We report new noble gas signatures of groundwaters, hot springs, and bedrock samples from two major fault systems that form the plate boundary suture between the Eurasian Plate and the Philippines Sea Plate. In the south, the Eurasian Plate dips east beneath the Philippine Sea Plate, and the boundary between the arc and accretionary prism is marked by the Chihshang Fault, which also dips east beneath the arc. The fault is well-defined by seismicity and extends to at least 25 km, close to the crust–mantle boundary. This fault could be an important conduit for the passage of mantle helium along the suture. In the north, as the subduction direction flips from the east-dipping Eurasian Plate to the north-dipping Philippine Sea Plate, the plate boundary fault is represented by a more complex system of east- and west-dipping structures. Low helium isotopes in this area evidence the weaker mantle signal, both before and after a M_w 6.4 earthquake. It is possible that as the subduction direction flips from south to north along strike, the tortuosity of the fault-related conduits increases, reducing the flow and limiting the release of mantle-derived gases.

中文翻译：

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主动弧-陆碰撞中板边界缝合线的氦同位素特征

我们报告了来自两个主要断层系统的地下水，温泉和基岩样品的新稀有气体特征，这两个主要断层系统构成了欧亚板块与菲律宾海板块之间的板块边界缝合线。在南部，欧亚板块在菲律宾海板块的下方向东倾斜，弧与增生棱镜之间的边界以赤山断裂带为标志，该断裂也向东延伸到弧形下方。断层是由地震活动明确界定的，并延伸至至少25 km，靠近地幔边界。该断层可能是地幔氦沿缝合线通过的重要管道。在北部，俯冲方向从东倾的欧亚板块向北倾的菲律宾海板块转变，板块边界断层由东，西倾结构的更复杂系统表示。中号_W¯¯ 6.4级地震。随着俯冲方向沿着走向从南向北翻转，与断层有关的导管的曲折度增加，从而减少了流量并限制了地幔衍生气体的释放。