Discovery of a c.370 Ma granitic gneiss clast from the Hwanggangri pebble-bearing phyllite in the Okcheon metamorphic belt, Korea

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• 作者：Kazuhiro Suzuki ; Daniel Dunkley ; Mamoru Adachi ; Ueechan Chwae
• 关键词：Okcheon metamorphic belt ; CHIME dating ; Xenotime ; Monazite ; Hwanggangri Formation ; Pebble-bearing phyllite
• 刊名：Gondwana Research
• 出版年：2006
• 出版时间：January 2006
• 年：2006
• 卷：9
• 期：1-2
• 页码：85-94
• 全文大小：576 K

文摘

The chemical Th–U total Pb isochron method (CHIME) of dating was carried out on accessory minerals in samples from the Okcheon metamorphic belt in Korea. Dated minerals include xenotime and monazite with overgrown mantles in a granitic gneiss clast from the Hwanggangri Formation, metamorphic allanite in garnet-bearing muscovite–chlorite schist of the Munjuri Formation, and polycrase and monazite in post-tectonic granite from the Hwanggangri area. Overgrowth of mantles took place at 369 ± 10 Ma on c. 1750 Ma cores of xenotime and monazite in the granitic gneiss. Allanite, occurring in textural equilibrium with peak metamorphic minerals, yields a CHIME age of 246 ± 15 Ma that is discriminably older than the polycrase (170 ± 6 Ma) and monazite (170 ± 3 Ma) ages of the post-tectonic granite. These chronological data suggest that some of the metasedimentary rocks in the belt formed through a single stage of metamorphism at c. 250 Ma from post-370 Ma sediments. Late Permian age signatures have also been reported from the Precambrian Gyeonggi and Yeongnam massifs that border the Okcheon metamorphic belt, and indicate that parts of the basement massifs and the metamorphic belt were affected by the same regional metamorphic event.