Hydrothermal methane plumes in the Mariana back-arc spreading centre
Hydrothermal methane plumes in the Mariana back-arc spreading centre
复制标题
马里亚纳弧后扩张中心的热液甲烷羽流
作者：
Y. Horibe;K.;H. Craig
海底热液喷口首先是通过测量加拉帕戈斯扩张中心的3He/4He比值异常以及偏离环境T-S关系而被明确探测到的1，2。从那时起，通过船上对流出水柱3-5中的3He，甲烷和锰的观测，证实了沿东太平洋隆起全长存在热液喷口。我们扩大了对洋脊中部扩张中心的喷口的研究，以寻找弧后盆地的流出羽流，这些盆地也被认为是海底扩张的活动区，在那里形成了新的洋壳。因此，沿着延伸轴的裂谷和保证应该为海水向下渗透和发展活跃的热液系统提供类似的机会。我们在马里亚纳海槽弧后盆地7和夏威夷热点现址的洛伊希西蒙特7山顶陨石坑中发现了大量富含甲烷的水，从而确立了海洋中普遍存在的“山脊外”热液喷口。然而，尽管Loihi喷口产生了富含3He和甲烷7的羽流，但令人惊讶的是，我们发现马里亚纳喷口富含甲烷，而没有相应的3He富集物。这是第一次观察到这两种流出羽流示踪剂的“脱钩”现象。
Submarine hydrothermal vents were first unequivocally detected by measurement of3He/4He ratio anomalies coupled with deviations from ambientT–Srelationships on the Galapagos spreading centre1,2. Since then the existence of hydrothermal vents along the entire length of the East Pacific Rise has been demonstrated by shipboard observations of3He, methane, and manganese in the effluent plumes3–5. We have extended our studies of vent fields at mid-ocean-ridge spreading centres to search for effluent plumes in back-arc basins, which are also thought to be active regions of seafloor spreading where new oceanic crust is formed6, and thus where rifting and Assuring along the axis of extension should provide similar opportunities for the downward penetration of sea water and the development of active hydrothermal systems. We have detected large plumes of methane-enriched water in the Mariana Trough back-arc basin7and also in the summit crater of Loihi Seamount7at the present site of the Hawaiian hotspot, thus establishing the widespread existence of ‘off-ridge’ hydro-thermal vents in the ocean. However, although the Loihi vents produce plumes enriched in both3He and methane7, we find that, surprisingly, the Mariana vents are enriched in methane without a corresponding enrichment in3He. This is the first time such a ‘decoupling’ of these two effluent plume tracers has been observed.