| Project/Area Number |
07404029
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | KOBE UNIVERSITY |
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Principal Investigator |
SATO Hiroaki FACULTY OF SCIENCE KOBE UNIVERSITY,PROFESSOR, 理学部, 教授 (60019495)
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| Co-Investigator(Kenkyū-buntansha) |
SUZUKI Keiko (KAMATA Kei) FAC.OF SCI.KOBE UNIVERSITY,ASSOC.PROF., 理学部, 助教授 (20192544)
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| Project Period (FY) |
1995 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥31,700,000 (Direct Cost: ¥31,700,000)
Fiscal Year 1998: ¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 1997: ¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1996: ¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1995: ¥24,200,000 (Direct Cost: ¥24,200,000)
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| Keywords | Unzen volcano / Fuji volcano / Takamatsu crater / amphibole / plagioclase / oscillatory zoning / vesiculation and degassing / マグマ含水量 / マグマ脱ガス / 異帯構造 / 鬼界アカホヤ噴火 / 累帯構造 / 発泡組織 / 溶融実験 / 斜長石の累帯構造 / 角閃石の安定条件 / 火砕流 / 溶岩ドーム / 噴火エネルギー / 脱ガス機構 / 火山灰粒子形態分析 / 噴火様式 / マグマ混合 |
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| Research Abstract |
(1) High pressure and high temperature experimental studies :
Phase stability experiments on Unzen dacite showed that the pressure of groundmass pargasite crystallization requires more than 60-100 MPa at 880 C, suggesting they crystallized at depth of more than 3 km. Chlorine content of the groundmass pargasite indicates that degassing of 2% of water from the magma had occurred before the groundmass crystallization, indicating the initial water content of the dacite is ca. 6 wt.%.
Preliminary vesiculation experiment through depressurization of hydrous melts were conducted, and compared with natural pumiceous ejecta of Kikai-Akahoya plinian erutpion, 6500 yr. b.p., in terms of vesicle size distribution and number density of vesicles in a unit mass of melt.
Another suite of experiments were conducted on the 1707A.D.basalt of Fuji volcano, to determine the Ca/(Ca+Na) ratio of liquidus plagioclase as a function of water content of the melt, yielding an equation An=6* (H2Owt%)+67 at 190 MPa. Using this relationship, we successfully obtained the degassing/mixing history of magmas from the compositional zoning of plagioclase phenocyrsts in the 1707 as well as 864 A.D.basalts.
(2) Analyses of natural rock textures
Compositional zonings of phenocrysts (plagioclase and homblende) in the Unzen 1991-1995 dacite showed both evidences of magma mixing at the rim of phenocrysts and of volatile input/degassing of magmas in the core of phenocrysts. Latter point is deduced from the minor element distributions (Fe, Mg, K in plagioclase and Cl in homblende), and provide new evidence concerning the behavior of volatiles in the magma chamber.
(3) numerical modeling.
We calculated the flow rate of the 1991 dome eruption of Unzen volcano usuing Hagen-Poiseuille law. Strong dependence of the viscosity of magma on the water content results in much faster uprise velocity of the dacite magma at depth more than 700 meters.
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