PERTEMUAN - 12 - PETROLOGI_2.pdf

7/25/2019 PERTEMUAN - 12 - PETROLOGI_2.pdf

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DefinitionsDefinitions Metamorphic Rock

- "Meta"= Change (Grk)

- "Morph"= form (Grk)

Metamorphic Rock- "Meta"= Change (Grk)

- "Morph"= form (Grk)

- a rock that has been changed

from its original form ( parent ) by

heat , pressure , and fluid activityinto a new rock ( daughter ).

- a rock that has been changed

from its original form ( parent ) by

heat , pressure , and fluid activityinto a new rock ( daughter ).

Metamorphic RocksMetamorphic Rocks


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HeatHeat

Magma- temperature of magma

- composition of magma

Magma- temperature of magma

- composition of magma

Geothermal gradient- temperature increases with depth of burial

-core of Earth is warmer than outer crust

Geothermal gradient- temperature increases with depth of burial

-core of Earth is warmer than outer crust

Sources Include.....Sources Include.....


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Uniform PressureUniform Pressure vs Directed Pressure Lithostatic

- "Lithos"= rock, static= unchanged (pressure)

-uniform (aka non-directed)

- equal intensity from all directions by rocks

Lithostatic- "Lithos"= rock, static= unchanged (pressure)

-uniform (aka non-directed)

- equal intensity from all directions by rocks


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Directed Pressureone direction of squeezing is much strongerthan the others

Minerals align themselves to reduce stress.


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Types of MetamorphismTypes of Metamorphism

Contact- caused by igneous activity

Dynamic- aka cataclastic

- associated with faults & earthquake zones

Regional- caused by tremendous pressures

associated with tectonic plate activity

Contact- caused by igneous activity

Dynamic- aka cataclastic

- associated with faults & earthquake zones

Regional- caused by tremendous pressures

associated with tectonic plate activity


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Contact MetamorphismContact Metamorphism

Igneous Intrusions- size and type of magma important

> mafic magma hotter than felsic

- heat decreases away from magma> forms a zone of altered country rocks called Aureoles

Igneous Intrusions

- size and type of magma important> mafic magma hotter than felsic

- heat decreases away from magma> forms a zone of altered country rocks called Aureoles

Sometimes creates a metamorphic rock called ahornfels -in essence a cooked rockSometimes creates a metamorphic rock called ahornfels -in essence a cooked rock


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Dynamic MetamorphismDynamic Metamorphism aka Cataclastic Metamorphism

associated with Fault Zones

-Places where the Earth's crust ruptured

- Rock pulverized> heat and pressure come from movement along the

Fault

resultant rock is known as a Mylonite

aka CataclasticMetamorphism

associated with Fault Zones

-Places where the Earth's crust ruptured

- Rock pulverized> heat and pressure come from movement along the

Fault

resultant rock is known as a Mylonite


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Regional MetamorphismRegional Metamorphism

Most common form of metamorphism

caused by large scale forces- lithospheric plate collision

covers very large areas- metamorphic belts or zones

- Zones are characterized by Index Minerals

> form under specific temperatures and pressures> metamorphic facies

commonly associated with- shields: stable areas of crystalline rocks

Most common form of metamorphism

caused by large scale forces- lithospheric plate collision

covers very large areas- metamorphic belts or zones

- Zones are characterized by Index Minerals

> form under specific temperatures and pressures> metamorphic facies

commonly associated with-

Shields and Mountains: areas of crystalline rocks


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Shields of the WorldShields of the World


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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

l


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Foliated TextureFoliated Texture

F l d


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Foliated TexturesFoliated Textures

Slatey- looks like blackboard

> dull surface

- smooth, thin layering

- breaks into flat slabs> referred to as slatey cleavage

-

no mineral grains visible

Phyllitic- looks like waxed surface

> has a "sheen" to it

-may have little "waves" onsurface

> referred to as crenulations

- some small grains visible

Slatey- looks like blackboard

> dull surface

- smooth, thin layering

- breaks into flat slabs> referred to as slatey cleavage

-

no mineral grains visible

Phyllitic- looks like waxed surface

> has a "sheen" to it

-may have little "waves" onsurface

> referred to as crenulations

- some small grains visible

Schistose-

- visible grains> garnets, staurolites

- may have shiny

> due to mica minerals

Gneissic- larger grains

- may look like igneous rock

- may have crude banding> intensely distorted

- different minerals than

schistose

Schistose-

distinct bands of minerals- visible mineral grains

> garnets, staurolites

- may have shiny

appearance

> due to mica minerals

Gneissic- larger grains

- may look like igneous rock

- may have crude banding> intensely distorted

- different minerals than

schistose

F l d MM R k


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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 isex osed to increasin directed ressure and tem erature

N f l d R kN f l d R k


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Marble:Marble:-- metamorphosedmetamorphosed

limestonelimestone

Quartzite:Quartzite:-- metamorphosedmetamorphosed

quartz sandstonequartz sandstone

Quartzite:Quartzite:-- metamorphosedmetamorphosed

quartz sandstonequartz sandstone

Non-foliated RocksNon-foliated RocksNon-foliated RocksNon-foliated Rocks


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Environment of Formation- EOF

look for specific minerals

Map out where those minerals are found

reconstruct T & P for given minerals

Find a modern setting that has similar T & Pusing Uniformitarianism

M h ZM hi Z


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Metamorphic ZonesMetamorphic Zones


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Metamorphic Zones-MapMetamorphic Zones-Map

M hi F iM t hi F i


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Metamorphic FaciesMetamorphic Facies distinctive metamorphic lithologies that occur in well

defined areas and named after the key rocks found

distinctive metamorphic lithologies that occur in well

defined areas and named after the key rocks found


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Metamorphism is common along most plate boundaries like this.

Metamorphic ZonesMetamorphic Zones

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PERTEMUAN - 12 - PETROLOGI_2.pdf