T. Nakagawa and P. J. Tackley $^{a}$
$^{a}$ Department of Earth and Space Sciences, University of California, Los Angeles, Los Angeles CA, USA
takashi@sys.eps.s.u-tokyo.ac.jp
Numerical simulations are used to investigate the compositional origin of strong heterogeneity at the base of mantle. High pressure experiments have been pointed out that the compositional distinct material at the base of mantle might be generated from the primordial origin which is the residue of initial differentiation between the mantle and core, and the recycling of oceanic crust which is the segregation of eclogitic material from ancient slabs.Here, the possibility of each origin was checked by calculating the seismicstructure using the similar model of mantle convection to {\it Christensen and Hoffmann}[1994]. The strong heterogeneous structure in the seismic structure at the base of mantle is observed in case of primordial layering combined with the segregation of oceanic crust at the base of mantle. The layering material forms the large scale of the isolated pile structure corresponding to the characteristic degree of the predicted heterogeneous structure at the base of mantle. On the other hand, without primordial layering, the strong heterogeneity in the seismic structure is not observed. In this case, the temperature anomaly is almost canceled out by the effect of compositional anormaly in the whole layer. These results indicate that the residue of the initial differentiation could not entrain into the core and has still distributed at the base of mantle beneath the segreated material from the oceanic crust.