Transcript Metamorphic Rocks

Metamorphic Rocks
The Rock Cycle
• If you bury a rock deep enough, it will melt
(IGNEOUS)
• Not so deep, a rock will become lithified
(SEDIMENTARY)
• At conditions (Pressures and
Temperatures) just right, metamorphism
occurs
http://voyagerstories.files.wordpress.com/2009/02/rock-cycle.jpg
What does “metamorphic” mean?
• “Meta” = after
• “Morph” = change in form
• So Metamorphic rocks are rocks that have
changed from their original state.
How do they change?
• Change in size
• Change in shape
• Change in minerals (sometimes)
How does metamorphism happen?
• Increase in Temperature (T)
– Increase in depth = increase in T
• Increase in Pressure (P)
– Increase in depth = increase in P
• Hydrothermal fluids that are rich in ions
that can make new minerals
http://www.jamstec.go.jp/chikyu/image_files/C00.jpg
Where does metamorphism occur?
Two main types
1) REGIONAL
METAMORPHISM
– Mountain building
(subduction of plates =
compression)
• Intense pressures
• Happens over large
regions (for instance,
several states)
http://www.emporia.edu/earthsci/student/geller2/subduction.jpg
Regional Metamorphism:
Triumph, SW Face, J Scurlock
Where does metamorphism occur?
2) CONTACT
METAMORPHISM
– Metamorphism in
contact with a batholith
– the igneous intrusion
will “bake” the rocks it
comes in contact with
• Happens over a much
smaller area than
regional metamorphism
http://www.windows.ucar.edu/earth/geology/images/meta_contact2.gif
Contact Metamorphism,
http://www.geol.umd.edu/~jmerck/geol100/lectures/16.html
Hey
WAKE UP! This is COOL!
How does metamorphism work?
Heat
• Heat is the most important factor
increased heat =
increased kinetic Energy =
increased chemical reactions =
REMINERALIZATION
(This is NOT melting! This is NOT melting!)
Remineralization (Metamorphism)
M. Miller
• This rock was
originally a shale, but
has been subjected to
HEAT and pressure
to form slate
(sedimentary 
metamorphic)
How does metamorphism work?
Pressure
• Pressure will confine the rock in one or
more directions
• Causes an alignment of flat minerals
• At its most intense, can cause “zonation”
of mafic and felsic minerals
What was the direction of greatest P?
http://sorrel.humboldt.edu/~jdl1/web.page.images/rocks/r_8.gif
Gneiss Central WI, M Miller
What can you say about this rock?
M. Miller
3 Terms you need to know
1) Protolith
– The “parent” rock of a metamorphic rock
(what it was before it metamorphosed)
– Proto = “earliest form of”
– Lith = rock
3 Terms you need to know
2) Grade
– Low grade = low P and T
– High grade = high P and T
3 Terms you need to know
3) Foliation
– Sheets upon sheets
upon sheets
• As in schist (can be
called schistosity)
• DUDE!
• We can also say a
metamorphic rock is
nonfoliated!
Protolith: sedimentary rock:
shale (mudstone)
• L to R (low grade to
high grade)
–
–
–
–
Slate (low grade)
Phyllite
Schist (foliated)
Gneiss (high grade)
M. Miller
Protolith: Igneous rock
Granite
• High grade
– Granite goes to gneiss
– (If you want to be
really cool, you would
call this an
orthogneiss)
– your choice
– What is that red
mineral?
– Is this foliated?
Protolith: sedimentary:
Quartz sandstone
• Quartzite
• Foliated?
Protolith: Sedimentary:
Limestone
• Marble
• Foliated?