蛇纹石化方辉橄榄岩弹性波速实验研究及其在地幔楔中的应用  

Influences of serpentinization on wave velocities of harzburgite and implications in the mantle wedge

作　　者：张佳蕾 马麦宁 张吉凯 曾欢 ZHANG JiaLei;MA MaiNing;ZHANG JiKai;ZENG Huan(Key Laboratory of Computational Geodynamics,College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院计算地球动力学重点实验室,中国科学院大学地球与行星科学学院,北京100049

出　　处：《岩石学报》2023年第8期2533-2540,共8页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42174114、41674089)资助。

摘　　要：地幔楔是俯冲带系统的重要组成单元,在地球内部物质循环、壳幔相互作用过程中起着承上启下的关键作用。俯冲板片脱水可以引起上覆地幔楔中橄榄岩类的蛇纹石化,而蛇纹石的波速显著低于地幔橄榄岩,所以不同蛇纹石化程度的地幔楔表现出不同的低速特征。本研究首先利用天然叶蛇纹石热压合成纯的蛇纹岩样品,利用橄榄石和斜方辉石热压合成方辉橄榄岩样品,然后在高压下分别测量合成的方辉橄榄岩和蛇纹岩样品的纵波速度(VP)和横波速度(VS),结合Voigt-Reuss-Hill岩石物理模型计算得到不同蛇纹石含量的方辉橄榄岩的波速,最后结合地震波资料,估算出不同俯冲带地幔楔的蛇纹石化程度。研究表明,在地幔楔蛇纹石化程度和含水量的估算中,必须考虑斜方辉石蛇纹石化的影响。相比前人研究,方辉橄榄岩的蛇纹石化可能更接近于实际情况。The mantle wedge is an important unit of the subduction zone system,which plays a key role in the material cycle and crust-mantle interaction in the interior of the earth.It is crucial to determine the degree of serpentinization of the mantle wedge which greatly affects the estimation of water contents in subduction zones.As the main product of the serpentinization of peridotite,antigorite's wave velocity can be applied to constraints the degree of serpentinization.In this study,we measured the compressional(V P)and shear(V S)wave velocities of an antigorite and a synthesized harzburgite composed of olivine and orthopyroxene at pressures up to about 8GPa at room temperature.Both V P and V S increase monotonically with increasing pressure.Based on current results,a model has been established to show the pressure and serpentinization dependences of P-wave velocities of serpentinized harzburgite.The model was used to estimate the degrees of serpentinization of some mantle wedges.The study shows that the influence of serpentinization of orthopyroxene must be considered when estimating the degree of serpentinization and water content of the mantle wedge.Compared with previous studies,the serpentinization of harzburgite maybe closer to the real situation.

关 键 词：弹性波速 方辉橄榄岩 叶蛇纹石 蛇纹石化 地幔楔 

分 类 号：P584[天文地球—岩石学] P588.125[天文地球—地质学] P589.1