| 1 | CO2-induced destabilization of pyrite-structured FeO2Hx in the lower mantle显示文摘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 CO_2 into a tetrahedral carbonate phase, Fe_4C_3O_(12), at conditions above 107 GPa—2300 K. At temperatures below 2300 K, no interactions are evidenced between goethite and CO_2, and instead a pyrite-structured FeO_2 Hx is formed as recently reported by Hu et al.(2016; 2017)and Nishi et al.(2017). The interpretation is that, above a critical temperature, FeO_2 Hx reacts with CO_2 and H_2, yielding Fe_4C_3O_(12) and H_2 O. 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 Fe_4C_3O_(12) would replace the pyrite-structured FeO_2 Hx 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 CO_2 and H_2 thermodynamic activities. | Eglantine Boulard Francois Guyot Nicolas Menguy Alexandre Corgne Anne-Line Auzende Jean-Philippe Perrillat Guillaume Fiquet | 2018 | National Science Review2018，5，6： | 2 |
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