A Partial Molten Low-Velocity Layer Atop the Mantle Transition Zone Beneath the Western Junggar: Implication for the Formation of Subduction-Induced Sub-Slab Mantle Plume
A Partial Molten Low-Velocity Layer Atop the Mantle Transition Zone Beneath the Western Junggar: Implication for the Formation of Subduction-Induced Sub-Slab Mantle Plume
复制标题
西准噶尔地幔过渡带顶部的部分熔融低速层：对俯冲诱发的亚板片地幔柱形成的启示
DOI：
10.1029/2021gc010150
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Dingding Zhang
中科院分区：
文献类型：
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作者：
Guohui Li;Yuanze Zhou;Lin Ding;Yuan Gao;Ling Bai;Heng Zhang;Le Hu;Zhengyang Pan;Changhui Ju;Dingding Zhang
板块的深俯冲一般会在俯冲带周围的地幔过渡带顶部形成部分熔融的低速层。但对于层积体对其上部岩石圈的影响，特别是俯冲板片向洋方向上的影响，人们还不太了解。本文利用新疆地震台网记录的西伯利亚西南部四次地震的三重P波和SH波波形与合成波波形进行匹配，对MTZ顶部的地震速度结构进行了成像。我们的观测结果表明，在中亚造山带西南部西准噶尔（WJ）之下的MTZ顶部存在部分熔融的LVL。当LVL厚度为29 km时，SH波速度下降为-5.6%，大于P波速度下降的-4.4%。推测古亚洲洋板块的俯冲作用促使俯冲板片下的含水MTZ物质上涌到上地幔，形成部分熔融的LVL。结合以往的地球物理和地质结果，我们提出了一个新的地球动力学过程，涉及岩石圈和MTZ下俯冲板片：在LVL的熔体很可能上升通过板片窗口，这可能是由洋中脊俯冲或自我维持。这种模式可以解释晚石炭世-早二叠世WJ中的同时代断裂的化石洋板块、洋岛、玄武岩类岩石、广泛的A型花岗岩类、埃达克岩和斑岩铜金等。
Deep subduction of plate generally could induce a partial molten low-velocity layer (LVL).atop the mantle transition zone (MTZ) around the subduction zone. But the effects of the LVL to its upper.lithosphere are less known, especially at the oceanward direction of subducted slab. Here, we image the seismic.velocity structure atop the MTZ by matching the synthetics and the observed triplicated P- and SH-wave.waveforms recorded by Xinjiang seismic network from four earthquakes in the southwestern Siberia. Our.observations reveal a partial molten LVL atop the MTZ beneath the western Junggar (WJ) in the southwestern.Central Asian Orogenic Belt. The SH-wave velocity drop for the LVL is −5.6% which is larger than −4.4%.of the P-wave when its thickness is 29 km. It is inferred that the subducted Paleo-Asian oceanic plate induces.hydrous MTZ materials underneath the subducted slab to upwell to the upper mantle, and form the partial.molten LVL. Combined with previous geophysical and geological results, we propose a new geodynamical.process involving the lithosphere and MTZ underneath the subducted slab: the melt in the LVL is likely to.upwell through slab window, which could be triggered by mid-oceanic ridge subduction or self-sustained.buoyancy. This mode could account for the contemporaneous break-off fossil oceanic plate, ocean island.basalts-type rocks, extensive A-type granitoids, adakite, and porphyry Cu-Au in the WJ during the late.Carboniferous to early Permian.