Gnaisse Turvo: registro de magmatismo paleoproterozoico no Terreno Paraguá - sudoeste do Cráton Amazônico, Vila Bela da Santíssima Trindade, Mato Grosso

Abstract

The Turvo Gneiss, object of this work, corresponds to a polideformed orthogneiss exposed in the region of Vila Bela da Santíssima Trindade, southwestern of state of Mato Grosso. From the tectonic point of view, is inserted into the Amazon Craton and represents the Paleoproterozoic basement of the Paraguá Terrain, one of the crustal blocks that form the Province Rondonian-San Ignacio (1.55 - 1.3 Ga). Two facies were identified from petrographic study: garnet-amphibole-biotite gneiss composed of granodiorite and biotite-amphibole gneiss, more abundant, with granodioritic to syenogranitic composition. The metamorphic paragenesis identified characterizes as responsible for these gneisses of amphibolite facies. The structural analysis features two stages of deformation in ductil crustal level. The oldest (F1) is responsible for developing the gneissic banding, while the structures of phase (F2), the second oriented N30-60W indicate compressive stress with tectonic transport from SW to NE. The minimum age of crystallization of the Turvo Gneiss defined by Pb-Pb method on zircon evaporation corresponds to 1651 ± 4 Ma and is interpreted as emplacement age of igneous protolith. The data indicate that significant lithogeochemical calcium-alkaline magmatism of high K, metaluminous to peraluminous, associated with magmatic evolution in a subduction environment (Lomas Manechis Orogeny - 1.7 to 1.6 Ga), dominated the period Estaterian in the Paraguá Terrain. The orthogneissic unit studied was later reworked, metamorphic and tectonic (F2), during the San Ignacio Orogeny (1.4 to 1.3 Ga).