Geologic evolution of the Serra dos Carajás, Pará, Brazil

Abstract

The Serra dos Carajas is located in southern Para, in the region between the Araguaia and Xingu rivers, and has been regarded very recently as the most promising and potentially interesting metallogenic province in South America. ln order to characterize its geologic evolution, a geochronological program was carried out by a cooperative effort of Docegeo and the CPGeo-USP, with the help of structural, petrologic and geological information. In the region, a polymetamorphic basement occurs in which gneisses arid related rocks are associated to the supracrustal rocks of the Salobo Formation. The iron formations and low grade metamorphics of the Grao-Para Group overlie the basement, and are covered by the sedimentary rocks of the Rio Fresco Formation. Post-orogenic and cratogenic granites occur, cutting through all the above mentioned units. The granitic rocks indicated Rb-Sr whole rock ages up to 1,850 m.y., K-Ar determinations on micas from the metamorphic indicated that the regional cooling occurred at about 1.950 m.y., after the main events of the Transamazonian orogeny. Some transamazonian results were also obtained on micaceous schists of the Salobo Formation. However, several analytical points, in a Rb-Sr isochron diagram, indicated a Late Archean age for their main rnetamorphic episode.