Order of magnitude increase in subducted H2O due to hydrated normal faults within the Wadati-Benioff zone
Order of magnitude increase in subducted H2O due to hydrated normal faults within the Wadati-Benioff zone
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DOI：
10.1130/g34730.1
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发表时间：
2014-03
期刊：
影响因子：
5.8
通讯作者：
T. Garth;A. Rietbrock
中科院分区：
文献类型：
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作者：
T. Garth;A. Rietbrock
洋壳地幔水化作用是由洋壳外隆正断层水化作用的结果，并将大量的水输送到地幔深部。然而，海洋地幔水化的程度受到现有观测的限制，并且是确定输送到地幔的总水量的不确定性的主要来源。对日本北方Wadati-Benioff带深层事件的分散P波到达进行全波形模拟，结果表明，在中间深度存在含水断层带结构。分析与板片顶部以下5-35 km处的事件相关的P波尾波，给出了俯冲洋壳地幔大量水化的总体指示，并且可以用40 km厚的层（17%-31%的蛇纹化）来解释。这表明大洋地幔顶部的水化程度为2.0- 3.5 wt%，俯冲温度为170-318 Tg/m. y。日本北方地下每米弧面的水含量。这一数量级的增加，在估计的H2 O流量在这个弧意味着在地球的年龄，相当于多达3.5个现今海洋的水可以被俯冲沿着千岛群岛和伊豆小笠原弧。这些结果提供了第一个直接测量较低的岩石圈水化在中间深度，并建议地幔的再气化比以前提出的更有力。
It is widely proposed that the oceanic mantle is hydrated by outer rise normal faults, and carries large amounts of water to the deep mantle. However, the extent of oceanic mantle hydration is poorly constrained by existing observations, and is a major source of uncertainty in determining the total water delivered to the mantle. Full waveform modeling of dispersed P-wave arrivals from events deep within the Wadati-Benioff zone of northern Japan shows that hydrated fault zone structures are present at intermediate depths. Analysis of the P-wave coda associated with events 5-35 km below the top of the slab gives an overall indication of the bulk hydration of the subducting oceanic mantle, and can be explained by a 40-km-thick layer that is 17%-31% serpentinized. This suggests that the top of the oceanic mantle is 2.0- 3.5 wt% hydrated, subducting 170-318 Tg/m.y. of water per meter of arc beneath northern Japan. This order-of-magnitude increase in the estimated H 2 O fl ux in this arc implies that over the age of the Earth, the equivalent of as many as 3.5 present-day oceans of water could be subducted along the Kuril and Izu-Bonin arcs alone. These results offer the fi rst direct measure of the lower lithosphere hydration at intermediate depths, and suggest that regassing of the mantle is more vigorous than has previously been proposed.