Subduction factory: 4. Depth-dependent flux of H2O from subducting slabs worldwide
Subduction factory: 4. Depth-dependent flux of H2O from subducting slabs worldwide
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DOI：
10.1029/2010jb007922
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发表时间：
2011-01-05
影响因子：
3.9
通讯作者：
Abers, Geoff A.
中科院分区：
文献类型：
--
作者：
van Keken, Peter E.;Hacker, Bradley R.;Abers, Geoff A.
最近全球汇编的俯冲带的热结构被用来预测变质相和H2O含量的下降板。我们的计算表明，矿物结合水可以有效地通过古老而快速的俯冲带（例如，在西太平洋），而热俯冲带，如卡斯卡迪亚看到几乎完全脱水的俯冲板。板块的顶部在所有俯冲带都足够热，预计包括沉积物和火山岩在内的上地壳会显著地下沉。地壳深部和上地幔脱水的程度和深度差异很大，主要取决于成分（辉长岩与橄榄岩）以及当地的压力和温度条件。除了最冷的俯冲带，上地幔在中间深度脱水。平均而言，约三分之一的约束H2O俯冲全球板达到240公里的深度，进行主要和大致相等的辉长岩和橄榄岩部分。预测的全球H2O向地幔深处的通量比以前的估计要小，但仍然相当于地球年龄的一个海洋质量。在这个速率下，整个地幔的H2O含量在地球的年龄内增加了0.037重量%（370 ppm）。这是定性一致的推断H2O浓度在地球的地幔，假设长期冷却的地球随着时间的推移增加了挥发性回收的效率。
A recent global compilation of the thermal structure of subduction zones is used to predict the metamorphic facies and H2O content of downgoing slabs. Our calculations indicate that mineralogically bound water can pass efficiently through old and fast subduction zones (e.g., in the western Pacific), whereas hot subduction zones such as Cascadia see nearly complete dehydration of the subducting slab. The top of the slab is sufficiently hot in all subduction zones that the upper crust, including sediments and volcanic rocks, is predicted to dehydrate significantly. The degree and depth of dehydration in the deeper crust and uppermost mantle are highly diverse and depend strongly on composition (gabbro versus peridotite) and local pressure and temperature conditions. The upper mantle dehydrates at intermediate depths in all but the coldest subduction zones. On average, about one third of the bound H2O subducted globally in slabs reaches 240 km depth, carried principally and roughly equally in the gabbro and peridotite sections. The predicted global flux of H2O to the deep mantle is smaller than previous estimates but still amounts to about one ocean mass over the age of the Earth. At this rate, the overall mantle H2O content increases by 0.037 wt % (370 ppm) over the age of the Earth. This is qualitatively consistent with inferred H2O concentrations in the Earth's mantle assuming that secular cooling of the Earth has increased the efficiency of volatile recycling over time.