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首页> 外文期刊>Gondwana research: international geoscience journal >Mantle dynamics of Western Pacific and East Asia: Insight from seismic tomography and mineral physics
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Mantle dynamics of Western Pacific and East Asia: Insight from seismic tomography and mineral physics

机译：西太平洋和东亚的地幔动力学：地震层析成像和矿物物理学的见解

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Recent results of high-resolution seismic tomography and mineral physics experiments are used to study mantle dynamics of Western Pacific and East Asia. The most important processes in subduction zones are the shallow and deep slab dehydration and the convective circulation (corner flow) processes in the mantle wedge. The combination of the two processes may have caused the back-arc spreading in the Lau basin, affected the morphology of the subducting Philippine Sea slab and its seismicity under southwest Japan, and contributed to the formation of the continental rift system and intraplate volcanism in Northeast Asia, which are clearly visible in our tomographic images. Slow anomalies are also found in the mantle under the subducting Pacific slab, which may represent (a) small mantle plumes, (b) upwellings associated with the slab collapsing down to the lower mantle, or (c) sub-slab dehydration associated with deep earthquakes caused by the reactivation of large faults preserved in the slab. Combining tomographic images and earthquake hypocenters with phase diagrams in the systems of peridotite+water, we proposed a petrologic model for arc volcanism. Arc magmas are caused by the dehydration reactions of hydrated slab peridotite that supply water-rich fluids to the mantle wedge and cause partial melting of the convecting mantle wedge. A large amount of fluids can be released from hydrated MORB at depths shallower than 55 km, which move upwards to hydrate the wedge corner under the fore-arc, and never drag down to the deeper mantle along the slab surface. Slab dehydration reactions at 120 km depth are the antigorite-related 5 reactions which supply water-rich fluids for forming the volcanic front. Phase A and Mg-surssasite breakdown reactions at 200 and 300 km depths below 700 degrees C cause the second and third arcs, respectively. Moreover, the dehydration reactions of super-hydrous phase B, phases D and E at 500-660 km depths cause the fluid transportation to the mantle boundary layer (MBL) (410-660 km depth). The stagnant slabs extend from Japan to Beijing, China for over 1000 km long, indicating that the arc-trench system covers the entire region from the Japan trench to East Asia. We propose a big mantle wedge (BMW) model herein, where hydrous plumes originating from 410 km depth cause a series of intra-continental hot regions. Fluids derived from MBL accumulated by the double-sided subduction zones, rather than the India-Asia collision and the subsequent indentation into Asia, are the major cause for the active tectonics and mantle dynamics in this broad region. (C) 2006 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
机译：高分辨率地震层析成像和矿物物理实验的最新结果用于研究西太平洋和东亚的地幔动力学。俯冲带中最重要的过程是板块的浅层和深层脱水以及地幔楔中的对流循环（角流）过程。这两个过程的结合可能导致了弧形盆地在劳流盆地的扩展，影响了俯冲菲律宾海平板的形态及其在日本西南部的地震活动，并导致了东北部大陆裂谷系统和板内火山活动的形成。亚洲，在我们的断层图像中清晰可见。在俯冲的太平洋板块下的地幔中也发现了缓慢的异常现象，这可能表示（a）小地幔柱，（b）与板块塌陷到下部地幔有关的上升流，或（c）与深部板块有关的子板脱水板块中保留的大断层的复活引起的地震。将橄榄岩+水系统中的层析图像和地震震源与相图相结合，我们提出了弧形火山岩的岩石学模型。弧状岩浆是由水合板状橄榄岩的脱水反应引起的，该反应将富含水的流体供应到地幔楔中，并导致对流的地幔楔部分熔融。深度小于55 km的水化MORB会释放出大量流体，这些流体向上移动以使前弧下方的楔形角水化，而不会沿板块表面向下拖动到更深的地幔中。板坯在120 km深度的脱水反应是与蛇纹石有关的5个反应，它们为形成火山前缘提供了富水流体。在700摄氏度以下200和300 km深度处的A相和Ms-苏铁矿击穿反应分别引起第二和第三弧。而且，超水相B，相D和E在500-660 km深度处的脱水反应导致流体输送到地幔边界层（MBL）（410-660 km深度）。停滞的平板从日本延伸到中国北京，长度超过1000公里，这表明弧形沟槽系统覆盖了从日本沟槽到东亚的整个区域。我们在这里提出一个大地幔楔（BMW）模型，其中410 km深度的含水羽状流引起一系列的陆内热区。两侧俯冲带从MBL积累的流体，而不是印度与亚洲的碰撞以及随后的亚洲凹陷，是造成这一大区域活跃构造和地幔动力学的主要原因。 （C）2006国际冈瓦那研究协会。由Elsevier B.V.发布。保留所有权利。

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