Noble gas transport into the mantle facilitated by high solubility in amphibole

Abstract

How noble gases are recycled from the atmosphere back into the mantle has been unclear. High-pressure experiments demonstrate that noble gases are highly soluble in an important hydrous mineral in altered oceanic crust, suggesting that subduction of this type of crust may be a significant pathway for noble gas flux back into the mantle. The chemical evolution of both the Earth’s atmosphere and mantle can be traced using noble gases1,2,3,4,5. Their abundance in mantle and atmosphere reflects a balance between the flux of noble gases from the Earth’s interior through magmatism, and the recycling of noble gases from the atmosphere back into the mantle at subduction zones. The flux of noble gases back into the mantle has long been thought to be negligible1. However, analyses of samples from the mantle now suggest that this recycling flux is more significant6,7,8, but the responsible mechanisms are unclear. Here we present high-pressure experimental measurements that demonstrate high solubility of noble gases in amphibole, an important hydrous mineral in altered oceanic crust9,10,11. Noble gas solubility correlates with the concentration of unoccupied A-sites, which consist of a pair of opposing tetrahedra rings. We conclude that A-sites are energetically favourable locations for noble gas dissolution in amphibole that could allow recycling of noble gases into the mantle by subduction of altered oceanic crust. As many hydrous minerals in subducting slabs, such as serpentine and chlorite, have lattice structures similar to the A-site in amphibole, we suggest that these minerals may provide even more significant recycling pathways7,11.