Well-preserved Late Paleoproterozoic volcanic centers in the Sao Felix do Xingu region, Amazonian Craton, Brazil

The Amazonian craton in the Sao Felix do Xingu city, southeast region of the Para state, north of Brazil, hosts exceptionally well-preserved Paleoproterozoic bimodal magmatic units grouped in the Sobreiro and Santa Rosa formations. These formations are correlated to the Uatuma magmatic event, which is largely distributed in the Amazonian craton occupying more than 1,500,000 km(2). Geological mapping and petrographical observations reveal distinct spectra of volcanic facies in both formations. The basal calc-alkaline Sobreiro Formation is composed mainly of andesitic and dacitic lava flows and associated volcaniclastic facies of autoclastic origin, with subordinate pyroclastic flow deposits. This formation shows inferred eruption style that is similar to those in Flood Basalt Provinces, with rare scutulum-type lava shields. The upper A-type Santa Rosa Formation was generated by multicyclic explosive and effusive episodes predominantly associated with large fissures and is materialized by voluminous ignimbrites with subordinated ash-fall tuff, crystal tuff, lapilli-tuff, co-ignimbritic breccias, rhyolitic dikes and domes, and associated granitic porphyries and equigranular granitic intrusions. Ignimbrite and rhyolite dikes reveal conspicuous vertical flow pattern pointing to a fissure-controlled eruption, similar to Sierra Madre Occidental ignimbrite province. The proposed evolutionary model for the Sao Felix do Xingu units differs from those of other occurrences related to the Uatuma magmatic event in the Amazonian craton, characterized by predominance of A-type volcanism and contemporaneous granites. (C) 2010 Elsevier B.V. All rights reserved.