High-pressure phase transitions of clinoenstatite

John D. Lazarz, Przemyslaw Dera, Yi Hu, Yue Meng, Craig R. Bina, Steven D. Jacobsen

Research output: Contribution to journalArticle

1 Scopus citations

Abstract

Clinoenstatite (Mg2Si2O6) undergoes a well-known phase transition from a low-pressure form (LPCEN, space group P21/c) to a high-pressure form (HPCEN, space group C2/c) at ~6 GPa. High-pressure structure refinements of HPCEN were carried out based on single-crystal X-ray diffraction experiments between 9.5 and 35.5 GPa to determine its P-V equation of state and structural evolution over an expanded pressure range relevant to pyroxene metastability. The best-fit isothermal equation of state to our data combined with the five data points between 5.34 and 7.93 GPa from Angel and Hugh-Jones (1994) yields a second-order Birch-Murnaghan equation with KT0 = 121(2) GPa and V0 = 403.9(5) Å3 (with K′T0 = 4 implied). Further reduction of misfit upon fitting a third-order Birch-Murnaghan equation is not significant at the 90% confidence level. At ~45 GPa, a transition from HPCEN to a P21/c-structured polymorph (HPCEN2) was observed, which is isostructural to the P21/c phase recently observed in diopside (CaMgSi2O6) at 50 GPa (Plonka et al. 2012) and in clinoferrosilite (Fe2Si2O6) at 30-36 GPa (Pakhomova et al. 2017). Observation of HPCEN2 in Mg2Si2O6 completes the third apex of the pyroxene quadrilateral wherein HPCEN2 is found, facilitating a broader view of clinopyroxene crystal chemistry at conditions relevant to metastability in the Earth's mantle along cold subduction geotherms.

Original languageEnglish (US)
Pages (from-to)897-904
Number of pages8
JournalAmerican Mineralogist
Volume104
Issue number6
DOIs
StatePublished - Jun 1 2019

Keywords

  • MgSiO
  • clinoenstatite
  • enstatite
  • pyroxene
  • single-crystal X-ray diffraction

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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