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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.
What drives the process of plate tectonics. Tectonic plates are pieces of the Earth's crust and uppermost mantle, together referred to as the lithosphere. The plates are around 100 km thick and consist of two principal types of material: oceanic crust and continental crust. The composition of the two types of crust differs markedly, with basaltic rocks dominating oceanic crust, while continental crust consists principally of lower density granitic rocks.