Metamorphic Rocks The Greek word meta means “change” and morph meaning “shape”. Metamorphic rocks were previously either sedimentary or igneous rocks, but they have been subjected to very high temperature and pressure. (Below the surface of the Earth)

Metamorphic Rocks The temperature was not high enough to make the rock melt (Metamorphic changes occur as the rock is in solid-state), but it was high enough to allow some crystals to grow, and for the minerals to begin to re-crystallize and thus form a new rock. As temperature rises, crystal lattices are broken down and reformed with different combinations of atoms. New minerals are formed.

Metamorphic Rocks The types of metamorphism Regional metamorphism Contact metamorphism Regional metamorphismContact metamorphism

Metamorphic Rocks Contact metamorphism In the case of contact metamorphism heat comes from contact with molten magma. -This type of metamorphism has a limited and local effect.

Metamorphic Rocks Regional metamorphism When rocks are forced toward the mantle during the formation of a mountain range and/or other tectonic activity, regional metamorphism occurs. -Large volumes of rock are altered in this way.

Metamorphic Rocks Metamorphism does not take place on the Earth’s surface. Rocks under the Earth’s surface are under great pressure from overlying rock layers. Deep burial- as depth increases, in the Earth’s crust, the temperature also increases. Tectonic forces in the Earth may apply lateral pressure to large volumes of rock.

Metamorphic Rocks

Metamorphic rocks have been exposed to the surface of the Earth because erosion has striped away overlying rocks. So, when we see a large area of metamorphic rocks we know we are looking at the core of an ancient mountain range.

Changes During Metamorphism Parent rock (protolith) Low temperature Low pressure Medium temperature Medium pressure High temperature High pressure Higher temp. Higher pressure shaleslatephyllite schist gneiss MELTING quartz sandstone quartzite limestonemarble basalt amphibolite or schist granitegneiss

Metamorphic Rocks Change in metamorphic grade with depth Increasing Directed Pressure and increasing Temps

Metamorphic Rocks Foliated metamorphic rock Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied in. Foliation: minerals have been rearranged into visible bands.

Metamorphic Rocks Increasing Directed Pressure and increasing Temps

Metamorphic Rocks Directed Pressure causes rocks to become folded, and minerals to reorient perpendicular to the stress: “ foliation ”

Schist

Gneiss

Slate

Metamorphic Rocks Non-foliated metamorphic rock Non-foliated metamorphic rocks do not have a platy or sheet-like structure. Metamorphic rock that does not show bands.

Marble

Quartzite