Application of multi-dimensional discrimination diagrams and probability calculations to Paleoproterozoic acid rocks from Brazilian cratons and provinces to infer tectonic settings |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources and School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;1. School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China;2. Faculty of Life and Environmental Sciences, University of Tsukuba, Ibaraki 305-8572, Japan;3. Centre for Tectonics, Exploration and Research, University of Adelaide, Adelaide, SA 5005, Australia;4. Department of Geology, University of Johannesburg, Auckland Park 2006, South Africa;1. Universidade Federal de Minas Gerais, Programa de Pós-Graduação em Geologia, CPMTC-IGC-UFMG, Av. Antônio Carlos 6627, Pampulha, 31270-901 Belo Horizonte, MG, Brazil;2. Universidade do Estado do Rio de Janeiro, Faculdade de Geologia, MULTILAB, Rua Francisco Xavier, 524, Maracanã, 20550-900 Rio de Janeiro, RJ, Brazil;3. Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro, Morro do Cruzeiro, 35400-000 Ouro Preto, MG, Brazil;4. TU Bergakademie Freiberg, Institute of Mineralogy, 09596 Freiberg, Saxony, Germany;1. Inner Mongolia Key Laboratory of Magmatic Mineralization and Ore-Prospecting, Geological Survey Institute of Inner Mongolia, Hohhot 010020, China;2. School of Earth Science and Engineering, Sun Yat-Sen University, Guangzhou 510275, China;3. Key Laboratory of Computational Geodynamics, College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | In present work, we applied two sets of new multi-dimensional geochemical diagrams (Verma et al., 2013) obtained from linear discriminant analysis (LDA) of natural logarithm-transformed ratios of major elements and immobile major and trace elements in acid magmas to decipher plate tectonic settings and corresponding probability estimates for Paleoproterozoic rocks from Amazonian craton, São Francisco craton, São Luís craton, and Borborema province of Brazil. The robustness of LDA minimizes the effects of petrogenetic processes and maximizes the separation among the different tectonic groups. The probability based boundaries further provide a better objective statistical method in comparison to the commonly used subjective method of determining the boundaries by eye judgment. The use of readjusted major element data to 100% on an anhydrous basis from SINCLAS computer program, also helps to minimize the effects of post-emplacement compositional changes and analytical errors on these tectonic discrimination diagrams. Fifteen case studies of acid suites highlighted the application of these diagrams and probability calculations. The first case study on Jamon and Musa granites, Carajás area (Central Amazonian Province, Amazonian craton) shows a collision setting (previously thought anorogenic). A collision setting was clearly inferred for Bom Jardim granite, Xingú area (Central Amazonian Province, Amazonian craton) The third case study on Older São Jorge, Younger São Jorge and Maloquinha granites Tapajós area (Ventuari-Tapajós Province, Amazonian craton) indicated a within-plate setting (previously transitional between volcanic arc and within-plate). We also recognized a within-plate setting for the next three case studies on Aripuanã and Teles Pires granites (SW Amazonian craton), and Pitinga area granites (Mapuera Suite, NW Amazonian craton), which were all previously suggested to have been emplaced in post-collision to within-plate settings. The seventh case studies on Cassiterita-Tabuões, Ritápolis, São Tiago-Rezende Costa (south of São Francisco craton, Minas Gerais) showed a collision setting, which agrees fairly reasonably with a syn-collision tectonic setting indicated in the literature. A within-plate setting is suggested for the Serrinha magmatic suite, Mineiro belt (south of São Francisco craton, Minas Gerais), contrasting markedly with the arc setting suggested in the literature. The ninth case study on Rio Itapicuru granites and Rio Capim dacites (north of São Francisco craton, Serrinha block, Bahia) showed a continental arc setting. The tenth case study indicated within-plate setting for Rio dos Remédios volcanic rocks (São Francisco craton, Bahia), which is compatible with these rocks being the initial, rift-related igneous activity associated with the Chapada Diamantina cratonic cover. The eleventh, twelfth and thirteenth case studies on Bom Jesus-Areal granites, Rio Diamante-Rosilha dacite–rhyolite and Timbozal-Cantão granites (São Luís craton) showed continental arc, within-plate and collision settings, respectively. Finally, the last two case studies, fourteenth and fifteenth showed a collision setting for Caicó Complex and continental arc setting for Algodões (Borborema province). |
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| Keywords: | Discriminant-function based diagrams Log-ratio transformation Probability calculations Tectonic setting Brazilian cratons SINCLAS computer program |
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