The presence of carbonates in inclusions in diamonds coming from depths exceeding 670 km are obvious evidence that carbonates exist in the Earth's lower mantle. However, their range of stability, crystal structures and the thermodynamic conditions of the decarbonation processes remain poorly constrained. Here we investigate the behaviour of pure iron carbonate at pressures over 100 GPa and temperatures over 2,500 K using single-crystal X-ray diffraction and Mössbauer spectroscopy in laser-heated diamond anvil cells. On heating to temperatures of the Earth's geotherm at pressures to ∼50 GPa FeCO3 partially dissociates to form various iron oxides. At higher pressures FeCO3 forms two new structures - tetrairon(III) orthocarbonate Fe4 3+C3O12, and diiron(II) diiron(III) tetracarbonate Fe2 2+Fe2 3+C4O13, both phases containing CO4 tetrahedra. Fe4C4O13 is stable at conditions along the entire geotherm to depths of at least 2,500 km, thus demonstrating that self-oxidation-reduction reactions can preserve carbonates in the Earth's lower mantle.

Cerantola, V., Bykova, E., Kupenko, I., Merlini, M., Ismailova, L., Mccammon, C., et al. (2017). Stability of iron-bearing carbonates in the deep Earth's interior. NATURE COMMUNICATIONS, 8 [10.1038/ncomms15960].

Stability of iron-bearing carbonates in the deep Earth's interior

Cerantola V
Primo
;
2017

Abstract

The presence of carbonates in inclusions in diamonds coming from depths exceeding 670 km are obvious evidence that carbonates exist in the Earth's lower mantle. However, their range of stability, crystal structures and the thermodynamic conditions of the decarbonation processes remain poorly constrained. Here we investigate the behaviour of pure iron carbonate at pressures over 100 GPa and temperatures over 2,500 K using single-crystal X-ray diffraction and Mössbauer spectroscopy in laser-heated diamond anvil cells. On heating to temperatures of the Earth's geotherm at pressures to ∼50 GPa FeCO3 partially dissociates to form various iron oxides. At higher pressures FeCO3 forms two new structures - tetrairon(III) orthocarbonate Fe4 3+C3O12, and diiron(II) diiron(III) tetracarbonate Fe2 2+Fe2 3+C4O13, both phases containing CO4 tetrahedra. Fe4C4O13 is stable at conditions along the entire geotherm to depths of at least 2,500 km, thus demonstrating that self-oxidation-reduction reactions can preserve carbonates in the Earth's lower mantle.
Articolo in rivista - Articolo scientifico
siderite; tetracarbonates; high pressure; high temperature; diamond anvil cell; laser heating; synchrotron; XRD; Mössbauer spectroscopy; phase transition; phase diagram; reactions; redox
English
Cerantola, V., Bykova, E., Kupenko, I., Merlini, M., Ismailova, L., Mccammon, C., et al. (2017). Stability of iron-bearing carbonates in the deep Earth's interior. NATURE COMMUNICATIONS, 8 [10.1038/ncomms15960].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/397745
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