Distinguish between regional and contact metamorphism. a. Contact metamorphism occurs when chemically active fluids flow through a large region of preexisting rock; regional metamorphism occurs when large quantities of rock are subjected to high heat and pressure during mountain building. b. Regional metamorphism occurs when magma intrudes existing rock and heats it enough to cause metamorphic changes; contact metamorphism occurs when large quantities of rock are subjected to high heat and pressure during mountain building. c. Contact metamorphism occurs when magma intrudes existing rock and heats it enough to cause metamorphic changes; regional metamorphism occurs when large quantities of rock are subjected to high heat and pressure during mountain building. d. Regional metamorphism and contact metamorphism both occur when quantities of rock are subjected to high heat and pressure during mountain building, but regional metamorphism affects over a greater area. e. Regional metamorphism occurs when chemically active fluids flow through a large region of preexisting rock; contact metamorphism occurs when magma intrudes existing rock and heats it enough to cause metamorphic changes.