plate tectonics 3

7/24/2019 Plate Tectonics 3

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Plate TectonicsHorizontal Movement of

Earths Lithosphere

Chapter 3

Additional Reading: USGS Plate Tectonics (Pdf) class web site


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Learning Objectives

Understand the processes that are continuously changing Earthssurface as lithospheric plates move relative to one another.Identify the role of oceanic ridges, transform faults and deep-sea

trenches in defining the edges of lithospheric plates.Eplain the distribution of magnetic anomaly stripes, seismicity,and volcanism in terms of the concept of global plate tectonics.!alculate spreading rates of ocean basins.


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Plate Tectonics

1. The Theory of Plate Tectonics

2. Plate Boundaries

a) Spreading Centers

b) Subduction Zones

c) Transform Faults

3. Plate Movement


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Continental Drift- theory* proposed by

Alfred Wagner, a erman meteorologist !"#"$)

* %ot accepted by scientific community

- no mechanism to e&plain plate mo'ement

The Theory of Plate Tectonics

(&plained by geologic fit fossils


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Plate Tectonicshttp++pubsusgsgo'+gip+dynamic+dynamichtml


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Plate Tectonics- e'idence for theory of continental

drift byHess, Heezen and Thar (!"#$%s)foundlithospheres plate boundaries that can be types") ridges !spreading centers)

.) trenches !subduction /ones)

) transform faults !plates sliding past one another)

The Theory of Plate Tectonics(contd.)


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major lates!

" 0acific 1 "2$ &"23 4m.

. (urasian - 52 &"23 4m.

Antarctic - 32 &"23 4m.

6 Australian - 6$ &"23 4m.

$ S American - 6$ &"23 4m.

3 African - 72 &"23 4m.5 % American - 32 &"23 4m.

"ithosheric Plates

minor lates!

" Cocos - $ &"23 4m.

. 0hillipine - 3 &"23 4m.

Caribbean - $ &"23 4m.

6 %a/ca - "$ &"23 4m.

$ Arabian - 7 &"23 4m.

3 8ndian - "2 &"23

4m.

5 Scotia - $ &"23 4m.

7 9uan de Fuca - . &"23 4m.

The Theory of Plate Tectonics(contd.)


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") Con'ection cells form :ensity differences 1 cool 's hot

.) Con'ection cells cause frictional drag on lithosphere

) ;ithosphere stretches due to con'ecti'e mo'ement

6) ;ithospheric crust


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$) Faulting 1 brea4 in o'erlying lithosphere3) =agma flo


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!reating ne" ocean crust


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0lates split apart -divergent plate bondar! %e< crust formed - constrctive plate

bondar!

a# $readin% centers & 'rift (ones)(contd.)

('olution of a mid-ocean ridge system

" >p


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Lithospheric Plates collide - convergent plateboundary

Crust destroyed - destrctive plate bondar! Forms trenches and mountains

Plate Boundaries(contd.)

*#$u*duction (ones


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types of subduction /ones

1. Ocean crust into continental crust1 form trenches and

mountain ranges

(& a) 9uan de Fuca plate into the % American plate - forms Cascade =tn ?ange

(& b) %a/ca plate into the S American plate - forms 0eru-Chile Trench and

the Andes =tn ?ange


*#$u*duction (ones(contd.)


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*#$u*duction (ones(contd.)2. Ocean crust into ocean crust1 forms trenches and island arcs

(& A) 0hilippine plate into the 0acific plate 1 formed the =arianna Trench

and the =arianna 8sland Arc system

(& @) % American plate into the Caribbean plate and then the % American

plate into the S American plate 1 formed the 8sthmus of 0anama



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3. Continental crust into continental crust1 form mountain ranges

(& A) 8ndian plate into the (urasian plate 1 formed the imalayas

(& @) (urasian plate into the African plate - closing up of the

=editerranean sea


*#$u*duction (ones(contd.)


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#riving $echanisms for %late $otions

#estructive margins

&ubduction 'ones

!onstructive margins$idocean ridges

&U$$()*


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0lates slide past one another ;ithospheric crust neither created nor destroyed - conservative plate

bondar!

(& A) 0acific plate sliding past % American plate 1 forms the San Andreas Fault

c# Transform faults



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+ype of boundary bet"een plates

!onstructive margins $idocean ridges

#estructive margins&ubduction 'ones

!onservative margins +ransform faults


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%e< crust is created at spreading centers at a rate of appro&imately

"-"2cm per year Bld crust is destroyed at the same rate at subduction /ones

Ho" do "e #no" these rates$ (%ate&distance'time)

Plate Movement


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&agnetic ano'aliesin ocean crustloo4 at spreading centers

paleomagnetism e'ery so often (arths magnetic field flips !e'ery 22D-$22D years)

Plate Movement (contd.)

magnetic signal recorded in crust at spreading center as its formed, forms

bands of crust


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$ore evidence of plate moving..


