Archean nucleii and the distribution of kimberlite and related rocks in the São Francisco Craton, Brazil

Abstract

Available gravimetric data allow defining the low Bouguer gravimetric anomaly associated with the Paleoproterozoic continental plate, which contains the Sao Francisco Craton. The high anomalies that mark the border of the relative low gravimetric anomaly are related probably to hidden sutures and dense rocks remains formed during sea-floor spreading and deformed later on along Neoproterozoic colisional belts. Kimberlite mineral analyses allied to interpretation of magnetic, geochronological and surface geology data suggest the presence of thick lithosphere below Archean terrains observed in the northern and southern portions of the craton. Important volcanism represented by kimberlite, kamafugite and alkaline intrusive complexes of Early and Late Cretaceous ages is recorded at the south-southwest border of the Sao Francisco Craton, along the Neoproterozoic Brasilia fold belt. Morphostructural and magnetic data suggest that besides the NW-SE structural control of the Alto Paranaiba high, a NE-SW extensional system is associated with igneous intrusions in inner Minas Gerais. Electron microprobe data on minerals from kimberlite sampled in northern and southern Sao Francisco Craton indicate that they contain temperatures belonging to the diamond stability field were recorded in some specific areas. Recovery of micro- and macrodiamonds confirm the assumption.