Chapter 13 - Earth Materials and Structure

8/8/2019 Chapter 13 - Earth Materials and Structure

1/20

Earth Material and Structure1

CHAPTER 13: Earth Materials and Structure

Columnar Basalt Flows. Titon Valley, Yakama County, Washington

Courtesy USGS

Physical geograhers recogni!e that to unco"er the satial relationshis o# earth sur#ace

henomena they must ha"e a goo$ un$erstan$ing o# what the %arth is comose$ o# an$ howit a##ects lan$scae $e"eloment. &ere we will re"iew the #un$amental 'uil$ing 'locks o#

%arth, how they change through time, an$ what e##ects they ha"e on %arth sur#ace rocesses

an$ #orm.

The Physical Environment: An Introduction to Physical Geography

8/8/2019 Chapter 13 - Earth Materials and Structure

2/20

Earth Materials and Structure Outline

The %arth(s )nterior

o The Crust

o The *antle

o

The Core Forces that Shae the Sur#ace o#

the %arth

+r$ers o# elie#

*inerals

ocks

o The ock Cycle

o )gneous ocks

o Se$imentary ocks

o *etamorhic ocks

e"iew

8/8/2019 Chapter 13 - Earth Materials and Structure

3/20

Earth Material and Structure3

The Earth's Interior

The $ee interior o# the %arth remains somewhat o# a mystery as we ha"e only enetrate$ the

"ery most outer ortion with our $ee $rilling e-loration. What knowle$ge we $o ha"e

comes #rom seismic wa"e $ata or la"a that has e-tru$e$ onto the sur#ace. What we $o know

is that the %arth(s interior is somewhat like a

concentric series o# rings, rogressing #rom the $ensean$ intensely hot inner core towar$ the 'rittle outer

shell o# the crust.

Figure %*. Seismograh recor$ing seismic acti"ity.

(Courtesy USGS &awaii Volcano +'ser"atory/

Seismic acti"ity gi"es us clues as to the internal

structure o# the %arth. Geoscientists o'tain seismic

$ata #rom naturally occurring earth0uakes or human1in$uce$ e-losions. Seismic energy

ro$uces two kin$s o# wa"es that are use#ul in stu$ying the %arth(s interior. Compressional

(P) wavesgenerate a 'ack1an$1#orth motion arallel to the $irection o# tra"el. Shear (S)

wavesmo"e u1an$1$own eren$icular to the $irection o# wa"e

transmission. Seismometers $etect these motions an$ recor$ them on a seismograph.

When seismic wa"es ass through rock, their amlitu$e an$ $irection changes. For instance,

wa"e "elocity generally increases as rock $ensity increases. Shear wa"es $o not enetratemolten masses an$ when they encounter a 'oun$ary 'etween two rock tyes o# $i##ering

$ensities, a ortion o# the wa"e tra"els along the 'oun$ary while another art returns to the

sur#ace. Such changes in seismic wa"e "elocities le$ Yugosla"ian geohysicist 2n$ri3a

*ohoro"icic 4567189:/ to $isco"er the 'oun$ary 'etween the crust an$ un$erlying mantle.

Wa"e "elocity increases through the ;Moho; $iscontinuity. )t is 'elie"e$ that the

$iscontinuity reresents a !one wheresima1tye minerals un$ergo a hase change that

ro$uces a new an$ $enser com'ination o# minerals. "%-amine P an$ S wa"es mo"ing

through %arth(s interior.; 4Courtesy ougall ?ittell/

The Physical Environment: An Introduction to Physical Geography

8/8/2019 Chapter 13 - Earth Materials and Structure

4/20

Figure %*.@ )nterior Structure o# the %arth

The Crust

The outer 'rittle shell o# the %arth is the crustthat #orms the ;skin; o# the lithoshere. The

crust is 'roken into se"eral continental an$ oceanic tectonic 4 lithosheric/ lates.These lates

ri$e ato the more lia'le mantle 'eneath, colli$ing to create great mountain systems an$

srea$ing aart to #orm ri#t "alleys.

The crust is $i"i$e$ into a 'asal !one calle$ the simalayer, an$ a less

$ensesiallayer. The simais rimarily comose$ o# a hea"y, $ark grou o# 'asaltic rocks.