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Hot sots 8slands of a


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(ge of Ocean !rusthttp://www.ngdc.noaa.gov/mgg/geology/geology.html


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!reating ne" ocean crust

Oceanic crust movesa"ay from $O) $idOceanic )idge andcools and subsides


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#riving $echanisms for %late $otions

#estructive margins

&ubduction 'ones

!onstructive margins$idocean ridges


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the 0acific ?ing of Fire 8S 62,222 4m long chain of 'olcanoes caused by Gcon'ergent tectonic platesG coming togetherH


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+ype of boundary bet"een plates

!onstructive margins $id ocean ridges

#estructive margins&ubduction 'ones

!onservative margins +ransform faults


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!onservative margins+ransform faults


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+he &an (ndreas faultin southern !alifornia

!onservative margins+ransform faults


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/ t & t 0


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/ot &pots0


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=antle plumes originate deep


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!oral )eefs


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(ir vie"


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&preading rates


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1 l i l


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1eological%eriods


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Precambrian 4.6 B - 570Ma solidification

Cambrian 514 Ma Gondwana, hard shell anim.

Ordovician 458 Ma separation, coldest

Silurian 425 Ma Laurentia collides with Baltica

Devonian !0 Ma pre-Pangea, equatorial forests

"arl# Carboni$erou% 56 Ma

&a'e Carboni$erou% 06 Ma western Pangea is complete

Permian 255 Ma deserts, reptiles, major ext.

(ria%%ic 27 Ma Life begins to rediersif!,Pangea)ura%%ic 1!5 Ma "inosaurs, Pangea starts to brea#

&a'e )ura%%ic 152 Ma Pangea rifts apart, $tlantic

Cre'aceou% !4 Ma %ew oceans, &ndia

*+( e,'inc'ion 66 Ma end of dinosaurs

"ocene 50.2 Ma&ndia collides with $sia

Miocene 14 Ma Modern loo#

u'ure orld /50 Ma %. $tlantic widens, Med. anish

u'ure /100Ma new subduction

u'ure /250Ma new Pangea

1eological%eriods


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%recambrianbrea2-up of thesupercontinent, )odinia,"hich formed 3344 millionyears ago. +he Late

%recambrian "as an 5Ice/ouse5 6orld, much li2e thepresent-day.

&ource """.scotese.com

!ambrian(nimals "ith hard-shellsappeared in great numbersfor the first time during the

!ambrian. +he continents"ere flooded by shallo"seas. +he supercontinent of1ond"ana had just formedand "as located near the&outh %ole.


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Ordovician#uring the Ordovician ancientoceans separated the barrencontinents of Laurentia,7altica, &iberia and

1ond"ana. +he end of theOrdovician "as one of thecoldest times in Earthhistory. Ice covered much ofthe southern region of1ond"ana.

&ilurianLaurentia collides "ith7altica closing the northenbranch of the Iapetus Ocean

and forming the 5Old )ed&andstone5 continent. !oralreefs epand and land plantsbegin to coloni'e the barrencontinents.


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#evonian7y the #evonian the early%aleo'oic oceans "ereclosing, forming a 5pre-%angea5. 8resh"ater fish

"ere able to migrate fromthe southern hemispherecontinents to 9orth (mericaand Europe. 8orests gre" forthe first time in thee:uatorial regions of (rtic!anada.

Early !arboniferous#uring the Early!arboniferous the %aleo'oicoceans bet"een Euramerica

and 1ond"ana began toclose, forming the(ppalachian and ;ariscanmountains. (n ice cap gre"at the &outh %ole as four-legged vertebrates evolved inthe coal s"amps near theE:uator.


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Late !arboniferous7y the Late !arboniferousthe continents that ma2e upmodern 9orth (merica andEurope had collided "ith the

southern continents of1ond"ana to form the"estern half of %angea. Icecovered much of thesouthern hemisphere andvast coal s"amps formedalong the e:uator.

%ermian;ast deserts covered"estern %angea during the%ermian as reptiles spreadacross the face of the

supercontinent.


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+riassic+he supercontinent of%angea, mostly assembled bythe +riassic, allo"ed landanimals to migrate from the&outh %ole to the 9orth %oles eye mar2s thelocation of impact site of a34 mile "ide comet causedglobal climate changes that

2illed the dinosaurs andmany other forms of life. 7ythe Late !retaceous theoceans had "idened, andIndia approached thesouthern margin of (sia.

Eocene?4 - ?? million years agoIndia began to collide "ith(sia forming the +ibetanplateau and /imalayas

destroying the last of+ethys ocean. (ustralia,"hich "as attached to(ntarctica, began to moverapidly north"ard.

!ollision of continental crust formation of /imalayas


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!ollision of continental crust @ formation of /imalayas


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Whereas oceanic ridges indicate tension, continental

mountains indicate compression forces are sKuee/ing theland together

&edimentary )oc2s &:uee'ed by !ompression


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$ioceneA4 million years ago,(ntarctica "as covered byice and the northerncontinents "ere cooling

rapidly. +he "orld has ta2enon a 5modern5 loo2, butnotice that 8lorida and partsof (sia "ere flooded by thesea. (rabia moved a"ayfrom (frica forming 1ulf of(den and )ed &ea

plate tectonics 3

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