Searching for incorporation of noble gases into potassium-rich silicate under lower mantle condition

Abstract

Noble gases are chemically stable and inert volatile elements. They are important tracers for exploring Earth's volatile cycle and its evolution of the atmosphere. In particular, xenon abundance on Earth and Mars is known to be depleted compared to other noble gas elements. However, the details of Xe reservoirs in the Earth's interior are still unknown. To solve this "missing xenon" problem, this study focused on identifying mineral species that could retain xenon in the Earth's interior. We experimentally explored the possibility of noble gas incorporation (especially Xe and Ar) into potassium-rich silicate KAlSi₃O₈, which is stable in the entire lower mantle. In-situ X-ray diffraction and Raman spectroscopy under high pressure using a laser-heated diamond anvil cell and chemical analysis of recovered samples were performed. The incorporation of noble gases into the crystal structure of KAlSi₃O₈ with a hollandite structure and its mechanism are discussed.