Primarily comose$ o# silica an$ magnesium, their high $ensity 4@5AA to 99AA kg=m9/ is $ue

to the large amounts o# iron an$ magnesium. The sial, name$ #or the two re$ominate

elements silicon an$ aluminum, is lighter in weight with $ensities aroun$ @7AA 1 @5AA

kg=m9

. +#ten geoscientists re#er to rocks o# the sial as ;granitic rock; as granite is are$ominant rock tye. The lower 'oun$ary o# the sial gra$es into the uer ortion o# sima.

The sial actually has 0uite a $i"ersity o# rock tyes, inclu$ing large amounts o# 'asaltic rocks.

The sima howe"er is almost e-clusi"ely 'asaltic in comosition.

The Mantle

The mantlecomrises 5A o# the %arth(s total "olume. )t is mainly comose$ o# a $ark,

$ense ultrama#ic rock calle$peridotite that is rich in iron an$ magnesium. Seismic wa"e

"elocity increases stea$ily through this !one. The uer mantle is $i"i$e$ into three #airly

$istinct layers. The lithosphereis a rigi$ cool layer comose$ o# the outer crust an$ the

uermost mantle. The asthenosphere is the least rigi$ ortion o# the mantle. )t is a so#t,easily $e#orme$ layer that is susceti'le to slow con"ection cause$ 'y ockets o# increase$

8/8/2019 Chapter 13 - Earth Materials and Structure

5/20

Earth Material and Structure5

heat #rom the $ecay o# ra$ioacti"e elements. Searating the uer mantle #rom the oceanic

crust is theMoho Discontinuity. Seismic wa"es assing though this 'oun$ary increase their

wa"e "elocity #rom mi 47 km/ er secon$ to 6 mi 45 km/ er secon$. The shi#t o# wa"e

"elocity is $ue to the change in rock comosition an$ $ensity. The rock o# the oceanic crust is

somewhat less $ense than the mantle an$ re#erre$ to as mafic rock$ue to the smaller

roortion o# iron an$ magnesium. Below the asthenoshere is the rest o# the uer mantlecomose$ o# rigi$, soli$ rock calle$ themesosphere4not to 'e con#use$ with the atmosheric

layer o# the same name/.

The Core

The coreis $i"i$e$ into the inner an$ outer cores. Though intense heat is generate$ at such

great $eths, geoscientists 'elie"e that un$er the enormous o"erlying ressure theinner

coreis ma$e o# soli$ iron an$ nickel. The outer coreis thought to 'e molten iron 'ecause

shear1wa"e "elocities $ro to !ero which occurs when they encounter a li0ui$. The

interaction 'etween the inner an$ outer core is though to ro$uce %arth(s magnetic #iel$.

Forces That Shae the Sur!ace o! the Earth

The crust is constantly 'eing altere$ 'y #orces #rom within an$ outsi$e the %arth system.

Great #orces #rom within causes the sur#ace to hea"e an$ 'uckle, sometimes with $isastrous

conse0uencesto humans. %nergy recei"e$ #rom the sun $ri"es rocesses like those that

create ma3estic san$ $unes an$ car"e magni#icent stream "alleys.

Endo"enic Processes

%n"ironmental rocesses or #orces that are $ri"en 'y the %arth(s "ast heat engine are calle$

endogenic forcesor processes. The mo"ement o# tectonic lates is thought to 'e a ro$uct o#

con"ection currents in the mantle. >ee within the %arth(s core, heat is generate$ 'y the

ra$ioacti"e $ecay o# elements like uranium, thorium, an$ otassium. The heat is trans#erre$

uwar$ to warm the mantle causing it to slowly circulate an$ tug on the lates a'o"e. 4Formore see Some Unanswered Questions,The Dynamic Earth, USGS/. 2s the crustal lates are

mo"e$ a'out, they interact 'y colli$ing, sli$ing 'y, or $i"erging #rom one another. The result

o# such mo"ement ro$uces #aults an$ earth0uakes, "olcanoes, the creation o# mountain

systems, or $ee "alleys an$ trenches. The great mountain systems o# %arth like the

&imalayas are a ro$uct o# the collision o# lithosheric lates. Similarly, the huge trenches

#oun$ on the ocean #loor, like the *arianas Trench, are cause$ 'y late interaction.

The Physical Environment: An Introduction to Physical Geography

8/8/2019 Chapter 13 - Earth Materials and Structure

6/20

Figure %*.a

*t. Shishal$in, 2laska is a comosite "olcano

)mage courtesy USGS

Figure %*.'

