Stability of the MgSiO3 analog NaMgF3 and its implication for mantle structure in super-Earths
Name
Shim_Stability of.pdf
Size
377.34 KB
Format
Adobe PDF
Checksum (MD5)
2d1efb46a4e409c8d784d31952e661a6
Author(s)
Grocholski, Brent
Shim, Sang-Heon Dan
Prakapenka, V. B.
Date Issued
July 2010
Journal
Geophysical Research Letters
Publisher
American Geophysical Union
Citation
Grocholski, B., S.-H. Shim, and V. B. Prakapenka (2010), Stability of the MgSiO3 analog NaMgF3 and its implication for mantle structure in super-Earths, Geophys. Res. Lett., 37, L14204, doi:10.1029/2010GL043645. ©2010. American Geophysical Union
Version
Final published version
Abstract
First-principles calculations on MgSiO(subscript 3) suggested a breakdown into MgO + SiO(subscript 2) 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 NaMgF(subscript 3) to NaF + MgF2 at 40 GPa, allowing for experimental examination. We found that NaMgF(subscript 3) is stable to at least 70 GPa and 2500 K. In our measurements on MgF(subscript 2) (an SiO(subscript 2) 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 MgSiO(subscript 3) and SiO(subscript 2), the breakdown of MgSiO(subscript 3) 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.
MIT Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1029/2010GL043645
