UNIVERSITY OF SOUTH ALABAMA
GY 111: Physical Geology
Lecture 27
Contact Metamorphism
Last Time
Regional Metamorphism
A) Foliated rocks
B) Non-foliated rocks
Web notes: 26
Regional Metamorphism
Involves both heat
and pressure
Regional Metamorphism
The most stable configuration for platy minerals like
clays and micas is perpendicular to the stress direction
Regional Metamorphism
The most stable configuration for platy minerals like
clays and micas is perpendicular to the stress direction
Foliated Rocks
But it can develop rock cleavage
Foliated Rocks
Higher P/T causes minerals to grow large enough to be
visible. The highest pressure can cause mineral
separation (distinct bands e.g., quartz, biotite, feldspars).
Low
Medium
slate
phyllite
Med-High
schist
High
gneiss
Foliated Rocks
Slate
Foliated Rocks
Phyllite
Foliated Rocks
Garnet-Mica schist
Foliated Rocks
Kyanite schist
Foliated Rocks
Gneiss
Non-foliated Rocks
Foliations can only develop during metamorphism if
there was mica and/or clay in the original parent rocks.
Marble (non-foliated)
Non-foliated Rocks
Warning: marble can look exactly the same as quartzite
Marble (non-foliated)
Quartzite (non-foliated)
Today’s Agenda
Contact Metamorphism
A) Metamorphic Aureoles
B) Isograds
C) Index minerals and metamorphic grade
Web notes: 27
Contact Metamorphism



Heat only
Induced by hot intrusions
Metamorphic aureoles
http://academic.brooklyn.cuny.edu/geology/grocha/monument/images/metheat.gif
Contact Metamorphism

Metamorphic grade
decreases from the
intrusion into the
country rock
Contact Metamorphism

Mixed parent
lithologies give
rise to varied
metamorphic
rocks
http://csmres.jmu.edu/geollab/Fichter/MetaRx/Images/contact.gif
Contact Metamorphism

Mixed parent
lithologies give
rise to varied
metamorphic
rocks
Hornfels
http://csmres.jmu.edu/geollab/Fichter/MetaRx/Images/contact.gif
Contact Metamorphism

Mixed parent
lithologies give
rise to varied
metamorphic
rocks
Hornfels
Metaconglomerate
http://csmres.jmu.edu/geollab/Fichter/MetaRx/Images/contact.gif
Contact Metamorphism

And different
metamorphic
minerals (more
on this shortly)
Contact Metamorphism

Contact
metamorphism
is commonly
very obvious in
outcrop
http://z.about.com/d/geology/1/0/A/z/contactmet500.jpg
Contact Metamorphism
Contact
metamorphism is Aureole
commonly very
obvious in outcrop
Limestone
Sill
Aureole
Shale
http://z.about.com/d/geology/1/0/A/z/contactmet500.jpg
Contact Metamorphism
Limestone
Marble
Sill
Hornfels
Shale
http://z.about.com/d/geology/1/0/A/z/contactmet500.jpg
Contact Metamorphism
Metamorphic Isograds
Isograds
Isograds around the
Kangmar Dome of Tibet
Contact
Metamorphism
http://www.geol.ucsb.edu/faculty/hacker/geo102C/lectures/KangmarIsograds.jpg
Isograds
Isograds in
Scotland
Regional
Metamorphism
http://www.geol.lsu.edu/henry/Geology3041
Isograds
•Index
Minerals:
minerals that
give you a hint
of metamorphic
grade
Pluton
Index Minerals (Felsic rocks)
Index Minerals (Mafic rocks)
Index Minerals (Mafic rocks)
Important observation: Amphibole only forms from parent rocks rich in
Fe and Mg. Therefore the parent rock of most amphbolites is basalt
Today’s Homework
1. Quiz (fill in the blanks; foliated and non foliated rocks)
2. Photo assignment due via email Friday (5:00 PM)
Next Time
1.
Metamorphic Facies/Retrograd Metamorphism
GY 302 Poster Session. Next Tuesday 1:00-3:00PM (Bonus)
Rock and Gem Show Thanksgiving weekend (Bonus)
proof of attendance required for both bonuses
GY 111: Physical Geology
Lecture 27: Contact Metamorphism
Instructor: Dr. Doug Haywick
dhaywick@southalabama.edu
This is a free open access lecture, but not for commercial purposes.
For personal use only.