Mesoproterozoic rapakivi granites of the Rondônia Tin Province, southwestern border of the Amazonian craton, Brazil — I. Reconnaissance U–Pb geochronology and regional implications

1999 ◽  
Vol 95 (1-2) ◽  
pp. 41-67 ◽  
Author(s):  
J Bettencourt
Keyword(s):  
2018 ◽  
Vol 3 (2) ◽  
pp. 54-73
Author(s):  
Elzio Da Silva Barboza ◽  
Anderson Costa dos Santos ◽  
Carlos José Fernandes ◽  
Mauro César Geraldes

The Paraguay Belt is composed by sediments deposited due to extensional events followed by inversion with deformation and magmatism and lastly collision of the Amazonian Craton and Paranapanema Block. The marine sedimentation, with Neoproterozoic ages, should have occurred in a continental shelf region, at about 800-550 Ma, when the closing of many oceans gave place to the amalgamation of the Gondwana supercontinent. Three areas were selected for this study which configuration define the perpendicular profile of the Paraguay Belt and allow the characterization of the main regional structures.The structural analysis in the sites here reported and surrounding areas allow suggesting that three deformational events are recorded in the rocks of this region. The sedimentary bedding S0, marked by alternations of dark gray and whitish coloration in the seritic phyllites is folded and the axial plane (Sn) is marked by a cleavage of ardosian. These surfaces are cut by two other deformations, Sn + 1 surface that plunges at high angles to SE as fracture cleavage and Sn + 2 that is orthogonal to the previous deformations and has NW-SE direction with vertical dips, where sometimes occurs quartz veins with high gold content. The Paraguay Belt fan geometry observed in the Sn foliation was developed during the closing of a Brazilian ocean that evolved between the Paranapanema Block and the Amazonian Craton. ResumoO Cinturão Paraguai é composto por sedimentos depositados durante eventos extencionais  seguidos de inversão com deformação e magmatismo e, por último, colisão do Craton Amazônico e do Bloco Paranapanema. A sedimentação marinha, com idades Neoproterozóicas, ocorreu  em uma região de plataforma continental, entre 800-550 Ma, quando o fechamento de muitos oceanos deu lugar à fusão do supercontinente Gondwana. Três áreas foram selecionadas para este estudo cuja configuração define um  perfil perpendicular do Cinturão do Paraguai e permite a caracterização das principais estruturas regionais.A análise estrutural nos locais aqui relatados e áreas adjacentes permite sugerir que as rochas do orógeno passou por três eventos deformacionais. O acamamento  sedimentar S0, marcado por alternâncias de coloração cinza-escura e esbranquiçada nos filitos e siltitos, é dobrado e o plano axial (Sn) é marcado por uma clivagem ardosiana. Estas superfícies são cortadas por outras duas deformações, Sn + 1 que mergulha em ângulos elevados para SE como clivagem de fratura e Sn + 2 que é ortogonal às deformações anteriores e tem direção NW-SE com mergulhos verticais, onde às vezes ocorrem veios de quartzo com alto teor de ouro. A geometria em leque  do Cinturão Paraguay observada na foliação de Sn foi desenvolvida durante o fechamento de um oceano brasileiro que evoluiu entre o Bloco Paranapanema e o Craton Amazônico.


Author(s):  
Nazaré A. Barbosa ◽  
Reinhardt A. Fuck ◽  
Valmir S. Souza ◽  
Elton L. Dantas ◽  
Stélio S. Tavares Júnior
Keyword(s):  

2009 ◽  
Vol 27 (2-3) ◽  
pp. 109-112
Author(s):  
Roberto Dall’Agnol ◽  
Reinhardt A. Fuck ◽  
Raimundo Netuno Nobre Villas

2016 ◽  
Vol 320 ◽  
pp. 75-87 ◽  
Author(s):  
Raquel Souza da Cruz ◽  
Carlos Marcello Dias Fernandes ◽  
Raimundo Netuno Nobre Villas ◽  
Caetano Juliani ◽  
Lena Virgínia Soares Monteiro ◽  
...  

Episodes ◽  
1999 ◽  
Vol 22 (3) ◽  
pp. 174-182 ◽  
Author(s):  
Colombo C.G. Tassinari ◽  
Moacir J.B. Macambira
Keyword(s):  

2017 ◽  
Vol 47 (3) ◽  
pp. 441-446 ◽  
Author(s):  
Cristóvão da Silva Valério ◽  
Moacir José Buenano Macambira ◽  
Valmir da Silva Souza ◽  
Elton Luiz Dantas

ABSTRACT: This paper approaches the record of SiO2-saturated potassic alkaline magmatism of Castanhal Quartz Monzonite, Mapuera Suite, and Ladeira da Vovó Quartz Syenite. These samples are located near the Northern border of the Amazon Basin. Such rocks show K2O + 2 > Na2O and K2O/Na2O < 2 values that confirm the potassic or shoshonitic character of these rocks. The Castanhal Quartz Monzonite contains less than 20% volume of quartz, which is also a characteristic of the shoshonitic or SiO2-satured potassic alkaline A-type magma signature observed on geochemical plots. Listric faults, representing the rifting phase of Amazon Basin formation, emplaced and reworked Ladeira da Vovó Quartz Syenite, which caused its granophyric texture, probably during the Tonian period. A group of 21 zircon crystals was extracted from a hornblende quartz monzonite and yields an average age of 1872 ± 6 Ma (MSWD = 2.4). However, an additional zircon crystal yielded a Trans-Amazonian age of 2062 ± 17 Ma. These potassic alkaline rocks of Orosirian (1872 Ma) age may correspond to a post-collisional setting. Dominantly negative εHft values and Hf TDM ages reveal a large contribution of a mafic crustal component from Mesoarchean to Neoarchean age (2.95 - 2.66 Ga), and a felsic crustal component from Neoarchean to later Siderian ages (2.51 - 2.34 Ga).


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