Secular variations of helium and nitrogen isotopes related to the 2015 volcanic unrest of Mt. Hakone, central Japan
Secular variations of helium and nitrogen isotopes related to the 2015 volcanic unrest of Mt. Hakone, central Japan
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与 2015 年日本中部箱根山火山爆发相关的氦和氮同位素的长期变化
DOI：
10.1029/2019gc008544
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
T.
中科院分区：
文献类型：
--
作者：
Kagoshima;T.;Sano;Y.;Takahata;N.;Lee;H.;Lan;T. and Ohba;T.
一个小的水火山爆发发生在山。2015年6月29日，日本中部的箱根，喷出少量火山灰和气体。我们已经进行了连续的调查，他同位素在Owaanani地热区靠近山。Komagatake，Mt.箱根黑蛋站的长期（十年尺度）数据显示，3 He/4 He比值通常为6.37 ± 0.06 Ra，其中Ra是经过空气校正后的大气3 He/4 He比值，为1.382 × 10 - 6。两个氦同位素站点的短期（月度）数据显示，从2015年5月到8月，氦同位素快速增加，到2018年2月逐渐减少，而地震活动在2015年3月开始加强，5月达到最大值，并且比氦同位素的减少速度更快。我们还测量了样品中的氮和氩同位素。δ 15 N-N2/36 Ar图解表明，它们可以通过大气和火山气源成分的混合得到很好的解释。空气校正的δ 15 N值的月变化表现为先快速下降后缓慢上升，与空气校正的3 He/4 He值变化相反，表明在流体和气体迁移过程中岩浆与地壳混合的共同机制。观测现象的时间序列表现为火山建筑物膨胀、最大群活动、潜水喷发和最大He、N同位素异常。氦和氮同位素的时间变化与奥瓦卡尼地热系统的激活和火山活动的终止相关，这可能为观测和评估世界各地的地热活动提供有用的信息。
A small hydrovolcanic eruption occurred on Mt. Hakone in central Japan on 29 June 2015, ejecting small amounts of volcanic ash and gas. We have conducted continuous surveys of He isotopes in the Owakudani geothermal area close to Mt. Komagatake, the central cone of Mt. Hakone. Long‐term (decadal‐scale) data from the Black‐egg site show generally constant3He/4He ratios with 6.37 ± 0.06 Ra, where Rais the atmospheric3He/4He ratio of 1.382 × 10‐6, after air correction. Short‐term (monthly) data of two fumarole sites indicate a rapid increase from May through August 2015 and a gradual decrease through February 2018, whereas seismic activity began to intensify in March 2015, reached the maximum in May, and decreased faster than the decrease in He isotopes. We also measured N and Ar isotopes in fumarole samples. A δ15N – N2/36Ar diagram shows that they are well explained by mixing of atmosphere and volcanic gas source components. Monthly variations of air‐corrected δ15N values shows a rapid decrease followed by a slow increase, contrary to the air‐corrected3He/4He variations, suggesting a common mechanism of mixing between magma and crust during migration of fluids and gases. The time sequence of observed phenomena shows inflation of the volcanic edifice, maximum swarm activity, phreatic eruption, and maximum He and N isotope anomaly. Temporal variations of He and N isotopes were correlated with activation of the Owakudani geothermal system and with termination of volcanic unrest, which may provide useful information for observing and assessing geothermal activity around the world.