【摘要】 大洋板块俯冲带是许多重要地质作用(例如脱水、部分熔融、岩浆和地震活动)发生的场所。对位于俯冲带之上的地震台站所检测到的不同剪切波的数据解析,可以获得源于上覆板块、地幔楔、俯冲板块和板下地幔的地震波各向异性的关键信息。本文系统总结了世界各地大洋俯冲带的剪切波分裂样式,对目前国际上流行的大洋俯冲带的地震波各向异性的主要成因模式(例如地幔楔拐角流、与海沟迁移有关的平行海沟的地幔流、橄榄石位错蠕变形成各类组构以及蛇纹石化的影响等)进行了较为详尽地评述。由橄榄石(010)[100]、(010)[001]、(100)[001]、{0kl}[100]、(001)[100]和{110}[001]位错蠕变形成的晶格优选定向(LPO)分别称之为A型、B型、C型、D型、E型和F型组构,其中A型、D型和E型组构总是导致剪切快波的偏振方向()平行于地幔流的方向,而B型组构则导致垂直于地幔流的方向。C型组构虽然也能使平行于地幔流方向,但快慢波之间的延迟时间(δt)则不如同等条件下A型组构形成的那么大。F型组构导致剪切波在垂直于地幔流动面的方向上传播时几乎不发生分裂。叶蛇纹石是俯冲板块地幔和地幔楔中最主要的含水矿物,具极低的流变强度、很低的地震波速和很大的弹性各向异性。蛇纹石化程度越高,变形地幔岩的各向异性就越大,则弧前地幔楔的剪切波分裂愈强。只要蛇纹石的含量超过10%～20%,则变形地幔岩的地震波各向异性特征将由蛇纹石的LPO主导。地幔楔的剪切波分裂特征主要取决于其蛇纹石化程度与俯冲角度,陡倾的俯冲和高程度的蛇纹石化有利于形成平行于海沟的。更多还原

【Abstract】 Subduction zones are critically important regions where significant geological processes(e.g.,phase transition,dehydration,partial melting,volcanism,and seismic activity) take place.Seismic anisotropy formed by different parts of subduction system(i.e.,the overriding plate,the mantle wedge,the subducting slab,and the subslab mantle) can be distinguished by analyzing seismic wave raypaths.Here we provide a state-of-art overview on shear wave splitting patterns measured from global oceanic subduction zones,and on mechanism models [e.g.,2D corner flow,3D trench-parallel flow induced by trench migration,olivine lattice preferred orientations(LPO) and serpentinization].Olivine LPOs formed by(010)[100],(010)[001],(100)[001],{0kl}[100],(001)[100] and {110}[001] slip systems are identified as A,B,C,D,E and F-type fabrics,respectively.The A,D,and E-type fabrics cause fast polarization directions() parallel to the mantle flow while  formed by B-type fabric is perpendicular to the mantle flow.Olivine C-type LPO also results in a  parallel to the mantle flow,but the resultant delay time(δt) is much smaller than that of A-type.F-type fabric results in almost no splitting in the direction normal to the mantle flow plane.In mantle wedge and subducting lithosphere mantle,the most important hydrous mineral is antigorite,which is characterized by extremely low flow strength,low seismic velocities,and high elastic anisotropy.Accordingly,the extensively serpentinized mantle wedge rocks usually have relative high seismic anisotropy and shear wave splitting.If more than 10%~20% serpentinization occurs,serpentine LPO would control the seismic anisotropy of the deformed mantle rocks.As the shear wave splitting in mantle wedge depends on both the degree of serpentinization and the slab dip,those highly serpentinized and steeply dipped subduction systems are more likely to produce a trench-parallel .更多还原