Japan Geoscience Union Meeting 2015

Presentation information

Oral

Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS30] Evolution of the Pelagic Realm

Tue. May 26, 2015 9:00 AM - 10:45 AM 304 (3F)

Convener:*Atsushi Matsuoka(Department of Geology, Faculty of Science, Niigata University), Toshiyuki Kurihara(Graduate School of Science and Technology, Niigata University), Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Tetsuji Onoue(Earth and Environmental Sciences, Graduate School of Science and Technology, Kumamoto University), Katsunori Kimoto(Japan Agency for Marine-Earth Science and Technology), Tatsuo Nozaki(Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology), Hayato Ueda(Department of Geology, Niigata University), Kenta Kobayashi(Department of Geology, Faculty of Science, Niigata University), Takashi Hasegawa(Division of Global Environmental Science and Engineering, Graduate School of Natural Science and Technology, Kanazawa University), Chair:Hayato Ueda(Department of Geology, Niigata University), Satoshi Takahashi(Department of Earth and Planetary Science, University of Tokyo)

9:30 AM - 9:45 AM

[MIS30-03] Stratigraphy and age of stratiform manganese deposits in the Chichibu Belt, Japan

*Yuki TOMIMATSU1, Tetsuji ONOUE1 (1.Earth and Environmental Sciences, Graduate School of Science and Technology, Kumamoto University)

Keywords:Chichibu Belt, stratiform manganese deposits, radiolarian biostratigraphy, Upper Triassic, Lower Jurassic, volcanic activity

The chert-hosted manganese deposits have been known to occur in the Triassic to Jurassic chert or chert-greenstone complex within a Jurassic accretionary complex, Chichibu Belt, southwest Japan. In order to reveal the specific age of the manganese deposits, this study investigated the occurrence and depositional age of the seven localities of manganese deposits (Taura, Tinu, Takahama, Kubodomari, Takahira, Kakinoo, Akimoto) in Saiki and Takachiho areas in the Chichibu Belt of eastern Kyushu.We also performed XRF analyses to infer the origin of manganese deposits.
Triassic and Jurassic radiolarian fossils were obtained from the 6 samples of the chert bed below the manganese deposits in the three localities (Takahama, Takahira, Akimoto). In Takahira locality, the manganese deposit occurs above the massive chert with akashiro silicastone. The red bedded chert above the manganese deposit yields radiolarian fossils such as; Trialatus longicornutus and Poulpus carcharus. These radiolarians show that age of manganese deposits can be correlated with the late Carnian age. In Takahama and Akimoto localities, the bedded chert above the manganese deposit is gray and occurs the Lower Jurassic radiolarian fossils (e.g., Trillus elkhornensis and Tricolocapsa plicarum). The XRF analysis revealed that the geochemical features of the manganese deposits in the study area is geochemically similar to the modern submarine hydrothermal manganese deposits. Consequently, manganese deposits in the eastern Kyushu were deposited by hydrothermal activity in an open-ocean setting around the late Carnian and Early Jurassic. The large volumes of flood basalts were erupted in the Carnian and Early Jurassic, and their ages are consistent with the depositional ages of the manganese deposits from the Chichibu Belt in eastern Kyushu.