地球化学
Online ISSN : 2188-5923
Print ISSN : 0386-4073
ISSN-L : 0386-4073
32 巻, 3 号
選択された号の論文の5件中1~5を表示しています
特別報告
1994年度日本地球化学会賞受賞記念論文
  • 野津 憲治
    1998 年 32 巻 3 号 p. 115-125
    発行日: 1998/08/25
    公開日: 2016/12/25
    ジャーナル フリー
    This paper summarizes advances in three topics of geochemical studies on island arc volcanoes, which I and my colleagues have been investigating. First one is strontium isotope studies of arc volcanic rocks mainly from Japanese island arcs. We have shown that the precise spatial distribution of the 87Sr/86Sr ratio reflects natures of the subduction structure and slab-mantle interaction. Based on the 87Sr/86Sr ratio of volvanic rocks in the northern Kanto district, where two plates subduct concurrently with different directions, the existence of an aseismic portion of the Philippine Sea plate ahead of the seismic one was suggested. Second one is geochemical monitoring of active arc volcanoes. 3He/4He ratio of volcanic volatiles was shown to be a good indicator to monitor the behavior of magma: ascent and drain- back of magma result in an increase and decrease in the ratio, respectively. In the case of 1986 eruptions of Izu-Oshima volcano, the ratio began to increase two months after big eruptions, reaching the maximum and decreased. Such delayed response is explained in terms of travelling time of magmatic helium from the vent area to the observation site along the underground steam flow. Third one is remote observation of volcanic gas chemistry of arc volcanoes, using an infrared absorption spectroscopy. During Unzen eruptions starting in 1990, absorption features of SO2 and HCl of volcanic gas were detected from the observation station at 1.3km distance. This was the first ground-based remote detection of HCl in volcanic gas. In the recent work at Aso volcano, we could identify 5 species (CO, COS, CO2, SO2 and HCl) simultaneously in the volcanic plume spectra.
1996年度日本地球化学会奨励賞受賞記念論文
  • 豊田 新
    1998 年 32 巻 3 号 p. 127-137
    発行日: 1998/08/25
    公開日: 2016/12/25
    ジャーナル フリー
    The ESR (electron spin resonance) dating method has been applied to faults, tephras, sediments and flints, using quartz. This paper summarizes the studies on thermal stabilities of paramagnetic defects observed in natural quartz, E1', Al and Ti centers. The age ranges to which ESR dating can be applied were estimated from the results of heating experiments. The decay kinetics of these three centers was found to be second order. A method to estimate the amount of oxygen vacancies in quartz was proposed, which involves measuring the intensity of the E1' center after irradiation to more than 200 Gy and subsequent heating at 300℃ for 15 minutes. Using this technique, oxygen vacancies were found to be much more stable than other paramagnetic centers. A correlation was observed between the geologic ages of the granites and of tephras and the amount of oxygen vacancies in quartz. The external β and γ rays can create the oxygen vacancies as indicated by the experiment of irradiation by 60Co source.
報文
  • 大沢 正人, 本間 久英, 中田 正隆
    1998 年 32 巻 3 号 p. 139-147
    発行日: 1998/08/25
    公開日: 2016/12/25
    ジャーナル フリー
    The reduction rate of gold (aq) complexes by humic acid simple organic materials were experimentally determined. The reduction rate of gold (aq) complex by humic acid in the range of 80-120℃ is fast. It's reaction rate constant is in the order of 10-5s-1 and the activation energy is 27 ± 3kJ・mol-1. Comparison of the obtained data with earlier works indicates that the activation energy on the reduction of gold (aq) complexes has a tendency to increase with the increase of the maturity of organic materials (humic acid-lignite-anthracitic coal). Simple organic materials, for example, alcohol and carboxylic acid, were also found to reduce gold (aq) complexes. Ethanol showed one order higher reaction rate constant than acetic acid (ethanol: the order of 10-5s-1, acetic acid : the order of 10-6s-1). It suggests that the reduction rate depends on functional group of organic material. The reaction rate of gold (aq) complexes by natural organic matters and the activation energy may depend on functional groups and their amounts, the maturity and structure of natural organic matters.
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