TEM OBSERVATIONS OF SEVERAL SPINEL-GARNET ASSEMBLIES - TOWARD THE RHEOLOGY OF THE TRANSITION ZONE

In order to better identify the mineral phase which controls the theol ogy of the transition zone (between 410 and 660 km depth) transmission electron microscopy observations were made on several coexisting spin el-garnet assemblies: alkremite xenolith; pyrope-rich - MgO:1.1Al(2)O( 3) spinel assembly deformed at 1173K, 800 MPa in a Griggs apparatus; ( Mg,Fe)(3)(Al,Mg,Si)(2)Si3O12 majorite - (Mg,Fe)(2)SiO4 spinel assembly synthesized in a laser heated diamond anvil cell. It was found that g arnet crystals systematically remain undeformed while spinel crystals are plastically deformed. These results are in accord with the assumpt ion that the theology of majorite is stronger than the theology of spi nel, in the conditions of the transition zone.