ESTUDO GEOCRONOLÓGICO PELO MÉTODO Rb/Sr EM ROCHAS DO BLOCO JUNDIAÍ E REGIÕES ADJACENTES

EBERHARD WERNICK, MARCOS AURÉLIO FARIAS DE OLIVEIRA, KOJI KAWASHITA, UMBERTO GIUSEPPE CORDANI, JACQUES DELHAL

Resumo


Field and petrological data, as well as radiometric results performed in granulitic, gnaissic, migmatitic, and granitic rocks from the "Jundiaí tectonic block" (States of São Paulo and Minas Gerais), show for that region the existence of two suporposed orogeneses. To the older, of transamazonian age whole rock Rb-Sr isochron of 2,010 m.y. (Sr87/Sr86 initial = 0.702), belongs the Amparo Group, composed of gnaisses, migmatites, and granulites, with intercalation of quartzites, schists and calc-silicate rocks. To the younger, of brazilian age whole rock Rb-Sr isochron of 690 m.y. (Sr87/Sr86 initial = 0.706), are related the feldspathization and migmatization of the Amparo Group, as well as the intrusion of granitic bodies. Possibly, also the metassediments around Jacareí belong to the Brazilian cycle. This pattern of geologic evolution is similar to that observed for the Serra dos Órgãos region [States of Rio de Janeiro and Minas Gerais).


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