Main Menu >  Rocks and Mining >  Rocks Transform >  Variations on a Metamorphic Theme Many metamorphic rocks contain large and beautiful crystals. The diverse colors and textures of these rocks resulted from different combinations of temperature and pressure produced by interactions of the gigantic tectonic plates that cover Earth’s surface. The rocks formed either where one plate sank below another (subduction zone) or where two plates collided. Two geotherms—temperature/pressure curves—show how these parameters increase as you go deeper into the Earth. One is for subduction zones, the other for collision zones.