Teton *ountains were create$ 'y #aulting

)mage courtesy USGS

E#o"enic Processes

Those rocesses acting at the sur#ace o# the earth an$ rimarily $ri"en 'y solar energy are

calle$ exogenic processes. For instance, win$ is create$ 'y the "ariation in ressure o"er

$istance 4pressure gradient force/. Pressure "ariations are, in art, create$ 'y the "ariation o#

sur#ace heating $ue to the une0ual $istri'ution o# solar energy receit. 2s win$ 'lows it

e-erts an erosi"e #orce on the sur#ace to $etach an$ transort soil articles. Win$ erosion is

there#ore an e-ogenic rocess. %rosion 'y rain is likewise $ri"en 'y the initial e"aoration

$ue to a'sortion o# energy an$ su'se0uent con"ersion into reciitation 'y con$ensation

rocesses. The geologic work o# glaciers is consi$ere$ an e-ogenic rocess. Glaciers #orm

when summer temeratures $ecrease to the oint where the re"ious winter(s snow#all $oes

not melt an$ accumulates o"er time e"entually comacting an$ metamorhosing into ice. Theaccumulating ice srea$s out as a great sheet sculting the sur#ace 'eneath it.

8/8/2019 Chapter 13 - Earth Materials and Structure

7/20

Earth Material and Structure7

Figure %*.6a Water %rosionSe"ere sheet erosion on #arm lan$

)mage courtesy

8/8/2019 Chapter 13 - Earth Materials and Structure

8/20

Figure %*.6c Win$ %rosion *assi"e $ust storm $uring the >ust Bowl

era. )mage courtesy USGS >>S@

Orders o! Relie!

The toograhy o# the %arth is a ro$uct o# en$ogenic an$ e-ogenic rocesses.Reliefis

simly the $i##erence in ele"ation 'etween two oints. When the sur#ace is relati"ely #lat wesay it has low relie#. Con"ersely, mountainous regions ha"e high relie#. The relie# #eatures o#

the earth are 'e $i"i$e$ into three or$ers 'ase$ on what create$ them an$ their si!e.

First Order Relief Features

Figure %*.: Crustal

lates

Photo Courtesy

8/8/2019 Chapter 13 - Earth Materials and Structure

9/20

Earth Material and Structure9

Second Order Relief Features

Second order relief featuresare the result o# late collision or $i"ergence. i#ts #orm where

lates $i"erge #rom one another. )# arallel ri#ting occurs, ri#t "alleys, like the Great i#t

Valley o# 2#rica can #orm. i#ting can 'e accomanie$ 'y "olcanic acti"ity as magma ours

out o# the ri#t. *t. Diliman3aro was #orme$ as a result o# the ri#ting that create$ the Great i#t

Valley o# 2#rica.

Figure %*.7 &imalaya *ountains.

8/8/2019 Chapter 13 - Earth Materials and Structure

10/20

Figure %*. 5 Pawnee Cir0ue, Colora$o

Front ange, US2 4Photo Courtesy *.

itter/

Pawnee cir0ue, the 'owl shae$ #eature in

the center o# Figure %*.5 was cause$ 'y an

aline glacier ero$ing into the si$e o# a

mountain. The 'owl1shae$ $eression le#t

'ehin$ reresents a thir$ or$er relie# #eature

o# the earth. The icture was shot #rom across )sa'elle Valley oneen$ing on the element, the resulting mineral(s $ensity an$

color can "ary consi$era'ly. The silicates are su'$i"i$e$ into the #erromagnesian an$ thenon#erromagnesian 4or aluminosilicates/. Ta'le %*. gi"es e-amles o# other imortant

mineral grous #oun$ in the crust.

Ta$le EM%1 I&ortant Mineral Fa&ilies o! the Crust

Te Co&ound E#a&les

Silicates 1 non#erromagnesian

4Silicate ion lack iron an$ magnesium ions/

Pyro-ene

*usco"ite *ica

+rthoclase 4Potassium/ #el$sar

Plagioclase #el$sar

uart!

