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Dynamic Earth: Igneous

Rocks continued

LECTURE 3a

ENM200: Dynamic EarthDr Bryan T Cronin (ext.cronin1@rgu.ac.uk)

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Shapes of plutons

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Exposed, exhumed granite plutons in SW England

Robert Gordon University5Cornish Granite

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Edinburgh Castle:

sitting on ancient

granite

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Robert Gordon University8Surtsey Island, Iceland

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Lava River, Hekla (Iceland) 1987

Robert Gordon University10Pillow Lavas, Devon (submarine lava)

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Pillow Lavas, eastern Turkey (Eocene)

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Though no pillow lavas have been seen forming in nature, this is probably what

happens.

Robert Gordon University13Horneblende Trachyte Iava

under the microscope)

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Mt St Helens, 90 minutes after eruption

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Pyroclastic Flow:

Ash expelled high into the

atmosphere during eruption

falls back and flows off the

flanks of volcanos as

pyroclastic flows

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Pyroclastic flow (Mt Pinatubo)

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London Clay with Ash layers: easy to date

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Dynamic Earth:

Metamorphic Rocks

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We know that material converts with pressure

and temperature

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Metamorphism

Rocks deform, mineralogy

changes with temperature

and pressue

Robert Gordon University23Simple diagram to show how rocks are buried,

then deform (metamorphism), then melt

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Robert Gordon University25Metamorphic Rock Example: Gneiss (deformed granite)

Robert Gordon University26Metamorphic Rock Example: Marble (deformed limestone)

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Metamorphic Rock Example: Slate (deformed mudstone)

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Granite slate contact

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Rosslare Gneiss

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Scottish

Metamorphic

Zones

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Chlorite Shale (Metamorphosed mudstone)

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