Metamorphic Rocks The Rock Cycle If you bury
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/C 00. 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/geller 2/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_contact 2. gif
Contact Metamorphism, http: //www. geol. umd. edu/~jmerck/geol 100/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!)
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/~jdl 1/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 • 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?
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