Dislocations in spinel and garnet high-pressure polymorphs of olivine and pyroxene: implications for mantle rheology.

The meteorite Tenham was observed by transmission electron microscopy and ringwoodite and majorite, the high-pressure polymorphs of olivine and pyroxene, were identified. Ringwoodite contains antiphase boundaries and straight dislocations that are probably dissociated. Mantle flow of spinel might proceed by pure climb, and whole-mantle convection may be possible if the grain size is small enough.