Transcript GLG101online_08A_Metamorphism_MCC_Leighty

Metamorphism
GLG 101 - Physical Geology
Bob Leighty
These notes and web links are your primary “lecture” content in this class.
Additionally, various articles are assigned each week to supplement this “lecture”
information. I believe you’ll have enough information to reference without having
to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes.
You’ll find they are loaded with imagery and streamlined text that highlight the
most essential terms and concepts. The notes provide a framework for learning
and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have
included numerous hyperlinks to external web sites (like the Wikipedia, USGS,
NASA, etc.). Follow the links and scan them for relevant info. The information
from linked web sites is meant to supplement and reinforce the lecture notes –
you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content
more independently than in a traditional class. As always, I will help guide you
through this learning adventure. Remember, email Dr. Bob if you have any
questions about today’s lecture ([email protected]).
Leave no questions behind!
Explore and have fun!
Metamorphism
Metamorphism Basics
 Changing pressure (P), temperature (T), and/or fluids cause
original composition (mudstone) > new, more stable one (slate)
without melting
 New minerals (e.g., garnet) may grow
 Any rock can be changed (metamorphosed)
mudstone
schist
Metamorphism
Metamorphism Basics
 Metamorphic grade – Describes intensity of P, T, & fluid activity
Metamorphism
Controlling Factors
Temperature
 Sources of heat:
>
burial
>
subduction
>
nearby intrusions (magmas)
Metamorphism
Controlling Factors
Pressure
 Confining Pressure - equal stress in all directions (lithostatic or
hydrostatic)
yields
 The arrangement of grains in a rock stays the same
 This stress creates nonlayered (nonfoliated) rock textures
Metamorphism
Controlling Factors
Pressure
 Directed Pressure - tectonic stress
 The arrangement of platy minerals (if any) becomes more
aligned
 This stress creates layered (foliated) rock textures
Metamorphism
Controlling Factors
Fluids (mostly water)
 Sources of fluids:
>
forced out by pressure during burial
>
driven out of a magma during
cooling & crystallization
>
driven out of a subducting tectonic
plate
Metamorphism
Index Minerals
 Index minerals record the metamorphic grade
 The type of index mineral depends on P, T, & composition of rock
being metamorphosed
low
grade
mudstone
high
grade
garnet schist
high
grade
Metamorphism
Types of Metamorphism
Metamorphism
Types of Metamorphism
lo P & hi T
hi P & hi T
Metamorphism
Types of Metamorphism
Burial (diagenesis)
(low P & low T)
 Increasing P & T during progressive burial
Metamorphism
Types of Metamorphism
Contact
(low P & variable T)
 Typically occurs near intrusions (batholiths, dikes, sills, etc.)
 The bigger the intrusion, the bigger the contact zone
Metamorphism
Types of Metamorphism
Contact
(low P & variable T)
 Creates nonfoliated metamorphic rocks (quartzite, marble, etc.)
Metamorphism
Types of Metamorphism
Hydrothermal
(low P & variable T & fluids)
 Movement of hot fluids (mostly water)
>
near magmas during crystallization
>
at hot springs and deep-sea
“black smokers”
Metamorphism
Types of Metamorphism
Regional
(variable P & T)
 Affects large areas (100's to 1000's km2),
typically in the lower crust
 Elevated P & T during mountain-building
at convergent margins
Metamorphism
Types of Metamorphism
Regional
(variable P & T)
 Directed pressures may create foliated rock textures
(slate, phyllite, schist, gneiss, etc.)
Metamorphism
Types of Metamorphism
Cataclastic (dynamic)
(localized high P & T)
 Crushing & shearing related to fault zones
 Creates foliated rocks (mylonites)
Metamorphism
Types of Metamorphism
Impact
(ultra-high P & T)
 Meteorite impacts melt & shatter rocks (yielding breccia & glass)
Metamorphism
WWW Links in this Lecture
> Metamorphism - http://en.wikipedia.org/wiki/Metamorphism
> Metamorphic grade - http://en.wikipedia.org/wiki/Metamorphism#Metamorphic_grades
> Index mineral - http://en.wikipedia.org/wiki/Index_mineral
> Foliation - http://en.wikipedia.org/wiki/Foliation_%28geology%29
> Diagenesis - http://en.wikipedia.org/wiki/Diagenesis
> Contact metamorphism -
http://en.wikipedia.org/wiki/Metamorphism#Contact_.28Thermal.29_metamorphism
> Intrusion - http://en.wikipedia.org/wiki/Intrusion_%28geology%29
> Quartzite - http://en.wikipedia.org/wiki/Quartzite
> Marble - http://en.wikipedia.org/wiki/Marble
> Hydrothermal metamorphism -
http://en.wikipedia.org/wiki/Metamorphism#Hydrothermal_metamorphism
> Regional metamorphism - http://en.wikipedia.org/wiki/Metamorphism#Regional_metamorphism
> Slate - http://en.wikipedia.org/wiki/Slate
> Phyllite - http://en.wikipedia.org/wiki/Phyllite
> Schist - http://en.wikipedia.org/wiki/Schist
> Gneiss - http://en.wikipedia.org/wiki/Gneiss
> Cataclastic metamorphism -
http://en.wikipedia.org/wiki/Metamorphism#Dynamic_metamorphism
> Mylonite - http://en.wikipedia.org/wiki/Mylonite