What causes sea floor spreading?

Sea floor spreading is primarily caused by convection currents in the mantle that create a movement of tectonic plates. As material in the mantle heats up, it becomes less dense and rises, while cooler material sinks. This movement generates currents that push the tectonic plates apart. At mid-ocean ridges, where the sea floor is spreading, magma from the mantle rises to fill the gap created by the diverging plates. This not only forms new oceanic crust but also drives the continuous process of sea floor spreading.

The mechanism of convection is fundamental in maintaining the motion of the plates, as these plates are essentially floating on a semi-fluid asthenosphere beneath them. This characteristic of mantle convection contributes significantly to the overall dynamics of plate tectonics and the formation of various geological features.

While other factors like magnetic anomalies, seismic activity, and gravitational forces play important roles in the broader context of plate tectonics, they do not directly initiate sea floor spreading in the same way that convection currents do.