Metamorphic Rocks

EES 101

What is metamorphism?

It is a change in condition resulting in new minerals and textures. It is change without melting. Rocks will progress from low to high grade.

What are the main agents of metamorphism?

Heat, pressure, and fluid

What are the sources of heat for metamorphism?

Magma/lava and the geothermal gradient

What are the limits for metamorphism?

Heat cannot exceed 700 degrees Celsius or melting will occur. There is no pressure limit.

What happens when uniform pressure is present during metamorphism?

It occurs because of the weight of the overlying rocks, increasing with depth. It is applied equally in all directions and results in volume reduction.

What happens when differential pressure is present during metamorphism?

Rock shape is distorted and a foliation structure appears.

What is the effect of fluids in metamorphism?

It enhances migration of ions and chemical reaction, in other words, grows more minerals. 

Many different types of rocks form from the metamorphism of shale. Place them in order from lowest grade to highest grade.

Slate, Phyllite, Schist, and Gneiss

How does foliation form?

During metamorphism, differential pressure causes the mineral bands to align in a parallel pattern.

What is a slaty cleavage texture?

It is a low grade texture found in slate. It is fine-grained and contains clay and chlorite.

What is schistocity?

It is a texture found in schist. It is distinctly foliated and is made of 50% platy minerals like Muscovite.

What is a gneissic texture?

It is a high grade texture found in gneiss. It has alternating bands of light quartz and dark biotite.

What is a non-foliated rock texture?

It is a texture with no preferred mineral orientation. Examples include amphibolite, marble, quartzite, and hornfels.

What is the porphyroblastic rock texture?

It is a texture of large grains surrounded by a fine grained matrix.

What are migmatites?

They are rocks in between metamorphic and igneous rocks. They form under extreme temperatures when they partially melt. 

What is the parent material of marble?

Limestone and dolostone

What is the parent material of quartzite?

Quartz sandstone

What is the parent material of hornfels?

Any rock type

What is the parent material of anthracite?

Bituminous coal

What is contact metamorphism?

It is intense heat that essentially bakes the rock. It is due to heat only. It results in an alteration zone in the adjacent rock called aureoles. Non-foliated rock forms here.

What is regional metamorphism?

It occurs with differential pressure and intense heat, though no igneous bodies are present. It is associated with mountain building.

What is hydrothermal metamorphism?

It occurs when water percolates through oceanic crust, warms, and dissolves out sulfide minerals. Hot fluid triggers metamorphic reactions. It is associated with oceanic spreading and the mid-ocean ridge.

What is impact metamorphism?

It occurs when meteorites strike the Earth. It is associated with ultra high pressure and low temperature.

What do index minerals tell us?

They indicate a specific range of temperatures and pressures.

What is the order of index minerals from low to high grade?

Chlorite, Muscovite mica, biotite mica, garnet, staurolite, and sillimanite. Quartz and feldspar are always present.