Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, 2007. / Submitted by Diogo Trindade Fóis (diogo_fois@hotmail.com) on 2009-10-14T18:31:31Z
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Previous issue date: 2007-03 / Esta dissertação reúne um conjunto de dados petrográficos, geoquímicos e geocronólogicos ID-TIMS U-Pb em zircão e de Sm-Nd em rochas da Série Acamadada Superior do complexo de Niquelândia no Brasil, bem como da Suíte Plutônica Kunene (SPK), no SW de Angola e NW da Namíbia. A similaridade de idades de cristalização Série Acamadada Superior do Complexo de Niquelândia de 1248 ± 23 Ma para (Pimentel et al. 2004) e da Suíte Plutônica Kunene com 1371 ± 2.5 Ma para (Mayer et al. 2004), bem como a similaridade litológica, gabro, troctolito, leucotroctolito e anortosito que caracterizam estes complexos motivaram esta pesquisa. Contudo, constatou-se que estes complexos são de natureza distinta e foram formados em ambientes distintos. A Série Acamadada Superior foi formada em um ambiente de crosta oceânica, similar ao N e T-MORB, enquanto que a Suite Plutonica Kunene foi formada a partir da coalêscencia de diversos pulsos magmáticos em ambiente extensional, anarogênico e intracontinental. O Complexo de Niquelândia é constituído por duas intrusões distintas conhecidas como Série Acamadada Inferior (800 Ma) e Série Acamadada Superior datada neste estudo por ID-TIMS U-Pb em zircão de gabronorito em 1245 ± 4 Ma e 780 Ma constatado em titanita metamórfica de meta-anortosito. Os valores positivos de eNd (T) indicam que a Série Acamadada Superior deriva de magma depletado e assinatura geoquímica similar ao N e T-MORB, sugerindo que a mesma foi formada em crosta oceânica. Estes novos dados contrastam com os apresentados para a Série Inferior de 800 Ma que apresenta valores de eNd (T) negativos, indicando que a mesma foi fortemente contaminada por material crustal mais antigo. Por outro lado, a Suíte Plutônica Kunene (SPK) no SW de Angola constituída essencialmente por uma suíte plutônica básica, caracterizada por intrusões gabro - anortosíticas e por uma suíte ácida constituída por "Granitos Vermelhos". Novos dados de ID-TIMS U-Pb em zircão de 1434 ± 2 Ma para leucogabro da intrusão Uanguembela, e 1403 ± 7 Ma para uma intrusão mangerítica ao sul de Otchindjau indicam que a suite básica é relativamente mais antiga que a suite ácida. Os valores negativos de eNd (T) das rochas básicas (-0.30 to -12.42) e ácidas (-0.67 to -11.02) indicam que a SPK foi submetida a diferentes graus de contaminação crustal. Contudo, alguns plutons máficos apresentaram eNd (T) positivo entre +0.67 to +1.12, sugerindo que estes magmas derivam de uma depletada. A suíte plutônica ácida é constituída por granitóides tipo - A, conhecidos genericamente como "Granitos Vermelhos", sugerindo que a Suite Kunene foi gerada em um ambiente intracontinental. A Suíte Plutônica Kunene é semelhante à Suíte Plutônica Nain (Labrador, Canadá) e apresenta potencial para hospedar depósitos magmáticos de Ni-Cu-PGE e Fe-Ti-V. _________________________________________________________________________________ ABSTRACT / This work presents petrographic, geochemistry and geochronologic data ID-TIMS U– Pb in zircon and Sm-Nd isotopic data of the Niquelandia complex Upper Series in Brazil, and of Kunene Plutonic Suite (KPS) located in SW Angola and NW Namibia. The similarities of U-Pb ages between the Niquelandia complex Upper Series with 1248 ± 23 Ma (Pimentel et al. 2004) and Kunene Plutonic Suite with 1371 ± 2.5 Ma (Mayer et al. 2004) and also the litologic similarities, both composed mainly by gabbro, troctolite, leucotroctolite and anorthosite rocks were the main reasons for this research investigations to find any relationship between them. However, this study found out that these Niquelandia complex Upper Series are quite different from Kunene Plutonic Suite. The age and tectonic significance of the Barro Alto, Niquelândia, and Cana Brava layered mafic–ultramafic complexes in Goias, central Brazil, have been a matter of debate and controversy during the last two decades. In many models, they have been considered to be representative of Paleoproterozoic intrusions metamorphosed during the Neoproterozoic, at approximately 0.79–0.76 Ga. In particular, the Niquelandia Complex has been described as formed by two different intrusions known as the Lower Series with 800 Ma and the Upper Series, of disputed age. New ID-TIMS U–Pb zircon data and Sm–Nd data presented in this study suggest that the Upper Series of Niquelandia Complex crystallized at 1245 ± 4 Ma and was metamorphosed around 780 Ma. The positive value of εNd (T) indicates that the original magma of the Upper Series derived from a strongly depleted mantle. Anorthositic rocks have positive Eu anomaly and gabbroic rocks have REE patterns similar to MORB. These new data reinforce the idea that the Upper Series of the Niquelandia Complex are of oceanic nature and, therefore, considerably different from the Lower Series which present negative εNd (T) values and trace element characteristics indicating extensive contamination with continental crust. The Kunene Plutonic Suite (KPS) in SW Angola and NW Namibia is one of the largest anorthositic complexes in the world, underlying an area of approximately 18.000 km2. It comprises a basic plutonic suite and an acid plutonic suite. The basic suite is mainly formed by gabbro-anorthositic intrusions and layered mafic bodies of different sizes. The acid suite includes mainly A-type “red granites”. This study presents new ID-TIMS U-Pb and Sm-Nd data as well as geochemistry and petrologic data for gabbroic, anorthositic and granitic rocks of the KPS. One sample of a layered gabbroic intrusion (Uanguembela) of the Otchinjau- Oncócua region was dated at 1434 ± 2 Ma. A mangeritic intrusion exposed to the east of the Otchindjau layered mafic intrusion yielded the U-Pb age of 1403 ± 7 Ma. These ages are slightly older than the age of ca. 1.37 Ga reported previously in the literature, suggesting that the Kunene Complex is formed by various plutons with different ages, indicating the existence of distinct magmas which underwent distinct cooling histories and crustal assimilation in multi-pulse gabbroic and anorthositic intrusions. The dominantly negative εNd (T) values of the basic (-0.30 to -12.42) and acid rocks (- 0.67 to -11.02) indicate that the KPS original mafic magmas has been contaminated by crustal material. However, some mafic plutons yielded positive εNd (T) between +0.67 to +1.12 which indicates that the magma of some mafic intrusions within the KPS derived from depleted mantle. The emplacement of the Kunene Complex requires an extensional setting and a significant thermal anomaly at the margin of the Congo Craton during the Mesoproterozoic. The Kunene Plutonic Suite resembles the large Proterozoic anorthosite plutonic suites such as the Nain Plutonic Suite (Labrador, Canada) and is, therefore, of great potential for Ni-Cu- PGE and Fe-Ti-V economic magmatic deposits.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.unb.br:10482/5685 |
| Date | 03 1900 |
| Creators | Baxe, Osmar Samir Serrão |
| Contributors | Pimentel, Márcio Martins, Ferreira Filho, Cesar Fonseca |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Source | reponame:Repositório Institucional da UnB, instname:Universidade de Brasília, instacron:UNB |
| Rights | info:eu-repo/semantics/openAccess |
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