Experimental determination of compressional wave velocities of olivine aggregate up to 1000°C at 1 GPa

The velocity of the compressional wave (Vp) was measured for olivine aggregate at temperatures up to 1000 degreesC at 1 GPa using a piston-cylinder high-pressure apparatus. The samples used in the present study were hot-pressed olivine aggregate with uniform chemical composition. The value of V-p at 1 GPa and an ambient temperature, is 8.42 km s(-1), which is identical to that in previous measurements of olivine single-crystals, The temperature derivative of V-p (partial derivativeV(p)/partial derivativeT = -4.7 X 10(-4)km s(-1) K-1) obtained from the present experiments at 1 GPa is smaller than the previously reported value at an ambient pressure. The temperature gradient for constant velocity (dT/dZ)(c) allowing the effect of anelasticity is calculated to be 4 degreesC km(-1). Taking into account, the temperature gradient in the upper mantle (15 degreesC km(-1) within the lithosphere and 0.6 degreesC km(-1) within the asthenosphere), it is suggested that the low velocity zone in the upper mantle could be caused by a drastic change in the temperature gradient at the lithosphere/asthenosphere boundary. (C) 2001 Elsevier Science B.V. All rights reserved.