Title: 18.3 Intrusive ActivityPage #: 108

Date: 5/16/2013

• Students will be able to compare and contrast features formed from magma that solidifies near the surface of Earth with those that solidify deep underground.

• Students will be able to classify different types of intrusive rock bodies.

• Students will be able to describe how geologic processes result in intrusive rocks that appear at Earth’s surface.

Igneous Rock: Rock formed by solidification of magma.

Intrusive Activity

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Intrusive Activity: Main Idea: Magma that

solidifies below ground forms geologic features different from those formed by magma that cools at the surface.

• Intrusive Activity

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• Plutons: Not all magma emerges at surface of Earth.– Most volcanism happens below

Earth’s surface.– When magma cools minerals begin

to crystallize.– Crystallized magma forms intrusive

igneous rock bodies.

• Igneous Rock Bodies: – May be only a few cm thick and 100s

of meters long.– May be huge – 100s of km^3.

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Plutons: Huge intrusive igneous rocks 100s km^3 large.• Plutons may be uplifted at Earth’s

surface.

Batholith: Largest plutons. • Irregularly shaped.• Coarse grained igneous rocks 100

km^2+• Usually granite.• Take millions of years to form.

Batholiths form within the earth.

Uplifting may expose batholithsTo Earth’s surface.

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Stocks: Smaller batholiths.

Both Batholiths and Stocks form between 5 and 30 km below Earth’s surface.

Both Batholiths and Stocks cut across older rocks.

Stocks are smaller batholiths.

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Laccoliths: Lens-shaped pluton with a round top and flat bottom.• Form when rising magma causes

overlying rock to bend.• Largest is 16 km wide.

Sills: Parallel intrusions to rock layers.• May be only a few cm thick, or 100s

of meters thick.• Effects: 1) Lifts overlying rock up.

2) Metmorphoses surrounding rock.

Laccoliths also form within the earth.Laccoliths are round on top and flat on bottom.

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Dikes: A pluton that cuts across pre-existing rock.• Form when magma invades cracks in

surrounding rocks.• Can be large or small.

Textures: Dikes and sills usually • Coarse-grained – Large crystals,

result from slow cooling deep in Earth’s surface.

• Fine-grained – Form close to Earth’s surface.

Dikes cut across PRE-EXISTING rock. So they are always younger.

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Plutons and Tectonics: Plutons form from mountain

building.Convergent boundaries:Continental – Continental – Collision

forces crust down into the mantle where is melts, intrudes into overlying rock and cools – Forms batholiths.

Oceanic – Oceanic – When magma from a suducted plate does not rise all the way to the Earth’s surface. Example: Sierra Nevada Batholith in California and Yosemite National Park.

When two plates converge and mountains crumple up, they also push material Into the mantle, where it melts. Melted material may cool to form plutons (Mountain Roots.)