下地幔温压下(Mg,Fe)SiO_3钙钛矿的相稳定性  

Stability of(Mg,Fe)SiO_3-Perovskite under the Condition of Lower Mantle Pressure and Temperature

作　　者：陈修芳[1] 于慧[2] 龚自正[3] 

机构地区：[1]武汉工业学院数理系,湖北武汉430023 [2]沈阳工业大学信息科学与工程学院,辽宁沈阳110023 [3]北京卫星环境工程研究所,北京100094

出　　处：《地球学报》2009年第2期210-214,共5页Acta Geoscientica Sinica

基　　金：国家自然科学基金面上项目(编号:40474033);武汉工业学院校基金(编号:07Y15)联合资助

摘　　要：在69～100GPa冲击压力(估算温度为2600～4300K)范围内进行了初始样品为(Mg0.92,Fe0.08)SiO3顽火辉石和MgO+SiO2的冲击压缩回收实验。对回收样品进行的X射线衍射(XRD)分析结果表明:两发顽火辉石回收样品的主相均是单链状结构硅酸盐,而非钙钛矿结构;另外,回收样品中均未观察到氧化物SiO2和(Mg0.92,Fe0.08)O的XRD特征谱线;两发MgO+SiO2回收样品中均观察到SiO2和镁橄榄石(Mg2SiO4)而没有氧化物MgO。实验结果表明:在冲击压缩过程中样品处于钙钛矿结构,在冲击卸载过程中样品发生了由钙钛矿结构向单链状结构的逆转相变;在实验的温压范围内,不可能发生由(Mg0.92,Fe0.08)SiO3向SiO2和(Mg0.92,Fe0.08)O的化学分解相变,顽火辉石的高压相——钙钛矿结构是稳定的。高压加载或卸载过程引起的晶格畸变导致回收样品和原始样品的谱线差异,而高压加载导致钙钛矿型(Mg0.92,Fe0.08)SiO3晶格畸变的可能性更大。Shock recovery experiments with the initial sample of （Mg0.92, Fe0.08）SiO3 and MgO＋SiO2 were conducted in the pressure range of 69-100 GPa （with the corresponding temperature estimated to be 2600-4300 K）. XRD microanalysis of the recovered samples has yielded the following understanding： （1）The main phase of the recovered sample is enstatite of the single-chain structure instead of that of the perovskite structure. Both the XRD characteristic spectrograms of oxides SiO2 and （Mg0.9〉 Fe0.08）O are not observed in the recovered samples; （2）the main components of recovered samples of MgO＋SiO2 are SiO2 and Mg2SiO4. The experiment results show that enstatite is transformed into the perovskite structure under the shock compression whereas the perovskite structure is transformed retrogressively into the single-chain structure during the process of pressure release. It doesn＇t exist the possibility of the chemical decomposition reaction from （Mg0.92, Fe0.08）SiO3 to oxides SiO2 and the production of （Mg0.92, Fe0.08）O under the temperature and pressure condition of the experiment, and hence the high-pressure phase of the enstatite-perovskite structure remains stable under the experimental condition. In addition, the spectral difference between the original sample and the recovered samples might be attributed to the crystal distortion under the shock compression or the release process, and the loading process might probably re- sult in such a distortion.

关 键 词：顽火辉石 冲击回收 相稳定性 XRD分析 

分 类 号：P511[天文地球—地质学] P578