unit 4 rockcycle 1314

8/12/2019 Unit 4 Rockcycle 1314

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Semester 2

Session 2012/2013

Unit 4 :

Rock Cycle & Rock Types

KNS 1102

Engineering Geology


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What is Rock Cycle?

Show interrelationships between 3 types of rock; igneous,sedimentary & metamorphic rock, through internal and

external processes.

involve superficial processes such as weathering,transportation, and deposition; and

internal processes such as magma generation and

metamorphism. Plate movement is the mechanism responsible for recycling

rock materials and therefore drives the rock cycle. Geologists recognize 3 major groups of rocks:

1. Igneous, sedimentary, and metamorphic.2. Each group contains a variety of individual rock types

that differ from one another on the basis of compositionor texture (the size, shape, and arrangement of mineralgrains).


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http://www.classzone.com/books/earth_scienc

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Further Explanation!
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Rocks

ROCK IS AN AGGREGATE OF ONE OR MANY

ROCK FORMING MINERALS

THREE MAIN TYPES

1. IGNEOUS ROCKS

2. SEDEMENTARY ROCKS

3. METAMORPHIC ROCKS

ROCKS AND SOILS ARE DESTROYED AND

FORMED IN A CYCLIC PROCESS (ROCK CYCLE)


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Igneousforged by fire

Sedimentarylayeredstorytellers

Metamorphicchanged

rocks

My name is Rock.

My family members

are


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What is Magma Made of ? All magmas contain Siand O

Upon cooling, bond together into silicon-oxygen tetrahedrons

More silica (i.e. felsic), more viscous (harder to flow, thicker) Also contain varying amounts of other elements like Na, K, Al,

Ca, Mg, Fe, etc

Dry magmasno volatiles

Wet Magmasup to 15% volatiles

Volatile content strongly effects the viscosity (ability to flow)

More volatiles, less viscous (easier to flow or more fluid)


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Magma Movement If magma did not move, no extrusive/volcanic rocks would

ever have formed

Magma rises because:

hotter and less dense than the surrounding rock and thereforebuoyantly rises.

the weight of the overlying rock (lithostatic pressure) literallysqueezes the magma out.

Analogy: Think of stepping on a tube of toothpaste to force it out, or mudsquishing through your toes when you step in a puddle

Viscosityaffects a magma or lavas ability to flow

Controlled by: Temperature (high temp - low viscosity)

Volatile content (more volatilesless viscous)

Silica contentsilica tends to form silica-oxygen tetrahedrons thatbond with each other to make long chains that ultimately resist flow(more silicamore viscous)


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Volatiles: A substance that can easily change

into a gas at relatively low temperatures (H2O,

CO2, etc).

The addition of volatiles at depth (mainly H2O)

seeps into rocks and helps break bonds (aids

in melting).


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What is Bowens Reaction Series

The order of crystalformation from magma as

cooling occurs

(how igneous rocksformed)


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Bowens Reaction Series

Bowens had confirmed that as magma cools,

minerals will crystallize out in a predictable

sequence from laboratory experiments.

The sequence called Bowens Reaction Series

Made up of 2-trends;

a. Discontinuous reaction series

b. Continuous reaction series


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Bowens Reaction Series In order to understand the melting and solidifying of magma we need to understand

Bowens reaction series. Bowen figured this out by melting rocks in an oven, lettingthem cool, and watching what minerals crystallized

This series outlines the order in which minerals form in a cooling melt Also applies in reverse order to rocks that are partially melted

Discontinuous series (different minerals form) and Continuous series (Plagioclase only)

So, a melt gets less mafic as it cools; In heating, the first minerals to melt are felsic.


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Explanation! Bowen reaction series can describes why different rocks are formed which

depend on the composition of magma itself, where cooling process ishappen and also the rate of cooling.

As magma cools, minerals crystals grow larger and some of them settle.

The crystals that remain suspended in the liquid react with the remaining

melt to form a new mineral at a lower temperature.

The process continues until the entire body of melt is solidified.

It can be classified into 2 groups:

1. Discontinuous Ferromagnesium reaction series which;

Minerals formed are having different chemical composition andcrystalline structure

2. Continuous Plagioclase feldspar reaction series which;

Minerals formed are having different chemical compositions but

similar crystalline structures


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Kilauea Volcano in Hawaii is currently erupting, sending molten

rock across the landscape and into the ocean. Every day, new

rocks are forming as the lava cools and solidifies.

