Mineral alignment occurs reflecting directional stresses, giving rocks a banded appearance termed foliation . Foliation forms perpendicular to directed stress. San Andreas - 1000 km long x 3km wide zone of fault breccia. Along magmatic intrusive contacts. Contact aureole or halo forms in country rock.
Hydrothermal fluids enhance the metamorphic process.
Responsible for the bulk of metamorphic rocks. Occurs at great depth in conjunction with mountain building. Metamorphic rocks generally become foliated with a gradation in metamorphism. Magmas are usually also present in the cores of mountain ranges. Can explain observed patterns of regional and contact metamorphism.