ON THE SEPARATION OF CRUSTAL COMPONENT FROM SUBDUCTED OCEANIC LITHOSPHERE NEAR THE 660 KM DISCONTINUITY

The recent mineral physics observations suggest that the crustal and m antle components of subducted oceanic lithosphere have distinct densit ies and viscosities. The deformation of such chemically stratified oce anic lithosphere as it collides with the 660 km discontinuity is exami ned using a simple analytical model. It is shown that the separation o f the crustal component can occur through a small scale folding (10-20 km) if the viscosity of the crustal (garnetite) layer is significantl y higher than the surrounding mantle (similar to 10(21) Pa s) but is l ess than similar to 10(23) Pa s, leading to a garnet-enriched transiti on zone behind subduction zones.