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 w ith the Paloproterozoic continental plate, which contains the São Francisco Craton. The high anomalies that mark the border of the relative low gravimetricanomaly are related probably to hidden sutures and dense rocks remains formed during sea-floor spreading and deformed later onalong Neoproterozoic colisional belts. Kimberlite mineral analyses allied to interpretation of magnetic, geochronological and surfacegeology data suggest the presence of thick lithosphere below Archean terrains observed in the northern and southern portions of thecraton. Important volcanism represented by kimberlite, kamafugite and alkaline intrusive complexes of Early and Late Cretaceousages is recorded at the south-southwest border of the São Francisco Craton, along the Neoproterozoic Brasília fold belt. Morphostructuraland magnetic data suggest that besides the NW-SE structural control of the Alto Paranaíba high, a NE-SW extensional system isassociated with igneous intrusions in inner Minas Gerais. Electron microprobe data on minerals from kimberlite sampled in northernand southern São Francisco Craton indicate that they contain temperatures belonging to the diamond stability field were recorded insome specific areas. Recovery of micro- and macrodiamonds confirm the assumption.