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Metamorphic Rocks

Metamorphic Rocks

Metamorphism – The transformation of pre-existing rocks into new types by the action of heat and pressure changes.

Photos by C.C. Plummer

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Metamorphic Rocks

Metamorphism – The transformation of pre-existing rocks into new types by the action of heat and pressure changes.

Heat – from magma intrusion, compression, or decay of radioactive elements. Generally, at depths of about 35 km, temps are high enough to begin melting rocks.

Metamorphic Rocks

Metamorphism – The transformation of pre-existing rocks into new types by the action of heat and pressure changes.

Pressure – generates heat, and along points of contact can melt rocks. Also generates the development of banded and foliated textures. Increasing pr4essure conditions force grains closer together and eliminates pore space.

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Metamorphic Rocks

Metamorphism – The transformation of pre-existing rocks into new types by the action of heat and pressure changes.

Chemically active fluids – chemical exchange of elements generate different mineral compositions.

Metamorphic Rocks

Two different types of metamorphism:

1. Contact metamorphism –occurs upon contact of hot igneous rocks and surrounding country rocks. As distance from intrusion increases degree of metamorphism decreases.

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Metamorphic Rocks

Two different types of metamorphism:

1. Regional metamorphism –occurs upon contact of hot igneous rocks and surrounding country rocks. As distance from intrusion increases degree of metamorphism decreases.

Metamorphic Rocks

Identifying metamorphic rocks using texture.

Foliation – parallel arrangement of minerals

Photos by C.C. Plummer

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Metamorphic Rocks

Identifying metamorphic rocks using texture.

Foliated rocks:

Slate – metamorphosed clayey rocks (shale). Sheety appearance

Photo by C.C. Plummer Photo by P.D. Rowley, USGS

Metamorphic Rocks

Identifying metamorphic rocks using texture.

Foliated rocks:

Schist

Photo by C.C. Plummer

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Metamorphic Rocks

Identifying metamorphic rocks using texture.

Foliated rocks:

Gneiss

Metamorphic Rocks

Identifying metamorphic rocks using texture.

Foliated rocks:

Gneiss

Photo by C.C. Plummer

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Metamorphic Rocks

Identifying metamorphic rocks using texture.

Nonfoliated rocks:

Marble

Quartzite

Photo by C.C. Plummer