mu-Erda developments in order to improve the water content determination in hydrous and nominally anhydrous mantle phases

作者：Raepsaet C^*; Bureau H; Khodja H; Aubaud C; Carraro A

来源：Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms , 2008, 266(8): 1333-1337.

DOI：10.1016/j.nimb.2008.01.028

• hydrogen
• ERDA
• microbeam
• Earth mantle
• Earth crust

The precise knowledge of the water content in geological samples such as mantle minerals, volcanic glasses and glassy inclusions proves to be crucial information for the Earth Sciences because water has a considerable influence on physical and chemical properties of Earth's mantle and crust. Among the nuclear microbeam techniques, elastic recoil detection analysis (ERDA) has been used at the nuclear microprobe of the Pierre Sue Laboratory (LPS) with a very good reliability for a long time to determine the water content of various materials. Previous ERDA measurements gave the total H content at a micrometric scale in the bulk of hydrous geologic samples. However, it was more difficult to characterize nominally anhydrous phases. Recent efforts allowed us to significantly improve the different steps of the ERDA analysis, from the sample preparation to the determination of the uncertainties of the resulting H concentration. A large series of very different geological samples has been measured: volcanic glasses and glassy inclusions, synthetic and natural nominally anhydrous minerals. Our new sample preparation protocol limited the thickness of the surface layer of H-pollution, leading to an easier differentiation of the bulk contribution. Simultaneous PIXE and RBS measurements allow the precise location of the interesting areas and also give information on the chemical characterization of the investigated samples, with respect to the major and minor elements. The processing of the list-mode acquisition files is made using the RISMIN software, allowing among other interesting features to check the absence of water loss under the beam. We will present the results of the H-content measurements and show the good agreement between our present results and those obtained by Fourier transform infrared spectroscopy (FTIR) for the same set of samples. The detection limit was measured on a dehydrated natural San Carlos olivine ((Mg,Fe)(2)SiO4) equal to 130 wt ppm H2O (15 wt ppm H or 300 at ppm H) and the relative uncertainties on the water concentration range from 10% to 15%.

• 出版日期2008-4
• 单位中国地震局