Elastic Wave Velocities of Polycrystalline Wadsleyite (β-Mg2SiO4) containing 0.26 - 1.00 wt.% H2O at Simultaneous High pressure and High temperature by Ultrasonic Interferometry in Conjunction with Synchrotron X-radiation.
Abstract
Compressional (P) and shear (S) wave velocities for synthetic polycrystalline hydrous wadsleyite specimens containing 0.25, 0.73, 1.00 wt.% H2O have been measured at simultaneous high pressure (P) and high temperature (T) to 10 GPa and 600 K using ultrasonic interferometry in conjunction with synchrotron X-radiation. Elastic wave travel times and X-ray data were collected along unique P and T paths to minimize effect of non-hydrostatic stress on the measurements. The elastic bulk (K) and shear (G) moduli and the pressure and temperature derivatives were obtained by fitting entire high P and T data set to functions of Eulerian strain to third-order and by linear regression of the data set, yielded consistent results within mutual uncertainty of the analytical techniques. The results are: KSO = 163.2 (1) GPa, GO = 106.7 (1) GPa, (∂KS/∂P)T = 5.05, (∂G/∂P)T = 1.51 (2); (∂KS/∂T)P = -0.017 (2) GPaK-1, (∂G/∂T)P = -0.018 (1) GPaK-1 for wadsleyite with 0.26 wt.% H2O; KSO = 161.5 (2) GPa, GO = 101.6 (1) GPa, (∂KS/∂P)T = 4.84 (4), ∂G/∂P)T = 1.68 (2), (∂KS/∂T)P = -0.013 (2) GPaK-1, (∂G/∂T)P = -0.015 (0.4) GPaK-1 for 0.73 wt.% H2O and KSO = 157.7 (4) GPa, GO = 102.1 (2) GPa, (∂KS/∂P)T = 4.73 (5), ∂G/∂P)T = 1.58 (2), (∂KS/∂T)P = -0.018 (2) GPaK-1, (∂G/∂T)P = -0.017 (0.4) GPaK-1 for 1.00 wt.% H2O. We find that whereas the pressure dependences of the bulk and the shear moduli are independent of OH content within mutual uncertainty of the data, K and G decrease linearly with the wadsleyite OH content. The magnitude of (∂G/∂T)P is greater than of (∂KS/∂T)P for wadsleyite with 0.26 and 0.73 wt.% H2O. Examination of the compressional and shear velocity contrasts between hydrous wadsleyite and olivine suggests that water content of less than 0.26 wt.% in the wadsleyite phase is required to satisfy the olivine content of the Earth transition zone based on the pyrolite model.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMMR24A..02G
- Keywords:
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- 3909 Elasticity and anelasticity;
- MINERAL PHYSICS;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 5139 Transport properties;
- PHYSICAL PROPERTIES OF ROCKS;
- 8124 Earth's interior: composition and state;
- TECTONOPHYSICS