8/8/2019 Chapter 13 - Earth Materials and Structure

11/20

Earth Material and Structure11

Silicates 1 #erromagnesian

4Silicate ionHiron an$ magnesium ions/

+li"ine

&orn'len$e

Biotite *ica

+-i$es 4+-ygen H element4s//

?imonite

&ematite

*agnetite

Sul#i$es 4Sul#ur H element4s//

Galena

Pyrite

Chalcoyrite

Car'onates 4Car'on1o-ygen ion H element4s// Calcite $olomite

Rocks

Rocksare assem'lages o# minerals. Unlike minerals, the comosition o# a articular rock

tye "aries #rom samle to samle $een$ing on the roortions o# minerals containe$

within. 2 hysical geograher nee$s a #un$amental un$erstan$ing o# the roerties an$

characteristic o# rocks to un$erstan$ the geograhical "ariation o# %arth sur#ace #eatures.

Rocks and the Rock Cycle

Figure %*.8 The ock Cycle 42#ter ?emke, et. al. @AA9/

The rock cycle reresents the alteration o# rock1#orming minerals

a'o"e an$ 'elow the %arth(s sur#ace. 2t the to o# the

$iagram molten rock material, magma, cools

4crystalli!ation/ to #orm igneous rocks. )#

magma is e-tru$e$ onto the sur#ace it is

calle$ lava. Cooling

a'o"e the

sur#ace

yiel$s rocks with #inete-tures, while those that

#orm #rom slow cooling

'eneath the sur#ace

tyically

ha"e large crystals.

)gneous rock may remelt

when e-ose$ intense heat to

#orm magma again, or 'e

change$ into

metamorphic rock. )gneous rocks

may also 'e e-ose$ to weathering, erosion an$

The Physical Environment: An Introduction to Physical Geography

8/8/2019 Chapter 13 - Earth Materials and Structure

12/20

$eosition to #orm sediment, #ragments o# weathere$ rock an$ the recursor #or se$imentary

rock.

2s se$iments accumulate they are su'3ecte$ to comaction an$ cementation to #orm

sedimentary rock. Se$imentary rocks may 'e 'roken $own 'y weathering an$ erosion to 'e

$eosite$ as se$iment, e-ose$ to intense heat an$ melting to return to magma, or 'e change$

into a metamorhic rock.Metamorphic rocksare those that ha"e 'een altere$ 'y e-osure to heat an$=or ressure. The

ressure can 'e create$ 'y the weight o# material lying a'o"e them. The collision o#

lithosheric lates creates ressure an$ heat that alters rock. )# entirely melte$, the rock

material #orms magma. %rosion an$ weathering 'reaks $own metamorhic rocks to #orm

se$iment, which can 'e comacte$ into se$imentary rock.

Igneous Rocks

)gneous rocks #orm 'y the cooling o# magma4molten rock material 'eneath the sur#ace/ or

la"a 4molten rock material e-tru$e$ onto the sur#ace/. *agma which originates at $eths as

great as @AA kilometers 'elow the sur#ace consists rimarily o# elements #oun$ in silicate

minerals along with gases, nota'ly water "aor. Because the molten material is less $ense

than the surroun$ing soli$i#ie$ rock, it works its way

towar$ the sur#ace where it #lows out onto the sur#ace

as la"a.

%*.A Granite, an intrusi"e igneous rock.

Cooling o# the magma initiates the crystalli!ation o#

elements containe$ within the molten rock. Usually,

cooling $oes not take lace at the same rate throughout the entire mass. 2s it cools, numerous

small crystal $e"elo an$ then ions are a$$e$ aroun$ these centers o# growth. +nce the

crystals grow enough #or their e$ges to meet, growth ceases an$ crystalli!ation commences in

another art o# the mass. +"er time the magma cools into a soli$i#ie$ rock o# interlocking

crystals. The rate o# cooling $etermines the $egree to which crystals can grow. Those that

#orm 'y slow cooling ha"e large crystals an$ are $escri'e$ as 'eing coarsegrained. !ine

gainedigneous rocks #orm 'y more rai$ly cooling when the molten material is e-ose$ at

the sur#ace. 2s a result, crystals $on(t ha"e a chance to grow "ery large.

