Amalgamation process of geological units in the Hida Belt-inferred from paleomagnetism and fission-track chronology.

1996 Fiscal Year Final Research Report Summary

• Project/Area Number: 06452096
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Geology
• Research Institution: HIMEJI INSTITUTE OF TECHNOLOGY
• Principal Investigator: MATSUDA Takaaki Himeji Institute of Technology, Science, Professor, 理学部, 教授 (50145827)
• Co-Investigator(Kenkyū-buntansha): KANO Takashi Yamaguchi University, Science, Professor, 理学部, 教授 (60108264) ; GOTO Atsushi Himeji Institute of Technology, Science, Assistant Professor, 理学部, 助手 (50211917) ; MORINAGA Hayao Himeji Institute of Technology, Science, Associate Professor, 理学部, 助教授 (40210182)
• Project Period (FY): 1994 – 1996
• Keywords: Hida belt / fission-track ages / paleomagnetism / Jiurassic granitoids / Cretaceous volcanic rocks / Yokoyama thrust

Research Abstract

1. Fission-track ages of the Jurassic Shimonomoto-type granitoids are determined as follows ; apatite : 39 to 49 Ma, zircon : 99 to 172 Ma, sphene : 121 to 146 Ma. These age data conbined with whole rock isochron Rb-Sr ages and hornblende and biotite K-Ar ages imply that the granitoids were rapidly cooled to 300ﾟC from their intrusion ages at about 200 Ma to 150 Ma and were slowly cooled from 150 Ma to the present in a constant rate.
2. Apatite and zircon fission-track ages of fault gauge breccia of the Yokoyama thrust which has been considered to be related to the thrust movement of the Hida Nappe on the Mino Belt, were determined. The apatite ages of granite blocks show about 40 Ma. The zircon ages of granite and sandstone breccia are 118 to 125 Ma and mixed ages from 140 to 180 Ma, respectively. These ages imply that temperatrue rised up to 110ﾟC and blow 240ﾟC during the thrust formation, and suggest that the thrust movement was continued was continued until the middle paleogene.
Paleomagnetic directions of the Simonomoto-type granitoids show shallow inclination (30ﾟ to 40ﾟ) and diverse declination. Their VGP distributes on a small circle around the North Pole to imply that the Hida area was situated at around 20ﾟ N in latitude during their intrusion or early cooling stages.
4. Paleomagnetic studies of Lat Crataceous to Early Paleogene volcanic rocks in and near the Hida Marginal Belt show largely easterly deflected declination, while those in the Mino Belt show that small easterly deflected declination. These data imply that ralative motion between the Hida Belt and Mino Belt occurred along the Hida Marginal Belt after the Cretaceous.