GEOLOGIA DA REGIÃO DE PORTO NACIONAL GO

Abstract (English)

Geological mapping and lithostructural studies have been carried out at the Porto Nacional region, northern Goiás State. Several units and features were recognízed related to the long-term evolution during the Archean-Middle Proterozoic interval, and to the Brasiliano reactivation and Phamerozoic development. The oldest units are the Porto Nacional Complex (acid to basíc granulítes, kinsigites, anorthosítes and leptínítes) and the Matança Suite (porphiroblastíc gnaissic granitoid), representatíve of Archean híghgrade and graníte-gneíss terraíns. These terraíns are part of two crustal blocks, juxtaposed seemly during the Jequié Event (ca. 2.5-2,8 Ga through a large ductile low-angle shear zone trending N 30E. The Morro do Aquiles Formation is the psamo-pelitic sequence of the Santo Antônio Fold Belt supposed to have been developed duríng the Transamazônico Cycle. It present metamorphism of high greenschist facíes and superposed deformations due to two or three phases. The granite and granophyre bodíes (Lajeado Suite) may be ínterpreted as transamazonian post-tectonic íntrusions (ca. 1.8 Ga)or cratonic manífestatíons aged 1.5-1.8Ga. The Natividade Group is a psamitic sequence with conglomeratic, pelitic and volcanic (?) intercalatíons, related to the Uruaçuano Cycle. The low greenschíst facies metamorphism and the Conceição Anticlimorium developed duríng the first sin-metamorphism folding phase are prominent features of this unit. Gentle folding wíth N40W subvertícal axial plane affected this sequence, as well as the Morro do Aquiles Formatíon and the Porto Nacional Complexo. The sedímentatíon of the ímature and red beds of the Monte do Carmo Formation, the íntrusion of dacíte and andesite dikes (ca. 1.1 Ga), the general cataclasís and assocíated low-grade recrystalizatíon, and the observed local crenulations, are related to Uruaçuano lateorogeníc intense faulting (Transbrasilian Lineament?). Diabase díkes frequently cut all the above Precambrian units. They are supposed to be related to fault reactivation and regional reheating of the Brasiliano Event (ca. 5OO Ma), and to the Mesozoic Wealdenian Reactívation, when most of the NE and NW faults were active. Silurian-Ordovician and Cenozoic sedimentary covers are present in the studíed area, indicating more stable periods of íts geolcgic history.