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Thermal equation of state of majoritic knorringite and its significance for continental upper mantle
Author(s) -
Dymshits Anna M.,
Litasov Konstantin D.,
Sharygin Igor S.,
Shatskiy Anton,
Ohtani Eiji,
Suzuki Akio,
Funakoshi Kenichi
Publication year - 2014
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2014jb011194
Subject(s) - pyrope , thermodynamics , thermoelastic damping , equation of state , thermal expansion , bulk modulus , debye model , chemistry , isothermal process , mineralogy , analytical chemistry (journal) , materials science , crystallography , thermal , physics , chromatography
The P‐V‐T equation of state (EoS) for majoritic knorringite Mg 3.19 Cr 1.60 Si 3.19 O 12 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, K 0,300 = 154 (4) GPa, and a pressure derivative, K ′ 0,300 = 5.4 (1.2). When fitting a high‐temperature Birch‐Murnaghan EoS using all of the P‐V‐T data at a fixed V 0 = 1549.08 Å 3 , we find that K 0,300 = 157 (2) GPa, K ′ 0, T = 4.5 (6), (∂ K 0, 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 θ 0 = 731 K yielded a Grüneisen parameter, γ 0 = 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 Cr 2 O 3 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.