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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
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1945-3027
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Volume 100, Issue 1

Issues

Thermo-compression of pyrope-grossular garnet solid solutions: Non-linear compositional dependence

Wei Du
  • Corresponding author
  • Lamont-Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University in the City of New York, Palisades, New York 10964, U.S.A.
  • Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan
  • Present address: Geodynamic Research Center, Ehime University, Matsuyama 790-8577, Japan.
  • Email
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Simon Martin Clark
  • Department of Earth and Planetary Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia
  • The Bragg Institute, Australian Nuclear Science and Technology Organization, Locked Bag 2001, Kirrawee DC, New South Wales 2232, Australia
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ David Walker
  • Lamont-Doherty Earth Observatory and Department of Earth and Environmental Sciences, Columbia University in the City of New York, Palisades, New York 10964, U.S.A.
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
Published Online: 2015-01-10 | DOI: https://doi.org/10.2138/am-2015-4752

Abstract

Unit-cell parameters of a series of synthetic garnets with the pyrope, grossular, and four intermediate compositions were measured up to about 900 K and to 10 GPa using synchrotron X-ray powder diffraction. Coefficients of thermal expansion of pyrope-grossular garnets are in the range 2.10-2.74 × 10-5 K-1 and uniformly increase with temperature. Values for the two end-members pyrope and grossular are identical within experimental error 2.74 ± 0.05 × 10-5 K-1 and 2.73 ± 0.01 × 10-5 K-1, respectively. Coefficients of thermal expansion for intermediate compositions are smaller than those of end-members and are not linearly dependent on composition. Bulk modulus of grossular is Κ0 = 164.3(1) GPa (with Κ0′ the pressure derivative of the bulk modulus fixed to 5.92) and bulk modulus of pyrope is Κ0 = 169.2(2) GPa (with Κ0′ fixed to 4.4) using a third-order Birch-Murnaghan equation of state, which are consistent with previously reported values. The bulk moduli of garnets of intermediate composition are between ~155 and ~160 GPa, smaller than those of the end-members no matter which Κ0′ is chosen. The compositional dependence of bulk modulus resembles the compositional dependence of thermal expansion. Intermediate garnets on this binary have large positive excess volume, which makes them more compressible. We find that excess volumes in the pyrope-grossular series remain relatively large even at high pressure (~6 GPa) and temperature (~800 K), supporting the observation of crystal exsolution on this garnet join. The curiously “W”-shaped compositional variation of thermal expansion and bulk modulus is anti-correlated with the compositional dependence of microstrain documented in our companion paper (Du et al. in preparation) on the excess volumes in this series of garnets. Minimum thermal expansions and bulk moduli go with maximum microstrains.

Keywords: Pyrope-grossular garnet solid solution; thermal expansion; compressibility; excess volume

About the article

Received: 2013-09-20

Accepted: 2014-07-19

Published Online: 2015-01-10

Published in Print: 2015-01-01


Citation Information: American Mineralogist, Volume 100, Issue 1, Pages 215–222, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-4752.

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© 2015 by Walter de Gruyter Berlin/Boston.

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