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Title: Phase transitions in orthopyroxene (En90) to 49GPa from single-crystal X-ray diffraction

Abstract

Synchrotron-based high-pressure single-crystal X-ray diffraction experiments were conducted on ~Mg0.9Fe0.1SiO3 (En90) orthopyroxene crystals at room temperature to a maximum pressure of 48.5 GPa. The sample was compressed in a diamond anvil cell with a neon pressure medium and a gold pressure calibrant. In addition to the previously described orthopyroxene to β-opx transition (designated HPCEN2 in previous studies), we observe two further phase transitions at 29.9 GPa and 40.3 GPa. However, we do not observe the γ-opx phase recently described in an Fe-rich orthopyroxene composition. The structures of both of the new phases were solved in space group Pca21. While their Mg-O layers remain pyroxene-like, their Si-O layers transform in a stepwise fashion to akimotoite-like sheets, with sites in 4-, 5-, or 6-fold coordination, depending on the specific structure and layer. Due to the increased Si-O coordination number, we designate the new structures α- and β-post-orthopyroxene (α-popx and β-popx). α-popx has one Si-O layer that is entirely tetrahedral, and one layer that contains both tetrahedra and 5-coordinated Si in distorted square pyramids. β-popx retains the mixed 4- and 5-coordinated Si layer found in α-popx, while the other Si layer adopts fully octahedral coordination. The α- and β-popx structures show a progressivemore » transformation towards the arrangement of Si layers found in akimotoite, a potentially important phase in the earth’s transition zone. Metastable transformations in pyroxenes are of interest for understanding possible metastability in geological environments such as subducting slabs and meteorite impacts« less

Authors:
 [1];  [2];  [1]
  1. Princeton Univ., NJ (United States)
  2. Univ. of Hawaii, Honolulu, HI (United States); Univ. of Chicago, IL (United States)
Publication Date:
Research Org.:
Carnegie Inst. of Science, Washington, DC (United States). Geophysical Lab.
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1338326
Alternate Identifier(s):
OSTI ID: 1251985
Grant/Contract Number:  
NA0002006
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of the Earth and Planetary Interiors
Additional Journal Information:
Journal Volume: 244; Journal Issue: C; Journal ID: ISSN 0031-9201
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Orthopyroxene; Phase transition; Crystallography; High pressure; Single-crystal X-ray diffraction

Citation Formats

Finkelstein, Gregory J., Dera, Przemyslaw K., and Duffy, Thomas S. Phase transitions in orthopyroxene (En90) to 49GPa from single-crystal X-ray diffraction. United States: N. p., 2014. Web. doi:10.1016/j.pepi.2014.10.009.
Finkelstein, Gregory J., Dera, Przemyslaw K., & Duffy, Thomas S. Phase transitions in orthopyroxene (En90) to 49GPa from single-crystal X-ray diffraction. United States. https://doi.org/10.1016/j.pepi.2014.10.009
Finkelstein, Gregory J., Dera, Przemyslaw K., and Duffy, Thomas S. 2014. "Phase transitions in orthopyroxene (En90) to 49GPa from single-crystal X-ray diffraction". United States. https://doi.org/10.1016/j.pepi.2014.10.009. https://www.osti.gov/servlets/purl/1338326.
@article{osti_1338326,
title = {Phase transitions in orthopyroxene (En90) to 49GPa from single-crystal X-ray diffraction},
author = {Finkelstein, Gregory J. and Dera, Przemyslaw K. and Duffy, Thomas S.},
abstractNote = {Synchrotron-based high-pressure single-crystal X-ray diffraction experiments were conducted on ~Mg0.9Fe0.1SiO3 (En90) orthopyroxene crystals at room temperature to a maximum pressure of 48.5 GPa. The sample was compressed in a diamond anvil cell with a neon pressure medium and a gold pressure calibrant. In addition to the previously described orthopyroxene to β-opx transition (designated HPCEN2 in previous studies), we observe two further phase transitions at 29.9 GPa and 40.3 GPa. However, we do not observe the γ-opx phase recently described in an Fe-rich orthopyroxene composition. The structures of both of the new phases were solved in space group Pca21. While their Mg-O layers remain pyroxene-like, their Si-O layers transform in a stepwise fashion to akimotoite-like sheets, with sites in 4-, 5-, or 6-fold coordination, depending on the specific structure and layer. Due to the increased Si-O coordination number, we designate the new structures α- and β-post-orthopyroxene (α-popx and β-popx). α-popx has one Si-O layer that is entirely tetrahedral, and one layer that contains both tetrahedra and 5-coordinated Si in distorted square pyramids. β-popx retains the mixed 4- and 5-coordinated Si layer found in α-popx, while the other Si layer adopts fully octahedral coordination. The α- and β-popx structures show a progressive transformation towards the arrangement of Si layers found in akimotoite, a potentially important phase in the earth’s transition zone. Metastable transformations in pyroxenes are of interest for understanding possible metastability in geological environments such as subducting slabs and meteorite impacts},
doi = {10.1016/j.pepi.2014.10.009},
url = {https://www.osti.gov/biblio/1338326}, journal = {Physics of the Earth and Planetary Interiors},
issn = {0031-9201},
number = C,
volume = 244,
place = {United States},
year = {Wed Oct 29 00:00:00 EDT 2014},
month = {Wed Oct 29 00:00:00 EDT 2014}
}

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Works referencing / citing this record:

Metastable silica high pressure polymorphs as structural proxies of deep Earth Silicate Melts
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Compressional Behavior of Hydrous Orthoenstatite: Insight into the Nature of LVZ under Continental Plate
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High‐Pressure γ ‐CaMgSi 2 O 6 : Does Penta‐Coordinated Silicon Exist in the Earth's Mantle?
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Phase Transitions in Orthoenstatite and Subduction Zone Dynamics: Effects of Water and Transition Metal Ions
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An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite
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High pressure phase transitions of paracelsian BaAl2Si2O8
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Pentacoordinated silicon in the high-pressure modification of datolite, CaBSiO 4 (OH)
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A New High-Pressure Phase Transition in Natural Gedrite
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High pressure phase transitions of paracelsian $BaAl_{2}Si_{2}O_{8}$
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Metastable silica high pressure polymorphs as structural proxies of deep Earth silicate melts
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High-pressure single-crystal X-ray diffraction and synchrotron Mössbauer study of monoclinic ferrosilite
journal, February 2019


Compressional Behavior of Hydrous Orthoenstatite: Insight into the Nature of LVZ under Continental Plate
journal, January 2020


High Pressure Single Crystal Diffraction at PX^2
journal, January 2017