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

Read each slide then fill in the blanks or chart. 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)

How do they form? 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.

Metamorphic Rocks 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. Magma Pressure from surface rocks metamorphic rock forming here heat

How are they Classified? Metamorphic rocks are classified by texture in 2 ways… Foliated Non-Foliated

Texture 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.

Foliated texture: 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)

Foliated Texture Foliated Texture

Foliated Textures Foliated Textures - - looks like blackboard • Slatey Slatey • • Schistose Schistose • - - looks like blackboard looks like blackboard - - distinct bands of minerals > > dull surface dull surface - - visible grains visible mineral grains - - smooth, thin layering smooth, thin layering > > garnets, staurolites garnets, staurolites - - breaks into flat slabs breaks into flat slabs - - may have shiny may have shiny > > referred to as slatey cleavage referred to as slatey cleavage appearance - - no mineral grains visible no mineral grains visible > > due to mica minerals due to mica minerals • • Phyllitic Phyllitic • • Gneissic Gneissic - - looks like waxed surface looks like waxed surface - - larger grains larger grains > > has a "sheen" to it has a "sheen" to it - - may look like igneous rock may look like igneous rock - - may have little "waves" on may have little "waves" on - - may have crude banding may have crude banding surface surface > > intensely distorted intensely distorted > > referred to as referred to as crenulations crenulations - - different minerals than different minerals than - - some small grains visible some small grains visible schistose schistose

Foliated MM Rocks Foliated MM Rocks phyllite phyllite slate slate schist gneiss schist gneiss MM Rocks that could form as a shale (sedimentary) parent rock is MM Rocks that could form as a shale (sedimentary) parent rock is exposed to increasing directed pressure and temperature

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

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

Metamorphic Zones Metamorphic Zones

Metamorphic Zones Metamorphic Zones • Metamorphism is common along most plate boundaries like this.

Then use the next two sides to complete the chart 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 Island arcs, active continental margins, and continental collision zones Most studies focus on orogenic belts, and the term, “regional metamorphism” is often used synonymously with “orogenic metamorphism”

Types of metamorphism Regional high-pressure metamorphism Shock Contact metamorphism Regional metamorphism Depth, km Oceanic crust 35 Continental crust Oceanic lithosphere 75 Continental mantle lithosphere Asthenosphere Water Seafloor metamorphism

Regional high-pressure metamorphism Shock metamorphism Regional Types of metamorphism Regional high-pressure metamorphism Shock metamorphism Regional metamorphism Contact metamorphism Regional metamorphism Depth, km Oceanic crust 35 Continental crust Oceanic lithosphere 75 Continental mantle lithosphere Asthenosphere Burial metamorphism

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

Images of content/ The End/ Thanks?

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