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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

Online
ISSN
1945-3027
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Volume 86, Issue 10

Issues

The Mg(Fe)SiO3 orthoenstatite-clinoenstatite transitions at high pressures and temperatures determined by Raman-spectroscopy on quenched samples

Peter Ulmer / Roland Stalder
  • Department of Earth Sciences, ETH-Zentrum, CH-8092 Zurich, Switzerland
  • Naturhistoriska riksmuseet, Sektionen för mineralogi, Box 50007, SE-10405 Stockholm, Sweden
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
Published Online: 2015-03-26 | DOI: https://doi.org/10.2138/am-2001-1014

Abstract

The phase boundaries limiting the stability fields of the three different Mg(Fe)SiO3 phases [orthoenstatite (Oen), low-temperature clinoenstatite (LCen), and high-pressure clinoenstatite (HCen)] that occur at the pressure-temperature conditions prevailing in the Earth’s upper mantle are inferred from Raman spectroscopy on quenched samples from high P-T experiments. There are subtle but significant differences between the spectra of Oen and the spectra of samples quenched within the stability field of HCen or LCen. The most prominent differences are additional peaks at 369 and 431 cm-1 in the spectrum of Cen and a systematic shift of the peak at 236 cm-1 in the Oen spectrum to 243 cm-1 in the Cen spectrum. However, no distinction can be made between samples quenched from the HCen and LCen stability fields. This is consistent with the fact that the HCen phase is non-quench- able and that the pyroxene phase observed in the experimental products is LCen as verified by pow­der X-ray diffraction.

Experiments performed in the pressure-temperature range 1.2-14 GPa and 750-1900 K have been used to constrain the Mg(Fe)SiO3 phase diagram. Pyroxene compositions cover the range from pure MgSiO3 to Mg0.9Fe0.1SiO3 with minor amounts of Al, Ca, Na, and Cr. The results are similar to previous determinations from X-ray and optical studies and tightly constrain the HCen-Oen phase boundary, which can be expressed by the equation P (GPa) = 0.00454 T (K) + 1.673. The LCen-Oen boundary is not as well constrained, but the data are sufficient to locate the invariant point where all three MgSiO3 phases coexist at 6.6 GPa and 820 °C.

About the article

Received: 2000-10-10

Accepted: 2001-06-04

Published Online: 2015-03-26

Published in Print: 2001-10-01


Citation Information: American Mineralogist, Volume 86, Issue 10, Pages 1267–1274, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2001-1014.

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© 2015 by Walter de Gruyter Berlin/Boston.

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