Metamorphism and Metamorphic Rocks

What is a metamorphic rock?

A rock that forms from pre-existing rocks due to changes in environments pressure, temperature, and presence of chemically active fluids

What is a protolith?

The original unmetamorphosed old rock from which a metamorphic rock forms

What variables change to produce a metamorphic rock?

Pressure, temperature, and fluids

What does metamorphism change? 

It changes mineralogy and texture

What happens to a rock during metamorphism?

Recrystallization; Neocrystallization; Pressure Solution; Plastic deformation

What is Recrystallization?

Minerals change size (gets larger) and shape due to dissolution and growth of crystals

What is Neocrystallization? 

The formation of new minerals from old ones 

What is Pressure Solution? 

the dissolution of minerals at grain-to-grain contacts into an aqueous pore fluid in areas of relatively high stress and either deposition in regions of relatively low stress within the same rock or their complete removal from the rock within the fluid.

What is Plastic Deformation?

Mineral grains soften and deform when rock is squeezed at elevated temperatures and pressures.

What formation does Hydrothermal Fluid result in?

The formation of veins

What is foliation? 

An alignment of minerals under pressure 

What is Metamorphic Grade?

is a term for the degree of metamorphism imparted on a rock

What is Contact Metamorphism?

intrusion of a magma and ‘contact’ heating

What is Regional Metamorphism? 

dominant in mountain building

What is Hydrothermal

water heated by magma, chemically alters oceanic crust (black smokers)

What is Subduction Metamorphism

Releases water to produce earthquakes and arc volcanoes