LAYERED RHEOLOGICAL STRUCTURE OF SUBDUCTING OCEANIC LITHOSPHERE

The subducting oceanic lithosphere, which was formed by petrological d ifferentiation of pyrolite at mid-ocean spreading centers, is in this paper no longer considered as a compositionally and mechanically homog eneous rigid plate or viscous slab as it was in earlier papers, but as a sandwich made up of different lithological layers. The effect of ph ase transformation as a function of depth with respect to changes in r heology of the downgoing slab is also considered. It is shown that the rheological behavior of the descending slab is strongly controlled by its lithological and thermal structure. Our results provide alternati ve and plausible interpretations for the distribution of seismicity wi thin the Wadati-Benioff zone and for the fate of subducted oceanic lit hosphere at the 670 km discontinuity. These results, although they are limited by the availability and quality of thermodynamical and rheolo gical parameters for different rock types, will advance our understand ing of rheological properties of the subducting oceanic lithosphere.