Stability of hydrous silicate at high pressures and water transport to the deep lower mantle
Stability of hydrous silicate at high pressures and water transport to the deep lower mantle
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DOI：
10.1038/ngeo2074
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发表时间：
2014-03-01
影响因子：
18.3
通讯作者：
Higo, Y.
中科院分区：
文献类型：
--
作者：
Nishi, M.;Irifune, T.;Higo, Y.
水的存在强烈地影响着地球深部地幔的结构、组成和动力学（1-4）。富镁含水硅酸盐在大洋板块俯冲过程中起着向地幔深部输送水的重要作用。据报道，这种含水硅酸盐的最高压力形式，D相，在约44 GPa的压力下（相当于1，250 km深度）分解成名义上无水相和水的组合物（5）。这样，自由水将在下地幔中部释放，这意味着没有水可以到达下地幔更深的区域。在这里，我们使用原位X射线测量结合使用烧结金刚石砧的多砧装置，以显示水合相是稳定的下地幔条件下高达50 GPa。我们发现，D相转变成一个组合与另一个水合硅酸盐（MgSiH 2 O 4），命名为H相，在压力约48 GPa以上。我们的研究结果表明，H相是下降板中占主导地位的含水硅酸盐，并可能在深度远远超过1,250公里。我们的结论是，大量的水被保留在下降的板片，并可能被输送到下地幔的最深处。
The presence of water strongly influences the structure, composition and dynamics of the Earth's deep mantle(1-4). Hydrous magnesium-rich silicates play an important role in transporting water into the deep mantle when oceanic plates subduct as slabs. The highest-pressure form of such hydrous silicates, phase D, was reported to dissociate into an assemblage of nominally anhydrous phases plus water at pressures of about 44 GPa, equivalent to 1,250 km depth(5). In this way, free water would be released in the middle region of the lower mantle, which suggests that no water can reach the deeper regions of the lower mantle. Here we use in situ X-ray measurements in conjunction with a multi-anvil apparatus using sintered diamond anvils to show that hydrous phases are stable under lower mantle conditions up to 50 GPa. We found that phase D transforms to an assemblage with another hydrous silicate (MgSiH2O4), named phase H, at pressures above about 48 GPa. Our results suggest that phase H is the dominant hydrous silicate in descending slabs, and may be found at depths far deeper than 1,250 km. We conclude that a significant amount of water is retained in the descending slabs and may be delivered to the deepest part of the lower mantle.