Intrusive Igneous Rock

When magma intru$es into re1e-isting rock it cools rather slowly 'ecause the surroun$ing

hostor country rock, as it is calle$, insulates the magma. 2s a result, crystals grow larger

gi"ing the rock mass a coarse te-ture. Such intrusive igneous" or plutonic rockswhere the

mineral grains are easily seen with the unai$e$ eye are calle$porphyritic. The rock mass

itsel# is calle$ apluton#

Figure %*. )ntrusi"e igneous lan$#orms

8/8/2019 Chapter 13 - Earth Materials and Structure

13/20

Earth Material and Structure13

Physical geograhers are esecially intereste$ in rocks that #orm 'eneath the sur#ace a#ter

they ha"e 'een e-ose$ 'y erosion o# the o"erlying host

rock. 2 'atholith is a huge intrusi"e igneous rock mass

or luton that when unco"ere$ creates toograhic highs

in mountainous regions. The )$aho Batholith #or

e-amle co"ers some :,AAA s0uare miles. These

lan$#orms are massi"e in character lacking linear ri$ges

an$ "alleys.

Figure %*.@ &al# >ome, a 'atholith in Yosemite

ikes o#ten #orm

on the #lanks o# "olcanoes. When e-ose$ 'y erosion they take the #orm o# a linear ri$ge.Shi, S@/

Extrusive Igneous Rocks

The Physical Environment: An Introduction to Physical Geography

8/8/2019 Chapter 13 - Earth Materials and Structure

14/20

Fine1graine$ rocks #orm i# molten rock cools rai$ly when it is e-tru$e$ onto the sur#ace.

$asaltis a common e-trusi"e igneous rock. Some

#ine graine$ rocks #orming at the e$ge o# a la"a

#low ha"e small holes or vesicleswhich are "oi$

saces le#t 'y escaing gasses. Very rai$ cooling

can ro$uce rocks with aglassy texture. +'si$ianis such a rock where there was too little time #or

ions to com'ine into an or$erly crystalline

structure.

Figure %*. +'si$ian has a glassy aearance

$ue to rai$ cooling.

Sedi&entar Roc)s

Se$imentary rocks are those #orme$ #rom the comaction an$ cementation o# #ragments o#

re1e-isting rocks calle$ clasts, or lant an$ animals remains. The e-ogenic rocesses o#

weathering an$ erosion create the raw materials #or se$imentary rocks. %arth material is

loosene$ an$ mo"e$ #rom higher to lower ele"ations where it is $eosite$ as transortation

agents like water, win$ or gra"ity lose their energy to mo"e se$iment. Streams an$ ri"erstransort se$iment to lakes or oceans, or $eosits it on near'y #loo$lains where it

accumulates. +n lan$, clastic se$iments consist mainly o# large 'oul$ers, co''les, gra"el,

san$, an$ silt. +n the continental shel"es at the margin o# continents, marine se$iment is

largely san$, silt, an$ clay. 2t the outer shel"es an$ on the ocean #loor, clays an$ chemically

reciitate$ calcium car'onate an$ the remains o# tiny marine animals accumulate.

Figure %*.6 San$stone 'e$s are easily seen in the cli##s o# Paria1Vermillion Canyon,

2ri!ona 4Courtesy U.S. Bureau o# ?an$ *anagement/

2s layers o# se$iment accumulate to great thickness, they are comacte$ an$ 'egin to har$en

into se$imentary rock. %ach layer they #orm is calle$ a %edor stratum, the rocess 'y which

this occurs is calle$stratification. The searation 'etween each 'e$ is calle$ a %edding

plane an$ signi#ies a cessation o# $eosition at that location #or a erio$ o# time. Be$s can

"ary hori!ontally $ue to $i##erences in the energy con$itions an$ $istance #rom the origin o#

the se$iments. For instance, a 'e$ may change #rom a conglomerate o# cemente$ gra"el, to

comacte$ silt calle$ siltstone, an$ #inally to shale which is cemente$ clay, in$icating the

$ecreasing ower o# water to transort these $i##erent si!e materials #rom away #rom their

source. Generally seaking, i# the layers ha"e not 'een $istur'e$, the ol$est layers are at the

'ottom. +#ten there is a cementing agent that hol$s the materials together. Because many

8/8/2019 Chapter 13 - Earth Materials and Structure

15/20

Earth Material and Structure15

se$imentary rocks are #orme$ #rom #ragments o# rocks, they are weaker than igneous or

metamorhic rocks.

Tes o! sedi&entar roc)s

Se$imentary rocks are $i"i$e$ into two grous, clastic or detrital, an$ nonclastic orchemical.

