CORRELATION-ANALYSIS BETWEEN SUBDUCTION IN THE LAST 180 MYR AND LATERAL SEISMIC STRUCTURE OF THE LOWER MANTLE - GEODYNAMICAL IMPLICATIONS

We have calculated the correlation between four recent tomographic models and reconstructions of past subduction sites to estimate the present positions of the lithosphere subducted during the Cenozoic and the Mesozoic. A significant correlation is found at a depth of about 1000 km for subduction younger than 120 Myr, while remnants of subduction older than 120 Myr are detected close to the core-mantle boundary (CMB). Somewhere in the depth range of 1300-2600 km a gap exists where no significant correlation is found in any time. The results suggest that the slabs do not pass through the lower mantle continuously. It is possible that both regimes, the catastrophic and the steady-state, may be important for different time periods. Fast seismic anomalies close to the CMB may be associated with a past catastrophic event, while the good correlation in the upper part of the lower mantle may be explained by a steady-state model, Other explanations for the very good correlation found at a depth of about 1000 km are either a predicted perovskite phase transition or a chemical boundary suggested by seismic array analysis.