Distribution of noble gases in Chinese tektites: Implications for neon solubility in natural gases

Abstract

Five indochinites from Hainan Island and the Leizhou Peninsula, China were analyzed for noble gas abundances and isotopic ratios. These splash-form tektites show vesiculation ranging from 0.4 vol% to 8 vol%, as determined by digital image analysis (software SXM®) on thin section photographs. To study the distribution of noble gases in vesicles and in glass, the gases were extracted by heating and by crushing, respectively, on 2 aliquots of the same sample. The results show that 5 to 53% of the total measured 20Ne resides in vesicles. The calculated concentration of neon dissolved in the glass is higher (0.7-1 x 10^(-7) cm3STP/g) than that expected from solubility equilibrium (1 10^(-8) cm3STP/g), assuming solubility data from MORB glasses. The neon concentration of splash-form tektites, those analyzed in this work and those from other strewn-fields worldwide, is correlated with the SiO2 content of glass and with the nonbridging oxygen per tetrahedral cation in the melt (hereafter NBO/T ratio), the latter being an index of the free-volume in the silica network where neon could be dissolved. These correlations suggest that the glass structure of tektite has a larger free-volume available for dissolving noble gases than MORB glasses.