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1 Seafloor spreading is one of the two major processes of plate tectonics, the other being subduction. 2  Seafloor spreading is the continuous process of forming new igneous rock at midocean ridges by injection of magma that forms new seafloor. Seafloor spreading is one of the two major processes of plate tectonics, the other being subduction. 2  Seafloor spreading is the continuous process of forming new igneous rock at midocean ridges by injection of magma that forms new seafloor.
A principal source of the heat that drives plate tectonics is the radioactive decay of uranium, thorium, and potassium in Earthâs crust and mantle. Characteristics. The mantle differs substantially from the crust in its mechanical properties as the direct consequence of the difference in composition (expressed as different mineralogy).