The effect of an equilibrated melt phase on the shear creep and attenuation behavior of polycrystalline olivine

The impact of a chemically and texturally equilibrated melt phase on the sh ear creep and attenuation behaviors of polycrystalline olivine has been mea sured experimentally at seismic-to-subseismic frequencies. The experiments were performed on aggregates that had a particularly uniform and fine grain size (similar to 3 mu m). The effect of the melt phase (similar to 5 vol%) is to decrease the (Newtonian) viscosity by a factor of similar to 6; ther e is no dramatic disaggregation effect of melt-induced plummeting of the sh ear modulus. Both the melt-free and melt-bearing aggregates display an atte nuation "band" of the form Q(G)(-1) proportional to f(-0.4). This response cannot be attributed to a variation in microstructure; it is intrinsic to t he diffusional creep behavior. There is no unique effect of the melt phase on the attenuation response: the slight increase in absorption of partial m elt specimens is explained fully by the effect of the texturally equilibrat ed melt on aggregate viscosity.