Gl. Chen et al., CROSS PRESSURE AND TEMPERATURE DERIVATIVES OF SELECTED ELASTIC-MODULIFOR OLIVINE FROM GIGAHERTZ ULTRASONIC INTERFEROMETRY, J GEO R-SOL, 101(B11), 1996, pp. 25161-25171
Techniques have been developed to measure the cross pressure and tempe
rature dependence of elastic moduli of olivine using the gigahertz ult
rasonic interferometric method in a gas pressure vessel (to 500 MPa) e
quipped with an internal heater (to 500 K), Special attention has been
drawn to the effect of the bond which couples the sample to the buffe
r rod. We obtained partial derivative(2)C(22)/partial derivative P par
tial derivative T = (2.8 +/- 0.9) x 10(-3) K-1 for a San Carlos olivin
e sample with a lapped contact. Selective values of partial derivative
(2)K(T)/partial derivative P partial derivative T (0, 0.5 x 10(-3), 1.
0 x 10(-3) K-1) are used to calculate their effect on cell volume, bul
k modulus, and bulk sound velocity for olivine at pressures to 14 GPa
and temperatures to 1800 K (410-km depth), using the high-temperature
form of the Birch-Murnaghan equation of state. The largest difference
between the cell volumes for partial derivative(2)K(T)/partial derivat
ive P partial derivative T = 1 x 10(-3) K-1 and for partial derivative
(2)K(T)/partial derivative P partial derivative T = 0 is about 0.6% at
the highest pressure and the highest temperature (14 GPa, 1800 K). Th
erefore PVT data with precision at least better than 0.6% are required
to distinguish between the extreme values of partial derivative(2)K(T
)/partial derivative P partial derivative T for olivine if the pressur
e and temperature data are free of errors. If the cross pressure and t
emperature derivative term is neglected (partial derivative(2)K(T)/par
tial derivative P partial derivative T = 0) in extrapolating laborator
y elasticity data to mantle pressure and temperature conditions, the b
ulk modulus of olivine can be underestimated by as much as 10% and the
bulk sound velocity by 3% at the 410-km seismic discontinuity. Thus t
he present study highlights the need to measure elastic properties of
mantle candidate minerals at the P-T conditions of the mantle transiti
on zone in order to establish a more precise model of the mantle miner
alogy.