HR: 1340h
AN: T13C-0486    [Abstracts]
TI: Geology of the Tamanoura region, Goto Islands, Kyushu, Japan
AU: * Yamamoto, A
EM: yamayama@geo.kyushu-u.ac.jp
AF: Kyushu University earth, 6-10-1 Hakozaki Higashi-ku, Fukuoka, 812-8581 Japan
AU: Kiyokawa, S
EM: kiyokawa@geo.kyushu-u.ac.jp
AF: Kyushu University earth, 6-10-1 Hakozaki Higashi-ku, Fukuoka, 812-8581 Japan
AB: Goto Islands which located in western part of Japan has importance to recognize the connection between Japan Island and Asian Continent, and consider tectonic history. We did ditailed mapping in Tamanoura region, southwestern margin of Goto Islands to notice stratigraphy and deformations. Continuous outcrop, about 18km long and 100m high bluff, preserved along the coast. Tamanoura region is composed of green volcaniclastics, alternation of sandstone and mudstone (Goto Group), white rhyolitic volcanics from bottom to top and intruded granitic porphyry. Green volcaniclastics have approximately 1200m in thickness, and are composed of massive green tuff breccia and accretionary lapilli. The Goto Group has 650m in total thickness in this region, is composed of sandstone and shale which are shallow water deltaic sediment, and form 5 coarsening upward sequences. Basement of the Goto Group includes fragments of green volcaniclastics. The Goto Group and green volcaniclastics are separated by faults. White rhyolitic volcanics have approximately 850m in thickness, and are composed of volcanic body with flow structure and pyroclastics with several ten centimeters in size of gravel. The depositional age of the Goto Group was reported Early to early Middle Miocene by plant fossils by Kawada at el. (1994), but didnOt appear in this study region. White rhyolitic volcanics age is 12.4+-0.6Ma, and granitic porphyry has similar age, 13.2+-1.0Ma (Kawada at el. (1994)). Two stage deformations are identified as two types faults. D1) NE-SW trending, NW dipping normal fault(F1). F1 is identified alongside high angle dipping beds. D2) NE-SW trending right lateral strike-slip fault(F2) which divides this region into 7 blocks; Tanna, Tamanoura, Kawaraura, Otonase, Imochi, Ohsezaki, and Daiho blocks from north to south. Especialy one divides Imochi block and Ohsezaki block is NE-SW trending right lateral strike-slip fault, and its lateral displacement is estimated at more than 700m. These deformations truncate 13-12Ma rhyolite volcaniclastics. These results indicate that green volcaniclastics and the Goto Group deposited between rifting of Japan Sea(20-15Ma), rhyolitic igneous activity occured in 13-12Ma, and D1 and D2 timing identified after rifting of Japan Sea.
DE: 8000 STRUCTURAL GEOLOGY
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8486 Field relationships (1090, 3690)
DE: 9320 Asia
DE: 9604 Cenozoic
SC: Tectonophysics [T]
MN: Fall Meeting 2005