Metamorphic rocks process of formation 2014

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Information about Metamorphic rocks process of formation 2014
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Published on September 23, 2014

Author: aalleyne

Source: slideshare.net

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S6E5. Students will investigate the scientific view of how the earth’s surface is formed.
c. Classify (metamorphic) rocks by their process of formation.

Learning Goal: Understand how metamorphic rocks are formed and classified.

 S6E5. Students will investigate the scientific view of how the earth’s surface is formed c. Classify (group) rocks (metamorphic) by their process of formation (formed)

 Rocks that have changed (metamorphism) due to HEAT and PRESSURE. These rocks form DEEP underground! Pressure from plate movement folds and buckles the crust. Magma heats up surrounding rock. View slide

 Metamorphic rocks are formed by the effect of heat and pressure on existing rocks.  This can greatly affect the hardness, texture or layer patterns of the rocks. metamorphic Magma Pressure from surface rocks rock forming here heat View slide

 Metamorphic rocks are classified by texture in 2 ways… 1.Foliated 2.Non-Foliated

 The processes of compaction and recrystallization change the texture of rocks during metamorphism.  Compaction The grains move closer together. The rock becomes more dense. Porosity is reduced.  Example: clay to shale to slate  Recrystallization Growth of new crystals. No changes in overall chemistry. New crystals grow from the minerals already present. A preferred orientation of minerals commonly develops under applied pressure. Platy or sheet-like minerals such as muscovite and biotite become oriented perpendicular to the direction of force. This preferred orientation is called foliation.

 Mineral grains flatten and line up in parallel bands OR layers. That are formed under directed pressure Slate: Foliated (with layers) Gneiss: Foliated (with banding)

FFoolliiaatteedd TTeexxttuurree

FFoolilaiatteedd TTeexxttuurreess • 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 a "sheen" to it - may have little "waves" on surface > referred to as as crenulations - some small grains visible • Schistose - distinct bands of minerals - visible mineral grains visible grains > garnets, garnets, staurolites - may have shiny appearance > due to mica mica minerals minerals • Gneissic - larger grains - may look like igneous rock - may have crude banding > intensely intensely distorted distorted - different minerals than schistose

FFoolliiaatteedd MMMM RRoocckkss pphhyylllliittee QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. ssllaattee sscchhiisstt ggnneeiissss MMMM RRoocckkss tthhaatt ccoouulldd ffoorrmm aass aa sshhaallee ((sseeddiimmeennttaarryy)) ppaarreenntt rroocckk iiss exposed to increasing directed pressure and temperature

 Mineral grains change, grow, and rearrange, but don’t form bands or layers. Formed under uniform pressures Quartzite Marble

• Marble: - metamorphosed limestone Quartzite: metamorphosed sandstone • - NNoonn--ffoolliiaatteedd RRoocckkss Examples Quartzite forms in two different ways. In the first way, under the high pressures and temperatures of deep burial, sandstone

MMeettaammoorrpphhiicc ZZoonneess

MMeettaammoorrpphhiicc ZZoonneess • Metamorphism is common along most plate boundaries like this.

The Types of Metamorphism Read this slide Then use the next two sides to complete the chart Regional Orogenic Metamorphism is the type of metamorphism associated with convergent plate margins • Dynamo-thermal: one or more episodes of orogeny with combined elevated geothermal gradients and deformation (deviatoric stress) • Foliated rocks are a characteristic product

Depth, km 0 35 Continental crust 75 Asthenosphere Regional metamorphism Oceanic crust Oceanic lithosphere SShhoocckk mmeettaammoorrpphhiissmm RReeggiioonnaall mmeettaammoorrpphhiissmm RReeggiioonnaall hhiigghh--pprreessssuurree mmeettaammoorrpphhiissmm CCoonnttaacctt mmeettaammoorrpphhiissmm Continental mantle lithosphere Water SSeeaafflloooorr mmeettaammoorrpphhiissmm Types of metamorphism

Depth, km 0 35 Continental crust Types of metamorphism Continental mantle lithosphere 75 Asthenosphere Regional metamorphism Oceanic crust Oceanic lithosphere SShhoocckk mmeettaammoorrpphhiissmm RReeggiioonnaall mmeettaammoorrpphhiissmm RReeggiioonnaall hhiigghh--pprreessssuurree mmeettaammoorrpphhiissmm CCoonnttaacctt mmeettaammoorrpphhiissmm BBuurriiaall mmeettaammoorrpphhiissmm

Pressure Sedimentary Igneous Pressure Sedimentary Igneous or Metamorphic or Metamorphic Rock Heat Heat Metamorphism Effect Classification based on Texture G r a i n s Heat & Pressure Foliated Nonfoliated NO Layers Bands ↑ Flatten Grains ↑ Slate Phyllite Schist Gneiss HEAT PRESSURE Layers Bands Slate Quartzite Marble Gneiss Pressure Heatt Heat

Learning Goal: Understand how metamorphic rocks are formed and classified. Do Now Q: What features do foliate metamorphic rocks show?

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