AUTHOR=Boulard Eglantine , Liu Yijin , Koh Ai L. , Reagan Mary M. , Stodolna Julien , Morard Guillaume , Mezouar Mohamed , Mao Wendy L. 

TITLE=Transformations and Decomposition of MnCO3 at Earth's Lower Mantle Conditions

JOURNAL=Frontiers in Earth Science

VOLUME=4

YEAR=2016

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2016.00107

DOI=10.3389/feart.2016.00107

ISSN=2296-6463

ABSTRACT=<p>Carbonates have been proposed as the principal oxidized carbon-bearing phases in the Earth's interior. Their phase diagram for the high pressure and temperature conditions of the mantle can provide crucial constraints on the deep carbon cycle. We investigated the behavior of MnCO<sub>3</sub> at pressures up to 75 GPa and temperatures up to 2200 K. The phase assemblage in the resulting run products was determined <italic>in situ</italic> by X-ray diffraction (XRD), and the recovered samples were studied by analytical transmission electron microscopy (TEM) and X-ray absorption near edge structure (XANES) imaging. At moderate temperatures below 1400 K and pressures above 50 GPa, MnCO<sub>3</sub> transformed into the MnCO<sub>3</sub>-II phase, with XANES data indicating no change in the manganese oxidation state in MnCO<sub>3</sub>-II. However, upon heating above 1400 K at the same pressure conditions, both MnCO<sub>3</sub> and MnCO<sub>3</sub>-II undergo decomposition and redox reactions which lead to the formation of manganese oxides and reduced carbon.</p>