Noble gas signatures in the Earthʹs interior-coupled or decoupled behaviour among each isotope systematics and problems related to their implication

In order to conjecture the degassing state of the Earthʹs interior, many kinds of noble gas systematics are used to characterize the source materials in the Earthʹs interior. Although some systematics show clear trends, others do not indicate any trends to identify each end-member and relationship. The He–Ne systematics indicates mixing of mantle component with the solar 20Ne/22Ne and the atmosphere-derived component. The Ar–Xe systematics seem to show some trends, but the effectiveness of the Ne–Ar systematics seems to be limited to samples derived from the area on regional scale. No clear correlation is observed in the Ne–Xe systematics for samples on global scale. Although such variations are affected by the elemental fractionation of the atmosphere-derived components to some extent, it is not sufficient to explain the range of observed variation. Lighter noble gases (He, Ne) seem to not always correlate with heavier noble gases (Ar, Kr, Xe), probably due to large difference in their mobilities. Based on the Ar–Xe systematics, the occurrence of recycled materials can be inferred, indicating a possibility of transport of heavier noble gases into the Earthʹs interior together with recycled materials. The thermal state in the Earthʹs interior on global scale might also control the noble gas signatures of magma sources as is the case for the South Pacific area.