2mong the chemical se$imentary rocks are those that are ;'iologic; in origin like coal. Theclastic se$imentary rocks #orm #rom the comaction o# rock #ragments, while the chemical

se$imentary rocks #orm 'y the reciitation o# elements.Sandstoneis a common clastic

se$imentary rock #orme$ 'y the comaction an$ cementation o# san$ 40uart!

grains/. Conglomerateis another clastic se$imentary rock #orme$ 'y the cementation o#

roun$e$ 'oul$ers, co''les, an$ e''les. +n the other han$, %reccia#orms #rom angular

'oul$ers, co''les, an$ e''les.Shale#orms #rom the comaction o# clays,

while siltstone4mu$stone/ #orms #rom the comaction o# silt.

Figure %*.:a San$stone

Figure %*.:' Conglomerate

You are ro'a'ly #amiliar with se"eral o# the nonclastic se$imentary rocks.&imestoneis

comose$ o# reciitate$ calcium car'onate. ?imestone sometimes contains "isi'le shells o#

marine organisms that ha"e accumulates on the ocean #loor.'olomiteis a calcium1

magnesium car'onate rock that #orms as a chemical reciitate or #rom the alteration o#limestone. ?imestone is "ery easily weathere$ in warm an$ moist climates to createkarst

topography.

Figure %*.7 ?imestone

Coal is consi$ere$ a se$imentary rock. Some might

classi#y it as a 'iologic se$imentary rock as it #orms #romthe comaction an$ alteration o# accumulate$ lant matter. Coal is classi#ie$ into one o# three

tyes $een$ing on its le"el o# $e"eloment.Ligniteis a so#t, 'rown coal an$ is the least

$e"eloe$ #orm. +ne might think o# it as an interme$iate ste 'etween eat an$

coal.Bituminous coal, also calle$ so#t coal though har$er than lignite, is a ro$uct o# $ee

'urial an$ comaction.Anthraciteis the har$est an$ most $e"eloe$ or ure #orm o# coal.

2nthracite #orms when 'ituminous coal is metamorhose$ in regions that ha"e un$ergone

mountain 'uil$ing. 2nthracite is the most "alue$ #orm o# coal #or its heat generating caacity

an$ low sul#ur content.

The Physical Environment: An Introduction to Physical Geography

8/8/2019 Chapter 13 - Earth Materials and Structure

16/20

Metamorphic Rocks

Metamorphic rocksare #orme$ 'y the alteration o# re1e-isting rocks #rom e-osure to heat

an$ ressure while remaining in a soli$ #orm. *etamorhism occurs 'y 'reaking 'on$s

'etween atoms in a mineral so that the atoms rearrange themsel"es into new, more sta'le,

mineral #orms. ocks are trans#orme$ an$ remain in a soli$ state 'ecause not all the 'on$s inthe rock(s minerals are 'roken 1 i# they were the rock woul$ melt. *etamorhism occurs in

soli$ rock 'ecause only some o# the 'on$s 'etween atoms are 'roken in an unsta'le mineral.

2s a result, the #ree$ atoms an$ ions can migrate to another location within the mineral, or

'on$ with atoms in a $i##erent mineral. The en$ result is to ro$uce minerals that are more

sta'le un$er the en"ironmental con$itions in which they e-ist.

*etamorhism in"ol"es the trans#ormation o# a re1e-isting rock to #orm new minerals an$

te-tures. The original mineral content o# a rock can change in se"eral ways. Unsta'le

minerals like clays will 'reak$own an$ their elements will recom'ine to #orm new minerals.

*ore sta'le minerals like 0uart!, will stay 0uart! 'ut change shae an$ si!e to #orm a new

con#iguration. 2t high temeratures, atoms an$ ions may mo"e into a new orientation an$

'on$ into more sta'le #orms. &ence, the tye o# minerals an$ its te-ture may change 'ut thechemical comosition o# the rock itsel# can stay the same.

ocks 'urie$ $ee 'eneath the %arth are e-ose$ to lithostatic pressure, the con#ining

ressure create$ 'y the material that sits a'o"e a articular location. ?ithostatic ressure is

e0ual in all $irections an$ comresses the "olume o# rock into a $enser material. 2t the

contacts 'etween mineral grains, the ressure 'reaks the 'on$s 'etween atoms allowing them

to migrate towar$ regions o# less ressure where they re'in$ with other atoms.

Figure %*.5 Gneiss $islays the 'an$ing o# minerals tyical o# a #oliate$ metamorhic rock

#orme$ #rom granite.

