岫玉的地震波速、各向异性、弹性力学性质及其构造地质意义  

Seismic Velocities,Anisotropy and Elastic Properties of Xiuyan Jade and its Geological Implications

作　　者：王茜[1,2] 邵同宾 嵇少丞 道林克祯[3] 近藤洋裕[3] 龙长兴[4] 孙圣思[5] 

机构地区：[1]中国科学院,广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 [2]加拿大蒙特利尔综合工学院民用、地质与采矿工程系,蒙特利尔H3C3A7 [3]日本静冈大学地球科学系,静冈422-8529 [4]中国地质科学院,地质力学研究所,北京100081 [5]西北大学地质学系,陕西西安710069

出　　处：《大地构造与成矿学》2014年第1期12-26,共15页Geotectonica et Metallogenia

基　　金：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);国家“深部探测计划”(编号:SinoProbe-07);国家自然科学基金(批准号:41090373、41174072);加拿大自然科学和工程研究基金会Discovery项目共同资助的成果

摘　　要：为了研究水化岩石圈地幔和地幔楔的地震波速、各向异性及其与蛇纹石化程度及应变状态的关系,作者实验测量了8块叶蛇纹岩（采自辽宁的岫玉）标本在不同构造主方向（X, Y和Z）上的纵、横波速度随围压（0~600 MPa）的变化规律,详细研究了叶蛇纹石在塑性变形过程中通过（001）[010]位错滑移形成很强的晶格优选定向和高达21%的纵波速度各向异性与24%的剪切波分裂的特征,发现高温叶蛇纹岩与低温利蛇纹岩具有截然不同的地震波性质,例如,在围压600 MPa 下,高温叶蛇纹岩的 Vp=6.73 km/s、Vs=3.74 km/s, Vp/Vs=1.80,而低温利蛇纹岩的Vp=5.10 km/s、Vs=2.32 km/s, Vp/Vs=2.20。前人利用低温蛇纹石化橄榄岩的波速数据解释温度高于300℃的水化地幔楔和岩石圈地幔的地震波速不可避免地要低估研究区域内蛇纹石化的程度和水含量。本研究查明叶蛇纹岩的地震波性质及其各向异性特征亦为解释全球大洋板块俯冲带乃至青藏高原地区的剪切波分裂资料提供了新的思路。Antigorite is a main contributor to the formation of anomalously low seismic velocities and high anisotropy in subducting oceanic slabs, forearc mantle wedges and subcontinental mantle shear zones. Here we report new results on P- and S-wave velocities and anisotropy in 8 antigorite serpentinite samples （“Xiuyan jade” from Liaoning, China）, measured at pressures up to 600 MPa. The results combined with previous experimental data allow us to distinguish the effects of low and high temperature （LT and HT） serpentinization on seismic velocities in the upper mantle. Serpentine contents in hydrous subducting slabs, mantle wedges and subcontinental mantle shear zones where temperature is＆gt;300 ℃should be at least twice as large as previous estimates based on LT serpentinization. The intrinsic Vp and Vs anisotropy of serpentinites, formed by plastic flow-induced lattice-preferred orientation （LPO） of antigorite, can be as high as 21%and 24%, respectively. Our results provide a new explanation for various anisotropy patterns observed in subduction systems worldwide. For a steeply subducting slab, antigorite is most likely deformed by nearly coaxial flattening and thus the trench-parallel seismic velocity is much faster than the trench-normal velocity. For a shallowly subducting slab, however, antigorite is most likely deformed by simple shear. Within the horizontal plane, the trench-normal velocity can be smaller, equal to, or larger than the trench-parallel velocity, depending on the dip angle of subduction. The geophysical characteristics of the Tibetan Plateau such as strong heterogeneities in seismic velocities and attenuation, shear wave splitting and electric conductivity can be equally explained by the presence of serpentinized shear zones within the subcontinental mantle.

关 键 词：岫玉 叶蛇纹岩 地震波速 各向异性 剪切波分裂 板块俯冲带 青藏高原 

分 类 号：P541[天文地球—构造地质学] P31[天文地球—地质学]