Transcript Introduction to Earth Science Ch. 01

Intrusive Igneous
Activity
• Plutons result from the cooling
and hardening of magma within
the earth
• Exposed at surface after uplift
and erosion
• Pluton refers to Pluto, the
Roman god of the underworld
Origin of Magma
• Magma is rock melted by
earth’s internal heat
• Magma results from melting of
the crust and upper mantle
• Earth’s internal temperature
increases with depth from 2030°C per kilometer
• Known as geothermal gradient
Where is Magma
Produced?
• Subduction zones, friction
between two tectonic plates
• Water decreases melting temp
at subduction zones
• Subduction creates continental
and marine volcanic arcs
• Hot spots, rising material melts
due to lessening of pressure
(decompression melting)
Earth’s Geothermal
Gradient
Temperature
increases with
depth within the
earth
Pluton Classification
• Plutons classified by size,
shape, and relationship to
surrounding rock layers
• Types of Plutons:
•
•
•
•
•
Sills
Laccoliths
Dikes
Batholiths
Stocks
Sills & Laccoliths
• A sill forms when magma is
injected between sedimentary
layers
• Sills resemble buried lava flows
• A laccolith is a type of sill that
pushes the overlying rock layers
into an arch shape
Sill
A sill results from
molten magma
injected into
sedimentary layers
Sill
Sills are parallel to the
layers
http://www.psrd.hawaii.edu/WebImg/Sill.gif
Sedimentary
layers
Perfect Sill
Sedimentary layers
are visible above and
below the sill
Sill
http://z.about.com/d/geology/1/0/J/S/sill.jpg
Laccolith
Bear Butte, a laccolith
near the Black Hills in
Wyoming, has been
exposed by
weathering
http://www.tulane.edu/~sanelson/images/laccolith.gif
Ship Rock, NM
Dike
Dikes
• Dikes are plutons that form
when magma is injected into
fractures that cut across
existing rock layers
• Dikes can radiate like spokes on
a wheel from a volcanic neck
http://www.rosssea.info/geology.html
Dike in Sedimentary
Layers
Notice how
the igneous
intrusion
(dike) has
cut across
existing
sedimentary
layers
Dike
Batholith
Batholiths can
form the cores
of mountains
• Largest plutons, often form
mountain ranges
• Surface exposure > 100 square
kilometers (km2)
• Stocks are < than 100 km2
Batholiths
Idaho
features
some large
batholiths
Half Dome at Yosemite, CA is
part of a batholith complex
Igneous Stock
•Devil’s Post
Pile in
California is
an igneous
stock
•Note the 6sided
columnar
jointing of the
basalt
http://www.anthroarcheart.org/tblt7.htm
Summary of Igneous
Bodies