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The effect of thermal decarbonation on stable isotope compositions of carbonates

  • Z. D. Sharp EMAIL logo , J. J. Papike and T. Durakiewicz
Published/Copyright: March 31, 2015
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American Mineralogist
From the journal American Mineralogist Volume 88 Issue 1

Abstract

Oxygen and C isotope compositions of CO2 gas released by thermal decomposition of siderite, calcite, and dolomite were measured using a new “real-time” continuous-flow technique to determine whether fractionation associated with simple thermal decarbonation could explain the large isotopic variations and mineralogy such as those found in the ALH84001 meteorite. Oxygen and C isotope fractionation between calcite or dolomite and evolved CO2 gas during thermal decarbonation in a 3 bar He pressure environment is very small. The δ13C and δ18O values of evolved CO2 gas are nearly identical to those of the carbonate, very different from the calculated equilibrium 18Ocalcite-CO2 value of -4 to -5‰ at 800-900°C or from previous experimental results of decarbonation in vacuum. The kinetic Δ18Osiderite-CO2 values are ~-2‰, whereas Δ13Csiderite-CO2 values increase logarithmically with time, from ~1‰ for the earliest stages of decarbonation to >5‰ in the final stages. Incomplete siderite decomposition produces both magnetite (δ18O = 3.5‰ SMOW) and minor graphite. CO and O2 were detected during the decarbonation process. The data can be explained by simultaneous oxidation and reduction by the reaction:

6FeCO3 → 2Fe3O4 + 2x CO + 4y CO2 +(6 - 2x - 4y) C + (5 - x - 4y) O2,

where x and y are between 0 and 1. Siderite decomposition in the presence of H2 gas produces wüstite and Fe metal in place of oxidized Fe minerals. The experiments in this study are not a perfect analog for possible decarbonation conditions that might have occurred to the carbonates in ALH84001. Nevertheless, the large δ13C and δ18O variations observed in ALH84001 (>10‰ for O) are significantly larger than those expected by thermal decarbonation, suggesting instead a low-temperature mechanism for their formation.

Published Online: 2015-3-31
Published in Print: 2003-1-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. A molecular dynamics study of the behavior of sodium in low albite
  2. Observation and interpretation of paramagnetic defects in Brazilian and Central African carbonados
  3. Dissolution of gibbsite: Direct observations using fluid cell atomic force microscopy
  4. Polytypes and higher-order structures of antigorite: A TEM study
  5. An infrared spectroscopic study of the basic copper phosphate minerals: Cornetite, libethenite, and pseudomalachite
  6. Influence of F content on the composition of Al-rich synthetic phlogopite: Part I. New information on structure and phase-formation from 29Si, 1H, and 19F MAS NMR spectroscopies
  7. NMR evidence for formation of octahedral and tetrahedral Al and repolymerization of the Si network during dissolution of aluminosilicate glass and crystal
  8. Thermodynamic properties of hercynite (FeAl2O4) based on adiabatic calorimetry at low temperatures
  9. The formation of Sr silicates at low temperature and the solubility product of tobermorite-like Sr5Si6O16(OH)2 .5H2O
  10. Thermal equation of state of omphacite
  11. The effect of thermal decarbonation on stable isotope compositions of carbonates
  12. Synthetic MgAl2O4 (spinel) at high-pressure conditions (0.0001–30 GPa): A synchrotron X-ray powder diffraction study
  13. The stability of antigorite in the systems MgO-SiO2-H2O (MSH) and MgO-Al2O3-SiO2-H2O (MASH): The effects of Al3+ substitution on high-pressure stability
  14. The fusion curve of albite revisited and the compressibility of NaAlSi3O8 liquid with pressure
  15. Correction of secondary X-ray fluorescence near grain boundaries in electron microprobe analysis: Application to thermobarometry of spinel lherzolites
  16. An overgrowth model to explain multiple, dispersed high-Mn regions in the cores of garnet porphyroblasts
  17. Synchrotron X-ray diffraction study of the structure and dehydration behavior of todorokite
  18. Retrograde mineral reactions in saline fluid inclusions: The transformation ferropyrosmalite ↔ clinopyroxene
  19. The effect of ionizing radiation on uranophane
  20. Hydration, expansion, structure, and dynamics of layered double hydroxides
  21. Relict edenite in a garnet lherzolite from the Chinese Su-Lu UHP metamorphic terrane: Implications for metamorphic history
  22. Norrishite, K(Mn23+Li)Si4O10(O)2, an oxymica associated with sugilite from the Wessels Mine, South Africa: Crystal chemistry and 40Ar-39Ar dating
  23. The amblygonite (LiAlPO4F)-montebrasite (LiAlPO4OH) solid solution: A combined powder and single-crystal neutron diffraction and solid-state 6Li MAS, CP MAS, and REDOR NMR study
  24. An X-ray Rietveld, infrared, and Mössbauer spectral study of the NaMn(Fe1–xInx)2(PO4)3 alluaudite-type solid solution
  25. Gatelite-(Ce), a new REE-bearing mineral from Trimouns, French Pyrenees: Crystal structure and polysomatic relationships with epidote and törnebohmite-(Ce)
  26. Hydroxyl in clinopyroxene from the deep subducted crust: Evidence for H2O transport into the mantle
  27. A model for the structure of the hydrated aluminum phosphate, kingite determined by ab initio powder diffraction methods
  28. The crystal structure of synthetic autunite, Ca[(UO2)(PO4)]2(H2O)11
https://doi.org/10.2138/am-2003-0111

