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Title: Stability of iron-bearing carbonates in the deep Earth’s interior

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. 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 Mossbauer spectroscopy in laser-heated diamond anvil cells. On heating to temperatures of the Earth’s geotherm at pressures to B 50 GPa FeCO 3 partially dissociates to form various iron oxides. Furthermore, at higher pressures FeCO 3 forms two new structures— tetrairon(III) orthocarbonate Fe$$3+\atop{4}$$C 3O 12 and diiron(II) diiron(III) tetracarbonate Fe$$2+\atop{2}$$ Fe$$3+\atop{2}$$C 4 O 13, both phases containing CO 4 tetrahedra. Fe 4 C 4 O 13 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.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ; ORCiD logo [6] ;  [7] ;  [3] ;  [6] ;  [3] ;  [3] ;  [3] ;  [3] ;  [3] ;  [8] ;  [3] ;  [9] ;  [6]
  1. European Synchrotron Radiation Facility (ESRF), Grenoble (France); Univ. of Bayreuth (Germany). Bavarian Geoinstitute
  2. Univ. of Bayreuth (Germany). Bavarian Geoinstitute; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
  3. European Synchrotron Radiation Facility (ESRF), Grenoble (France)
  4. Univ. of Milan (Italy). Dept. of Earth Sciences
  5. Center for Hydrocarbon Recovery, Moscow (Russia). Skolkovo Inst. of Science and Technology
  6. Univ. of Bayreuth (Germany). Bavarian Geoinstitute
  7. Univ. of Bayreuth (Germany). Bavarian Geoinstitute; National Univ., of Science and Technology, Moscow (Russia). Material Modeling and Development Lab.
  8. Univ. of Cologne (Germany). Inst. of Geology and Mineralogy
  9. Univ. of Chicago, IL (United States). Center for Advanced Radiation Sources
Publication Date:
Grant/Contract Number:
FG02-94ER14466; AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Nature Communications
Additional Journal Information:
Journal Volume: 8; Journal ID: ISSN 2041-1723
Publisher:
Nature Publishing Group
Research Org:
Univ. of Chicago, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1393163