| 韧性剪切带中片麻岩和超高压榴辉岩变形特征及其与地震波速各向异性的关系：来自中国大陆科学钻探（CCSD）680～1200米岩心的证据 |
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| 引用本文： | 陈意,金振民,欧新功,金淑燕,徐海军.韧性剪切带中片麻岩和超高压榴辉岩变形特征及其与地震波速各向异性的关系：来自中国大陆科学钻探（CCSD）680～1200米岩心的证据[J].岩石学报,2004,20(1):97-108. |
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| 作者姓名： | 陈意 金振民 欧新功 金淑燕 徐海军 |
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| 作者单位： | 1. 中国地质大学,武汉,地球科学学院,武汉,430074;中国科学院地质与地球物理研究所,北京,100029
2. 中国地质大学,武汉,地球科学学院,武汉,430074 |
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| 基金项目： | 国家重点基础研究发展规划项目(2003CB716500)，国家重大科学工程项目“中国大陆科学钻探工程”，中国地质大学地质学理科基地项目联合资助 |
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| 摘 要： | 中国大陆科学钻探(CCSD)680-1200米区段发育了多个韧性剪切带,带中主要岩石类型包括片麻岩和超高压榴辉岩。片麻岩中的变形石英、面理化榴辉岩中的拉长石榴石和绿辉石的应变轴比都表现为X>Y>Z,Flinn系数分别为0.11-0.27、0.22-0.23和0.23-0.24。随着糜棱岩化作用的增强,变形石英的C轴组构由Z轴极密逐渐向Y轴极密和叶理面上的大圆环带转变。在常温常压下测试了样品的波速,计算出片麻岩Vp和Vs的各向异性分别为30.17％-60.97％和11.52％-35.79％,榴辉岩Vp和Vs的各向异性分别为0.17％-11.19％和2.41％-6.70％。影响各向异性的主要因素有岩石的结构构造、矿物的晶格优选方位(LPO)、形态优选方位(SPO)和定向微裂隙。随着糜棱岩化作用的增强,岩石的P波各向异性逐 渐升高。变形岩石中的黑云母、石英、绿辉石的LPO和SPO是地震波各向异性的主要控制因素。饱水后的片麻岩样品的P波各向异性明显低于干燥片麻岩样品。在东海钻井中的强反射带主要是由于不同岩层之间的波阻抗差异而造成的,榴辉岩/强退变榴辉岩和黑云斜长片麻岩之间的接触界面会产生较强的地震深反射。此外,与LPO相关的地震波各向异性会增强地震波的反射,所以韧性剪切带中的糜棱岩化片麻岩可能是地震反射的良好载体。韧性剪切带中岩石弹性波速度的强各向
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| 关 键 词： | 韧性剪切带 片麻岩 超高压榴辉岩 各向异性 地震深反射 中国大陆科学钻探 |
| 文章编号： | 1000-0569/2004/020(01)-0097-08 |
| 修稿时间： | 2003/11/30 0:00:00 |
Deformation features of gneiss and UHP eclogite from ductile shear zone and its relation with seismic velocity anisotropy: Evidences from core samples at depth of 680 ~ 1200m of CCSD |
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| China University of Geosciences,Wuhan,China Institure of Geology and Geophysics,Chinese Academy of Sciences,Beijing,China.Deformation features of gneiss and UHP eclogite from ductile shear zone and its relation with seismic velocity anisotropy: Evidences from core samples at depth of 680 ~ 1200m of CCSD[J].Acta Petrologica Sinica,2004,20(1):97-108. |
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| Authors: | China University of Geosciences Wuhan China Institure of Geology and Geophysics Chinese Academy of Sciences Beijing China |
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| Abstract: | Several ductile shear zones developed at depth of 680 - 1200m of CCSD. The main rock types in the shear zone include gneisses and UHP eclogites. The strain axes of deformed quartz in gneisses and stretch garnets and omphacites in eclogites are expressed as X > Y > Z ratios. Their flinn coefficients vary from 0. 11 to 0. 27 , 0. 22 to 0. 23 and 0. 23 to 0. 24, respectively. In the gneiss sample the C - axis fabric of deformed quartz shows a great circle normal to the foliation and a maximum near Z. With the strengthening of mylonitization, the fabrics become a great circle near the foliation and a maximum near Y. P- and S-wave velocities were measured at room temperature and pressure. Calculated P- and S-wave velocity anisotropies of gneisses vary from 30. 17% to 60.97% and 11.52% to 35.79%, while those of eclogite vary from 0. 17% toll.19% and 2.41% to 6.70%, respectively. Seismic velocity anisotropies are mainly caused by lattice preferred orientation( LPO) , shape preferred orientation( SPO) of the major minerals, and oriented microcracks. P-wave velocity anisotropies of gneiss increase with strengthening mylonitization. LPO and SPO of biotite, quartz and omphacite are responsible for the velocity anisotropy of deformed rocks. P-wave velocity anisotropies of water-saturated gneiss are lower than those of dry gneiss. The strongly reflective zone beneath the Donghai drill site can be explained by the impedance contrasts between the different lithologies. Contacts between eclogite/retrograde eclogite and biotite-plagioclase gneiss may give rise to strong seismic reflections. In addition, lattice preferred orientation-related seismic anisotropy can increase reflectivity, thus the mylonitized gneiss in ductile shear zone may be good reflectors. The strong anisotropy of ductile shear zone provides important constraints on interpretations of seismic deep reflection results. |
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| Keywords: | Ductile shear zone Gneiss UHP eclogite Anisotropy Seismic deep reflection Chinese Continental Scientific Drilling(CCSD) |
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