Metamorphic Rocks Metamorphic rocks are rocks that have

Metamorphic Rocks Metamorphic rocks are rocks that have undergone a fundamental change of form

Increases in temperature and pressure, and chemical changes due to hot fluids can cause metamorphism All metamorphic rocks have a distinctive protolith (parent rock), which can be any three of the major rock types Rocks can undergo different grades of metamorphism, ranging from high to low Protolith Metamorphic rock

There are several different types of metamorphism that can occur: 1) Regional metamorphism – Widespread metamorphism due to strong tectonic forces 2) Contact metamorphism – Metamorphism due to an igneous intrusion into the country rock 3) Cataclastic metamorphism – High-pressure metamorphism found along a fault zone 4) Hydrothermal metamorphism – Metamorphism due to the movement of hot fluids through a rock 5) Burial metamorphism – Metamorphism of sedimentary rocks due to the build up of overlying sediments and rocks - most important

All of the types of metamorphism imprint a new texture, which can be grouped as either Foliated or Nonfoliated l Foliated rocks display foliation, a set of flat or wavy planes, which is due to the presence of platy minerals (micas). There are 4 different types of foliation:

1) Slaty Foliation – Low grade, seen in slate 2) Phyllitic Foliation – Low to Med. grade, seen in phyllite

3) Schistose Foliation – Med. grade, seen in schist 4) Gneissic Layering – High grade, seen in gneiss

l As metamorphic grade increases, the degree of foliation increases, along with the grain size

l Nonfoliated rocks do not display any foliation, but display different types of textures. Common nonfoliated textures include: 1) Fused Grains – When a sandstone undergoes metamorphism the sand grains that make up the rock become fused together, seen in quartzite

2) Stretched Pebbles - When a conglomerate undergoes metamorphism the clasts that make up the rock become stretched, seen in metaconglomerate 3) Crystalline Texture – Smooth intergrown crystals (usually calcite) uniform in size, seen in marble

Metamorphic grade can also be inferred by the minerals present in the rock, which can also be used to determine different metamorphic facies