Experimental geochemistry of iodine, argon and xenon: Implications for the outgassing histories of the Earth and Mars.

Abstract

This dissertation presents results from experiments measuring the silicate-melt solubility of iodine conducted at one atmosphere and the mineral/melt partitioning behavior of iodine, argon and xenon conducted at one atmosphere and 15kbars. The solubility of iodine in silicate melts is strongly correlated with the molar volume and the degree of polymerization of the melt. Results of mineral/melt partitioning studies show that iodine is at least ten times more incompatible than xenon. The values of argon mineral/melt partition coefficients determined in this study fall in the low range of those determined in previous investigations. These results, along with other parameters are used to assess the timing and extent of early mantle outgassing for the Earth and Mars. If outgassing alone is responsible for the xenon isotopic composition of the mantle source of the mid-ocean ridge basalts, then the mantle outgassed 99 percent of it's volatiles within the first 100 million years following the nucleosynthesis process, which preceded the formation of the solar system. Furthermore, the mantle experienced a nearly 100 percent molten state sometime during this period. Straight forward early outgassing cannot explain the isotopic composition of the martian atmosphere. A two-stage outgassing scenario can explain it, but requires the existence of an as yet unsampled mantle reservoir. Alternatively, water solubility fractionation very early in martian history may have played a significant role in determining the isotopic composition of the present-day martian atmosphere.