Question

Where do most metamorphic changes to rock occur?

Answer 1

In regional metamorphism.

Explanation:

Regional metamorphism, or dynamothermal metamorphism, generally occurs over large areas. Most regional metamorphism is accompanied by deformation under non-hydrostatic or differential stress conditions. It occurs due to high temperatures and pressures. This produces rocks that are usually more foliated (like gneiss or schist).

Regional metamorphism takes place away from rising magma (which would be contact metamorphism), which is why it's more common. That is to say the creation of regionally metamorphosed rocks occurs away from a significant temperature gradient. As far as the location itself is concerned, it tends to happen in places where tectonic forces have compressed the crust and put high pressure on the rocks.