高校地质学报2018，Vol.24Issue(1)：1-12,12.DOI:10.16108/j.issn1006-7493.2017056
电子背散射衍射和傅里叶变换红外光谱结合测量橄榄石的原位含水量
In Situ Water Contents of Olivine from Combined Electron Backscatter Diffraction and Fourier Transform Infrared Analysis
摘要
Abstract
Water contents in olivine have significant effects on physical and chemical properties of the upper mantle. Water concentration in nominally anhydrous minerals is mainly determined by Fourier transform infrared(FTIR)spectroscopy based on the absorption coefficients of infrared light, which vary along different crystallographic directions in anisotropic minerals. Ideally, water contents in olivine should be analyzed on oriented grains using the polarized infrared light. However, this method is very time consuming because it requires mineral separation and orientation. Previous studies usually used unpolarized infrared light and calculated the average water content of many olivine grains in a thin section by Paterson(1982) calibration. However, application of unpolarized light assumes random orientation of mineral grains, which may underestimate water contents in olivine. Olivine in the upper mantle often develops lattice preferred orientation.In order to obtain water contents in olivine in a more effective and accurate way, this paper presents a new method to measure in situ water contents of olivine in a thin section using the combined electron backscatter diffraction(EBSD)and FTIR analysis.Based on results of Bell et al.(2003),an ellipsoid of the water absorption coefficient(W)is established using W values along three crystallographic axes[100],[010]and[001].Then based on the EBSD-derived orientation of an olivine grain,the specific water absorption coefficient along a certain direction(Ws)in the ellipsoid is determined.Finally,water content of the olivine grain is calculated using the Beer-Lambert equation. This method is applied to measure water concentration of olivine from garnet peridotite xenoliths brought by Muskox kimberlites in the Slave Craton(Canada).The results demonstrate that this method allows us to determine in situ water distribution of olivine in microscale and investigate the relationship between water contents and fabrics of olivine.关键词
橄榄石/含水量/傅里叶红外光谱/电子背散射衍射/晶格优选定向Key words
olivine/water content/Fourier transform infrared/electron backscatter diffraction/lattice preferred orientation分类
天文与地球科学引用本文复制引用
闫浩洁,王勤..电子背散射衍射和傅里叶变换红外光谱结合测量橄榄石的原位含水量[J].高校地质学报,2018,24(1):1-12,12.基金项目
国家自然科学基金重大项目(41590623) （41590623）
