Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • High-pressure single-crystal elasticity and thermal equation of state of omphacite and their implications for the seismic properties of eclogite in the Earth's interior
Title: High-pressure single-crystal elasticity and thermal equation of state of omphacite and their implications for the seismic properties of eclogite in the Earth's interior
Omphacite is a major mineral phase of eclogite, which provides the main driving force for the slab subduction into the Earth's interior. We have measured the single‐crystal elastic moduli of omphacite at high pressures for the first time up to 18 GPa at ambient temperature using Brillouin spectroscopy. A least‐squares fit of the velocity‐pressure data to the third‐order finite strain equation of state yields KS0'=4.5(3), G0'=1.6(1) with ρ0=3.34(1) g/cm3, KS0=123(3) GPa, and G0=74(2) GPa. In addition, the synchrotron single‐crystal X‐ray diffraction data have been collected up to 18 GPa and 700 K. The fitting to Holland‐Powell thermal‐pressure equation of state yields KT0'=4.6(5) and α0=2.7(8) ×10‐5 K‐1. Based on the obtained thermoelastic parameters of omphacite, the anisotropic seismic velocities of eclogite are modeled and compared with pyrolite between 200 to 500 km. The largest contrast between the eclogite and pyrolite in terms of seismic properties is observed between ~310 to 410 km.  more » « less
Award ID(s):
1646527
PAR ID:
10086596
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Journal of Geophysical Research: Solid Earth
ISSN:
2169-9313
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, Minerals)
    Clinopyroxene (Cpx) is commonly believed to be the best structural water (hydrogen) carrier among all major upper mantle nominally anhydrous minerals (NAMs). In this study, we have measured the single-crystal elastic properties of a Cpx, a natural omphacite with ~710 ppm water at ambient pressure (P) and temperature (T) conditions. Utilizing the single-crystal X-ray diffraction (XRD) and electron microprobe data, the unit cell parameters and density were determined as a = 9.603(9) Å, b = 8.774(3) Å, c = 5.250(2) Å, β = 106.76(5)o, V = 255.1(4) Å3, and ρ = 3.340(6) g/cm3. We performed Brillouin spectroscopy experiments on four single crystals along a total of 52 different crystallographic directions. The best-fit single-crystal elastic moduli (Cijs), bulk and shear moduli were determined as: C11 = 245(1) GPa, C22 = 210(2) GPa, C33 = 249.6(9) GPa, C44 = 75.7(9) GPa, C55 = 71.2(5) GPa, C66 = 76(1) GPa, C12 = 85(2) GPa, C13 = 70(1) GPa, C23 = 66(2) GPa, C15 = 8.0(6) GPa, C25 = 6(1) GPa, C35 = 34.7(6) GPa, and C46 = 8.7(7) GPa, KS0 = 125(3) GPa, and G0 = 75(2) GPa, respectively. Compared with the anticipated elastic properties of an anhydrous omphacite with the same chemical composition, our results indicate that the incorporation of ~710 ppm structural water has no resolvable effect on the aggregate elastic properties of omphacite, although small differences (up to ~9 GPa) were observed in C13, C25, C44, and C66. 
    more » « less
  2. ; ; ; ; (, American Mineralogist)
    Abstract The 13 single-crystal adiabatic elastic moduli (Cij) of a C2/c jadeite sample close to the ideal composition (NaAlSi2O6) and a natural P2/n diopside-rich omphacite sample have been measured at ambient condition by Brillouin spectroscopy. The obtained Cij values for the jadeite sample are: C11 = 265.4(9) GPa, C22 = 247(1) GPa, C33 = 274(1) GPa, C44 = 85.8(7) GPa, C55 = 69.3(5) GPa, C66 = 93.0(7) GPa, C12 = 84(1) GPa, C13 = 66(1) GPa, C23 = 87(2) GPa, C15 = 5.4(7) GPa, C25 = 17(1) GPa, C35 = 28.7(6) GPa, C46 = 14.6(6) GPa. Voigt-Reuss-Hill averaging of the Cij values yields aggregate bulk modulus KS = 138(3) GPa and shear modulus G = 84(2) GPa for jadeite. Systematic analysis combing previous single-crystal elasticity measurements within the diopside-jadeite solid solution indicates that the linear trends are valid for most Cij values. The νp and νs of omphacite decrease with diopside content, though the velocity changes are small as diopside component exceeds 70%. We also found that both the isotropic νp and νs, as well as the seismic anisotropy of eclogite, changed strongly with the bulk-chemical composition. The relationship between the anisotropic velocities of eclogite and the chemical composition can be a useful tool to trace the origin of the eclogitic materials in the Earth's mantle. 
