Signification structurale des anomalies gravimetriques de la partie sud du craton de Sao Francisco (Bresil)

Abstract The relationships between the cratonic area and orogenic belts of the southern part of the state of Minas Gerais (Brazil) are analyzed using data from a recent Bouguer anomaly map. The interpretation was carried out using inverse-anomaly approach and statistical analysis. The stable area is characterized by elongate anomalies trending NNE-SSW which correspond to a higher level of the basement under the upper Precambrian sedimentary cover (Bambui and Macaubas groups). They can be related to rejuvenated NNE-SSW-trending fractures. The gravity trends are either deformed or interrupted over the Brasilian fold belt where an important negative linear anomaly is present. This anomaly is produced by a thick sequence of folded sedimentary or metasedimentary terrains which can be interrupted as miogeoclinal units. The Alfenas mobile belt is characterized by a strong positive anomaly, probably associated with heavy infracrustal rock complexes (granulites, charnockites). A crustal thickening, probably associated with a pre-Brazilian continental collision, can be inferred from a long-wavelength linear negative anomaly.