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

• Main Authors: Hiroo Kagami, Toshiaki Simura, Masaki Yuhara, Masaaki Owada, Yasuhito Osanai, Kazuyuki Shiraishi
• Format: Report
• Language: English
• Published: Graduate School of Science and Technology, Niigata University/Department of Geology, Niigata University/Department of Earth System Science, Fukuoka University/Department of Earth Sciences, Yamaguchi University/Department of Earth Sciences, Okayama University/National Institute of Polar Research 2003
• Subjects: Rb-Sr whole-rock isochron age; metamorphism; Sr isotopic homogenization; partial melting; fluids; closure temperature; Polar geoscience
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3130; http://id.nii.ac.jp/1291/00003130/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3130&item_no=1&attribute_id=18&file_no=1

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.