2long the 'oun$ary o# tectonic lates where collision or su'$uction is occurring, directed

pressureis e-erte$ on rock. Un$er these circumstances, ressure is imose$ in a articular

$irection. >irecte$ ressure #lattens an$ lengthens the rock in the $irection o# greatest

ressure. The ressure is not great enough to a##ect new minerali!ation howe"er. )nstea$,

$irecte$ ressure a##ects the shae an$ arrangement the minerals. Un$er great ressure,

mineral grains may 'e smeare$ or artially melte$ an$ recrystalli!e$ into 'an$s aligne$

eren$icular to the $irection o# greatest ressure. This createsfoliated metamorphic rockswith minerals in $istinct 'an$s.

Occurrence of metamorphism

*etamorhism occurs un$er a "ariety o# $i##erent con$itions that controls the geograhic

$istri'ution o# metamorhic rocks an$ their signi#icance to earth sur#ace #eatures. When

magma intru$es into host rock, locali!e$ contact metamorphism occurs along the contact

'etween the re1e-isting rock mass an$ the cooling luton. The heat intro$uce$ 'y the

intru$ing magma controls the $egree o# metamorhism. Contact metamorhism occurs un$er

low to mo$erate ressure an$ low to high temerature con$itions. Temeratures o#

metamorhism "ary wi$ely #rom AA1AAAIC. The amount o# metamorhism is go"erne$ 'y

a "ariety o# #actors, among which are the $i##erences 'etween the temerature o# the lutonan$ the country rock, the heat caacity an$ con$ucti"ity o# 'oth magma an$ country rock.

8/8/2019 Chapter 13 - Earth Materials and Structure

17/20

Earth Material and Structure17

&y$rothermal #lui$s circulating through the surroun$ing rock are also imortant in

metamorhosing the rock as they transort heat. Flui$s are articularly imortant in the

metamorhism o# car'onate rocks.

Tyically, contact metamorhism occurs at shallower le"els o# the crust, where the ressure is

relati"ely low. 2t those shallow $eths, the stresses characteristic o# orogenic 'elts are

generally small or a'sent thus ro$ucing metamorhic rocks that lack #oliation. Contactmetamorhism commonly ro$uces #ine1graine$ rocks. The metamorhose$ rock

surroun$ing the 'o$y o# magma along the !one o# contact is calle$ anaureole. *any

ro#ita'le mines are situate$ in metal1rich aureoles #orme$ 'y contact metamorhism.

Regional metamorphismoccurs o"er 'roa$ areas o# the crust. There are two 'asic kin$s o#

regional metamorhism, dynamothermal metamorphisman$ %urial metamorphism.

>ynamothermal metamorhism occurs in areas that ha"e un$ergone $e#ormation $uring

mountain 'uil$ing that ha"e since 'een ero$e$ to e-ose the metamorhic rocks. )t is cause$

'y the $i##erential stress resulting #rom late su'$uction or collision along late 'oun$aries.

egional metamorhism occurs in a linear 'elt in the late o"erri$ing the su'$ucting one $ue

to increasing temerature an$ ressure as a result o# comression, thrusting, #ol$ing, an$

intrusion o# magmas #rom 'elow.

Figure %*.8 uart!ite is a non#oliate$ metamorhic rock

#orme$ #rom san$stone, a se$imentary rock.

Burial metamorhism occurs in $ee 'asins where se$iments or

se$imentary rocks ha"e accumulate$. 2t a $eth o# a'out A

kilometers, the con#ining ressure o# the o"erlying material

com'ine$ with geothermal heat is great enough to metamorhose rocks. Because the

comression $oes not imose a $irecte$ ressure, metamorhic rocks #orme$ #rom 'urial are

nonfoliated an$ lack any 'an$ing o# minerals.

