Metamorphic Rocks
3 Causes of Metamorphism
1. Heat
•
•
From interior & it affects rocks as they are pushed beneath
From igneous intrusions in contact w/other rocks
2. Pressure
•
•
From internal pressure beneath crust
From vertical pressure of rising magma
3. Chemically active fluids
•
Superheated water changes the rock on contact
3 Causes of Metamorphism (cont’d)
**Remember**
Rocks must remain solid
Complete melting forms
magma = igneous rocks
Grades of Metamorphism
Combinations of heat & pressure create dif. Forms
of met. Rocks
1. High-grade - rocks form under greatest heat &
pressure before melting completely
2. Medium grade
3. Low-grade - rocks form under the least heat
and pressure
Types of Metamorphism
3 main types of metamorphism
1. Regional – caused when high temps & pressures affect
a large region
2. Contact – rocks changed by rising magma (high temps.
but med – low pressure
3. Hydrothermal – caused by water and heat which can
dissolve, breakdown, & deposit new minerals
Metamorphic
Textures
Foliated & nonfoliated
1. Wavy layers are characteristic of foliated rocks
*Layers form perpendicular to direction of pressure*
2. Nonfoliated rocks - do not form the banded or layered appearance
Metamorphic Textures cont’d
Porphyroblasts
Large and small pieces, from the
reorganization of atoms in solid rock
during contact and regional metamorphism
Ex/ Garnet Schist