TEMPERATURE-VARIATION OF HARDNESS OF OLIVINE AND ITS IMPLICATION FOR POLYCRYSTALLINE YIELD STRESS

The variation of hardness with temperature was measured for olivine on a number of crystal faces by the Vickers diamond pyramid technique (up to 800o C9 and by a mutual indentation technique (for temperatures up to 1500oC). A comparative review of hardness data and compressive creep measurements obtained under large confining pressures confirms the hypothesis of Rice (1971) that single-crystal hardness measurements, corrected for elastic effects, can be correlated to the fully ductile yielding of a polycrystal by intragranular dislocation mechanisms, including dislocation climb and glide. The computed differential yield stresses, sigma (in gigapascals), which empirically correspond to a strain rate epsilon of 10-5 s-1, were well represented by an equation of the form sigma = 9.1 (+-0.3) - 0.23(+-0.01)T 1/2, where T is of the absolute temperature (in degrees Kelvin), and the quoted variances are for 1 standard deviation. The olivine data therefore predict a high-stress polycrystalline flow law that may be expressed as epsilon = 1.3 x 1012 exp - (60 x 103)/T) (1 - (sigma/9.1))2 where epsilon is the strain rate in s-1.-Authors