1989 Fiscal Year Final Research Report Summary
CHARACTERISTICS OF QUATERNARY TECTONIC MOVEMENT ESTIMATED FROM UPLIFTED CORAL REEFS OF DAITO ISLANDS, THE RYUKYUS, JAPAN
| Project/Area Number |
62302062
|
|---|
| Research Category |
Grant-in-Aid for Co-operative Research (A)
|
| Allocation Type | Single-year Grants |
|---|
| Research Field |
自然地理学
|
|---|
| Research Institution | Yokohama National University |
|---|
Principal Investigator |
OTA Yoko YOKOHAMA NATIONAL UNIVERSITY, FACULTY OF EDUCATION, PROFESSOR, 教育学部, 教授 (80017714)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
KOBA Motoharu KANSAI UNIVERSITY, FACULTY OF LITERATURE, ASSOCIATE PROFESSOR, 文学部, 助教授 (40141949)
KAWANA Toshio THE UNIVERSITY OF RYUKYUS, FACULTY OF EDUCATION, ASSOCIATE PROFESSOR, 教育学部, 助教授 (60044955)
YONEKURA Nobuyuki THE UNIVERSITY OF TOKYO, FACULTY OF SCIENCE, ASSOCIATE PROFESSOR, 理学部, 助教授 (30011563)
OMURA Akio KANAZAWA UNIVERSITY, FACULTY OF SCIENCE, ASSOCIATE PROFESSOR, 理学部, 助教授 (70019488)
|
|---|
| Project Period (FY) |
1987 – 1989
|
| Keywords | Coral reef terrace / Kita-and Minami-Daito Islands / Last interglacial stage / Uplift rate / U-series age / Quaternary tectonic movement / ESR age / Uplifted atoll |
|---|
| Research Abstract |
Purpose of this study is to establish uplift rate and to discuss characteristics of Quaternary tectonic movement of Kita- and Minami-Daito Islands, located on Philippine Sea Plate, east of the Ryukyu Trench, comparing to other islands on Eurasian Plate. Occurrence of fossil corals and related emerged landforms were investigated and samples for 230-Th/234-U dating and ESR dating were collected. Main results are as follows: 1) 58 autochihonous corals and 32 allochthonous corals were sampled and emerged benches and notches were investigated from 7 locations of two islands. 2) The upper limit of authochtonous corals is 8.1 m on Kita-Daito and 11 m on Minami-Daito. 3) 230-Th/234-U age of authochotonous corals is 113<plus-minus>6-133<plus-minus>6ka on Kita-Daito and 116<plus-minus>6-133<plus-minus> 7ka on Minami-Daito (except for one sample). These ages represent the last interglacial maximum stage, corresponding to isotope stage 5e. 4) ESR age and 226-Ra/238-U age for some of samples are approximately same to 230-Th/234-U age. 5) The upper limit of emerged landforms is 10m on Kita-Daito and 12.7m on Minami- Daito. 6) Thus, the uplift rate since the last interglacial is very small, only 0.04-0.05m/ka. 7) There is a significant difference of uplift rate between these two islands and other islands on Eurasian Plate(1.5m/ka-0.2m/ka), being subducted by Philippine Sea Plate. 8) Sense of vertical movement changed here from subsidence to uplift, judged by the presence of uplifted atolls surrounded by uplifted fringing reefs. This change is probably a result of northwestward migration of Philippine Sea Plate to form an upward bulge close to the trench, but the timing for change could not be identified because of lack of suitable samples for dating. 9) Some of allochthonous corals are dated at 100ka or younger, suggesting the presence of sea level records corresponding to stage 5c or 5a, but coral reefs of these stages were not found
|