Articles in the same Issue

  1. A molecular dynamics study of the behavior of sodium in low albite
  2. Observation and interpretation of paramagnetic defects in Brazilian and Central African carbonados
  3. Dissolution of gibbsite: Direct observations using fluid cell atomic force microscopy
  4. Polytypes and higher-order structures of antigorite: A TEM study
  5. An infrared spectroscopic study of the basic copper phosphate minerals: Cornetite, libethenite, and pseudomalachite
  6. Influence of F content on the composition of Al-rich synthetic phlogopite: Part I. New information on structure and phase-formation from 29Si, 1H, and 19F MAS NMR spectroscopies
  7. NMR evidence for formation of octahedral and tetrahedral Al and repolymerization of the Si network during dissolution of aluminosilicate glass and crystal
  8. Thermodynamic properties of hercynite (FeAl2O4) based on adiabatic calorimetry at low temperatures
  9. The formation of Sr silicates at low temperature and the solubility product of tobermorite-like Sr5Si6O16(OH)2 .5H2O
  10. Thermal equation of state of omphacite
  11. The effect of thermal decarbonation on stable isotope compositions of carbonates
  12. Synthetic MgAl2O4 (spinel) at high-pressure conditions (0.0001–30 GPa): A synchrotron X-ray powder diffraction study
  13. The stability of antigorite in the systems MgO-SiO2-H2O (MSH) and MgO-Al2O3-SiO2-H2O (MASH): The effects of Al3+ substitution on high-pressure stability
  14. The fusion curve of albite revisited and the compressibility of NaAlSi3O8 liquid with pressure
  15. Correction of secondary X-ray fluorescence near grain boundaries in electron microprobe analysis: Application to thermobarometry of spinel lherzolites
  16. An overgrowth model to explain multiple, dispersed high-Mn regions in the cores of garnet porphyroblasts
  17. Synchrotron X-ray diffraction study of the structure and dehydration behavior of todorokite
  18. Retrograde mineral reactions in saline fluid inclusions: The transformation ferropyrosmalite ↔ clinopyroxene
  19. The effect of ionizing radiation on uranophane
  20. Hydration, expansion, structure, and dynamics of layered double hydroxides
  21. Relict edenite in a garnet lherzolite from the Chinese Su-Lu UHP metamorphic terrane: Implications for metamorphic history
  22. Norrishite, K(Mn23+Li)Si4O10(O)2, an oxymica associated with sugilite from the Wessels Mine, South Africa: Crystal chemistry and 40Ar-39Ar dating
  23. The amblygonite (LiAlPO4F)-montebrasite (LiAlPO4OH) solid solution: A combined powder and single-crystal neutron diffraction and solid-state 6Li MAS, CP MAS, and REDOR NMR study
  24. An X-ray Rietveld, infrared, and Mössbauer spectral study of the NaMn(Fe1–xInx)2(PO4)3 alluaudite-type solid solution
  25. Gatelite-(Ce), a new REE-bearing mineral from Trimouns, French Pyrenees: Crystal structure and polysomatic relationships with epidote and törnebohmite-(Ce)
  26. Hydroxyl in clinopyroxene from the deep subducted crust: Evidence for H2O transport into the mantle
  27. A model for the structure of the hydrated aluminum phosphate, kingite determined by ab initio powder diffraction methods
  28. The crystal structure of synthetic autunite, Ca[(UO2)(PO4)]2(H2O)11
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