Quiz Seven (2:00 to 2:02 PM)
UNIVERSITY OF SOUTH ALABAMA
GY 111: Physical Geology
Lecture 22: Agents of
Metamorphism
Instructor: Dr. Douglas W. Haywick
Last Time
Rock Deformation
A) Confining pressure and rock deformation
B) Elastic versus permanent deformation
C) Types of deformation
D) Test review?
Web notes 21
Lab Manual Chapter 5
Rock Deformation
Rock deformation: any change in the volume, shape or orientation of a
rock body.
Rock Deformation
Orientation (or attitude): sedimentary bedding starts off horizontal, but can
be “deformed” into any configuration.
Law of Superposition
Law of Original Horizontality
Two of the 5 Stratigraphy
Principles
Stratigraphic Principles
1) The principle of superposition that states in any sedimentary succession that
has not been overturned, the oldest strata* occur on the bottom.
2) The principle of original horizontality that states sedimentary layers are
originally deposited as horizontal sheets
*the generic name we use when we are discussing sedimentary rock layers
Rock Deformation
The strength of materials (including rocks) can be tested in labs using hydraulic
presses. All materials behave elastically up to a point.
Once past the elastic limit, deformation becomes permanent.
Demonstration
Stress & Strain
Stress: a force applied to an area (Example: tire pressure in psi)
Strain: the amount of deformation produced by stress
Elastic strain: analogous to a steel spring or rubber band
Plastic strain: analogous to deforming mud or putty
Brittle strain: analogous to breaking glass
Stress vs. Strain Diagrams
• Illustrate the mechanical behavior of rock materials
• Ductile deformation requires a significant component of
plastic mechanical behavior
Ductile Deformation
plastic
Elastic Limit
Stress
Distortion below the elastic limit is
100% recoverable
Strain %
Stress vs. Strain Diagrams
• Illustrate the mechanical behavior of rock materials
• Brittle: rocks near the surface of the Earth behave as brittle
materials
Brittle Deformation
Rupture
Stress
Distortion below the elastic limit is
100% recoverable
Strain %
Mechanical Behavior of Rocks
Near-surface rocks that are under low T-P conditions behave
as brittle material:
– Fault fracture (slippage)
– Joint fracture (no slippage)
Deep rocks under elevated T-P conditions behave as ductile
material:
– Folding
Today’s Agenda
Metamorphism 1
1.Agents of Metamorphism
2. Types of metamorphism
3. Hydrothermal fluids (webnotes only)
Web notes: 22
Agents of Metamorphism….
….but first a word from our sponsor:
The Rock Cycle
The Rock Cycle
The Rock Cycle
Igneous
Loop
Metamorphic
Loop
Sedimentary
Loop
Metamorphism
Metamorphism: a solid state change (recrystallization)
of a parent rock by physical “agents” using operating
deep within the interior of the Earth.
Shale (Parent Rock)
Slate (Metamorphic Rock)
Metamorphism
Agents of Metamorphism
1. Heat (25˚C to 800˚C; up to
the point of melting)
Geothermal Gradient: the increase in
ambient temperature with depth.
15 to 30°C/km under stable continental
rocks
200°C/km under mid oceanic ridges
http://www.geo.umn.edu/courses/1001/Summer_Session/MeltingVsDepth.jpg
Metamorphism
Agents of Metamorphism
1. Heat (25˚C to 800˚C; up to
the point of melting)
2. Pressure (1 bar to 12 kbars)
1 bar = 1 atmosphere
12 kbar = 12,000 atmospheres
http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/hydrostat.jpg
Metamorphism
Agents of Metamorphism
1. Heat (25˚C to 800˚C; up to
the point of melting)
2. Pressure (1 bar to 12 kbars)
3. Chemically active fluids
(AKA hot water)
http://news-service.stanford.edu/news/2005
Types of Metamorphism
Regional (heat and pressure)
Associated with convergent
plate boundaries
http://www.indiana.edu/~geol105/images/gaia_chapter_5/regmeta.jpg
Types of Metamorphism
Regional (heat and pressure)
Isograds vs Isotherms
Types of Metamorphism
 Contact (heat only)
Metamorphic
aureole
Metamorphic aureoles
Types of Metamorphism
 Contact (heat only)
Metamorphic aureoles
Types of Metamorphism
 Cataclastic (pressure only)
Mylonites
Shear zones
http://www.cliffshade.com/colorado/homestake/hsz01.jpg
Types of Metamorphism
 Cataclastic (pressure only)
http://instruct.uwo.ca/earth-sci/200a-001/03dymet.gif
Today’s Homework
1.
Rock/mineral photo Assignment (due Friday November 11th)
2. GY 302 mineral poster show (Tues Nov 22nd, 12-2 PM)
BONUS
3. Mobile Rock and Gem Society Show (Nov 25-27) Bonus
Next Time
1.
Regional metamorphism
GY 111: Physical Geology
Lecture 22: Introduction to Metamorphism
Instructor: Dr. Doug Haywick
[email protected]
This is a free open access lecture, but not for commercial purposes.
For personal use only.