Evidence for xenon silicates at high pressure and temperature

Abstract

We present evidence for the stability of xenon silicate phases at deep crustal conditions. High pressure-temperature investigations of the Xe-SiO2 system were conducted using diamond-anvil cells combined with laser heating and external resistive heating. A new compound was synthesized at 0.7-1.5 GPa and 1500-1750 as evidenced by Raman spectroscopy. Upon temperature quenching, the material undergoes a back transformation to another Xe-SiO2 phase stable up to 2.14 GPa. X-ray diffraction data show that this second phase has a cubic structure [a = 8.03(±0.03) Å] and a bulk modulus of 20(±0.6) GPa. The phase was found to have a minimum of 4 wt% Xe from electron microprobe analysis. These results indicate that the chemical affinity of Xe and silica increases at high pressures and temperatures. Hence Xe can be potentially hosted by silicates in the crust, which helps to resolve the geochemical paradox of the 'missing Xe' in the atmospheres of the Earth and Mars.