CO2-induced destabilization of pyrite-structured FeO2Hx in the lower mantle

作     者：Eglantine Boulard Franois Guyot Nicolas Menguy Alexandre Corgne Anne-Line Auzende Jean-Philippe Perrillat Guillaume Fiquet 

作者机构：Synchrotron SOLEIL Sorbonne Universit Musum National d’Histoire Naturelle Sorbonne Universit Musum National d’Histoire Naturelle Instituto de Ciencias de la TierraUniversidad Austral de Chile ISTerre Universit Grenoble Alpes Laboratoire de Gologie de LyonUMR CNRS 5276Universit Claude Bernard Lyon 1—ENS de Lyon 

出 版 物：《National Science Review》 (国家科学评论(英文版))

年 卷 期：2018年第5卷第6期

页      面：870-877页

核心收录：

学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 

基　　金：support from the French National Center for Scientific Research (CNRS) The transmission electron microscopy facility at Institut de Minralogie, Physique des Matriaux et Cosmochimie is supported by Rgion Ile de France grant SESAME 2000 E 1435 

主　　题：deep carbon cycle FeOOH high pressure 

摘      要：Volatiles, such as carbon and water, modulate the Earth’s mantle rheology, partial melting and redox state,thereby playing a crucial role in the Earth’s internal dynamics. We experimentally show the transformation of goethite FeOOH in the presence of CO2into a tetrahedral carbonate phase, Fe4C3O12, at conditions above 107 GPa—2300 K. At temperatures below 2300 K, no interactions are evidenced between goethite and CO2, and instead a pyrite-structured FeO2Hx is formed as recently reported by Hu et al.(2016; 2017)and Nishi et al.(2017). The interpretation is that, above a critical temperature, FeO2Hx reacts with CO2and H2, yielding Fe4C3O12and H2O. Our findings provide strong support for the stability of carbon-oxygen-bearing phases at lower-mantle conditions. In both subducting slabs and lower-mantle lithologies, the tetrahedral carbonate Fe4C3O12would replace the pyrite-structured FeO2Hx through carbonation of these phases. This reaction provides a new mechanism for hydrogen release as H2 O within the deep lower mantle. Our study shows that the deep carbon and hydrogen cycles may be more complex than previously thought, as they strongly depend on the control exerted by local mineralogical and chemical environments on the CO2and H2thermodynamic activities.