What do you call the phenomenon when seafloor spreading creates a new seafloor, but the diameter of the Earth doesn't increase because another process melts old seafloor back into magma?

The term that describes the phenomenon when seafloor spreading creates a new seafloor, but the diameter of the Earth doesn't increase because another process melts old seafloor back into magma is called seafloor spreading. It is the process of making new crusts through volcanic activities