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Distinct slab interfaces imaged within the mantle transition zone
Nature Geoscience ( IF 18.3 ) Pub Date : 2020-11-09 , DOI: 10.1038/s41561-020-00653-5
Xin Wang , Qi-Fu Chen , Fenglin Niu , Shengji Wei , Jieyuan Ning , Juan Li , Weijun Wang , Johannes Buchen , Lijun Liu

Oceanic lithosphere descends into Earth’s mantle at subduction zones and drives material exchange between Earth’s surface and its deep interior. The subduction process creates chemical and thermal heterogeneities in the mantle, with the strongest gradients located at the interfaces between subducted slabs and the surrounding mantle. Seismic imaging of slab interfaces is key to understanding slab compositional layering, deep-water cycling and melting, yet the existence of slab interfaces below 200 km remains unconfirmed. Here, we observe two sharp and slightly dipping seismic discontinuities within the mantle transition zone beneath the western Pacific subduction zone that coincide spatially with the upper and lower bounds of the high-velocity slab. Based on a multi-frequency receiver function waveform modelling, we found the upper discontinuity to be consistent with the Mohorovičić discontinuity of the subducted oceanic lithosphere in the mantle transition zone. The lower discontinuity could be caused by partial melting of sub-slab asthenosphere under hydrous conditions in the seaward portion of the slab. Our observations show distinct slab–mantle boundaries at depths between 410 and 660 km, deeper than previously observed, suggesting a compositionally layered slab and high water contents beneath the slab.



中文翻译:

在地幔过渡带中成像的不同平板界面

海洋岩石圈在俯冲带下降到地幔中,并推动地球表面与其深层内部之间的物质交换。俯冲过程在地幔中产生化学和热非均质性,最强的梯度位于俯冲板与周围地幔之间的界面处。板坯界面的地震成像是了解板坯成分分层,深水循环和融化的关键,但尚未确定200 km以下板坯界面的存在。在这里,我们在西太平洋俯冲带下方的地幔过渡带中观察到两个尖锐且略微倾斜的地震不连续点,它们在空间上与高速平板的上下限相吻合。基于多频接收器功能波形建模,我们发现上不连续性与地幔过渡带俯冲海洋岩石圈的Mohorovičić不连续性一致。较低的不连续性可能是由于在含水条件下,板坯向海部分中的软板软流圈的部分融化引起的。我们的观察结果显示,在410至660 km的深度处,板-地幔边界明显不同,比以前观察到的要深,这表明板是组成分层的板,板下含水量很高。

更新日期:2020-11-09
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