RECENT GEODYNAMIC EVOLUTION OF CONVERGENT PLATE MARGINS AND THE RECONSTRUCTION OF FOSSIL PLATE BOUNDARIES

The discovery of paleoplates buried in the upper mantle leads to an in terpretation of the subduction as a discontinuous process running in c ycles and shifting the place of its operation in or against the direct ion of ocean floor spreading. This mechanism explains the distribution of calc-alkaline volcanism of different age in fossil convergent plat e boundaries. The establishment of regular spatial correlation of the aseismic gap in the Wadati-Benioff zones with the distribution of calc -alkaline volcanism enables to reconstruct fossil plate boundaries and to define allochtonous terranes in apparently homogeneous continental plates. The hampering effect of the ocean floor morphology and of the fragments of continental plates approaching the trench, which substan tially influences the rates of subduction and the geodynamic history o f active continental margins in different domains along the trench, al lows us to understand the complicated geological development of contin ental wedges in fossil convergent plate margins. The establishment of the segmented nature of active subduction zones and the dramatic morph ology of the lower limit of the active subducted slab along the trench help us to interpret extensive lateral gaps in volcanic chains overly ing active as well as fossil subduction zones.