Características estruturais, petrográficas e geoquímicas de enxame de diques máficos intrusivo em rochas metassedimentares do greenstone belt de Crixás, Goiás

Abstract

Mafic dikes and stocks are a common feature in the Archean terrain of Goias, Central Brazil, where they occur as swarms of 2.3 - 2.5 Ga within the granite-gneiss complexes (2.8 e 2.7 Ga), as well as intrusions related to the komatiite and basalt flows of the greenstone belts lower stratigraphic units, but were unknown within the upper metasedimentary units. Detailed study of core sections from several drill-sites in the area of the Crixas greenstone belt gold deposits showed that dike intrusion occurred after the main Paleoproterozoic deformation and metamorphism of the metasedimentary units, and literature data indicate that the magmatic zircons from the dikes yielded an age of 2,170 ± 17 Ma. Petrographic and geochemical data show that they have the composition of epicratonic high-Ti diabases, which are similar to the large continental flood basalts of the Parana Basin. The age of the intrusions may be correlated with the short time-interval of the Rhyacian (2.20 to 2.17 Ga), during which successive localized episodes of mantle plume volcanism occurred on the Earth.