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 Stress Elastic Limit 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 Stress Rupture 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 Metamorphic Loop Igneous 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 aureoles Metamorphic aureole
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 22 nd, 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 dhaywick@southalabama.edu This is a free open access lecture, but not for commercial purposes. For personal use only.