New geochronological data for charnockitic rocks from Guaxupe association, Varginha Complex

Rb/Sr dating of granulites of charnockitic, sienitic, mangeritic, and enderbitic compositions from Sao Jose do Rio Pardo (Sao Paulo State) region, Varginha Complex, yielded late proterozoic ages. Single outcrop whole rock isochrons indicated 650±40, 660±125 and 550±55 Ma, with 87Sr/86Sr initial ratios of 0.7078, 0.7093, and 0.7114, respectively. Field petrographic and structural data indicate a complex evolution with anatexis and migmatite formation being the last important event, associated with the Brazilian ages, now determined. At this time, the hypersthene bearing rocks recrystallized, with the pyroxenes becoming relicts in a deformed matrix rich in perthitic microcline and plagioclase (oligoclase-andesine). Results of U-Pb age determinations in two zircon samples with an upper intercept of 780 Ma in a Concordia plot are presented and discussed