Plate tectonic settings for Precambrian basic rocks from Brazil by multidimensional tectonomagmatic discrimination diagrams and their limitations

摘要

Multidimensional discrimination diagrams (2006-2011) for basic and ultrabasic igneous rocks were applied to Precambrian rock suites from the Amazonian and Sao Francisco cratons, and the Tocantins Province, Brazil, to infer their possible tectonic settings. The chosen study cases in the Amazonian craton include the ca. 3.0Ga metabasalts of the Identidade greenstone belt, 1.87-1.80Ga Parauapebas anorogenic basalt-rhyolite dikes, 1.86-1.82Ga Rio Branco anorogenic gabbro-basalt association, ca. 1.76-1.74Ga Aripuana and Teles Pires intracratonic basalt-felsic volcanic associations, and 1.76-1.74Ga Jamari and 1.60-1.53Ga Serra da Providencia arc-related gabbroic rocks. In the Sao Francisco craton, we selected 1.48Ga arc-related amphibolites of the Rio Capim greenstone belt, continental mafic dikes of Uaua (2.6Ga), Curaca and Chapada Diamantina (1.5Ga), and Espinhaco (ca. 1.0Ga). In the Tocantins Province, ca. 3.0Ga komatiites associated with oceanic basalts of the Crixas and Guarinos greenstone belts were studied. The application of the diagrams generally provided consistent results with the authors' proposed tectonic settings based on field relationships and geochemical data. The exceptions are some within-plate (continental) mafic dikes and basalts for which our diagrams do not work well. For comparison, we also used two ternary and two bivariate traditional discrimination diagrams for the data from the Amazonian craton, whose results were poorer than the newer multidimensional diagrams.