High-pressure phase transitions of clinoenstatite

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

doi:10.2138/am-2019-6740

Article navigation

Research Article| June 01, 2019

High-pressure phase transitions of clinoenstatite

John D. Lazarz;

John D. Lazarz

Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.

* Present address:

Shock and Detonation Physics, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A

. E-mail: [email protected]

Search for other works by this author on:

GSW

Google Scholar

Przemyslaw Dera;

Przemyslaw Dera

Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A.

Search for other works by this author on:

GSW

Google Scholar

Yi Hu;

Yi Hu

Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A.

Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A.

Search for other works by this author on:

GSW

Google Scholar

Yue Meng;

Yue Meng

HPCAT, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.

Search for other works by this author on:

GSW

Google Scholar

Craig R. Bina;

Craig R. Bina

Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.

Search for other works by this author on:

GSW

Google Scholar

Steven D. Jacobsen

Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.

Search for other works by this author on:

GSW

Google Scholar

Author and Article Information

John D. Lazarz

Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.

Przemyslaw Dera

Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A.

Yi Hu

Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A.

Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawai’i at Manoa, Honolulu, Hawaii 96822, U.S.A.

Yue Meng

HPCAT, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.

Craig R. Bina

Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.

Steven D. Jacobsen

Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.

* Present address:

Shock and Detonation Physics, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A

. E-mail: [email protected]

Publisher: Mineralogical Society of America

Received: 19 Jul 2018

Accepted: 30 Jan 2019

First Online: 03 Jun 2019

Online ISSN: 1945-3027

Print ISSN: 0003-004X

Mineralogical Society of America

American Mineralogist (2019) 104 (6): 897–904.

https://doi.org/10.2138/am-2019-6740

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 K_T0 = 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.