摘要
人们发现火山喷发释放出的硫含量比前期估测火山喷发溶体中所容纳的硫高出了几个数量级,这就是火山喷发的“硫过量”问题.经过多年的研究,关于过量硫的来源问题人们提出了多种可能,但仍是一个谜团.本工作利用自主发展的CALYPSO晶体结构预测方法结合第一性原理计算,预言了一种新型硫氧化合物S_(3)O_(4).该化合物包含S(+Ⅱ)和S(+Ⅳ)混合价态,并且在79 GPa以上的压力条件下可以稳定存在.第一性原理计算表明,在深地幔的高压条件下,S_(3)O_(4)可以通过硫酸盐和硫化物与铁和针铁矿经氧化还原反应生成,并在地球浅层压力条件下可以分解为SO2和S单质.因此,本工作预言的S_(3)O_(4)是促进含硫矿物分解产生SO2的关键中间化合物.研究工作为解决火山喷发过程中的“硫过量”问题提供了新的思路,同时也为理解地球表面和下地幔深部之间的硫交换提供了重要的理论储备.
The amount of sulfur in SO2 discharged in volcanic eruptions exceeds that available for degassing from the erupted magma.This geological conun drum,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 S_(3)O_(4) compound containing a mixture of sulfur oxidation states+11 and+IV is predicted to be stable at pressures above 79 GPa.We speculate that S_(3)O_(4) 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,decomposing to SO2 and S at shallow depths.S_(3)O_(4) may thus be a key intermediate in promoting decomposition of sulfates to release SO2,offering an alter native source of excess sulfur released during explosive eruptions.These findings provide a possible resolution of the"excess sulfur degassing"paradox and a viable mechanism for the exchange of S between Earth's surface and the lower mantle in the deep sulfur cycle.
基金
supported by the National Natural Science Foundation of China(12034009,91961204,11774127,12174142,11404128,11822404,52090024 and 11974134)
the Program for Science and Technology Innovative Research Team of Jilin University。
