Primordial Noble Gases from Earth's Mantle: Identification of a Primitive Volatile Component

Abstract

Carbon dioxide well gases in Colorado, New Mexico, and South Australia show excesses of 124–128 Xe correlated with 129 I-derived 129 Xe and 20 Ne/ 22 Ne ratios that are higher than the atmospheric 20 Ne/ 22 Ne ratio. The xenon isotopic data indicate the presence of a solarlike component deep within Earth. The presence of this component in crustal and upper mantle reservoirs may be explained by a steady-state transport of noble gases from the lower mantle, which still retains much of its juvenile volatile inventory. These measurements also indicate that the mantle source of these noble gases in the carbon dioxide well gases cannot be the source of Earth's present atmosphere. The variations observed in 129 Xe/ 130 Xe between solar wind xenon, Earth's atmosphere, and mantle samples may be generated by variations of iodine/xenon in terrestrial reservoirs, as opposed to rapid early degassing.