Resetting and closing codition of Rb-Sr whole-rock isochron system: some samples of metamorphic and granitic rocks from the Gondwana super-continent and Japan Arc

Abstract

The closure temperature of the Rb-Sr whole-rock system for felsic rocks has been generally considered to be ca. 700゜C, but it falls to ca. 400゜C, as a result of efficient action of fluids,especially H_2O. Thus,the Rb-Sr whole-rock ages obtained by rocks collected from a single outcropto specimen-size are not always coincident with those of emplacement of granitic magma or partial melting under high grade metamorphism.Although the Rb-Sr whole-rock isochron ages of metamorphic rocks collected from a wide area have been sometimes interpreted as those of metamorphism,careful consideration for these ages is needed