Relationship between 3He/4He ratios and subduction of the Philippine Sea plate beneath southwest Japan
Relationship between 3He/4He ratios and subduction of the Philippine Sea plate beneath southwest Japan
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DOI：
10.1029/2012jb009409
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发表时间：
2012-10
影响因子：
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通讯作者：
K. Umeda;Tomohiro Kusano;K. Asamori;G. McCrank
中科院分区：
文献类型：
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作者：
K. Umeda;Tomohiro Kusano;K. Asamori;G. McCrank
[1]地幔氦的区域和局部变化提供了对地幔-地壳构造耦合以及来自地球内部的热量和/或质量传递的深入了解。为了进一步阐明日本西南部地区3 He/4 He比值的地理分布，对来自总共924个站点的数据进行了汇编和综合。这些数据包括来自北方九州岛和北方中国地区的48个额外的温泉和饮用水井的数据。氦同位素比值的变化与用来确定菲律宾板块俯冲构造的地球物理证据之间似乎有很好的相关性。地震学研究表明，东亚板块的前缘并没有延伸到北方中国地区，也没有延伸到大坂湾地区，在那里的气体样品与显着升高的3 He/4 He比发生。这是一致的幔源氦在这些地区，从熔融和/或地幔流体归因于上涌的软流圈没有受到阻碍的下降PHS板。与此相反，在覆盖地壳与俯冲PHS直接接触的地区，气体样品主要是来自地壳的放射性氦，因为没有地幔楔，地幔氦的最合理的来源。由于板内地震的地震活动性和震源机制的突变，PHS被认为在纪伊海峡和/或纪伊半岛东部下方存在西北-东南方向的板裂。然而，异常高的3 He/4 He比值的透镜排列似乎并不是沿假设的板状撕裂沿着呈NW-SE趋势，而是在发生低频事件的撕裂之间形成了一个宽的ENE-WSW趋势区。半岛中部3 He/4 He比值升高的气体的喷出可以解释为来自PHS上方地幔楔和/或来自PHS内部的水化板状地幔通过N-S向裂隙介质的地幔挥发分向上活动。因此，在地球表面观察到的氦同位素可能是一个相对年轻的，温暖的地球化学构造的指标，特别是在地震活动不活跃的地区是有用的。
[1] Regional and local variations in mantle helium provide insight into the coupling of mantle-crust tectonics, and heat and/or mass transfer from the Earth's interior. In order to further elucidate the geographic distribution of3He/4He ratios in southwest Japan, the data from a total of 924 sites were compiled and synthesized. These include data from 48 additional hot spring and drinking water well sites on the northern Kyushu Island and in the northern Chugoku region. There appears to be good correlation between variations in helium isotope ratios and the geophysical evidence used to determine the configuration of the subducting Philippine Sea plate (PHS). Seismological studies reveal that the leading edge of the aseismic slab does not extend to the northern Chugoku region nor to the Osaka Bay area, where gas samples with significantly elevated 3He/4He ratios occur. This is consistent with a mantle-derived helium in these areas, from melts and/or mantle fluids ascribed to upwelling asthenosphere without being hindered by the descending PHS slab. In contrast, gas samples in the regions where the overriding crust comes into direct contact with the subducting PHS are dominated by radiogenic helium derived from the crust because of the absence of a mantle wedge, the most plausible source of mantle helium. Owing to the abrupt changes in the seismicity and focal mechanisms of intraplate earthquakes, the PHS is considered to have slab tears beneath the Kii Channel and/or the eastern Kii Peninsula oriented in a NW-SE direction. However, the lenear alignment of anomalously high3He/4He ratios does not appear to be NW-SE trending along the assumed slab tears but rather forms an broad, ENE-WSW trending zone between the tears where low-frequency events occur. The emanation of gas with elevated3He/4He ratios in the central peninsula can be explained by the upward mobilization of mantle volatiles derived from the mantle wedge above the PHS and/or transferred from the hydrated slab mantle through the N-S trending fractured medium within the PHS. Accordingly, the helium isotopes observed on the Earth's surface may be efficient geochemical indicators of the configuration of a relatively younger, warm aseismic slab, and be especially useful in seismically inactive areas.