Transcript Metamorphic Rocks

Metamorphic Rocks
Mr. Ahearn
Earth Science 2010
What are Metamorphic Rocks?
• Form at conditions between those that
produce igneous and sedimentary rocks
• Most found under thousands of meters sed. rx
Conditions Promoting
Metamorphism
• Heat
• Pressure
• Circulating Fluids
Types of Metamorphism
• Regional
• Contact
• Other
– Hydrothermal
– Fault
– Shock
– Pyrometamorphism
Regional Metamorphism
• Large belts of regional metamorphism are
produced when high temperature and
pressure affect large regions of Earth’s crust.
• can be low grade, intermediate grade, and
high grade.
Regional Metamorphism
• Some key minerals are used to map
metamorphic zones.
Contact Metamorphism
• contact metamorphism occurs when molten
rocks, such as those in an igneous intrusion,
come in contact with solid rock. (small scale)
• High temperature and moderate-to-low
pressure form the mineral assemblages that
are characteristic of contact metamorphism.
Contact Metamorphism
• temperature decreases
with distance from an
intrusion, metamorphic
effects also decrease with
distance.
• limited to thin zones.
Metamorphic Textures
Foliated metamorphic rocks are characterized by
wavy layers and bands of minerals.
– High pressure during metamorphism causes minerals
with flat or needlelike crystals to form with their long
axes perpendicular to the pressure.
Metamorphic Textures
Nonfoliated metamorphic rocks lack mineral
grains with long axes in one direction.
– Nonfoliated rocks are composed mainly of minerals that
form with blocky crystal shapes.
– Ex.  Quartzite and marble.
Common Metamorphic Rocks
• Foliated
– Slate
– Phyllite
– Schist
– Gneiss
• Nonfoliated
– Marble
– Quartzite
– Hornfels
Metamorphic Facies and Plate
Tectonics
• Metamorphic Facies – assemblages of
different minerals that are commonly found
together
– Indicate specific temp & pressure conditions
– Indicators of ancient subduction zones
• Low temp/ high pressure
• High temp/ high pressure
• High temp/ low pressure
Metamorphic Rock Uses
• Strength and Stability
– Building materials
• Valued highly for appearance
– Sculptors- marble, serpentinite
– Talc- powder, flame resistant asbestos
– Garnet- abrasive
– Minerals associated with meta rx
• Zinc, lead, copper, iron, gold
The End