A stagnant slab in a water-bearing mantle transition zone beneath northeast China: implications from regional SH waveform modelling
A stagnant slab in a water-bearing mantle transition zone beneath northeast China: implications from regional SH waveform modelling
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DOI：
10.1111/j.1365-246x.2011.05063.x
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发表时间：
2011-08
影响因子：
2.8
通讯作者：
L. Ye;Juan Li;T. Tseng;Z. Yao
中科院分区：
文献类型：
--
作者：
L. Ye;Juan Li;T. Tseng;Z. Yao
利用密集区域地震台网记录的SH波形，对中国东北地区上地幔过渡带的剪切波速度结构进行了约束。通过模拟三重波波形，我们发现，130公里厚的层增加地震速度是覆盖一个广泛的轻微凹陷660公里的不连续性。这种异常可能与停滞的太平洋板块的向西向延伸有关，该板块被偏转并且仍然很冷。过渡区总体上具有低剪切波速度和高Vp/Vs比的特征，推测H2O含量为0.2- 0.3wt%。660 km不连续面顶部的H/Si值为（3.0-4.5）× 104 ppm。我们解释说，快速东退的日本海沟促进板片压扁时，俯冲的海洋岩石圈击中底部的过渡带，板片的前缘目前被困在中国东北部的含水地幔。
SUMMARY SH waveforms recorded by a dense regional seismic network are used to constrain the shear wave velocity structure of the upper-mantle transition zone beneath northeast China. By modelling triplication waveforms we show that a 130-km-thick layer of increased seismic velocities is overlying a broad slightly depressed 660 km discontinuity. This anomaly can be associated with the westward extension of the stagnant Pacific slab that is deflected and still cold. The transition zone, as a whole, is featured by low shear wave velocity and high Vp/Vs ratio, which infer H2O content of ∼0.2–0.3 wt. per cent [(3.0–4.5)×10 4 ppm H/Si] atop the 660 km discontinuity. We interpret that the fast eastward retreat of the Japan Trench facilitated the slab flattening when the subducting oceanic lithosphere hit the bottom of the transition zone, and the leading edge of the slab is currently trapped in a water-bearing mantle beneath northeast China.