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Observation and investigation for the formation SPM originates in high temperature volcanic gas

高温火山气体SPM形成的观测与研究

基本信息

批准号：
15310126
负责人：
OHBA Takeshi
金额：
$ 3.78万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2006
项目状态：
已结题

项目摘要

The high temperature fumarolic gasi is the source of SPM emitted from active volcanoes. In order to investigate the control on the chemical composition of high temperature volcanic gas, a degassing model of magma was constructed based on the data observed at Mt. Unzen. The volcanic gas rich in CO_2 and SO_2was estimated to be separated from magma at depth -8 km from surface. The degassed magma again exsolved a gas phase rich in H_O and CH1 at depth shallower than -1 km.The amount of SPM would be proportional to the flux of SO_2 gas. As a case study, the mechanism of SO_2 degassing was investigated at Miyakejima volcano. A diffused SO_2 gas was sampled at the flank of volcano by using the so called chemical trap method. In the method, a KOH solution was exposed over several months under open air. The volcanic SO_2 gas was absorbed into the KOH solution. At the absorption, the occurrence of a kinetically isotopic fractionation was confirmed by an laboratory experiment. Employing the experimentally determined isotopic fractionation, the δ^<34>S of S in magma of Miyakejima volcano was estimated to be identical to the value typical to the Quarternary volcanoes in Japan. The temporal change in the observed δ^<34> S of SO_2 gas, a monotonically decreasing, δ^<34> S, could be attributed to the open system degassing of magma. The isotopic fractionation between gas phase and magma depends on oxygen fugacity. The oxygen fugacity necessary to produce the isotopic fractionation compatible to the open degassing of magma was estimated to be +0.6 to +1.2 log unit higher than Ni-NiO oxygen fugacity buffer.

高温富马罗气体是活火山喷发的SPM的来源。为了探讨高温火山气体化学成分的控制作用，根据云仙山的观测资料，建立了岩浆脱气模型。富含CO_2和so_2的火山气体是在离地表-8 km的岩浆中分离出来的。脱气岩浆在深度小于-1 km处再次释放出富含H_O和CH1的气相。SPM的量与SO_2气体的通量成正比。以三宅岛火山为例，对SO_2脱气机理进行了研究。采用化学捕集法对火山侧面的SO_2扩散气体进行了取样。在该方法中，KOH溶液在露天环境下暴露数月。火山SO_2气体被KOH溶液吸收。在吸收时，通过实验室实验证实了动力学同位素分馏的发生。利用实验测定的同位素分馏，估计了三宅岛火山岩浆中S的δ^<34>S与日本第四纪火山的典型值相同。SO_2气体δ^<34> S随时间变化呈单调递减的趋势，可能与岩浆的开放系统脱气有关。气相和岩浆之间的同位素分馏取决于氧逸度。与开放脱气岩浆相适应的同位素分馏所需的氧逸度估计比Ni-NiO氧逸度缓冲液高+0.6 ~ +1.2 log单位。