文档介绍：Chapter 8: Metamorphism and Metamorphic Rocks:New Rocks from Old
What is Metamorphism? (1)
Metamorphism is the change in form that happens in Earth’s crustal rocks in response to changes in temperature and pressure.
What is Metamorphism? (2)
There are six major factors in metamorphism:
position.
The change in temperature.
The change in pressure.
The presence or absence of fluids.
How long a rock is subjected to high pressure or high temperature.
Whether the rock is pressed or is twisted and broken during metamorphism.
position of Original Rock
The greatest factor in determining the mineral assemblage of a metamorphic rock.
The position of the original rock controls the mineralogy of the metamorphosed rock.
Temperature And Pressure (1)
The heat source is Earth’s internal heat.
Rock can be heated by burial or by nearby igneous intrusion.
Burial is inevitably panied by an increase in pressure due to the weight of the overlying rocks.
An intrusion may be shallow, resulting in low pressure, or deep, resulting in high pressure.
A grain of in a -biotite gneiss, the small inclusions are relicts from early assemblage formed under P-T conditions different from those that formed the gneiss
P-T path for a body of rock undergoing metamorphism along a subduction zone
Temperature And Pressure (2)
Low-grade metamorphism is the result of metamorphic processes that occur at temperatures from about 100oC to 500oC, and at relatively low pressures.
High-grade metamorphism is the result of metamorphic processes at high temperatures (above 500oC), and at high pressure.
The metamorphic grade
Stress
Stress is applied pressure that results in deformation in a solid, and the development of new textures.
Uniform stress occurs if pressure is equal in all directions.
Differential stress occurs if pressure is different in different directions.
Texture is controlled by differential versus uniform stress.