Metamorphism and the Rock Cycle - Chapter 5

What is metamorphism?

The transformation of existing rock by heat, pressure, or fluids without melting.

What is a metamorphic rock?

A rock changed from a preexisting rock by heat, pressure, or fluids.

What is a protolith?

The original rock before metamorphism.

Does metamorphism involve melting?

No. Melting produces magma, which can form igneous rock.

What is recrystallization?

Minerals change size or shape without changing overall composition.

What is a metamorphic phase change?

A mineral changes its crystal structure while keeping the same chemical composition.

What are metamorphic reactions?

Existing minerals react to form new minerals stable under new conditions.

What is plastic deformation?

Minerals change shape without breaking.

What is pressure solution?

Minerals dissolve at stressed contacts and may reprecipitate elsewhere.

What are the three main agents of metamorphism?

Heat, pressure or stress, and chemically active fluids.

Why does temperature increase with depth?

Earth's internal heat creates a geothermal gradient.

Why does pressure increase with depth?

The weight of overlying rocks increases.

What is confining pressure?

Pressure applied approximately equally from all directions.

What is overburden pressure?

Pressure caused by the weight of overlying material.

What is differential stress?

Unequal stress that can deform or align mineral grains.

What is compression?

Stress that squeezes and shortens rock.

What is tension?

Stress that pulls and stretches rock.

What is shear?

Stress that causes parts of rock to slide past one another.

What are equant grains?

Mineral grains with approximately equal dimensions.

What are inequant grains?

Elongated or flattened mineral grains.

What are hydrothermal fluids?

Hot, mineral-rich fluids that circulate through rock.

What is metasomatism?

Chemical alteration of rock by fluids adding or removing elements.

How are metamorphic rocks classified?

Mainly by texture, especially foliation, and mineral composition.

What is foliation?

Parallel alignment or layering of minerals caused by metamorphism.

What causes foliation?

Differential stress and growth or alignment of minerals.

What are the four main foliated metamorphic rocks?

Slate, phyllite, schist, and gneiss.

What is slate?

A fine-grained, low-grade foliated rock commonly formed from shale.

What is phyllite?

A foliated rock with fine mica and a silky sheen.

What is schist?

A medium- to coarse-grained foliated rock with visible platy minerals.

What is gneiss?

A high-grade metamorphic rock with light and dark mineral bands.

What is metamorphic differentiation?

Separation of minerals into compositionally different bands during metamorphism.

What is a non-foliated metamorphic rock?

A metamorphic rock without a prominent layered or aligned texture.

What are common non-foliated metamorphic rocks?

Marble, quartzite, and hornfels.

What does limestone become during metamorphism?

Marble.

What does quartz sandstone become during metamorphism?

Quartzite.

What is metamorphic grade?

The relative intensity of metamorphism, mainly reflecting temperature and pressure.

What is the typical increasing metamorphic grade sequence for shale?

Slate → phyllite → schist → gneiss.

What is contact metamorphism?

Metamorphism caused mainly by heat near a magma intrusion.

What is regional metamorphism?

Large-scale metamorphism during mountain building and tectonic deformation.

What is burial metamorphism?

Metamorphism caused by deep burial and increasing temperature and pressure.

What is hydrothermal metamorphism?

Rock alteration by circulating hot, chemically active fluids.

What is dynamic metamorphism?

Metamorphism caused mainly by intense deformation along faults.

What is subduction-zone metamorphism?

Metamorphism often involving high pressure and relatively low temperature.

How does metamorphism differ between an accretionary prism and a collisional mountain range?

Accretionary prisms tend toward high-pressure, low-temperature conditions; collisional roots become hotter during deep burial.

What is exhumation?

The return of deeply buried metamorphic rocks toward Earth's surface through uplift and erosion.

Where are metamorphic rocks commonly exposed?

Eroded mountain belts, continental shields, and deeply uplifted crust.

What is the rock cycle?

Processes that transform rocks among igneous, sedimentary, and metamorphic types.

How do plate tectonics drive the rock cycle?

Subduction, collision, uplift, volcanism, weathering, and burial transform and recycle rocks.