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Clerical:
It's a beautiful day for metamorphism.
Themes of the Day:
- Defining Metamorphism
- Pioneers - History of Metamorphism
- Types of Metamorphism
Defining Metamorphism
- Metamorphism - textural and/or mineralogical changes that affect a rock in the solid state
Some examples of changes:
- Textural: limestone to marble - recrystallization; shale to slate - realignment of minerals, new mineral growth
- Mineralogical: clays to micas to garnet, staurolite, and aluminosilicates in pelitic rocks; dehydration and decarbonation reactions
- Often isochemical - otherwise metasomatic
- Fluids (esp. H2O, CO2) generally move about freely
- Important Variables:
- Protolith composition
- Temperature, Pressure, Fluid conditions
- Timing/Kinetics
- Metamorphism - a poem by Tuefelin Peare
Pioneers - History of Metamorphism
- Hutton - quote from "Theory of the Earth", 1785 - significantly clarified by Lyell
- Hall - effects of pressure - experimentalist
- Barrow - defines mineral isograds in Scotland
- Goldschmidt - applied thermodynamics to the understanding of calc-silicates in the Oslo, Norway region
- Eskola - metamorphic facies concept & thermodynamics - metamafic rocks of Finland
- Much recent development due to better experimental control on the thermodynamics of geological materials; also microscopic and electron microprobe improvements; Plate Tectonic Paradigm puts metamorphism in a global context
Types of Metamorphism
- Static (most are local)
- Burial metamorphism (Regional)
- Contact metamorphism
- Shock metamorphism
- Pyrometamorphism
- Dynamothermal (most are regional)
- High P, Low T - subduction zones - accretionary wedge/downgoing slab
- High P, High T - continent-continent collisions, deep roots of volcanic arcs
- Low P, High T - shallow in volcanic arcs, mid-ocean ridges
- Hydrothermal Metamorphism
- Prograde
- Increasing P,T
- Grain size increases (exception: mylonites), increasing polygonalization
- Minerals get denser (due to increasing P)
- Minerals get dryer (due to increasing T)
- Retrograde
- Decreasing P,T
- Hydration
- most reactions are sluggish - lack activation energy
- Progressive Metamorphism
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