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