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5. Under Pressure

Metamorphic Rocks

Metamorphism

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Metamorphism

Heat and pressure

Can affect any rock

Low-High grade

Solid state change

Hand specimens

First impressions?

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Metamorphism

Temperature >200°C

AND/OR

Pressure >300 MPa (3 kbar)

AND/OR

Chemically active fluids

Metamorphic facies

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Thermal metamorphism

Igneous intrusion bakes surrounding rocks

Thermal metamorphism

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Hornfels

Marble

Thermal metamorphism

Marble crystals

Limestone grains

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Metamorphism by pressure

Metamorphism by pressure SLATE

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Metamorphism by pressure

SLATE

SLATE

Regional metamorphism

High temps and pressures

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= High-grade metamorphism

Mechanical metamorphism

Mylonite = milled

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Chemical metamorphism

Metasomatism:

Soapstone

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Key metamorphic features

Cleavage:

Slaty cleavage

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Welsh slate

belts

Penrhyn Slate Quarry,

Bethesda, c. 1900

Foliation

Schist under the microscope

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Multiple foliation

Banding Gneiss, Stockholm

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Partial melting migmatite

Metamorphic zones

andalusite

Almandine garnet

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Metamorphic facies

Next week Folds, Faults & Plate Tectonics