Magma As the super-hot magma cools, it

solidifies to form an igneous rock.

How does this

happen??

Most commonly magma spills are from a

volcanic eruption. As the magma moves

quickly from the super-hot conditions of

Earth's interior to the much cooler

environment at the surface, it cools andsolidifies rapidly.

EXTRUSIVE IGNEOUS ROCKS

-fine grained

Some magma that never

makes it to the surface

solidifies relatively slowly

because it takes it a long

time to cool inside the hotEarth.

OR

INTRUSIVE IGNEOUS ROCKS

-coarse grained


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Igneous Rock Types In general, there are

two basic types ofigneous rocks

Extrusive/Volcanic:Igneous rocks that

form due to thefreezing of meltsabove the surface ofthe Earth

Includes rocks madeof volcanic ash

(pyroclastics)

Intrusive/Plutonic:Form by freezing ofmelts below the

surface of the Earth.


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Igneous Rocks

Also can be classified according to their

mineral content.

FELSIC or acidic MAFIC or basic

Light coloured Dark coloured

Quartz Olivine,pyroxene

amphibole

& biotiteThis remind me

of Bowens

reaction series


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Extrusive Igneous Rock Environments Explosive eruptionsgenerally occur

when source magma is:

High in silica (felsic-intermediate)

Low temp

High in volatiles

These volcanoes form

Lava domes

Ash clouds and ash flows

Ef fusive eruptionsgenerally occur when

source magma is:

Low in silica (mafic)

High temp

Low in volatiles

These volcanoes form

Fluid lava flows

Fire fountains (if volatiles), lava tubes

Hawaii

CascadesNW USA

S bd i d l i


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Subduction and VolcanismSubducti on creates

volcanism

1- The down-going slab haslots of volatiles (e.g. H2O).

At depth, these volatiles are

heated and are squeezed

from the rock and migrate

into the asthenosphere

above the plate.2- The addition of volatiles,

as we now know, changes

the melting point of rocks

and causes the

asthenosphere to melt above

the sinking plate.3- The sinking plate may

partially melt too, but most

melting occurs in the

asthenosphere above the

slab.


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Intrusive Igneous Rock Environments Magma rises by percolating between grains and/or by forcing open cracks in

the subsurface

The magma that doesnt reach the surface of the Earth cools into intrusiveigneous rocks

Country rock or wall rock:The pre-existing rock that magma intrudes into

Intrusive contact:The boundary between the igneous intrusion and the wall rock

Tabular intrusions: Dike, Sill, Laccolith (pseudo-tabular, or sheet-like)

Non-tabular intrusions: Pluton, Batholith, Stock

Mt.

Rushmore is

carved out of

a granitic

igneous

intrusion


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Dikes:igneousintrusions that cut

across layering, i.e.discordant

Sills:igneousintrusions that

follow layering, i.e.concordant

Dikes and Sills

k h d h l h


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Dikes in the Sierra Nevada Batholith

Near Ruby Lake, CA @ ~12,000 ft


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Laccolith:a dome-like sill that bends the layers above it into a

dome shape

Laccoliths


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Non-Tabular Intrusions: Plutons

Pluton:Irregular blob-shaped

discordantintrusions thatrange in size from 10s of m, to

100s of km

Batholith:A pluton that is 100 km2

in surface exposure

Stock:A pluton that is


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The Sierra Nevada Batholith

Eff t f I t i


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Effects of Intrusions

Dikes form in regions of

crustal stretching

Sills may cause uplift at the

surface of the Earth

Eff t f I t i


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Dikes form in regions of

crustal stretching

Sills may cause uplift at the

surface of the Earth

La Sal Mountains, Utah were uplifted by a laccolithScotland was stretched during the Cenozoic

Eff t f I t i


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Plutons disrupt the

surrounding layers of rockand may cause crustal

stretching above

Plutons grow bystoping:

opening cracks andassimilating xenolithic

blocks in the melt

C li f M d L


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Cooling of Magma and Lava

Magma cools forseveral reasons Removal of

volatiles

It rises to a coolerlocation and hastime to cool

Cooling dependsvery much on thegeometry (surfacearea) of theintrusion.

