Evolução geológica da região de Tucuruí - Pará

Abstract

The northern part of the Araguaia Belt is exposed in the Tucuruí region and their stratigraphic, structural, metamorphic and magmatic features had been studied aiming at contributing for the understanding of the geological evolution of the area. The oldest stratigraphic unit of the area is represented by the Xingu Complex, composed by gneisses and granitos and subordinated schists and anphibolites. These rocks show evidence of a polycyclic metamorphic and structural history. Over this unit, during the niddle Proterozoic, the Tucuruí Group was developed. The bottom of this unit is composed by a sequence of tholeiitic basal-tic flows which were hera enclosed in the Caripé Formation. The Morrote Formation, is made up of graywackes, and constitutes the upper part of the Tucurui Group. The geossinclinal evolution of the Araguaia Belt took place during the Uruaçuano Cycle. This geotectonic unit is represented in the studied area by the Couto Magalhães Formation (Tocantins Group) which comprises pelitic and psamitic metasediments. These rocks show a greenshist facies metamorphism and structures generated by two phases of deformation in conditions of lower structures level. After the metamorphism of the Araguaia Belt, the Couto Magalhães Formation acted as the place of mafic and ultramafic intrusion and, lately, the Tucuruí Fault thrusted the metamorphic rocks of the Tocantins Group over the Tucuruí Group lithotypes. This faulting, besides generating a. series of structural features in the both groups as well as in the later migmatites, has also induced a dynamic metamorphic event into the rocks under green-schist facies conditions. Through the statistic treatment of structural data from the denso fault population which cuts the area, it was possible to deduce the shertening and the eterlding directiors related to the progressivo deformation induced by the thrust faulting had acted from E to W. Post-faulting mafic dykes represent the last magmatic event related to the Mesozoic Era. During the Cenozoic the area was a place of Tertiary sedimentation (Barreiras Formation), with sand, clays and conglomeratic levels. A final reactivation was responsible for the fracturing and faulting showed by the Barreiras Formation lithotypes Quatérnaty deposits mostly alluvial sediments, are the final units of the area.