Metamorphic Rocks
Metamorphic Rock
• “Meta” means Change• “Morph” means Form• Definition: A
sedimentary/igneous/metamorphic rock that has been changed from its original form by heat, pressure, and/or fluid activity, into a new rock.
Formation of Metamorphic Rock
• Previously existing rock (parent rock) usually recrystallized.
• Recrystalization is the process of increasing the size of the minerals crystals or rock clasts and/or changing the mineral composition without melting.
• 2 ways of recrystalizing parent rock.– Contact metamorphism– Regional metamorphism
Contact Metamorphism• When older rocks come in contact with the
magma of an intrusion or lava of an extrusion , the heat and mineral fluids of the liquid rock alter the older rock.
Characteristics of Contact Metamorphism• In the contact metamorphism zone there will
be 3 distinct layers
Magma
Met
amor
phic
rockParent Rock
Met
amor
phic
rock Parent Rock
Parent rock changed to metamorphic rock
Regional Metamorphism
• Colliding tectonic plates often result in mountain building. The closer an area is to the boundary of the colliding plates, the greater the increase in temperature and pressure.
• The increase in temperature and pressure transforms older rocks to a series of metamorphic rocks.
• This is called Regional metamorphism, because it takes place over a large region of the earth.
Regional Metamorphism
Regional Metamorphism
Textures of Metamorphic Rocks
• 2 major types of textures • Foliated • Non-foliated
Metamorphic TexturesMetamorphic Textures• Foliated
- Folios = page or leaf-like- rock has distinct banding or layering
> often not smooth like in sedimentary rocks- formed under directed pressure
• Non-foliated- no distinct layering character- often a massive crystalline texture- formed under uniform pressures
• Foliated- Folios = page or leaf-like- rock has distinct banding or layering
> often not smooth like in sedimentary rocks- formed under directed pressure
• Non-foliated- no distinct layering character- often a massive crystalline texture- formed under uniform pressures
Banding vs Layering
Which texture banding or layering?
Which texture banding or layering?
Foliated rocks
• These rocks have layers of minerals crystals that have formed by recrystallization usually under regional metamorphism
• These rocks are composed of two or more minerals and are made of interconnected mineral crystals.
• There are 4 types of foliations
Foliated TexturesFoliated Textures• Slate
- looks like blackboard> dull surface
- smooth, thin layering- breaks into flat slabs
> referred to as slatey cleavage- no mineral grains visible
• Phyllite
- looks like waxed surface> has a "sheen" to it
- may have little "waves" onsurface
- some small grains visible
-
• Schist
- -
> garnets, staurolites- may have shiny
> due to mica minerals
• - larger grains- may look like igneous rock- may have crude banding
> intensely distorted- different minerals thanschistose
distinct bands of minerals visible mineral grains
appearance
Gneiss
Foliated MM RocksFoliated MM Rocks
slateslate
schistschist gneissgneiss
phyllitephyllite
MM Rocks that could form as a shale (sedimentary) parent rock isMM Rocks that could form as a shale (sedimentary) parent rock isexposed to increasing directed pressure and temperature
Non-foliated metamorphic rocks
• These rocks are not layered because the minerals are not flat, or sheet like, and/or the rocks were not subjected to directional pressure.
• These rocks are composed of interconnected mineral crystals
• Marble:- metamorphosed
limestone
• Quartzite:- metamorphosed
quartz sandstone
• Quartzite:- metamorphosed
quartz sandstone
Non-foliated RocksNon-foliated Rocks