The dynamics of big mantle wedge, magma factory, and metamorphic–metasomatic factory in subduction zones
The dynamics of big mantle wedge, magma factory, and metamorphic–metasomatic factory in subduction zones
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DOI：
10.1016/j.gr.2009.07.002
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发表时间：
2009-12
影响因子：
6.1
通讯作者：
S. Maruyama;A. Hasegawa;M. Santosh;T. Kogiso;S. Omori;Hitomi Nakamura;K. Kawai;Dapeng Zhao
中科院分区：
文献类型：
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作者：
S. Maruyama;A. Hasegawa;M. Santosh;T. Kogiso;S. Omori;Hitomi Nakamura;K. Kawai;Dapeng Zhao
东亚大陆边缘的下面是由太平洋板块从东部和菲律宾海板块从南部俯冲形成的停滞板。我们将该区上地幔划分为三个主要区域：（a）交代-变质工厂（MMF）、俯冲带岩浆工厂（SZMF）和“大地幔楔”（BMW）。而对流模式是逆时针方向的MMF域，它主要是顺时针方向的SZMF和宝马，沿着一个横截面从南。在这里，我们定义为一个小的楔角，这是由俯冲太平洋板块驱动，由脱水反应产生的富H2O流体为主，并富含大离子亲石元素（LILE），导致交代作用。SZMF是介于MMF域和BMW域之间的一个区域，构成了楔状体反向角流部分熔融产生陆壳的主要区域。在200 km深度处产生的大的含水羽流导致粘度的大范围降低，而在60 km和200 km之间的较小规模的含水羽流也导致SZMF粘度的总体降低。更肥沃和高温的橄榄岩从入口处提供给这个域。构造域向火山前缘倾斜延伸，然后与俯冲板片一起摆动回地幔深部。BMW占据了西太平洋上地幔的主要部分，并以顺时针方向将东部海沟移向海洋。在410 km深度处的含水羽流的零星形成和邻近海沟的幕流导致弧后扩张。我们设想，BMW的热源可能是地幔过渡带底部积累的TTG（英云闪长岩-奥长花岗岩-花岗闪长岩）地壳。花岗岩地壳向地幔过渡带的持续输送过程，除了太平洋板块和菲律宾海板块的俯冲作用外，还表现为菲律宾海板块从南部俯冲的5个洋内弧的深俯冲。MMF、SZMF和BMW域的动力学受俯冲角度的控制;日本西南部的宽范围MMF域是由菲律宾海板块的浅角度俯冲引起的，马里亚纳海沟的明显小的MMF域是由于太平洋板块的高角度俯冲引起的。日本东北部和九州地区的域介于这两者之间。在第三纪，由于俯冲带沿特提斯亚洲南缘向北沿着移动近2000 km，形成了一系列边缘盆地，这可能与印度与亚洲的碰撞和凹陷有关。亚洲大陆南缘上地幔体积大幅度减小，导致亚洲大陆东缘向洋向沿着向海沟退缩，形成一系列边缘盆地。西太平洋板块总体上具有双面俯冲的特征：东面是最古老的太平洋板块，南面是最古老的印度-澳大利亚板块。因此，古老的板块甚至在其中心区域也被广泛地水合，因此温度较低。裂缝允许水进入板片的较深部分的运输和这些域提供含水流体，甚至到上地幔的底部。因此，西太平洋上地幔流体主导了许多微板块，促进了板块边界过程。
The East Asian continental margin is underlain by stagnant slabs resulting from subduction of the Pacific plate from the east and the Philippine Sea plate from the south. We classify the upper mantle in this region into three major domains: (a) metasomatic–metamorphic factory (MMF), subduction zone magma factory (SZMF), and the ‘big mantle wedge’ (BMW). Whereas the convection pattern is anticlockwise in the MMF domain, it is predominantly clockwise in the SZMF and BMW, along a cross section from the south. Here we define the MMF as a small wedge corner which is driven by the subducting Pacific plate and dominated by H2O-rich fluids derived by dehydration reactions, and enriched in large ion lithophile elements (LILE) which cause the metasomatism. The SZMF is a zone intermediate between MMF and BMW domains and constitutes the main region of continental crust production by partial melting through wedge counter-corner flow. Large hydrous plume generated at about 200 km depth causes extensive reduction in viscosity and the smaller scale hydrous plumes between 60 km and 200 km also bring about an overall reduction in the viscosity of SZMF. More fertile and high temperature peridotites are supplied from the entrance to this domain. The domain extends obliquely to the volcanic front and then swings back to the deep mantle together with the subducting slab. The BMW occupies the major portion of upper mantle in the western Pacific and convects largely with a clockwise sense removing the eastern trench oceanward. Sporadic formation of hydrous plume at the depth of around 410 km and the curtain flow adjacent to the trench cause back arc spreading. We envisage that the heat source in BMW could be the accumulated TTG (tonalite–trondhjemite–granodiorite) crust on the bottom of the mantle transition zone. The ongoing process of transportation of granitic crust into the mantle transition zone is evident from the deep subduction of five intra-oceanic arcs on the subducting Philippine Sea plate from the south, in addition to the sediment trapped subduction by the Pacific plate and Philippine Sea plate. The dynamics of MMF, SZMF and BMW domains are controlled by the angle of subduction; a wide zone of MMF in SW Japan is caused by shallow angle subduction of the Philippine Sea plate and the markedly small MMF domain in the Mariana trench is due to the high angle subduction of Pacific plate. The domains in NE Japan and Kyushu region are intermediate between these two. During the Tertiary, a series of marginal basins were formed because of the nearly 2000 km northward shift of the subduction zone along the southern margin of Tethyan Asia, which may be related to the collision of India with Asia and the indentation. The volume of upper mantle under Asia was reduced extensively on the southern margin with a resultant oceanward trench retreat along the eastern margin of Asia, leading to the formation of a series of marginal basins. The western Pacific domain in general is characterized by double-sided subduction; from the east by the oldest Pacific plate and from the south by the oldest Indo-Australian plate. The old plates are hence hydrated extensively even in their central domains and therefore of low temperature. The cracks have allowed the transport of water into the deeper portions of the slab and these domains supply hydrous fluids even to the bottom of the upper mantle. Thus, a fluid dominated upper mantle in the western Pacific drives a number of microplates and promote the plate boundary processes.