The 1.88 Ga Uatumã Magmatism in the Serra dos Magalhães region: petrology and implications to the extension of the south-eastern edge of the Amazonian Craton

Abstract

The Amazonian Craton (AC) is a Pre-Cambrian tectonic segment that extends over 4.3 × 10⁵ km² at the northern portion of the South American Platform. Phanerozoic sedimentary basins cover most of the edges of the AC and sparse occurrences of Precambrian rocks may aid the definition of its extension. One of these occurrences is the volcano-plutonic rocks that outcrop in the Serra dos Magalhães region, which relates to the Uatumã Magmatism, an expressive Orosirian magmatic event that constitutes a Siliceous Large Igneous Province. Effusive rhyodacites and rhyolites comprise the volcanic unit and the plutonic counterpart consists of epizonal monzogranites. Whole-rock geochemistry indicates an A2-type granite affinity to all magmatic rocks. Contrasting signatures suggest a magmatic evolution from a single stratified magma chamber. U-Pb zircon crystallization ages are 1870 ± 11 Ma for the rhyodacites, 1879 ± 5 Ma for the monzogranites, and a slightly younger age of 1863 ± 14 Ma for the rhyolites. Interpretation of satellite and geophysical images allows the recognition of regional lineaments in the Parecis and Bananal basins that suggest the extension of the AC up to the Tucurui Fault in the eastern portion (Bananal Basin) and up to the Brasnorte High in the southern part (Parecis Basin).

KEYWORDS:
volcano-plutonism; petrography; geochemistry; geochronology; Parecis Basin