Tabular-shape = fastcooling

Spherical shape =slow cooling

Cooling times varyfrom days minutes

to millions of years


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OBSIDIAN (VOLCANIC)

VERY FINE GRAINED


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GRANITE (ACID INTRUSIVE ROCK)

COARSE GRAINED

Sedimentary rock


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Sedimentary rock

I am the Layered Storytellers made up of SEDIMENTSeroded from igneous, metamorphic,

other sedimentary rocks, and even the remains of dead plantsand animals. These materials are DEPOSITEDin layers, or

strata, and then are squeezed and compressed into rock. Most

fossils are found in sedimentary rocks.

Taman Negara Mulu Batu Cave

Undergo

LITHIFICATION

SEDIMENTS

Sedimentary rocks

The process by

which sediments

become compacted

and cemented

together into a

sedimentary rock.

W h i d E i


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Weathering and Erosion Sedimentloose fragments of rocks or

minerals broken off of bedrock,minerals that precipitate directly out of

water, and shells of organisms.

Deposition / Sedimentationoccurswhen sediment settles out aswinds/water current die down, or asglaciers melt.

Lithifiedsediment that has beencemented together by geologicprocesses to form a rock

Rocks are broken down and turned intosediments by two main processes Physical Weathering

Plumbers snake

Chemical Weathering Liquid Drain-O

Highly weathered sandstone in Bryce Canyon N.P., UT

Ho do Sedimentar Rocks Form?


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How do Sedimentary Rocks Form?

1) Erosionmobilizes particles by weathering, most

commonly by rainfall & gravity. 2) TransportationOccurs when currents of wind, water,

and moving ice (glaciers) transport particles to newlocations (downhill or downstream)

3) Depositionsediment is deposited when the

transporting current slows to the point that it can no longercarry its load.

4) BurialAs layers of sediment accumulate, the layersaccumulate in sedimentary basins. Older, previouslydeposited sediments are compacted. These layers remain at

depth until either erosion or tectonic processes act onthem.

5) Diagenesis & LithificationRefers to the physical andchemical changes that lithifysediment into rock. Includespressure, heat and chemical reactions

The following applies to Clastic/Detritalrocks; biochemical and chemical sed rocks are different


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SEDIMENTSthe layered storyteller

origin

Detrital

sediments

Form from broken pieces of rock

Organic

Sediments

sediments deposited from theremains of plants and animals

Chemical

Sediments

form when a solid chemicalcomes out of a solution of water

The Sedimentary Stages of the Rock Cycle


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Sedimentaryrocks

Metamorphicrocks

Plutons

Desert

Playalake

Delta

Glacier

The Sedimentary Stages of the Rock Cycle

Weatheringbreaks downrocks.

Erosion carriesaway particles.

Transportation movesparticles downhill.

Deposition occurswhen particlessettle out orprecipitate.

Diagenesis lithifiesthe sediment to make

sedimentary rocks.

Burial occursas layers of

sedimentaccumulate.


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SEDIMENTSwho are they? MECHANICALLY FORMED: DETRITALOR CLASTIC SEDIMENTS.

MADE UP OF BROKEN PIECES OF MINERALS AND ROCKS,VOLCANIC ERUPTIONS OR SEA SHELLS. GRAIN SIZE >200mm

(BOULDER) 200-60 COBBLE, 60-2 GRAVEL, 2-0.06 SAND, SILT

AND CLAY. SHAPE MAY BE ROUNDED, SEMI-ROUNDED OR

ANGULAR. CHEMICALLY FORMED: INORGANIC REACTIONS OF DISSOLVED

MATERIALS IN GROUNDWATER, SEAWATER, LAKES ETC. (Na, Cl,

Ca ETC.)

ORGANIC SEDIMENTS: SKELETONS OF ANIMALS, CORALS,PLANT REMAINS OR VEGETABLE MATTERS.


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NAMES OF SEDIMENTS

NAME OF SEDIMENT DEPOSITION ENVIRONMENTALLUVIUM (ALLUVIAL) RIVER (FLUVIAL)

AEOLINE (WIND) DESERT OR COAST

LACUSTRINE (LAGOONAL) LAKE

GLACIAL POLAR/MOUNTANEOUS

COLLUVIUM GRAVITY FALLS/LANDSLIDES

LITTORAL MARINE/COASTAL AND DELTAS

SHALLOW SEA SEDIMENT MARINE SHALLOW SEA

DEEP SEA SEDIMENTS MARINE DEEP SEA


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Sedimentary rocks classified into:

