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
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
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
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) • 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
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?