High Strained Rocks

The shear zones is a region in the Earth’s crust where rocks are highly strained than the surroundings. These highly strained rocks can be found in the highly structural deformed terrains. These highly strained rocks can be cohesive or they can loose cohesion.

These high strained rocks are classified on the basis of Cohesion, Foliation and fine matrix percentage .

• Rocks which are not cohesive can be divided into Fault breccia (<70% matrix) and fault gouge (>70% breccia).
• The cohesive rocks can be divided into Foliated and Non-foliated.
  • The non-foliated rocks are Microbreccia (<70% matrix) and Cataclasite (>70% matrix)
  • The foliated rocks are Mylonite

Important points

• Some Geologists uses the term Phyllonite to indicate a mica-rich mylonite.
• All high strained rocks are characterized by Grain-size reduction.
• Impactites are highly strained rocks which formed due to catastrophic events like impact craters and is characterized by shocked crystals, multiple set of planar features, glassy phases, melting and even vaporising some minerlas.
• When there is wide ductile shear zone, Stripped gneiss is formed. It has distinct strips of dark and light color bands in a dominant ductile deformation. (generally at convergent plate boundary)

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