Stability of the MgSiO3 analog NaMgF3 and its implication for mantle structure in super-Earths

B. Grocholski, S. H. Shim, V. B. Prakapenka

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


First-principles calculations on MgSiO3 suggested a breakdown into MgO + SiO2 at pressure above 1000 GPa with an extremely large negative Clapeyron slope, isolating the lowermost mantles of larger super-Earths (∼10M) from convection. Similar calculations predicted the same type of breakdown in NaMgF3 to NaF + MgF2 at 40 GPa, allowing for experimental examination. We found that NaMgF3 is stable to at least 70 GPa and 2500 K. In our measurements on MgF2 (an SiO2 analog), we found a previously unidentified phase ("phase X") between the stability fields of pyrite-type and cotunnite-type (49-53 GPa and 1500-2500 K). A very small density increase (1%) at the pyrite-type → phase X transition would extend the stability of NaMgF3 relative to the breakdown products. Furthermore, because phase X appears to have a cation coordination number intermediate between pyrite-type (6) and cotunnite-type (9), entropy change (δS) would be smaller at the breakdown boundary, making the Clapeyron slope (dP/dT = δS/δV) much smaller than the prediction. If similar trend occurs in MgSiO3 and SiO 2, the breakdown of MgSiO3 may occur at higher pressure and have much smaller negative Clapeyron slope than the prediction, allowing for large-scale convection in the mantles of super-Earth exoplanets.

Original languageEnglish (US)
Article numberL14204
JournalGeophysical Research Letters
Issue number14
StatePublished - Jul 1 2010
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)


Dive into the research topics of 'Stability of the MgSiO3 analog NaMgF3 and its implication for mantle structure in super-Earths'. Together they form a unique fingerprint.

Cite this