Abstract
Geochronological, petrographic and lithochemical data have been used to characterize the crustal evolution and the thermochronology of the Costeiro Complex, Sao Paulo State, Brazil. This part of the Ribeira Fold Belt is composed of paraderived rocks to the East, and orthoderived rocks to the West, which are organized along a ductile shear zone forming a positive flower structure whose axis runs ENE-WSW. The main amphibolite occurrences are found within predominant garnet-paragneisses along this axis. The age of crystallization of the intrusive basic magmas which originated the amphibolites was 580 Ma (U-Pb SHRIMP). They formed tabular intrusions or secondary magma chambers, that locally still preserve continental tholeiitic geochemical characteristics. The close proximity of the basic magmatism and the metamorphic peak is evident from the 570 Ma, U-Pb age determination of the overgrowths on detritic zircon crystals in the paragneisses. This suggests a tectonic environment where the basic magmas intruded a back-arc sedimentary basin established over continental crust. The source areas were probably rocks differentiated from the mantle between the Paleoproterozoic and Neoproterozoic.
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