Magma engine theory of plate tectonics. Illustration showing an Earth globe centred on the Pacific Ocean, showing the areas of magma underlying the major continents, oceans and tectonic plates. According to the magma engine theory of plate tectonics, the movement of the plates is driven by the heat and movement produced by magmatism, the melting of rocks under the immense pressure and heat generated inside the Earth. The resulting interplay of convection (mantle plumes) and gravity (tilted plates) results in the slow movement, creation and destruction of the Earth's tectonic plates over geological time.