Metamorphism & Tectonics

Pressure - Temperature - Time models

Clockwise path -Regional metamorphism

Counterclockwise path - granulite facies terranes

Fig 19.10

Many granulite terranes show early rapid increase in temperature at relatively low pressures, succeeded by pressure increase and later by cooling.

Must be magmatic heat input. But how do you get later thickening?

New research suggests that you can get heating first, then increase in pressure from magma loading.

Collisional metamorphism

In Himalayas, thrust faults dip to N, sense of motion to south. Now, tectonically thickened crust.

What are possible consequences of thickening?

Melting of lower crust or uplift and preservation of inverted metamorphic gradient

Himalayas -> granites are 20-30 ma younger than initial collision.

So two possibilities