Petrological And Geochemical Characteristics Of The Granulitic Terrain Of Brejses, Bahia, Brazil

Barbosa, Johildo Salomão Figueirêdo; Silva, Fernando Alves da; Sapucaia, Najara Santos; Iyer, Brijesh

doi:10.1016/s1342-937x(05)70850-9

Cited by 2 publications

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“…The southern Bahia granulitic domain consists of the Jequié block to the west and the Itabuna belt to the east. They are separated by an amphibolite-facies mafic to intermediate plutonic domain, with subordinate iron formation, aluminous gneisses and garnetbearing quartzites forming the Ipiau Band (Barbosa, 1990;Barbosa et al, 1998) (Fig. 3).…”

Section: The Southern Granulitic Domainmentioning

confidence: 99%

“…3). The country rocks of the domes consist of four distinct granulite types (SP, HG, CH1 and CH2 in chronological order) (Barbosa et al, 1998). A set of CH6 charnockites is intrusive in the previous ones and only found within the domes (Fig.…”

Section: Geological Setting Of the Brejões-santa Inês Areamentioning

confidence: 99%

“…Heterogeneous granulites mainly consist of dark green granulites with charnockitic characteristics that commonly contain boudins and enclaves of metagabbros, quartz feldspathic layers and supracrustal rocks (Barbosa et al, 1998). The heterogeneous granulites had as protolith plutonic rocks of amphibolite facies that were transformed to granulites by the regional metamorphism.…”

Section: Heterogeneous Granulite (Hg)mentioning

confidence: 99%

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Palaeoproterozoic dome-forming structures related to granulite-facies metamorphism, Jequié block, Bahia, Brazil: petrogenetic approaches

Barbosa

Martin

Peucat

2004

Precambrian Research

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Dome structures in the São Francisco craton (Northeast Brazil), have been identified in the regions of Brejões and Santa Inês within the granulitic Jequié block. Domes are mainly composed of CH6 charnockites, which intrude various granulites of the basement. The Brejões dome is surrounded by a rim of supracrustal rocks. The enderbite-charnockite suites CH1 and CH2, which are partially included in the basement and were previously dated ca 2.8-2.7 Ga, are similar to modern calc-alkaline suites and could be derived by partial melting of an enriched tholeiite (degree of fractionation ca 24-23%). An older Archaean component is suggested by negative ε Nd values at 2.8-2.7 Ga which range between −1 and −4 and Nd model ages with an average ca 3.1 Ga. These magmatic suites are ascribed to the amphibolite-facies based on preserved prograde mineral assemblages and results of geochemical modelling. The CH6 rocks formed in domes are of granitic composition. They mainly derive from partial melting of the 2.7 Ga CH2 basement suite. The hercynite-quartz assemblage in supracrustal rocks surrounding the Brejões dome suggests very high temperature (>1000 • C) for the CH6 magmas which would have induced partial melting in adjacent supracrustal rocks, forming garnet-cordierite-bearing granitic melts. Emplacement of domes is constrained by the age of the granulite facies metamorphism in the Jequié block (ca 2.1 Ga) and the average cooling age of monazite which occurred in the syn-dome charnockite and the surrounding heterogeneous granulites of the basement at 2045 ± 2.5 Ma. A southern dome exhibits a younger monazite age of 2026 ± 1 Ma, which may suggest a broader age span for the doming event.

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Section: The Southern Granulitic Domainmentioning

confidence: 99%

Section: Geological Setting Of the Brejões-santa Inês Areamentioning

confidence: 99%

Section: Heterogeneous Granulite (Hg)mentioning

confidence: 99%

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Palaeoproterozoic dome-forming structures related to granulite-facies metamorphism, Jequié block, Bahia, Brazil: petrogenetic approaches

Barbosa

Martin

Peucat

2004

Precambrian Research

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“…Entre trabalhos anteriores descrevendo essas rochas, podemos citar os de Cordani (1973), Pedreira et al (1975), Sighinolfi & Sakai (1977), Costa & Mascarenhas (1982) e Miranda et al (1985, sendo que poucos deles se basearam em estudos petroquímicos. Trabalhos mais recentes (Barbosa 1986(Barbosa , 1989Barbosa & Fonteilles, 1991;Barbosa et al, 1998;Barbosa & Sabaté, 2002 usando dados petroquímicos melhoraram, não somente o conhecimento das rochas da região, mas, também, evidenciou as principais feições tectônicas e metamórficas a elas associadas. Os litotipos do embasamento são representados por granulitos heterogêneos (rochas orto-e pára-derivadas), rochas chanockíticas, charnoenderbíticas, enderbíticas e gabro-anortosíticas do bloco Jequié, rochas orto-e pára-gnaíssicas associadas a anfibolitos da banda de Ipiaú e os metatonalitos associados a metagabros e os metamonzonitos do da parte sul do bloco Itabuna-Salvador-Curaçá.…”

