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K–Ar and 40 Ar/ 39 Ar phengite ages of Sanbagawa schist clasts from the Kuma Group, central Shikoku, southwest Japan
Author(s) -
Nuong Nguyen D.,
Itaya Tetsumaru,
Hyodo Hironobu,
Yokoyama Kazumi
Publication year - 2009
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/j.1440-1738.2008.00621.x
Subject(s) - phengite , schist , geology , clastic rock , metamorphic rock , lithology , pelite , geochemistry , petrology , paleontology , sedimentary rock , subduction , tectonics , eclogite
Conglomerates of the Kuma Group, central Shikoku, southwest Japan contain Sanbagawa schist clasts with a variety of metamorphic grades and lithologies. K–Ar and 40 Ar/ 39 Ar dating of phengite show all the pelitic schist clasts from low‐ to high‐grade zones have similar phengite ages (82–84 Ma) that are significantly older than those from the in situ Sanbagawa sequence of central Shikoku. This is because the Kuma–Sanbagawa sequence was exhumed earlier than the in situ Asemi sequence with an exhumation process intermediate between those for the Kanto Mountains and the in situ Asemi sequences. 40 A/ 39 Ar plateau ages (103 and 117 Ma) of phengite in amphibolites indicate the timing of the early stage of the exhumation of the metamorphic pile, probably close to the peak metamorphic age.