    more » « less
  3. ; ; ; ; ; (, American Mineralogist)
    Abstract Understanding the natural petrologic and tectonic processes, such as slab subduction, requires accurate determination of the metamorphic pressure (P) and temperature (T) conditions of the exhumed rocks. Recent development of elastic thermobarometry based on the difference between the thermoelastic properties of mineral inclusions and their hosts allows constraining the formation P-T conditions of the inclusion/host system without assuming thermodynamic equilibrium. However, the reliability of elastic thermobarometry heavily depends on the accurate determination of the high P-T single-crystal elastic properties of relevant minerals. In this study, we performed the first high P-T single-crystal elasticity measurements of zircon, which is one of the most common inclusion/host minerals in metamorphic rocks, using Brillouin spectroscopy at pressures up to 7 GPa and temperatures up to 700 K. The single-crystal elastic properties of zircon at ambient conditions were determined as: ρ0 = 4.6674(4) g/cm3; KS = 231(3) GPa; G = 108(11) GPa; C11 = 428(2) GPa; C33 = 484(3) GPa; C44 = 113.5(8) GPa; C66 = 46.9(8) GPa; C12 = 75(2) GPa; and C13 = 151(1) GPa. We also obtained the P and T derivatives of the elastic moduli as ∂KS0/∂P = 5.0(2), ∂KS0/∂T = −0.019(2) GPa/K, ∂G0/∂P = 0.73(6), and ∂G0/∂T = −0.011(1) GPa/K. Compared with other common rock-forming minerals (e.g., quartz, pyroxene, olivine), zircon is extremely incompressible (high KS) and its stiffness (KS) has relatively small T dependence, making it an ideal mineral for the application of elastic thermobarometry. Finally, we utilized the high P-T single-crystal elasticity data of zircon and garnet to evaluate the potential applications of zircon-in-garnet in elastic thermobarometry via elastic modeling. 
    more » « less
  4. ; ; ; ; ; ; ; (, American Mineralogist)
    Abstract As a major nominally anhydrous mineral (NAM) in the Earth’s upper mantle, orthopyroxene could host up to several hundred parts per million H2O in its crystal structure and transport the H2O to the deep Earth. To study the effect of structural H2O on the elasticity of orthopyroxene, we have measured the single-crystal elasticity of Mg1.991Al0.065Si1.951O6 with 842–900 ppm H2O and 1.64 ± 0.20 wt% Al2O3 at ambient conditions using Brillouin spectroscopy. The best-fit single-crystal elastic moduli (Cijs), bulk (KS0), and shear (G0) modulus of the hydrous Al-bearing orthopyroxene were determined as: C11 = 235(2) GPa, C22 = 173(2) GPa, C33 = 222(2) GPa, C44 = 86(1) GPa, C55 = 82(1) GPa, C66 = 82(1) GPa, C12 = 75(3) GPa, C13 = 67(2) GPa, and C23 = 49(2) GPa, KS0 = 111(2) GPa, and G0 = 78(1) GPa. Systematic analysis based on the results presented in this and previous studies suggests that the incorporation of 842–900 ppm H2O would increase C13 by 12.0(7)% and decrease C23 by 8.6(8)%. The effects on C11, C22, C33, C44, C66, KS0, and VP are subtle if not negligible when considering the uncertainties. The C55, C12, G0, and VS are not affected by the presence of structural H2O. Although laboratory experiments show that Fe,Al-bearing orthopyroxenes can host up to 0.8 wt% H2O in its structure, future high-pressure-temperature elasticity measurements on orthopyroxene with higher H2O content are needed to help better quantify this effect. 
    more » « less
  5. ; ; ; ; ; ; (, American Mineralogist)
    Xu, Hongwu (Ed.)
    Abstract We have measured the sound velocities and elasticity of synthetic polycrystalline β-Mg2SiO4 containing 1.2 wt% H2O to 10 GPa and 600 K using ultrasonic interferometry with synchrotron X-radiation. We determined sample length at high pressure and temperature using the sample’s X-radiographic image and applied travel times bond corrections appropriate to the experimental cell assembly configuration. Fitting the entire moduli data to third-order finite strain equations yields the adiabatic bulk [KS0 = 153.3(4) GPa] and shear [G0 = 101.8(2) GPa] moduli, their pressure derivatives (∂KS/∂P)T = 5.15(6) and (∂G/∂P)T = 1.68(3) and temperature derivatives (∂KS/∂T)P = −0.0179(9) GPa/K and (∂G/∂T)P = −0.0151(7) GPa/K. Comparing the bulk sound velocity contrast between the new hydrous wadsleyite data and olivine (0.38 wt% H2O) with seismic bulk sound velocity contrasts of 3.5% and 4.0% yields 53% and 60% olivine content, respectively, assuming an iso-chemical mantle model of the Earth. The results suggest that a hydrous mantle transition zone with a pyrolite model composition could explain the 410 km seismic velocity jump. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email