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Metamorphic RocksHow a little bit of heat & pressure transform rocks!

How a little bit of heat and pressure transform rocks!

The Rock Cycle Metamorphism (Increased T & P)

Partial MeltingMagma

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MetamorphismMetamorphic Rocks

5(Usually progressively higher temperatures and pressures)Its Morphin Time!

Metamorphic means to change form.

Definition Re-crystallization of minerals while still solid into minerals that are stable at different temperatures and pressures

From bread to toast!

MetamorphismMetamorphic RocksWhy do the minerals recrystallize?To reach chemical equilibrium!!!

10When you add pressure somethings got to give!

The minerals have to get to

Chemical equilibrium!

Evidence of MetamorphismFor example Sedimentary Rocks stable at normal T & P

Bend under pressure!

ShaleGneiss14

Evidence of Metamorphism Differential pressure squashes rock and included features2. Flattened PebblesConglomerateMetaconglomerate17FoliationRocks with planar texture have foliation

Foliation

3. Crystalline Texture Minerals tightly interlocking due to recrystallization under pressure

Evidence of MetamorphismQuartz SandstoneQuartzite20Where do we find heat and pressure?!

Evidence of Metamorphism

4. New mineral assemblages Example: Shale: Clay minerals (some quartz)

Metamorphism(Mid-grade)

Forms Schist: Mica, Feldspar and other silicate minerals 28Recipe of Metamorphism1. Parent RockEven though minerals will change most elements are provided by parent rock, except water and some dissolved ions

Shale Schist29Characteristic Metamorphic Minerals

For more images: http://skywalker.cochise.edu/wellerr/mineral/

kyaniteandalusitesillimanitestaurolitegarnet30Show sample of kyanite!!!Tracing changes in pressure and temperature conditions that a rock experienced gives insight into plate tectonic settings!!

31B. Recipe of Metamorphism2. HeatGeothermal gradient: more pressure = more heat!!Minerals stable at lower temperatures converted to minerals stable at higher temperaturesSolid state chemical reactions are accelerated

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Temp. (C)ABCACB32B. Recipe of Metamorphism2. HeatGeothermal gradient: more pressure = more heat!!Minerals stable at lower temperatures converted to minerals stable at higher temperaturesSolid state chemical reactions are accelerated

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Temp. (C)ABCACB33Ingredients of Metamorphism4. Addition or removal of fluids (and elements)Water (and other fluids) within rocks and mineralsMoving during metamorphism Accelerates solid-state chemical reactions and May change rock composition5. Time Millions of years!

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Metamorphic FaciesThe minerals in a rock are clues to the (pressure and temperature) history of the rockFacies = a set of metamorphic conditions Each facies is characteristic of itsTectonic environmentSource rocks in the environment (like shale)

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To change formOther rocks are exposed to high heat & pressure

SummaryEvidence of metamorphismDeformed layers, flattened pebbles, crystalline texture, & new mineral assemblages The ingredients of metamorphismParent rock, heat, pressure, fluids, & timeClassifying metamorphic rocksLow grade --> high grade & faciesMetamorphism of shale (& other parent rocks!)Shale --> Gneiss, Sandstone --> Quartzite, Limestone --> MarbleMetamorphic mineralsMuscovite and Garnet = Index mineralsMetamorphic Rock TypesThere are two types of metamorphic rocks.Each is classified according to its composition and texture.FoliatedNonfoliated

How do we identify meta. rocks?FoliatedNon-foliated

Foliated Metamorphic RocksFOLIATED -the minerals have been flattened and pushed down into parallel layers. The bands in foliated metamorphic rock look like pages in a book.

Foliation

Compressive Stress

Shear StressCauses Foliation

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Evidence of Metamorphism Differential pressure squashes rock and included features2. Flattened PebblesConglomerateMetaconglomerate45Metamorphic GradeHigh grade (High P & T)Low grade (Low P & T)

Intensity of Metamorphism:46Metamorphism of Shale

Fig. Story 9.7bnot found in nature47Slaty foliation- Rock splits into flat, thin layers.

Schistose foliation- minerals have been squashed into flakes of mica.

A Piece of SchistMetamorphically speakingSchist happens

Holey Schist

Types of Foliation:Gneissic Foliation- minerals are squished into bands.

Zebra Stripes

Gneissic = Zebra stripes

Metamorphic Rocks of other Parent Rocks

Limestone Marble

Bioclastic calcite Crystalline calciteNonfoliated56Limestone turns into Marble!

Metamorphic Rocks of other Parent RocksQuartz Sandstone Quartzite

Granular quartz Crystalline quartz

Nonfoliated61Decided to study geologySchist just got real