1994 Fiscal Year Final Research Report Summary
Study on Neotectonics of Kyusyu
| Project/Area Number |
05453001
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Geology
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| Research Institution | Kumamoto University |
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Principal Investigator |
MURATA Masafumi Kumamoto University Faculty of Science Professor, 理学部, 教授 (00004309)
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| Co-Investigator(Kenkyū-buntansha) |
TOYOHARA Fujio Kumamoto University Faculty of Science Lecturer, 理学部, 講師 (20011752)
IWASAKI Yasuhide Kumamoto University Faculty of Science Professor, 理学部, 教授 (40013750)
ITAYA Tetsumaru Okayama University of Science Natural Science.R.I.Professor, 自然科学研究所, 教授 (60148682)
HASE Yoshitaka Kumamoto University Dept.of General Ebu.Associate Professor, 理学部, 助教授 (40040109)
OBATA Masaaki Kumamoto University Faculty of Science Professor, 教養部, 教授 (20126486)
ODA Motoyoshi Kumamoto University Faculty of Science Professor, 理学部, 教授 (60108454)
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| Project Period (FY) |
1993 – 1994
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| Keywords | Kyusyu / Miyazaki Group / Biochronology / Radiometric age / Hisatsu volcanic province / Volcanic stratigraphy / Yatsushiro-Kai / Seismic profiling survey |
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| Research Abstract |
Intercalated tuff layrs in the Miyazaki Group seem to be correspond to tephra which is produced by volcanic activity at southern and central parts of Kyusyu during the Late Neogene. There are three peaks of active volcanic activities through the sequence of the Miyazaki Group on the basis of frequenices of tuff layrs. Periods of three peaks are at about 6 Ma, 4 Ma and 3-2Ma based upon both the radiometric age assignments of the tuff layrs and planktic foraminiferal biochronology. Last pea ; (3-2Ma) in the Miyazaki Gruop seems to be correspond to the late Pliocene volcanic activity at the Hisatsu volcanic province which mainly consists of lava flows, tuff breccias, pyroclastic flow deposits, lapilli tuff and pumice fall deposits that erupted from many volcanos in Pliocene in southern Kyushu, Japan. These volcanic activities are supposed to be related with subduction of the Phillipine Sea Plate. Among three peaks recognized in the sequence of the Miyazaki Group, time of the first peak (6
… More
Ma) is concordant with the time of onset of the subduction of PSP.Further study is needed to clarify the relationship between the later two peaks and motion of PSP.
The geographical processes of the Kuma and Hitoyoshi areas are summarized as follows : 1) the peneplain was fomed from late Miocene to early Pliocene, 2) the movement which the blocks were uplifted and tilted in the early Pliocene. 3) the northeast part of the northern Kuma mountains has been uplifted about 1700m in height, and the southwestern part about 750m as the result of the movement during last 3 Ma. On the other hand, these pyroclastics in the Hisatsu province deposited in the lowlands of the basements.
In the central part of the Yatsushiro Kai area, Seismic profililing survey has been done to get fine sicemic profiling records of which total lenght 210 kirometers and distribution of Quaternary fault. Acoustic classification is divided into five units (A,B,C,D,E) on the basis of analysis of reflective patterns. Cunit is further sundivided into three (1,2,3) layrs. C2 layr corresponds to Ito pyroclastics flow deposite which is displaced by two faults. Therefore, these faults are Quaternary faults, forming fraben.
The chronology of two piston corefrom the East China Sea is estimated on the basis of AMS ^<14>C dating of planktic foraminifera and two ash layrs. As a result, two piston cores cover the last 30,000years. Less
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