Thermal equation of state of majoritic knorringite and its significance for continental upper mantle

Anna M. Dymshits, Konstantin D. Litasov, Igor S. Sharygin, Anton Shatskiy, Eiji Otani, Akio Suzuki, Kenichi Funakoshi

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)


The P-V-T equation of state (EoS) for majoritic knorringite Mg3.19Cr1.60Si3.19O12 at pressures to 17 GPa and temperatures to 1673 K was obtained from in situ X-ray diffraction experiments using a Kawai-type multi-anvil apparatus. Fitting of the room-temperature P-V data to a third-order Birch-Murnaghan EoS yielded an isothermal bulk modulus, K0,300 = 154 (4) GPa, and a pressure derivative, K0,300 = 5.4 (1.2). When fitting a high-temperature Birch-Murnaghan EoS using all of the P-V-T data at a fixed V0 = 1549.08 Å3, we find that K0,300 = 157 (2) GPa, K0,T = 4.5 (6), (∂K0,T/∂T)P = -0.019 (4) (GPa K-1), a = 3.00 (14) × 10-5 K-1, and b = 0.65 (24) × 10-8 K-2, where α = a + bT is the volumetric thermal expansion coefficient. Fitting the Mie-Grüneisen-Debye EoS with the present data with a Debye temperature fixed at θ0 = 731 K yielded a Grüneisen parameter, γ0 = 1.34 at q = 1.0 (fixed). The thermoelastic parameters of pure knorringite were estimated and were compared with the previous data on other garnet compositions. The presence of Cr2O3 in pyrope garnets in the upper mantle decreases P- and S-velocities by 1.6% and the density increases by 1.7% (for 20 mol.% knorringite end member) compared to pure pyrope. The results show the importance of accounting knorringite end-member for accurate estimation of mantle garnet acoustic velocities.

Original languageEnglish
Pages (from-to)8034-8046
Number of pages13
JournalJournal of Geophysical Research: Solid Earth
Issue number11
Publication statusPublished - 2014 Nov


  • acoustic velocity
  • equation of state
  • experiment
  • garnet
  • knorringite
  • peridotite

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science


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