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geology - metamorphism in a plate boundary context

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Metaplate

  1. 2. Regional metamorphism Contact/thermal metamorphism Dynamic metamorphism Plate setting for metamorphism
  2. 3. Hydrothermal Metamorphism - diverging boundary dynamic
  3. 6. 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
  4. 7. Metamorphism - transform faults dynamic
  5. 8. Paired metamorphic belts
  6. 10. 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
  7. 11. 1.High pressure low temp greenschist/ blue facies 2. Low pressure, high temp amphibole facies diapirs Paired metamorphic belts

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