Iron-rich carbonates stabilized by magnetic entropy at lower mantle conditions

Zhi Li (1, 2) , Stephen Stackhouse (1)

1 University of Leeds
2 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement

Constraining the flux of carbon in and out of the interior of the Earth due to long-term geological processes is important, because of the influence that it has on climate change. On timescales of billions of years, host minerals such as carbonate phases could play a significant role in the global carbon cycle, transporting carbon into the lower mantle as a component of subducting slabs. We use density functional theory based calculations to study the high-pressure, high-temperature phase stability of Mg 1-x Fe x CO 3. Our results show that iron-rich phases, where carbon is in tetrahedral coordination, are only stable at lower mantle conditions due to their magnetic entropy, which is also responsible for the unusual shape of their phase boundary. Low-pressure carbonate phases are found to be highly anisotropic, but highpressure carbonate phases are not, which has important implications for their seismic detectability. Our work confirms that future discussions of the global carbon cycle should include the deep Earth.

Domains: Sciences of the Universe [physics]

Zhi Li, Stephen Stackhouse. Iron-rich carbonates stabilized by magnetic entropy at lower mantle conditions. Earth and Planetary Science Letters, 2020, 531, pp.115959. ⟨10.1016/j.epsl.2019.115959⟩. ⟨insu-03029803⟩