Where does the material for new mountain ranges come from

In the formation of mountain ranges and all other landforms, there is always a cycle involved. As one mountain comes up, another land gets pushed down into the hot mantle, where the rock will melt. Due to convection currents, the tectonic plates move and their boundaries cause them to interact with each other. As mountain ranges are formed, other land gets pushed up forming what we know are mountains, with rising magma from other parts of the world solidifying creating new rock to fill the empty space.