Section: Introductionunclassified

Teores de potássio, urânio, tório e taxa de produção de calor radiogênico no embasamento adjacente às bacias sedimentares de Camamu e Almada, Bahia, Brasil

2005

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ABSTRACT.The bedrock adjacent to Camamu and Almada sedimentary basins is characterized mainly by rocks of granulite and amphibolite facies, with archean and paleoproterozoic ages, which belong to orogen Itabuna-Salvador-Curaçá. The units in major proportion in this context are the metatonalites associated with basic and metamonzonites belonging to Itabuna belt. In smaller area occur the Teolândia granite and the Moenda granodiorite associated with the Ipiaú band amphibolites, the charnockites and charnoenderbites of Jequié bloc, the neoproterozoic sienites and the mafic dikes. The K, U and Th contents of the rocks vary from 0,02 to 6,33% for K, from < 0, 2 to 9,10 ppm for U and from < 0, 4 to 64,38 ppm for Th. These contents are higher in the charnockites, Moenda granodiorite, Teolândia granite and sienites, intermediate in the metatonalites and metamonzonites and lower in the basic granulites. The heat production rates are higher in the lithologies where K, U and Th are also higher, varying from 0,58 to 5, 57 µW m -3 . The coverage areas of such lithologies are, however, small compared with that of the metatonalitic granulites, metamonzonitic granulites and sienites where the rates vary from 0,10 to 1, 44 µW m -3 , 0,23 to 5, 55 µW m -3 and 0,60 to 2, 24 µW m -3 , respectively. In this case, the heat production rates vary from 0,10 to 1, 44 µW m -3 . The basic granulites have the smaller rates, from 0,06 to 0, 36 µW m -3 . The observation of the lithologies in the margins of the two basins suggest that, in the bedrock under the younger sediments, may predominate the metatonalites, followed by the metamonzonites, with some significant participation of sienites in the Almada basin. In those lithologies, the volumetric heat production rates, with one standard deviation range, are 0, 41 ± 0, 30 µW m -3 for metatonalites, 0, 71 ± 0, 57 µW m -3 for metamonzonites and 1, 20 ± 0, 51 µW m -3 for sienites.Keywords: gamma-ray spectrometry, heat production in rocks, K, U and Th in rocks. RESUMO.O embasamento adjacenteàs bacias sedimentares de Camamu e Almadaé caracterizado, principalmente, por rochas das facies granulito e anfibolito, com idades arqueanas e paleoproterozoicas, pertencentes ao orógeno Itabuna-Salvador-Curaçá. As unidades em maior proporção neste contexto são os granulitos metatonalíticos associados aos granulitos básicos e metamonzoníticos pertencentes ao cinturão Itabuna. Em menorárea, tem-se o granito de Teolândia e o granodiorito de Moenda associado aos anfibolitos da banda de Ipiaú, os charnockitos e charnoenderbitos do bloco Jequié, os sienitos neoproterozóicos e os diques máficos. Os teores de K, U e Th nessas rochas variam de 0,02 a 6,33% para o K, < 0, 2 a 9,10 ppm para o U e < 0, 4 a 64,38 ppm para o Th. Esses teores são mais altos nos charnockitos, no granodiorito de Moenda, no granito de Teolândia e nos sienitos, têm valores intermediários nos metatonalitos e metamonzonitos e são mais baixos nos granulitos básicos. As taxas de produção de calor nessas rochas são mais altas onde os teores de K, U ...

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Petrological And Geochemical Characteristics Of The Granulitic Terrain Of Brejses, Bahia, Brazil

Cited by 2 publications

References 0 publications

Palaeoproterozoic dome-forming structures related to granulite-facies metamorphism, Jequié block, Bahia, Brazil: petrogenetic approaches

Palaeoproterozoic dome-forming structures related to granulite-facies metamorphism, Jequié block, Bahia, Brazil: petrogenetic approaches

Teores de potássio, urânio, tório e taxa de produção de calor radiogênico no embasamento adjacente às bacias sedimentares de Camamu e Almada, Bahia, Brasil

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