ABSTRACT
The gradual heating of the descending slab has one other important effect. As temperatures rise at the upper surface of the descending plate, a partial melting of the oceanic crust occurs. Virtually all the islands on the surface of the plate are members of basalt ridges created by the passage of the plate surface across a stationary hot spot. The Pacific plate subducts beneath the oceanic crust of the small Philippine plate, which in turn subducts beneath the continental crust of China along the Ryukyu trench – island arc system. Sediments accumulated along the western margin of South America for some time before active subduction initiated an island arc on the Nazca plate. Partial melting of oceanic crust from the descending plate would provide the material for the modern volcanoes along the mountain chain. Continental crust is therefore produced during orogenesis, and continents grow by the accretion of orogenic belts along their margins.
