Regional metamorphism

Contact/thermalmetamorphism

Dynamicmetamorphism

Plate setting for metamorphism

Hydrothermal

Metamorphism - diverging boundary

dynamic

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

Metamorphism - transform faults

dynamic

Paired metamorphic belts

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

1.High pressure low tempgreenschist/ blue facies

2. Low pressure, high tempamphibole facies

diapirs

Paired metamorphic belts