K–Ar and 40Ar/39Ar phengite ages of Sanbagawa schist clasts from the Kuma Group, central Shikoku, southwest Japan
Article first published online: 3 JUN 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Asia Pty Ltd
Volume 18, Issue 2, pages 282–292, June 2009
How to Cite
Nuong, N. D., Itaya, T., Hyodo, H. and Yokoyama, K. (2009), K–Ar and 40Ar/39Ar phengite ages of Sanbagawa schist clasts from the Kuma Group, central Shikoku, southwest Japan. Island Arc, 18: 282–292. doi: 10.1111/j.1440-1738.2008.00621.x
- Issue published online: 28 MAY 2009
- Article first published online: 3 JUN 2008
- Received 29 May 2007; accepted for publication 30 January 2008.
- 40Ar/39Ar age;
- argon closure system;
- exhumation tectonics;
- K–Ar age;
- Kuma Group;
- Sanbagawa schist clasts
Conglomerates of the Kuma Group, central Shikoku, southwest Japan contain Sanbagawa schist clasts with a variety of metamorphic grades and lithologies. K–Ar and 40Ar/39Ar 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. 40A/39Ar 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.