Metamorphic Rocks

Mt Shuksan and Mt Baker, J Scurlock

Mt Shuksan N Face, J Scurlock

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 factorincreased heat =

increased kinetic Energy =

increased chemical reactions =

REMINERALIZATION

(This is NOT melting! This is NOT melting!)

Remineralization (Metamorphism)

• This rock was originally a shale, but has been subjected to HEAT and pressure to form slate (sedimentary metamorphic)M. Miller

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 rockGranite

• 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?