2003 Fiscal Year Final Research Report Summary
Tectonics and evolution of the Philippine volcanic arc
| Project/Area Number |
13573010
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 海外学術 |
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| Research Field |
Geology
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
OBATA Masaaki Kyoto Univ., Graduate School of Science, Professor, 大学院・理学研究科, 教授 (20126486)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIKAWA Naoto KYOTO UNIVERSITY, Graduate School of Integrated Human Studies, Associate Professor, 人間環境学研究科, 助教授 (30202964)
TATSUMI Yoshiyuki Japan Marine Science & Technology Center, Institute for Frontier Research on Earth Evolution, Program Director, 固体地球統合フロンティア研究センター, 領域長 (40171722)
KAMATA Hiroki Kyoto Univ., Graduate School of Integrated Human Studies, Professor, 総合人間学部, 教授 (80303791)
YAMADA Ryuji National Research Institute for Earth Science and Disaster Prevention, Solid Earth Science Division, Research Fellow, 固体地球研究部門, 研究員
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| Project Period (FY) |
2001 – 2003
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| Keywords | Volcanic belt / Island Arc / Philippine / Central Kyushu / Rifting / Subduction / K-Ar age / XRF |
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| Research Abstract |
The purpose of this study is to elucidate the development of island arc and its history through comparison of Philippine and Japan islands. We found followings :
(1) To understand the conditions of development and evolution of volcanic belt in the across-arc direction at the junction of arcs, we studied magmatism related to the rifting in central Kyushu, which has a tectonic setting similar to the Macolod Corridor, southwestern Luzon, Philippines. With a particular focus on the Yamakogawa Rhyolite of Hohi Volcanic Zone, we carried out K-Ar and (U,Th)/He dating and petrologic study and reconstructed its volcanic eruption history and mode.
(2) K-Ar ages of 37 samples collected from the Bicol peninsula, the Luzon island, Philippines, were determined by the unspiked sensitivity method in order to constrain the timing of initiation of subduction along the Philippine Trench. The measured K-Ar ages range from 0-7 Ma with two old outliers of 27 and 43 Ma. Together with K-Ar ages previously reported on volcanics in Leyte and eastern Mindanao, subduction volcanism has likely propagated from north to south : 〜6.6 Ma in Bicol and 〜3.5 Ma in Leyte and its vicinity.
(3) Lavas from the February to March 2000 eruption of Mayon Volcano were deposited as blocky lava flows on the southeast sector of the volcano, and ballistics that range from bomb to lapilli size. Compared with chemical data from older lavas particularly from 1968 to 1993, the 2000 lava shows minor variations. It is possible that the 2000 magma is part of a batch of magma that has erupted since 1968. Including 2000, there are then 5 eruptions for this batch of basaltic andesite magma.
(4) We conducted geochronologic and petrologic study of historical lavas from the Island of Hawaii to establish K-Ar geochronology of young volcanic rocks. We found that mass fraction of argon occurs in hotspot volcanoes and that extraneous 40Ar can be sufficiently reduced by using groundmass samples.
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