SUPERPLASTICITY IN EARTHS LOWER MANTLE - EVIDENCE FROM SEISMIC ANISOTROPY AND ROCK PHYSICS

In contrast to the upper mantle, the tower mantle of the Earth is elas tically nearly isotropic, although its dominant constituent mineral [( Mg,Fe)SiO3 perovskite] is highly anisotropic. On the bads of high-temp erature experiments on fabric development in an analog CaTiO3 perovski te and the elastic constants of MgSiO3 perovskite, the seismic anisotr opy was calculated for the lower mantle. The results show that absence of anisotropy is strong evidence for deformation by superplasticity. in this case, no significant transient creep is expected in the lower mantle and the viscosity of the lower mantle is sensitive to grain siz e; hence, a reduction in grain size with result in theological weakeni ng.