Mantle Transition Zone Structure Beneath Northeast Asia From 2‐D Triplicated Waveform Modeling: Implication for a Segmented Stagnant Slab
Mantle Transition Zone Structure Beneath Northeast Asia From 2‐D Triplicated Waveform Modeling: Implication for a Segmented Stagnant Slab
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DOI：
10.1029/2018jb016642
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发表时间：
2019-02
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通讯作者：
Y. Lai;Ling Chen;Tao Wang;Z. Zhan
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作者：
Y. Lai;Ling Chen;Tao Wang;Z. Zhan
俯冲带中地幔过渡带的结构是理解深部地幔俯冲动力学及其地表响应的基础。基于二维三重波波形模拟，建立了东北亚MTZ的P（Vp）和SH速度（Vs）结构图像。在上MTZ，三重数据要求Vp正常，但Vs层比IASP 91低2.5%。在MTZ的下部，我们的结果显示了一个相对较高的速度层（与IASP 91相比，Vp为+2%，Vs为-0.5%），厚度约为140 km，长度约为1，200 km，位于660 km的不连续面之上。将该异常作为停滞板片，考虑到晚新生代西太平洋地区板块收敛速率为7-10 cm/a，推断停滞板片的俯冲年龄小于30 Ma。这表明，所观察到的板片停滞在MTZ在东北亚之下可能发生不早于早渐新世。根据Vp和Vs构造的约束条件，整个东北亚MTZ的Vp/Vs比值较高，这可能意味着富水和/或碳酸盐环境。在整体高速停滞板内，进一步检测到低速异常，宽度约为150 km，Vp和Vs相对于IASP 91分别降低了1%和3%。这样的一个缺口可能为深部地幔热物质提供了一个通道，使其穿过厚板块，进入长白山火山。
The structure of the mantle transition zone (MTZ) in subduction zones is essential for understanding subduction dynamics in the deep mantle and its surface responses. We constructed the P (Vp) and SH velocity (Vs) structure images of the MTZ beneath Northeast Asia based on two‐dimensional (2‐D) triplicated waveform modeling. In the upper MTZ, a normal Vp but 2.5% low Vs layer compared with IASP91 are required by the triplication data. In the lower MTZ, our results show a relatively higher‐velocity layer (+2% Vp and −0.5% Vs compared to IASP91) with a thickness of ~140 km and length of ~1,200 km atop the 660‐km discontinuity. Taking this anomaly as the stagnant slab and considering the plate convergence rate of 7–10 cm/year in the western Pacific region during the late Cenozoic, we deduced that the stagnant slab has a subduction age of less than 30 Ma. This suggests that the observed stagnancy of the slab in the MTZ beneath Northeast Asia may have occurred no earlier than the Early Oligocene. From the constraints derived individually on Vp and Vs structures, high Vp/Vs ratios are obtained for the entire MTZ beneath Northeast Asia, which may imply a water‐rich and/or carbonated environment. Within the overall higher‐velocity stagnant slab, a low‐velocity anomaly was further detected, with a width of ~150 km, Vp and Vs reductions of 1% and 3% relative to IASP91. Such a gap may have provided a passage for hot deep mantle materials to penetrate through the thick slab and feed the Changbaishan volcano.