E N D
1. Metamorphic Rocks
2. Metamorphic Rocks Recrystallization in the solid state
Caused by changes in T, P or fluids
New environment = new minerals
Growing minerals create a new texture
4. Metamorphism Recrystallization
T, P or change in pore fluids initiate change in the mineral assemblage
Reaction occur entirely in the solid state
5. Textural changes occur during metamorphism
New minerals grow during metamorphism
Precursor rock textures are modified
9. Origin of Metamorphic Rocks Metamorphism
Temperature exceeds 200OC
Pressure exceeds 300 M Pa (approx. 10,000 ft deep)
Metamorphism ends when melting begins
Melting begins at ~700oC
11. Source of heat
Proximity to igneous intrusions
Contact metamorphism
Different metamorphic grade ring the intrusion
Depth of burial
15-30oC increase per km
Geothermal Gradient
19. T & P determine degree of metamorphism
Low-grade metamorphism- 200 to 350 OC
Intermediate-grade metamorphism-350 to 550 OC
High-grade metamorphism - very high temperatures, above 550OC
23. Metamorphic Rocks Classified by texture and composition
Texture is divided into foliated & nonfoliated rocks
Mineral composition qualifies textural name
27. Phyllite
Similar to slate
More Recrystallization
Crystals are larger
Common Protolith:
shales
28. Schist
Strongly foliated rock
Medium to coarse grained
-dominated by platy minerals
Protoliths: multiple??
30. Gneiss
Coarse grained granular rock
Foliation: alternating bands of light & dark minerals
Quartz, feldspar, amphibole,
biotite
Protoliths: ??
31. Nonfoliated Rocks Marble
Interlocking, coarse grained calcite
Recrystallization of limestone or dolostone
Sedimentary features
destroyed
32. Quartzite
Metamorphism of quartz sandstone
Entire rock is recrystallized
33. Amphibolites & Eclogites
Metamorphism of mafic rocks
Mineral assemblage
gives green color
34. Regional Metamorphic Zones Index minerals
A mineral that forms within a specific,often narrow range of conditions
Identifies a specific grade of metamorphism
Allows further subdivision of rock types
36. Protolith controls final mineral assemblage
Different mineral assemblages form at a given P & T for various parent rocks
Metamorphic facies describe a group of minerals formed under similar conditions
May be found in different rocks
39. Metamorphic Rocks & Tectonics Most metamorphic rocks develop due to plate collisions
Processes are not observable in the field
Conditions at various plate boundaries define possible P & T range
Parent rocks present control mineral assemblages