Water Content in the Mantle Transition Zone Beneath the North Pacific Derived From the Electrical Conductivity Anomaly
Water Content in the Mantle Transition Zone Beneath the North Pacific Derived From the Electrical Conductivity Anomaly
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DOI：
10.1029/168gm13
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发表时间：
2006-01-01
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影响因子：
--
通讯作者：
Hae, Ryota
中科院分区：
文献类型：
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作者：
Koyama, Takao;Shimizu, Hisayoshi;Hae, Ryota
福考等人。 (2004) 反演北太平洋地幔过渡带三维电导率结构的半全球电磁网络数据。在本文中，我们使用地幔材料实验室实验确定的偏导数，根据地幔过渡带中的水分布来解释电导率结构。福考等人。 (2004) 由于高电导率与低地震速度的总体重合，用热异常解释了电导率和地震 P 波速度异常。然而，在马里亚纳群岛下方发现了显着差异，地震层析成像表明温度异常很小，而电磁层析成像则表明温度较高。尽管空间分辨率存在限制和差异，但这一结果表明这一特殊特征可能无法仅用热效应来解释。考虑到该区域充满了俯冲板片，我们进一步假设这种差异是由这些板片脱水造成的。在此假设下，通过结合 Nernst-Einstein 关系（例如 Karato，1990）和最近实验室测量瓦兹利石中氢扩散率的结果（Hae 等，2006），根据电导率异常估计了含水量异常。我们发现马里亚纳群岛下方的地幔过渡带可能含有约 0.3% 重量的水。
Fukao et al. (2004) inverted semi-global electromagnetic network data for three-dimensional electrical conductivity structure in the mantle transition zone beneath the north Pacific. In this paper we interpret the electrical conductivity structure in terms of the water distribution in the mantle transition zone, using partial derivatives determined by laboratory experiments on mantle materials. Fukao et al. (2004) explained both electrical conductivity and seismic P-wave velocity anomalies with thermal anomalies because of the overall coincidence of high electrical conductivity with low seismic velocity. However, a significant discrepancy is found beneath the Mariana islands where the seismic tomography would indicate little temperature anomaly, while electromagnetic tomography implies high temperatures. Despite limitations and differences in spatial resolution, this result indicates that this particular feature may not be explained by only a thermal effect. Taking into consideration that this region is well populated by subducted slabs, we further assume that this discrepancy is caused by water dehydrated from those slabs. Under this assumption, by combining the Nernst-Einstein relationship (e.g. Karato, 1990) and the recent result of laboratory measurements of hydrogen diffusivity in wadsleyite (Hae et al., 2006), the water content anomaly was estimated from the electrical conductivity anomalies. We find that the mantle transition zone beneath Mariana islands could contain about 0.3 weight % water.