GEOMETRIA DE GREENSTONE BELTS ARQUEANOS DA REGIÃO DE RIO MARIA (SUDESTE DO PARÁ, BRASIL), A PARTIR DE INTERPRETAÇÃO GRAVIMÉTRICA

Abstract

The aim of this paper is to discuss the geometric and tectonic aspects of the granite-greenstone terrain located in the Rio Maria region, SE Para, Brazil. It is based on the correlation of surface geological data and a gravity profile observed between Rio Maria and Xinguara towns. The gravity profile shows two highs related to the Serrinha and Identidade greenstone belts. The former has a flat shape, while the later one behaves as an assymetric synformal body with southern its flank plunging slightly toward the north. The continuity between these two bodies suggests that, originally, the Serrinha and Identidade belts were connected and belonged to a single unit that was subsequently divided by the forceful intrusion of the surrounding granitoids. The gneissic terrains observed in the northern part of the Identidade area owe their geometry, probably to listric faults reaching the base of the continental crust The geometric and tectonic constructions show that the two greenstone belts can be figured by different two-dimensional shapes, but they are restricted to the shallow part of the continental crust; their depth never exceeds 5 km. On the other hand, the thickness of the late Archean crust reached at least 18 km at the time of the metamorphic event