenschist facies, one of medium-grade amphibolite facies and a third block of high-grade metamorphism. / Dissertation (MSc)--University of Pretoria, 2012. / Geology / unrestricted

Greenstone belts are dominated by volcanic rocks with lithogeochemical characteristics that reflect a range of possible geodynamic settings. Many analogies with modern tectonic settings have been suggested. Increasing exploration and comprehensive sampling of volcanic rocks in modern oceans provides the unique opportunity to characterize different melt sources from intraoceanic settings. This thesis examines geochemical data from more than 2850 submarine mafic and more than 2200 submarine felsic volcanic rocks, representing a wide range of settings. The results show significant geochemical variability spanning the full range of compositions of volcanic rocks found in ancient greenstone belts. This diversity reflects complex rift and spreading regimes, variations in crustal thickness, dry melting versus wet melting, mantle mixing and crustal contamination. Highly variable melting conditions are thought to be related to mantle heterogeneities, complex mantle flow regimes and short-lived tectonic domains, such as those caused by diffuse spreading, multiple overlapping spreading centers and microplate breakouts. Systematic differences in the volcanic rocks are revealed by a combination of principal components analysis and unsupervised hierarchical clustering. Rocks from most arc-backarc systems have strongly depleted mantle signatures and well-known subduction-related chemistry. This contrasts with rocks in Archean greenstone belts, which show no, or at least weaker, subduction-related chemistry and stronger mantle enrichment resulting from a less-depleted mantle, less wet-melting, and variable crustal contamination. The geochemistry of the modern volcanic rocks reflects lower mantle temperatures, thinner crust and subduction-related processes of present-day settings. However, rocks that are geochemically identical to those in Archean greenstone belts occur in many modern back-arc basins, such as the Lau Basin. Crustal growth and area-age relationships in the Lau Basin are similar to observed ages and compositions of volcanic assemblages in greenstone belts, such as the Blake River Group of the Abitibi Greenstone Belt. Such settings are recognized as favorable locations for volcanogenic massive sulfide (VMS) deposits, and therefore the particular geochemical signatures of the volcanic rocks are important for enhanced area selection in base and precious metal exploration.

The Round Lake Batholith is a composite granitic intrusion into the Archean metavolcanics of the Abitibi Greenstone Belt, Superior Province. The mafic metavolcanics are mainly high iron tholeiitic basalts of ocean floor origin. The intrusion of the batholith has metamorphosed the metavolcanics to amphibolite grade. Moving towards the contact there is no change in the metavolcanics grain size, but mineralogy changes quickly from the actinolite zone with relict pumpellyite to the hornblende zone. Field evidence as well as thin section and chemical analyses have shown that the dioritic appearing hybrid rock, near the contact, is a product of the mafic meta volcanics assimilation into the batholith. / Thesis / Bachelor of Science (BSc)

<p> Sulfide-poor platinum-group element (PGE) mineralization occurs within the Archean Boston Creek Flow ferropicrite, Abitibi greenstone belt, Canada. The PGE mineralization (∑PGE+Au = up to 1000 ppb) is manifest as metre-scale platinum-group mineral-bearing pods of disseminated chalcopyrite and pyrite (< 1 modal%) within titaniferous magnetite-rich gabbroic rock at the base of its central gabbroic layer. This mineralization is distinct in character from well known PGE mineralization associated with massive Fe-Ni-Cu sulfides at the base of komatiite flows at Kambalda, Western Australia and elsewhere. Exploration strategies presently used to search for PGE in mafic and ultramafic volcanic rock terrains are based on the geological and geophysical characteristics of sulfide-rich PGE mineralization. Consequently, refinements in exploration strategies are required if economic concentrations of sulfide-poor PGE mineralization are to be discovered in volcanic terrains.</p> <p> To begin development of such exploration criteria, ground-based magnetic and VLF surveys were conducted over the PGE mineralization along a single cross-section through the BCF. Drill core samples were collected along this transect to characterize the volume magnetic susceptibility and natural remanent magnetization (NRM) of the mineralization. Magnetic highs ranging in intensity from 64000 to 65000 nT were recorded for the base of the gabbroic layer, including mineralized outcrops. Susceptibilities of up to 9700 cgs and high remanence values with variable directions were determined. VLF, as expected, was not useful in identifying the mineralized horizons. The peridotite at the base of the flow appears to be the only conductive rock in the BCF.</p> <p> The magnetic highs associated with the base of the gabbroic layer define a positive anomaly that appears to be podiform in outline and up to ten metres in maximum dimension. This result suggests that the titaniferous magnetite-rich rock is itself podiform, like the enclosed PGE mineralization. This magnetic anomaly is not extensive enough to be evident on a regional scale aeromagnetic map as a separate anomaly within the BCF, and is not evident through VLF techniques. The rocks hosting the PGE mineralization is defined by the paleomagnetic results but this is not a practical field method.</p> <p> The geophysical characterization of the PGE mineralization host rocks, and of the BCF in general, demonstrates the potential of detailed magnetic and susceptibility mapping, together with petrographic and petrologic studies, in the search for economic PGE concentrations of sulfide-poor PGE mineralization in other volcanic and possibly plutonic rocks as well. Specifically, the results suggest that podiform magnetic anomalies within titaniferous magnetite-rich pyroxenites and gabbroic rocks may have potential use in the exploration for economic sulfide-poor PGE mineralization. Although the paleomagnetic methods used in this study are probably not of direct use in exploration, they were able to distinguish the different lithologies in the BCF. This substantiates the results of the susceptibility measurements in characterizing PGE mineralized, titaniferous magnetite-bearing rocks. The results of the paleomagnetic study also show that the NRM of the Ghost Range intrusive complex is not primary and therefore the Archean apparent polar wander path as it is currently defined is incorrect.</p> / Thesis / Bachelor of Science (BSc)

