Regional

Regional metamorphism affects large volumes (regions) of rock, especially in the mountain chains that form when continents collide.

Regionally metamorphosed rocks usually have a squashed, or foliated appearance – examples include slate, schist and gneiss (pronounced “nice”), formed by metamorphism of mudstones, and also marble which is formed by metamorphism of limestone.

View an animation showing metamorphism.

The diagram below shows how mountains are built when continents collide.

In the “roots” of the mountain belt, rocks may be buried to depths of 20 km or so.

They get very hot (500^oC or more) and so re-crystallise to form new minerals and textures.

Rocks metamorphosed at depth may later be pushed up along faults, bringing them closer to the surface.

As the mountains are eroded away by glaciers and rivers, these rocks become exposed for us to see.