CONSIDERAÇÕES SOBRE A GEOLOGIA DA REGIÃO ENTRE PORTO NACIONAL E IPUEIRAS, GO

Abstract

The present study carried out in the area between Porto Nacional and Ipueiras (northern Goias) allowed to recognize several steps of its geologic evolution. 1. The Porto Nacional complex, Morro do Aquiles Formation, and Matanca Suite essemble the oldest rocks of the area. They represent strongly modified mafic/ultramafic, varied granitold, and supracrustal rocks, which were sheared, disrupted, and imbricated by progressive non-coaxial deformation, and metamorphosed and migmatized at high-amphibolite facies conditions. Taking into account the regional information, lhe deformation and metamorphic processes are linked to an event of collision tectonics of two crustal blocks (Brasilia and Araguacema), involving movements towards N-330 and oblique suture with N-30 direction. This event is presumed lo be of Late Archean (Jequie) age. 2. Besides these features, the mentioned rocks were also affected by younger transcurrent ductile shear zones, mainly with N-30 trend, which are interpreted as due lo mass rotation during the Early Proterozoic (transamazonian). 3. The granitoid of the Lajeado Suite (1.8 Ga) intruded those rocks and are viewed as anorogenic bodies. like acid intrusions of the eastem Amazonian region. 4. During the Middle Proterozoic-Ordovician interval, an intricated fault system was formed , mostly trending N-30 (Transbrasiliano Lineament). Also, an ensialic basin could develop and the filling rocks were weakly folded and metamorphosed (Natividade Group). 5. The Parnaiba Basin developed during the Ordovician-Jurassic interval in a stable tectonic setting: only the oldest sedimentary formations (Serra Grande and Pimenteiras ) are present in lhe area . 6. Gravity faults and diabase dykes of Jurassic-Cretaceous age formed during the South American Reactivation event. 7. The Cenozoic has been time of tectonic stability and lhe sediments of this age are correlative to morphogenetic episodes.