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Forty years ago when plate tectonics was first discovered, there was a major shift in thinking in the Earth Sciences. Little was known at that time about the deep mantle because of the lack of knowledge about material properties, the absence of any seismic tomography or concepts such as mantle convection. Thus the theory of platetectonicswasbuiltonsurfaceobservationsandkinematicconstraints.Thetheory of plate tectonics is not independent but consists of several assumptions. Examples are the origin of arc magma, MORB or OIB, and the distribution of earthquakes and the plate margin processes are...