Evolução tectônica de um fragmento do Cráton São Francisco Meridional com base em aspectos estruturais, geoquímicos (rocha total) e geocronológicos (Rb-Sr, Sm-Nd, Ar-Ar, U-Pb).

This thesis present the results of gneisses, amphibolites, gabbronorite and gabbros from Claudio, Supracrustal and Mafic Fissural Units and displayimperative information for the evolution of the Campo Belo Metamorphic Complex (CBC) in the southern part of the Sao Francisco Craton. Using petrography,structural, geochemistryinwholerock, Rb-Sr and Sm-Nd in whole rock, Ar-Ar for amphibole and biotite, and U-Pb for zircons, we have provide important information about the timing and tectono-metamorphic historyfromthe Archaean to the Proterozoic. Based on petrographyfeatures, three distinct and anachronic metamorphic peaks were registered: the first, of highest metamorphic grade related to the granulite facies,is present in the rocks of the Gneissic Units and of the Amphibolitic Unit. The second, inthe amphibolite facies, is observed in the mafic-ultramafic and clastic-pelitic rocks ofthe Supracrustal Unit. The third is characterized by regional retrograde metamorphic processes, which reached the greenschist faciesand cover the whole region. The mainly and the most expressive structural pattern is characterized bya vigorous regional migmatization process and by the generation of the NE/SW Claudio Shear Zone, presenting dextral kinematic movement. The later expressive event isrepresented by a fissure mafic magmatismplaced in the NW-SE regional structures. For geochemistryanalyses werechosen gneisses from the three units: Claudio, Itapecerica and Candeias. Bycombining major and trace elements evidence it was possible to identifyelement losses caused by prograde dehydration in the gneisses rocks (essentially in the charnockites and enderbites). Those rocks displayrelative depletion insome of the most incompatible elements (i.e. Cs, Rb, U, Nb, Ta and W) inmulti-element spider diagrams. Some elements (i.e. Cs, Rb and U) have traditionally been considered mobile with fluids but we found that others (i.e. Nb, Ta, W), which are often considered immobile, are also deficient in our samples. The geochronological results of gneiss, amphibolites, gabbronorite and gabbros displayed results at about 2.9-2.7 Ga (U-Pb), 2.6 Ga (Rb-Sr),2.05 Ga (U-Pb), 2.0-1.9 Ga (Ar-Ar), 1.7 Ga, 1.0Ga (Ar-Ar), 0.5 Ga (U-Pb). Combining each of these results with petrography, structural and geochemistryrecords it was possible to make link toa distinct tectonic episode that might took place in the Campo Belo Metamorphic Complex as follow: 2.9-2.7 Ga event is correlated to the protolith age, the 2.6 Ga is linked to the metamorphic age and might be associated to the deformational event responsible for the dextral strike-slip Claudio shear zone. The 2.05Ga correspond to high-grade metamorphic event as attested by U-Pb data for charnockites. It is the peak ofthe prograde metamorphic event that achieves the granulite facies metamorphismfollowed by charnockiteformation. Asa consequence, the ages at about 2.0-1.9Ga can be correlatednot onlywith the age of exhumation of the CBC but the age of the retrograde metamorphic processes fromthis high-grade metamorphic event at about 2.05 Ga. The data suggests that the CBC was largelyand quicklyexhumedafter the 2.05Ga metamorphic event. The ages at about 1.7 and 1.0Ga can be correlated to the emplacement and crystallization of the two swarmdykes. The NW-SE structures into which these swarmdykes were emplaced can be correlated withthe Staterian continental rift scenario (1.8-1.6Ga). The latest thermal evidence in the CBC is the emplacement of the ~1.0Ma gabbros, emplaced in preexisting NW-SE structures and can be correlated to the Macaubas rift. The results displayed in this studystand for the final stabilization of the CBC that happened in the Mesoproterozoic and not in the Achaean. The 0.5 Ga correspond to no more than the disturbance of the systemattested in the U-Pb date. The new dataplaced imperative information on the tectonic evolution in the Campo Belo Complex which appears comparable in manywaysto the others Archaean continental crust.