Den övergripande tanken med projektet är att ta reda på vad som hände på Västra Gräddmanhällan,utanför Kalix kust, för 2 miljarder år sedan. Det görs genom att ta reda på vad det är för bergarter ochstrukturer som hittats på området och hur de korrelerar till varandra. De två huvudsakliga delarna somprojektet fokuserar på är de stromatolitiska strukturerna som finns i de sedimentära bergarterna på VästraGräddmanhällan och de magmatiska intrusionerna som går genom de sedimentära bergarterna. De skaidentifieras med hjälp av tre olika metoder som ska komplettera varandra. Alla tre metoder kräver attprover från platsen hämtas till Uppsala Universitet där de kan slipas ned till tunnslip. Det kommer finnastotalt åtta prover tagna från olika stromatolitiska strukturer, både från land och Västra Gräddmanhällanoch två stycken tunnslip från de magmatiska intrusioner som tidigare antagits vara antingen kimberliteller lamprofyr. Alla tunnslip kommer att studeras i ett optiskt mikroskop och då kommer vissa tunnslipväljas ut för att undersökas i SEM och sedan Elektronmikrosond. Det finns vissa egenskaper i de olikabergarterna som är avgörande för resultatet. I de stromatolitiska strukturerna är spår av paleobiologiviktigt. De saker som kommer att kunna ge en indikation på tidigare liv i en stromatolit är bland annatorganiskt kol och pyrit. Fynd av antingen opaka mineral, organiskt kol eller andra intressanta struktureri det optiska mikroskopet kommer därför påverka projektets gång. För de magmatiska intrusionerna blirdet istället mineralsammansättning och eventuella karbonater som blir viktiga för hur synen på Sverigesgeologiska historia kommer se ut i fortsättningen. / The overall idea of the project is to find out what happened on the Western Gräddmanhällan, off thecoast of Kalix, two billion years ago. This is done by finding out what rocks and structures that are foundin the area and how they correlate to each other. The two parts that this project focuses on is thestromatolitic structures found of the Western Gräddmanhällan and the igneous intrusions that passthrough the sedimentary rocks. They must be identified using three different methods that willcomplement each other. All three methods require samples from the site to be brought to Uppsalauniversity and then be ground down to thinsections. There will be a total of eight thin sections takenfrom different stromatolitic structures, both from the coast and the western Gräddmanhällan and twopieces of thin sections from the magmatic intrusions that are already assumed to be either kimberlite orlamprophyre. All thin sections will be studied in an optic microscope and then certain thin sections willbe selected to be examined in SEM and then Electron Microprobe. There are certain properties in thedifferent rock types that are decisive for the result. In the stromatolitic structures, traces of paleobiologyare important. The things that will be able to give an indication of past life in a stromatolite includeorganic coal and pyrite. Findings of either opaque mineral, organic carbon or other interesting structuresin the optical microscope will therefore affect the progress of the project. For the magmatic intrusions,it will instead be the mineral composition and possible carbonates that will be important for how theview of Sweden's geological history will look in the future.