Detrital sediments formrocks

Eg: Shale, Sandstone,Conglomerate

CLASTIC

organic and chemicalsediments

Eg: Limestone, Coal

NON-

CLASTIC

Clastic Sedimentary Rocks


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Clastic Sedimentary Rocks A clastic/detrital rock forms in five stages:

1- Weather ing/Erosion

2- Transportation3- Deposition

4- Bur ial

5- L ithi f ication and Diagenesis

(compaction+cementation)

Grain size is reduced as sediment is transported

Classifying Clastic Sedimentary Rocks


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Classifying Clastic Sedimentary RocksClastic/Detrital rocks are classified by:

1. Clast size 2. Clast composition

3. Angularity and Sphericity 4. Sorting

5. Type of cement


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CLASTIC SEDIMENTARY ROCKSCOMPOSITION GRAIN SIZE FEATURES NAME

Mainly quartz,

feldspar, rock

fragments and clays

Gravel (> 2 mm) Rounded grains Conglomerate

Angular grains Breccia

Sand (0.06252.00

mm)

Mostly grains of

quartz, feldspar, rock

fragments or mixed

with much silt and clay

Sandstone

Subgroups are named

according to features

Silt (0.00390.0625mm)

Nonfissile (compact) Siltstone

Fissile (splits easily) Shale

Clay (less than 0.0039

mm)

Nonfissile (compact) Claystone

Fissile (splits easily) Shale


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NON-CLASTIC SEDIMENTARY ROCKSMINERAL

COMPOSITION

GRAIN SIZE FEATURES ROCK NAME

Calcium Carbonate

(CaO3)

Gravel to clay Shells or shell

fragments cemented

Skeletal Limestone

(subgroup name

according to grain

size)

Spherical grains ordeposited crystals

Chemical Limestone(subgroup name

according to grain

size)

Dolomite

(CaMg(CO3)2

All sizes Commonly altered

from limestone

Dolostone

Quartz (SiO2) Crystalline oramorphous

Layers, lenses,nodules

Chert

Halite (NaCl) All sizes Crystals deposited as

inorganic chemical

precipitates

Rock salt

Gypsum (CaSO42H2O) Rock Gypsum

Plant fragments All sizes or dense with

conchoidal fracture

Black and non-porous Bituminous Coal


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Sedimentary Rockmy story


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CONGLOMERATE (CLASTIC)

Conglomerate could be thought of as a giant sandstone,

containing grains of pebble size (greater than 4 mm) and

cobble size (>64 mm).


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SHALE (NON-CLASTIC)

Shale is a claystone that is fissile, splitting in

layers. Shale is usually soft and does not crop

out unless harder rock protects it.


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Metamorphic rocks produced when sedimentary or igneous rocks are

transformed by heat and/or pressure.

Metamorphic rocks are either foliated or non-foliated.

These extreme conditions are only present deepinside the Earth.

E.g. Marble, Slate, Quartzite, Schist, Gneiss

Metamorphic

rock a.k.a

ChangedRocks

How Do We Identify Metamorphic Rocks?


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How Do We Identify Metamorphic Rocks?

1- Metamorphic Texturesgrains are interlocked and grew in place.

Many different types of metamorphic textures

2- Metamorphic MineralsCertain minerals only grow under

metamorphic temperatures and pressures.

- Called a metamorphic mineral assemblage, or metamorphic facies

3- FoliationThe alignment of platy minerals or alternating layers of light

(felsic) and dark (mafic) minerals.

A foliated

Outcrop

of Gneiss

Formation of Metamorphic Textures


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Formation of Metamorphic Textures

Recrystalizationchanges the shape and size of grains,but the same mineral remains. E.g. Sandstone mayrecystallize into quartzite. See (a)

Phase ChangeWhen a mineral keeps the samecomposition but the atoms arrange into a new form(polymorph). E.g. quartz (SiO2) may change to coesite(SiO2).

Metamorphic reaction/neocrystallizationThe result of

chemical processes that decompose minerals andproduce new minerals. Happens through diffusion ofatoms through solid crystals. Very slow process. See (b)

Pressure SolutionMineral grains dissolve where theirsurfaces are in contact. Occurs when rock is squeezed inone direction more than the others, at low temps, and

usually in the presence of water. Usually zig-zag shapedand common in carbonates. See (c)

Plastic DeformationAt high temps, minerals canbehave like soft plastic and become squished orstretched. Takes place without forming cracks andwithout changing the composition of the minerals. See

(d)

How do metamorphic textures form?

