Dynamic metamorphism

Dynamic (cataclastic) metamorphism is metamorphism of rock masses caused primarily by stresses that yield relatively high strain (deformation) rates. The deformation may be dominantly brittle, in which case rock and mineral grains are broken and crushed, or it may be dominantly ductile, in which case plastic behaviour and flow occur via structural changes within and between grains. Temperatures during dynamic metamorphism are typically elevated and may be caused by the deformation process.

Both local and regional dynamic metamorphism are recognised. At the local scale, in narrow zones from less than 1 cm to several meters wide, brittle or ductile deformation along faults and fold limbs causes rock to break. Brittle and ductile deformation processes also operate at the regional scale.

The rocks produced at all scales by dynamic metamorphism are rocks composed of fragments of pre-existing material, surrounded by a deformed matrix. Such rocks, which fit into the broad category of clastic rocks, referred to as dynamoblastic rocks.

Fault breccia Shallow dynamic metamorphismrocks shatter due to CATACLASIS

Gouge is a breccia crushed to powder

mylonite

Deeper more intense metamorphismHigher temperatures and pressures, more deformation and recrystallisation to give a fine grained foliated/banded textureMay have lens shaped porphyroblasts in a fine grained streaky matrix