EXPERIMENTAL DETERMINATION OF COMPRESSIONAL WAVE VELOCITIES OF OLIVINE AGGREGATE UP TO 1000°C AT 1GPA

Abstract

The velocity of the compressional wave (VP) was measured for olivine aggregate at temperatures up to 1000°C at 1GPa 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 VP at 1GPa and an ambient temperature, is 8.42kms-1, which is identical to that in previous measurements of olivine single-crystals. The temperature derivative of VP (#VP/#T=-4.7x10-4kms-1K-1) obtained from the present experiments at 1GPa 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°Ckm-1. Taking into account, the temperature gradient in the upper mantle (15°Ckm-1 within the lithosphere and 0.6°Ckm-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.