云南高黎贡山典型斜长角闪岩地震波速、各向异性及其晶格优选定向的研究  

Seismic Velocities, Anisotropy and Petrofabrics of Amphibolite from the Gaoligong Mts., Yunnan

作　　者：嵇少丞[1,2] 道林克祯[3] 邵同宾 赵卫华[2] 近藤洋裕[3] 王红才[2] 

机构地区：[1]加拿大蒙特利尔综合工学院民用、地质与采矿工程系,加拿大蒙特利尔H3C 3A7 [2]中国地质科学院地质力学研究所,中国北京100081 [3]日本静冈大学地球科学系,日本静冈422-8529

出　　处：《地质论评》2013年第4期769-780,共12页Geological Review

基　　金：中国国土资源部“青藏高原东部和东南部岩石圈流变学及地球物理性质研究”(编号1212011121274);“深部探测项目”(SinoProbe-07);加拿大自然科学和工程研究基金会资助项目的成果

摘　　要：斜长角闪岩和角闪岩相变质岩石是大陆中—下地壳、岛弧深部地壳以及俯冲大洋地壳中最重要的组成岩石之一,查明目前地壳中斜长角闪岩的体积含量、空间分布及其应变状态对于深入研究大陆地壳的形成与演化过程极其重要。笔者等实验测量了云南高黎贡韧性剪切带典型变形斜长角闪岩7个关键性方向上的地震(P和S波)波速随静水围压(0～600MPa)的变化规律,并利用电子背散射衍射(EBSD)技术测定了主要造岩矿物角闪石、斜长石和石英的晶格优选方位,查清斜长角闪岩中地震波速各向异性与剪切波分裂的成因,确定斜长角闪岩中有限应变椭球与波速椭球的对应关系,为今后利用原地地震波速的各向异性调查地壳深部区域构造应变场提供必要的实验和理论基础。A large portion of the deep crust beneath the continents and oceanic island arcs may consist of amphibolites dominated by hornblende and plagioclase. An amphibolite can be derived from prograde metamorphism of either mafic igneous rocks or greywackes, or retrograde metamorphism of eclogites and mafic granulites. Furthermore, partial melting of amphibolitic lower crust or subducted oceanic crust is the most likely source for the formation of plutonic bodies of granites, migmatites and trondhjemite-tonalites during orogenic events. Here we report new results on P- and S-wave velocities and anisotropy in a typical amphibolite from the Gaoligong ductile shear zone, Western Yunnan, China, measured along 7 key directions at confining pressures up to 600 MPa. At 600 MPa, P- and S-wave anisotropy coefficients are 14.5% and 12.0%, respectively. The maximum shear wave splitting （0.38 km/s） occurs in the propagating direction at an angle of 55° with each of the three main axes of the finite strain ellipsoid （X is parallel to the stretching lineation, Y parallel to the foliation but perpendicular to the lineation, and Z normal to the foliation）. To the first approximation, the spatial distribution of P-wave velocities in the amphibolites can be represented by an ellipsoid whose longest, moderate and shortest axes are parallel to the X, Y and Z axes of the strain ellipsoid, respectively. Electron backscattering diffractions （EBSD） showed that the （100） planes of hornblende are parallel or subparallel to the XY plane, the [001] crystallographic directions have a strong concentration parallel to X and the [010] directions are parallel to Y. This petrofabric pattern suggests that the hornblende deformed by （100）[001] slip accommodated by anisotropic growth. The seismic anisotropy and shear wave splitting can be well explained by the lattice preferred orientations of hornblende （87 vol%）, plagioclase （7 vol%） and quartz （6 vol%）, characterized using EBSD techniques. The results provide a new calib

关 键 词：斜长角闪岩 地震波速 各向异性 晶格优选定向 有限应变 高黎贡山 

分 类 号：P588.122[天文地球—岩石学]