PALEOPLATES BURIED IN THE UPPER MANTLE AND THE CYCLIC CHARACTER OF SUBDUCTION

Results of detailed investigations into the deep seismicity patterns in convergent plate margins of the Andes, Tonga-Kermadec, Vanuatu and Kamchatka-Kuriles-Hokkaido are presented in order to interpret the history of evolution of the subduction process. The subduction, caused by continuously operating ocean floor spreading, appears to run in cycles, each cycle being characterized by its proper trench, subduction zone and chain of calc-alkaline volcanism. The discontinuity of subduction can be documented by the existence and position of paleo-plates buried in the upper mantle and by the occurrence of paleovolcanic chains, both phenomena being shifted in the same direction in relation to the corresponding spreading centre. The seismic activity of paleoslabs is explained by their collision with the active subduction zones and the clusters of intermediate and deep earthquakes are interpreted as collision centres. The cyclic course of the subduction process can be correlated with major geological phenomena in convergent plate margins such as uplift, erosion, subsidence, sedimentation and volcanic activity.