Water input into the Mariana subduction zone estimated from ocean-bottom seismic data
Water input into the Mariana subduction zone estimated from ocean-bottom seismic data
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DOI：
10.1038/s41586-018-0655-4
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发表时间：
2018-11-15
期刊：
影响因子：
64.8
通讯作者：
Eimer, Melody
中科院分区：
文献类型：
--
作者：
Cai, Chen;Wiens, Douglas A.;Eimer, Melody
尽管俯冲作用是水向地球深处输送的唯一机制，但人们对俯冲带的水循环仍知之甚少。以前对水通量的估计（1-3）表明，俯冲深度超过100公里的水量变化很大。在这些计算中，不确定性的主要来源是俯冲的最上层地幔的初始含水量。以往的活动震源地震研究表明，在海沟附近的板块弯曲区，俯冲板块可能普遍水化（4-7）。然而，这些研究并没有限制水化作用的深度，而且大多数研究的是年轻的俯冲板块，这使得俯冲带对老俯冲板块的水收支不确定。在这里，我们展示了马里亚纳海沟中部地壳和上地幔的地震图像，这些图像来自宽带海底地震数据的瑞利波分析。这些图像显示，由于地幔水合作用导致的低地幔速度在莫霍不连续之下延伸了大约24公里。结合对俯冲地壳水的估计，这些结果表明，该地区的俯冲水至少是以前计算的4.3倍(3)。如果其他古老的、寒冷的俯冲板块含有相应厚的含水地幔层，就像在古老的、寒冷的俯冲板块上进入的板块断裂的相似性所表明的那样，那么，与以前的估计相比，对深度大于100公里的地幔的全球水通量的估计必须增加大约三倍(3)。由于长期净流入地球深处的水与地质记录不一致(8)，对火山弧和弧后盆地排出的水的估计可能也需要向上修正(9)。
The water cycle at subduction zones remains poorly understood, although subduction is the only mechanism for water transport deep into Earth. Previous estimates of water flux(1-3) exhibit large variations in the amount of water that is subducted deeper than 100 kilometres. The main source of uncertainty in these calculations is the initial water content of the subducting uppermost mantle. Previous active-source seismic studies suggest that the subducting slab may be pervasively hydrated in the plate-bending region near the oceanic trench(4-7). However, these studies do not constrain the depth extent of hydration and most investigate young incoming plates, leaving subduction-zone water budgets for old subducting plates uncertain. Here we present seismic images of the crust and uppermost mantle around the central Mariana trench derived from Rayleigh-wave analysis of broadband ocean-bottom seismic data. These images show that the low mantle velocities that result from mantle hydration extend roughly 24 kilometres beneath the Moho discontinuity. Combined with estimates of subducting crustal water, these results indicate that at least 4.3 times more water subducts than previously calculated for this region(3). If other old, cold subducting slabs contain correspondingly thick layers of hydrous mantle, as suggested by the similarity of incoming plate faulting across old, cold subducting slabs, then estimates of the global water flux into the mantle at depths greater than 100 kilometres must be increased by a factor of about three compared to previous estimates(3). Because a long-term net influx of water to the deep interior of Earth is inconsistent with the geological record(8), estimates of water expelled at volcanic arcs and backarc basins probably also need to be revised upwards(9).