What Causes Metamorphism?


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What Causes Metamorphism?

1. Heat - Increased heat allows chemicalbonds to break easier.

2. Pressurehigh pressures causeminerals with open lattices to collapse,

forming more dense crystals. Most

metamorphic rocks form at 40-100 km

depth where pressures are 10,000-

30,000 times greater than the surface ofthe Earth.

3. Differential StressWhen forces arenot equal in all directions, minerals may

deform and change shape.

4. Hydrothermal FluidsMore thanjust water, hydrothermal fluids are

solutions that chemically react with

minerals.

A nice sample of gneiss

Recrystallized limestone becomes marble


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Process involved - METAMORPHISM

occurs when a rock is exposed to hot magmainside the Earth.

The intense heat of the magma alters the rock,often causing its minerals to recrystallize.

The area of rock affected by contactmetamorphism is appropriately known as the

baked zone.

CONTACT

METAMORPHISM

occurs during the formation of mountain ranges

As tectonic plates collide and converge, intensepressuredeforms and alters sedimentary andigneous rocks already buried in the Earth

folds or curves in the rocks indicate thedirection of the intense pressure.

REGIONAL

METAMORPHISM


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Metamorphic rocks classified into:

the minerals have beenflattened and pushed downinto parallel layers.

Eg: Slate, Schist, Gneiss

FOLIATED

do not display layers.

Eg: Quartzite, MarbleNON-

FOLIATED

Types of Metamorphic Rocks


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Types of Metamorphic Rocks

Metamorphic rocks are grouped into two main

categories:

Foliated Metamorphic Rocks

Non-Foliated Metamorphic Rocks

But what exactly isfoliation?

Foliation


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Foliation FoliationThe repetition of planar surfaces or layers in a

metamorphic rock. Layers can be paper-thin or meters thick.

Happens because when rocks are subjected to differential stress, platyminerals align or alternating light and dark layers form, giving the rock a

planar fabric, called foliation. Note that this is different than bedding.

Slate, a foliated metamorphic rock makes nice

roof shingles because its foliation creates

cleavage planes that easily break

Foliation and Compression Direction


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Foliation and Compression Direction

Slaty Cleavageforms perpendicular to the compression

direction, i.e. a horizontal squish will create vertical cleavage

planes. Compression also commonly results in folding.


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SOME METAMORPHIC ROCKS

FOLIATED METAMORPHIC ROKS

CRYSTAL SIZE ROCK NAME TEXTURE

VERY FINE SLATE SLATY CLEVAGE

FINE PHYLITE PHYLLITIC

COARSE SCHIST PARALLEL

ARRANGEMENT OF PLATY

MINERAL GRAINS

COARSE GNEISS COLOUR BANDING DUE

TO ALTERNATING LAYERS

OF DIFFERENT MINERALS

NON-FOLIATED METAMORPHIC ROCKS ARE MANY. EG. QUARTZITE,

CONGLOMERATE, AMPHIBOLITE, HORNFELS, MARBLE, GRAPHITE ETC.


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SLATE

NON-FOLIATED, MADE FROM SHALE

(SEDIMENTARY ORIGIN)

FOLIATIONS


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FOLIATIONS

(E.G. MIGMATITE GNEISS)

SCHIST (NO FOLIATIONS BUT LOT OF


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SCHIST (NO FOLIATIONS BUT LOT OF

ORDER)


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How are the Rock Cycle and PlateTectonics Related Heating within Earths interior results in convection cells that power

the movement of plates, and also magma, which forms intrusive and

extrusive igneous rock.

Movement along plate boundaries may result in volcanic activity,

earthquake and in some cases mountain building.

The interaction between atmosphere, hydrosphere and biosphere

contributes to the weathering of rocks exposed on Earths surface.

Plates descending back into Earths interior are subjected to

increasing heat and pressure, which may lead to metamorphism as

well as generation of magma and yet another recycling of materials.

The rock cycle never ends!!


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References

1. Harwant Singh Bujang Kim Huat, Basic Eng

Geology for Tropical Terrain

2. http://www.beyondbooks.com

3. http://www.classzone.com

4. http://www.appstate.edu
http://www.classzone.com/http://www.appstate.edu/http://www.appstate.edu/http://www.classzone.com/


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THANK YOU

Prepared by:

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unit 4 rockcycle 1314

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