Title: Intrusive Igneous Activity
1Intrusive 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
2Origin of Magma
- Magma is rock melted by earths internal heat
- Magma results from melting of the crust and upper
mantle - Earths internal temperature increases with depth
from 20-30C per kilometer - Known as geothermal gradient
3Where 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)
4Earths Geothermal Gradient
Temperature increases with depth within the earth
5Pluton Classification
- Plutons classified by size, shape, and
relationship to surrounding rock layers - Types of Plutons
- Sills
- Laccoliths
- Dikes
- Batholiths
- Stocks
6Sills 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
7Sill
A sill results from molten magma injected into
sedimentary layers Sills are parallel to the
layers
Sedimentary layers
http//www.psrd.hawaii.edu/WebImg/Sill.gif
8Perfect Sill
Sedimentary layers are visible above and below
the sill
Sill
http//z.about.com/d/geology/1/0/J/S/sill.jpg
9Laccolith
Bear Butte, a laccolith near the Black Hills in
Wyoming, has been exposed by weathering
http//www.tulane.edu/sanelson/images/laccolith.g
if
10Dikes
Ship Rock, NM Dike
- 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
11Dike in Sedimentary Layers
http//www.rosssea.info/geology.html
Notice how the igneous intrusion (dike) has cut
across existing sedimentary layers
Dike
12Batholith
Batholiths can form the cores of mountains
- Largest plutons, often form mountain ranges
- Surface exposure gt 100 square kilometers (km2)
- Stocks are lt than 100 km2
13Batholiths
Idaho features some large batholiths
Half Dome at Yosemite, CA is part of a batholith
complex
14Igneous Stock
- Devils Post Pile in California is an igneous
stock - Note the 6-sided columnar jointing of the basalt
http//www.anthroarcheart.org/tblt7.htm
15Summary of Igneous Bodies