富铁橄榄石的水溶性实验研究  

Experimental study of water solubility in iron rich olivine

作　　者：杨家英[1,2] 张琼 赵永红[1,2] 李杨[2] KOHLSTEDT David L YANG JiaYing;ZHANG Qiong;ZHAO YongHong;LI Yang(Department of Geophysics,Peking University,Beijing 100871,China;Department of Earth Science,University of Minnesota,Minneapolis MN55455,USA)

机构地区：[1]北京大学地球物理系,北京100871 [2]美国明尼苏达大学地球科学系,MN 55455

出　　处：《岩石学报》2022年第4期1280-1284,共5页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40874043、41274094、40872133)资助.

摘　　要：地幔的力学性质主要受橄榄石流变性的控制,含水对橄榄石流变性质的影响很大,而橄榄石的水溶性受到温度和铁含量的影响,因此,本文进行了不同铁含量橄榄石在不同温度下的水溶性实验研究。实验使用的样品为天然橄榄石单晶Fa_(17)和Fa_(24.7)(Fe_(No.)=100×molar Fe/(Mg+Fe))以及人工合成的橄榄石单晶Fa_(22);橄榄石单晶的水溶性实验在300MPa围压和1273~1473K的温度条件下进行,每隔50K进行一组实验,氧逸度被控制在Ni NiO水平上。实验结束后,对橄榄石单晶沿b面进行双面研磨抛光,用电子探针分析确定橄榄石单晶成分,采用EBSD精确测量橄榄石的单晶方向,使用红外光谱仪(FTIR)的非偏振光路测试橄榄石单晶在b轴上的吸收光谱。对FTIR吸收光谱进行积分得到富铁橄榄石的水溶性实验结果:当温度由1273K升至1473K时,橄榄石单晶Fa_(17)的水溶性变化为600~1200H/10^(6) Si,橄榄石单晶Fa_(24.7)的水溶性变化为1000~1300H/10^(6) Si,人工合成的橄榄石单晶Fa_(22)的水溶性变化为500~900 H/10^(6) Si。因此,相同铁含量橄榄石单晶的水溶性随温度的增加而增加,相同温度条件下,天然形成的橄榄石的水溶性随着铁含量的增加而增加,百分之一的铁含量的增加,可以导致约百分之十的水溶性的增加。本文所研究的不同铁含量的橄榄石可以为更好地估算上地幔水溶性提供依据。The mechanical property of the upper mantle is controlled by the rheological properties of olivine.Water has great influence on the mechanical properties of olivine.Results showed that different temperatures and iron contents have influence on the water solubility of olivine.Therefore,the water solubility experiment was conducted on olivine with different iron contents at different temperatures in this paper.The olivine single crystals used in this study include natural San Carlo olivine single crystal Fa_(17),Fa_(24.7)(Fe_(no.)=100×molar Fe/(Mg+Fe))and synthetic olivine single crystal Fa_(22).Experiments were performed at temperatures between 1273K and 1473K with 50K increments at a confining pressure of 300MPa in a gas medium apparatus with oxygen fugacity buffered by the Ni NiO.After the test,the olivine single crystal was double polished along b-plane.The composition was measured by Electron Probe,the orientation was determined by Electron Backscattered Diffraction(EBSD)and the OH absorption spectra were recorded by infrared spectroscopy,respectively,for each of the single crystal.Results showed that,when the temperature changes from 1273K to 1473K,the water solubility of Fa_(17) olivine varied from 600 to 1200 H/10^(6) Si,Fa_(17) olivine from 1000 to 1300 H/10^(6) Si and the synthetic Fa_(22) olivine from 500 to 900 H/10^(6) Si,respectively.Therefore,the water solubility of the olivine with the same iron content increases with the increase of the temperature.The water solubility of the olivine at the same temperature increases with the increase of the iron content for natural San Carlo olivine.One percent increase in iron content resulted in ten percent increase in water solubility.In this paper,the water solubility in olivine at several Fe contents can be used to estimate the water storage in the upper mantle.

关 键 词：橄榄石 水溶性 温度 铁含量 

分 类 号：P589.1[天文地球—岩石学]