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Volume 33 (1999)
- Issue 4 Pages 207-
- Issue 3 Pages 141-
- Issue 2 Pages 67-
- Issue 1 Pages 1-
Volume 33, Issue 3
Displaying 1-5 of 5 articles from this issue
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Review in series “New Approaches to Geochemistry”
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Kozo UTO, Osamu ISHIZUKA1999 Volume 33 Issue 3 Pages 141-154
Published: August 25, 1999
Released on J-STAGE: December 29, 2016
JOURNAL FREE ACCESSThe laser-heating 40Ar/39Ar dating method is now widely applied to the precise dating of a small amount of rocks and minerals. In this review paper, we first mention the principle of the dating method, and describe the analytical system established at the Geological Survey of Japan. We, then, emphasize the importance of determining the three-dimentional fast-neutron flux gradient within the irradiation capsule in order to obtain precise 40Ar/39Ar ages Reliable ages of standard minerals are also the key to the higher accuracy of ages of samples because the 40Ar/39Ar technique is a dating method relative to the age of a standard sample irradiated together with samples to be dated. GSJ mineral standard, SORI biotite, is considered to be accurate in age within a half percent comparing with other age standards elsewhere. Finally, preliminary studies are presented for the Tertiary volcanic rock and plagioclase phenocryst from a Quaternary tephra. Incremental laser-heating experiment for a Miocene lava from the Takashibiyama Formation was successful to obtain a reliable and precise age of its eruption. Totalfusion experiments were done for plagioclase separates from the Yabakei pyroclastic flow deposit. Each experiment by fusing 3-4 grains gave age with relatively large uncertainties of about 20%, but the weighted average of five runs gave an age of 0.92 ±0.09 Ma, which agrees with the K-Ar age of 0.99 ± 0.03 Ma for this deposit. Our case studies show that the laser-heating 40Ar/39Ar dating technique is a promising tool to reveal the history of volcanism.View full abstractDownload PDF (1535K)
The Geochemical Society of Japan Award for Young Researchers
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Hikaru IWAMORI1999 Volume 33 Issue 3 Pages 155-175
Published: August 25, 1999
Released on J-STAGE: December 29, 2016
JOURNAL FREE ACCESSStudies on the processes of magma generation and migration are reviewed, with special reference to geochemical and numerical modeling. A full set of governing equations for describing melting and melt migration by porous flow are introduced, in which the relationships between the equations (conservation of mass, momentum and energy) and the variables are investigated. Based on the governing equations, characteristics of the melt-solid flow systems with chemical reactions are described, which shows that the chemistry of the melt and solid can be used to investigate the processes involved quantitatively (e. g., the style of melt migration). Application of these theories and numerical modeling to the magmatism at mid-ocean ridges revealed that more than 80 per cent of the melt produced beneath the ridges is transported towards the surface without significant chemical reaction on ascent within a short period of time (e. g., less than 1,000 years). Magmatism and metamorphism in subduction zones are also modeled, which suggests that transportation of H2O and melting depend strongly on the age of the subducting slab. Associated with subduction of young (<10 m. y.) slabs and ridges, transition in terms of magmatism and metamorphism occurs within 10 m. y., from (1) normal arc melting in mantle wedge, (2) forearc mantle melting (high-Mg andesitic) to (3) slab melting in which a significant amount (〜100 km3) of granitic melt is produced. The model results newly show that, this event of ridge subduction should cause synchronous formation of granitic batholith by slab melting and regional paired-metamorphic belts, such as Ryoke-Sanbagawa belt in Japan. These results show that the geochemical and numerical modeling is a useful approach in order to understand the melt generation and migration processes and their roles in the Earth's history.View full abstractDownload PDF (2256K)
The Merit Prize of the Geochemical Society of Japan
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Keizo YANAI1999 Volume 33 Issue 3 Pages 177-189
Published: August 25, 1999
Released on J-STAGE: December 29, 2016
JOURNAL FREE ACCESSFor the recent 30 years, about 20 thousand specimens of extraterrestrial material so called "Antarctic meteorites" recovered from the South Pole region as results of numerous meteorite search expeditions of the most US and Japan. Japan now keeps almost 10 thousand Antarctic meteorite specimens and it is the one of the biggest collection of meteorites in the world. The collection are distributing to researchers as unique and important research materials under the Japanese Antarctic meteorite distribution system during the last 30 years. The Antarctic meteorites have been giving a strong impact to the planetary sciences especially meteorite studies in Japan and world. However, Antarctic meteorites have been recovered under unpredicable hand condition such as very low temperature (under -30℃) with strong wind at a very dangerous places where are numerous deep hidden crevasses. Auther report here some interesting activities and histories of Antarctic meteorite expeditions including most of Japan and US-Japan team led by author in the early stage of Antarctic meteorite search.View full abstractDownload PDF (2479K)
Review
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Masanobu YAMAMOTO1999 Volume 33 Issue 3 Pages 191-204
Published: August 25, 1999
Released on J-STAGE: December 29, 2016
JOURNAL FREE ACCESSAlkenone paleothermometry has been used for generating late Quaternary records of sea surface temperature from deep-sea core sediments. This paper summarizes its principles, applications, problems and future. A critical problem comes from culture experiments of Emiliania huxleyi and Gephyrocapsa oceanica. The results indicate large variations in the U37K'-temperature relationship among different species or strains. Even single strains show variations in U37K' in different growth phases and culture conditions. These suggest that some physiological or environmental factor, in addition to temperature, affects U37K'. To find this factor is strongly sought for the future application of alkenone paleothermometry.View full abstractDownload PDF (1374K)
Abstract of doctoral thesis
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Yoshiro Nishio1999 Volume 33 Issue 3 Pages 205-
Published: August 25, 1999
Released on J-STAGE: December 29, 2016
JOURNAL FREE ACCESSDownload PDF (180K)
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