Geologia, geoquímica e geocronologia da suíte intrusiva Serra do Baú : ênfase no Gnaisse Rio Fortuna - Terreno Paraguá, SW do Craton Amazônico – Brasil

Abstract

The paleoproterozoic basement of the Paraguá Terrane is constituted by three main litoestratigráficas units defined originally for Litherland et al. (1986), as: Chiquitania Gneissic Complex, San Ignacio Schist Group, Lomas Manechis Granulitic Complex). In Brazilian territory the gneiss orthoderivative Chiquitania type, corresponds to the Intrusive Suite Serra do Baú, Ruiz (2005), while the granulitic lithotype are rare and of small dimensions. Giving to bigger include on Rio Fortuna Gneiss that constitutes part of the Intrusive Suite Serra do Baú, as well as the other intrusions correlates in the region of Fortuna Headquarters (BR), the Retiro Gneisses, Retiro I and Córrego Vermelho. In bolivian territory gneisses studied is correlatos to gneisses of type B, dominant orthoderivative, of the Chiquitania Gneissic Complex de Litherland et al. (1986). Initially called as Água Branca Gneiss, Jesus and Assis (2006), the fact of this body to correspond to a prolongation, in Brazilian territory, of the Rio Fortuna Gneiss described in Bolivia for Litherland et al. (1986), were opted to using this original denomination. The data set of field folloied for the petrographic, geochemical and geocronological analyses (U-Pb in zircon) had demonstrated that to the Paraguá Land in the conception of Ruiz (2009) and Bettencourt et al. (2010) it extends in Brazilian territory in the region of the Detachment Fortuna. In this region it was identified composed to a paleoproterozoic basement for granulit and amphibolites (xenoliths) that they had served of calkalcaline lithologies for gnaiss of acid composition the intermediate bunched in the Intrusive Suite Serra do Baú. Three metamorphic events, of barrovian nature, associates to the deformation phases had been identified. The first one corresponds to the regional metamorphism of facies granulit, with performance during the Orosiriano period, that generated gneissic banding in the Intrusive Suite Serra do Baú. As, characterized for a regional metamorphism of facies Amphibolite, taken the effect in the Ectasiano period, that is responsible for the deformation and banding gneissose of the Intrusive Suite Serra do Baú and gneissification of the Tarumã unit. E third, represented for the paragenesis of grenschist facies and retrometamorphism, developed in the period Esteniano/Toniano, associates to the clivagem of crenulation in both gneiss and deformation of the Aguapeí Covering.