The amount of sulfur in SO2 discharged in volcanic eruptions exceeds that available for degassing from the erupted magma.This geological conundrum,known as the"sulfur excess",has been the subject of considerable interests but remains an open question.Here,in a systematic computational investigation of sulfur-oxygen compounds under pressure,a hitherto unknown S3O4 compound containing a mixture of sulfur oxidation states+Ⅱ and+Ⅳ is predicted to be stable at pressures above 79 GPa.We speculate that S3O4 may be produced via redox reactions involving subducted S-bearing minerals(e.g.,sulfates and sulfides)with iron and goethite under high-pressure conditions of the deep lower mantle,decompos-ing to SO2 and S at shallow depths.S3O4 may thus be a key intermediate in promoting decomposition of sulfates to release SO2,offering an alternative source of excess sulfur released during explosive eruptions.These findings provide a possible resolution of the"excess sulfur degassing"paradox and a viable mech-anism for the exchange of S between Earth's surface and the lower mantle in the deep sulfur cycle.

Siyu Liu;Pengyue Gao;Andreas Hermann;Guochun Yang;Jian Lü;Yanming Ma;Ho-Kwang Mao;Yanchao Wang

State Key Laboratory of Superhard Materials&International Center of Computational Method and Software,College of Physics,Jilin University,Changchun 130012,China;Centre for Science at Extreme Conditions and Scottish Universities Physics Alliance,School of Physics and Astronomy,The University of Edinburgh,Edinburgh EH9 3FD,UK;State Key Laboratory of Metastable Materials Science&Technology and Key Laboratory for Microstructural Material Physics of Hebei Province,School of Science,Yanshan University,Qinhuangdao 066004,China;International Center of Future Science,Jilin University,Changchun 130012,China;Center for High Pressure Science and Technology Advanced Research,Beijing 100094,China

科学通报（英文版）

[1]Siyu Liu;Pengyue Gao;Andreas Hermann;Guochun Yang;Jian Lü;Yanming Ma;Ho-Kwang Mao;Yanchao Wang-.Stabilization of S3O4 at high pressure:implications for the sulfur-excess paradox)[J].科学通报（英文版）,2022(09):971-976

S3O4,states+,and+,decompos

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