Answer:
Convection.
Step-by-step explanation:
Convection currents in the Earth's mantle cause the tectonic plates to move apart from each other allowing, magma to ascend and solidify into the mid-Atlantic Ridge.
Convection is a process that transfers heat from areas with high temperatures to others of lower temperature throughout materials. In this case, the material is magma. When convection takes place, the hot magma in the mantle rises due to its high temperature. Then, the magma settles in the Ocean ridge where the temperature is lower, causing the magma's solidification.