Pressure-induced Pbca-P21/c phase transition of natural orthoenstatite: The effect of high temperature and its geophysical implications

Jin S. Zhang, Bruno Reynard, Gilles Montagnac, Jay D Bass

Research output: Contribution to journalArticle

Abstract

In-situ high-pressure (P) high-temperature (T) Raman spectroscopy has been used to investigate the effect of temperature on the high-pressure phase transition of Mg-rich orthoenstatite (OEN) to a newly-discovered P21/c phase (HPCEN2) up to 673K and 18.2(10)GPa. Two natural orthoenstatite samples were used in this study: near end-member Mg orthoenstatite (Zabargad Island, Egypt), and Al+Fe-bearing orthoenstatite (San Carlos, Arizona). For San Carlos OEN (SC-OEN), the experiment was performed at room temperature, 373, 573 and 673K; For Zabargad Island OEN (Zabg OEN), experiments were performed at 573 and 673K. The three phases OEN, HPCEN2, and another high-pressure phase with space group C2/c (denoted by HPCEN) are readily distinguished by a characteristic doublet, triplet, or singlet, respectively, in the 660-680cm-1 range. Similarly, splitting of a peak near 1100cm-1 is indicative of an OEN→HPCEN2 transition. For both samples, no phase other than OEN and HPCEN2 was observed within the investigated P-T range. The recovered products after slow cooling for over 24h from 673K and 16.6(9)GPa were OEN. The Clapeyron slope (dP/dT) of this transition is bracketed between +0.020 to -0.0026GPa/K for Zabg-OEN, and +0.0023 to -0.0049GPa/K for SC-OEN. Our results suggest a possible stability field for HPCEN2 at the bottom of the upper mantle.

Original languageEnglish (US)
Pages (from-to)150-159
Number of pages10
JournalPhysics of the Earth and Planetary Interiors
Volume228
DOIs
StatePublished - Mar 2014

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enstatite
phase transition
Egypt
Earth mantle
Raman spectroscopy
slopes
cooling
room temperature
products
effect
temperature
upper mantle
experiment

Keywords

  • High-pressure clinoenstatite
  • High-pressure phase transition
  • Orthoenstatite
  • Raman spectroscopy
  • Upper mantle

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

Cite this

Pressure-induced Pbca-P21/c phase transition of natural orthoenstatite : The effect of high temperature and its geophysical implications. / Zhang, Jin S.; Reynard, Bruno; Montagnac, Gilles; Bass, Jay D.

In: Physics of the Earth and Planetary Interiors, Vol. 228, 03.2014, p. 150-159.

Research output: Contribution to journalArticle

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abstract = "In-situ high-pressure (P) high-temperature (T) Raman spectroscopy has been used to investigate the effect of temperature on the high-pressure phase transition of Mg-rich orthoenstatite (OEN) to a newly-discovered P21/c phase (HPCEN2) up to 673K and 18.2(10)GPa. Two natural orthoenstatite samples were used in this study: near end-member Mg orthoenstatite (Zabargad Island, Egypt), and Al+Fe-bearing orthoenstatite (San Carlos, Arizona). For San Carlos OEN (SC-OEN), the experiment was performed at room temperature, 373, 573 and 673K; For Zabargad Island OEN (Zabg OEN), experiments were performed at 573 and 673K. The three phases OEN, HPCEN2, and another high-pressure phase with space group C2/c (denoted by HPCEN) are readily distinguished by a characteristic doublet, triplet, or singlet, respectively, in the 660-680cm-1 range. Similarly, splitting of a peak near 1100cm-1 is indicative of an OEN→HPCEN2 transition. For both samples, no phase other than OEN and HPCEN2 was observed within the investigated P-T range. The recovered products after slow cooling for over 24h from 673K and 16.6(9)GPa were OEN. The Clapeyron slope (dP/dT) of this transition is bracketed between +0.020 to -0.0026GPa/K for Zabg-OEN, and +0.0023 to -0.0049GPa/K for SC-OEN. Our results suggest a possible stability field for HPCEN2 at the bottom of the upper mantle.",
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AB - In-situ high-pressure (P) high-temperature (T) Raman spectroscopy has been used to investigate the effect of temperature on the high-pressure phase transition of Mg-rich orthoenstatite (OEN) to a newly-discovered P21/c phase (HPCEN2) up to 673K and 18.2(10)GPa. Two natural orthoenstatite samples were used in this study: near end-member Mg orthoenstatite (Zabargad Island, Egypt), and Al+Fe-bearing orthoenstatite (San Carlos, Arizona). For San Carlos OEN (SC-OEN), the experiment was performed at room temperature, 373, 573 and 673K; For Zabargad Island OEN (Zabg OEN), experiments were performed at 573 and 673K. The three phases OEN, HPCEN2, and another high-pressure phase with space group C2/c (denoted by HPCEN) are readily distinguished by a characteristic doublet, triplet, or singlet, respectively, in the 660-680cm-1 range. Similarly, splitting of a peak near 1100cm-1 is indicative of an OEN→HPCEN2 transition. For both samples, no phase other than OEN and HPCEN2 was observed within the investigated P-T range. The recovered products after slow cooling for over 24h from 673K and 16.6(9)GPa were OEN. The Clapeyron slope (dP/dT) of this transition is bracketed between +0.020 to -0.0026GPa/K for Zabg-OEN, and +0.0023 to -0.0049GPa/K for SC-OEN. Our results suggest a possible stability field for HPCEN2 at the bottom of the upper mantle.

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