[SIT21-P15] Determination of the noble gas partition coefficients between metal-silicate melts under high-pressure and high-temperature conditions
In order to investigate noble gas partitioning behavior between the core and mantle, noble gases were dissolved into metal-silicate melts under high temperature and pressure conditions, and then the samples were quenched, recovered, and analyzed for noble gas concentrations. Sample synthesis was performed at the Geodynamics Research Center, Ehime University. Noble-gas doped silicate glass and iron were melted and equilibrated under high pressure and temperature (3-6 GPa, 1700 and 1800 °C) using a multianvil apparatus. The sample capsule was cut and the polished surface of the section was investigated with scanning electron microscope and Raman spectroscopy. The chemical compositions of silicate and metal phases were determined with electron microprobe. And then, the noble gases in the silicate phase were extracted by an ultraviolet laser ablation apparatus and analyzed using a noble gas mass spectrometer at the University of Tokyo.
From the Raman spectra, it was found that crystallization (clinopyroxene) had occurred in samples synthesized at pressures of 6 GPa or higher, indicating that the sample quenching was not enough rapid. There is a possibility that noble gas may not be contained much in the crystallized part because a previous study showed that noble gas content in pyroxene crystal is smaller than those in glass (melt) by about 10-4 (Heber et al., 2007). The noble gas concentrations in silicate glass phase are fairly homogeneous, even where a crack is formed during quenching. In future we will measure the noble gases in the iron part and determine the partition coefficient of the noble gases.
References: Bouhifd et al, Nature Geoscience. 6, 982-986, 2013; Mukhopadhyay, Nature 486, 101-104, 2012; Porcelli & Ballentine, Rev. Mineral. Geochem. 47, 411-480, 2002; Trieloff & Kunz, Phys. Earth Planet. Inter. 148, 13-38, 2005; Herber et al, Geochim. Cosmochim. Acta. 71, 1041-1061, 2007