Ta$le EM%* Co&&on Meta&orhic Roc)s

Roc) Parent Roc) +e MineralsMeta&orhic

En,iron&ent

Foliated Slate ShaleClay minerals, micas.

chlorite. grahite

elati"ely low temerature

an$ ressure

Foliated SchistShale, 'asalt, graywackesan$stone, imure

limestone

*ica, chlorite, garnet,talc, e$io$te,

horn'len$e, grahite,

staurite, kyanite

)nterme$iate 1 to 1 high

temerature an$ ressure

Foliated Gneiss

Shale, #elsic igneous rocks,

graywacke, san$stone,

granite, imure limestone

Garnet, mica, augite,

horn'len$e, staurolite,

kyanite, sillimanite

&igh Temerature an$

ressure

-on!oliated *ar'le Pure limestone calcite, $olomite

Contact with hot magma,

or con#ining ressure #rom

$ee 'urial

-on!oliated uart!ite Pure san$stone, chert uart! Contact with hot magma,or con#ining ressure #rom

The Physical Environment: An Introduction to Physical Geography

8/8/2019 Chapter 13 - Earth Materials and Structure

18/20

$ee 'urial

8/8/2019 Chapter 13 - Earth Materials and Structure

19/20

Earth Material and Structure19

Earth Materials and Structure

Revie

Use the links 'elow to re"iew an$ assess your learning. Start with the ;)mortant Terms an$

Concets; to ensure you know the terminology relate$ to the toic o# the chater an$

concets $iscusse$. *o"e on to the ;e"iew uestions; to answer critical thinking 0uestionsa'out concets an$ rocesses $iscusse$ in

the chater. Finally, test your o"erall

un$erstan$ing 'y taking the ;Sel#1

assessment 0ui!;.

)mortant Terms an$ Concets

e"iew uestions

Sel#1assessment 0ui!

!dditional Resources

Use these resources to #urther e-lore theworl$ o# geograhy

Multimedia

;The Chemistry o# %arth; The orld of

!hemistry"i$eo series 42nnen'erg=CPB/

;Silicon, a cornerstone o# the high1tech

in$ustry, is one o# the elements o# the %arth highlighte$ in this rogram.; 2$$itional

in#ormation a'out %arth structure an$ mineral #ormation is inclu$e$. Go to theThe Worl$ o#

Chemistry site an$ scroll to ;The Chemistry o# %arth;. +ne1time, #ree registration may 'e

re0uire$ to "iew #ilm.

;)ntrusi"e )gneous ocks;Earth e#ealed "i$eo series 42nnen'erg=CPB/

*ost magma $oes not e-tru$e onto %arthJs sur#ace 'ut cools slowly $ee insi$e %arth. This

magma sees into cre"ices in e-isting rock to #orm intrusi"e igneous rocks. %-erts ro"i$e a

grahic illustration o# this rocess an$ e-lain the tyes an$ te-tures o# rocks such as granite,

o'si$ian, an$ 0uart!. +nce again, late tectonics is shown to 'e in"ol"e$ in the rocess. Go to

the %arth e"eale$ site an$ scroll to ;)ntrusi"e )gneous ocks;. +ne1time, #ree registration

may 'e re0uire$ to "iew #ilm.

;*etamorhic ocks;Earth e#ealed "i$eo series 42nnen'erg=CPB/ ;The weight o# a

mountain creates enough ressure to recrystalli!e rock, thus creating metamorhic rocks. This

rogram outlines the recrystalli!ation rocess an$ the tyes o# rock it can create K #romclaystone an$ slate to schist an$ garnet1'earing gneiss. The relationshi o# metamorhic rock

to late tectonics is also co"ere$.; Go to the %arth e"eale$ site an$ scroll to ;*etamorhic

ocks;. +ne1time, #ree registration may 'e re0uire$ to "iew #ilm.

;Se$imentary ocks;L The Dey to Past %n"ironmentsEarth e#ealed "i$eo series

42nnen'erg=CPB/ This rogram returns to the Gran$ CanyonL its e-ose$ layers o#

se$imentary rock allow scientists to eer into the geologic ast. The mo"ement o# se$iment

an$ its $eosition are co"ere$, an$ the rocesses o# lithi#ication, comaction, an$

cementation that ro$uce se$imentary rocks are e-laine$. +rganic comonents o# rock are

also $iscusse$. Go to the %arth e"eale$ site an$ scroll to ;Se$imentary ocksL The Dey to

Past %n"ironments;. +ne1time, #ree registration may 'e re0uire$ to "iew #ilm.

The Physical Environment: An Introduction to Physical Geography

8/8/2019 Chapter 13 - Earth Materials and Structure

20/20

Readings

Unco"ering &i$$en &a!ar$s in the *ississii Valley4USGS/

The *ississii Valley1;Whole ?otta Shakin( Goin( +n; 4USGS/