Intensive hydration of the mantle transition zone beneath China caused by ancient slab stagnation
Intensive hydration of the mantle transition zone beneath China caused by ancient slab stagnation
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DOI：
10.1038/ngeo1250
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发表时间：
2011-10
影响因子：
18.3
通讯作者：
T. Kuritani;E. Ohtani;J. Kimura
中科院分区：
文献类型：
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作者：
T. Kuritani;E. Ohtani;J. Kimura
地幔过渡带位于上地幔和下地幔之间410-660 km深处，是地球内部重要的水资源库。然而，在水的分布中存在区域尺度的不均匀性。特别是中国东北地区的地下含水量非常高，但它是何时以及如何含水的仍然不确定。本文将联合收割机对中国东北晚新生代玄武岩的地球化学分析与已发表的地球化学分析结果相结合。我们发现玄武岩的地球化学和低速区的分布在下伏地幔，被解释为地幔过渡带的羽流上涌之间的空间相关性。因此，我们用玄武岩地球化学推断地幔过渡带的组成。玄武岩具有较高的Ba/Th和207 Pb/206 Pb比值，这可能是10亿年前俯冲板片脱水的结果。我们认为，这一古老的水化事件，结合最近的水化事件与俯冲太平洋板块脱水，可以解释中国地幔过渡带的含水性质。我们的研究结果表明，地幔过渡带可以作为一个稳定的水库在地球内部的时间尺度超过十亿年。
The mantle transition zone, located at depths of 410–660 km between the lower and upper mantle, is an important water reservoir in the Earth’s interior,,,. However, there are regional-scale heterogeneities in the distribution of water,. The zone beneath northeast China, in particular, is remarkably hydrous, but when and how it became hydrous remains uncertain. Here we combine analyses of the geochemistry of late Cenozoic basalts in northeast China with published geochemical analyses. We find a spatial correlation between basalt geochemistry and the distribution of a low-velocity zone in the underlying mantle that is interpreted as a plume upwelling from the mantle transition zone. We therefore use the basalt geochemistry to infer the composition of the mantle transition zone. The basalts have high Ba/Th and207Pb/206Pb ratios, which we suggest record an ancient hydration event in the transition zone that occurred more than one billion years ago, probably as a result of dehydration of a subducted slab. We suggest that this ancient hydration event, combined with a more recent hydration event linked to dehydration of the subducted Pacific slab, can account for the hydrous nature of the mantle transition zone beneath China. Our results demonstrate that the mantle transition zone can remain as a stable water reservoir in Earth’s interior for timescales of more than a billion years.