metaplate
DESCRIPTION
geology - metamorphism in a plate boundary contextTRANSCRIPT
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Regional metamorphism
Contact/thermalmetamorphism
Dynamicmetamorphism
Plate setting for metamorphism
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Hydrothermal
Metamorphism - diverging boundary
dynamic
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Metamorphism at a mid-ocean ridge
* Crust hottest, and isotherms closest together, above the active zone of magmatism, so only low-grade metamorphism away from the ridge
* Metamorphic reactions are hydration reactions, for basic protolith compositions, and water penetrates only the upper few km, except at fracture zones
* Hence typical metamorphism only reaches zeolite to greenschist facies
* In addition to metamorphism, convective circulation of warm water between ocean and mid-ocean ridge causes METASOMATISM of ridge material
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Metamorphism - transform faults
dynamic
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Paired metamorphic belts
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Paired Metamorphic Belts of Japan
*The NW belt (away from the trench) is the Ryoke Belt
i. Dominant meta-pelitic sediments, and isograds up to the sillimanite zone have been mapped
ii. A high-temperature-low-pressure belt, and granitic plutons are common
* Outer belt, called the Sanbagawa Belt
i. It is of a high-pressure-low-temperature nature
ii. BASIC rocks are more common than pelitic rocks, and in these GLAUCOPHANE is developed (giving way to hornblende at higher grades)
iii. Rocks are commonly called BLUESCHISTS - glaucophane is blue
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1.High pressure low tempgreenschist/ blue facies
2. Low pressure, high tempamphibole facies
diapirs
Paired metamorphic belts