Contact metamorphism
Magmatic intrusion can subject rocks to high T, Degree of metamorphism declines with distance from the heat source
- The restricted zone around the intrusion is a “contact aureole”
Regional metamorphism
Occurs over large areas subject to high confining and differential stress
Usually results from tectonic forces that produce compression, as in when two continental masses collide
During collision, rocks are taken from the surface to high T and P
Often occurs in core of mountain ranges
Dynamic metamorphism
Occurs in narrow zone near faults due to mechanical shear deformation
Porphyroblasts
Larger, recrystallized grains occurring in a finer groundmass of a
metamorphic rock