applying plate tectonics

8/14/2019 Applying Plate Tectonics

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2. APPLYIN6 PLATE TECTONICS THEORY:PLATE BOUNDARIE5 AND THETR A55OCIATEDLANDFORM5 AND PHENOMENA(o) Types of Plqie Boundories: Poiterns of disfribution. Driven by underlying convection currents, tectonic plotes ore constontly on lhemove.. There ore three types of plote boundo.ies ( Fi9 15):i) Divergeni or constructive plofe boundoriesii\ Convetgenl ot desfructive ploie boundqriesiii) Tronsforrn or conservotive plote bouhdories

PrarF6ourDifii (Yo1jrc P1!JEB0ur0!fi1

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i) Divergenlboundories. Zones ol tension where 2 liihospheric plqfes move oporl frorn one onofher.. Two types of divergent plqte boondories:> Oceanic vs- Oceanic: Locofed in the middle of woald's rnojor ocecnic bosins,which mork the locotaon of spreodang centres._> Conlinental ys. Confinenlal: Locoted in Eosfern Af.ico.

ii) Convergenl boundories. Zone of compaessiondl forces ond defoamolion whete lwo plotes move towordseoch ofher.. Three types ol convergent plote boundories> Oceanic vs Oceanic: Moinly locoted on the western morqins of the Pdcific

Q99q4 olong the Pocific Rinq of Fire> Cohtinenfal vs Cohtinenlal: Locoted in Northern fndio> Oceanic vs contihenlal Moinly locoted ot the eostern norqins of the PdcificAceon olong the edges of the conlanents North Americo dnd Soalh Ame.aco-

Pocific Ring of Fire:. Also known a5 the Circun Pactfic Rtng of Fire.- The Pacific Ping of Fire is an are.r af frequent eartltquokes and volcanic erupfionsencirc/ing the bastn of the Paciftc Oceon. t he Bing of Fre has 452 volcanoes and i5 home lo aver /52 of the world s dcrive

ond domonl volcanoes.'. f he "Ring of fire" is dn drc tfrefchlng frotn New Zealand. along lhe eostern edge ofAsid ( Jap.In, Philippines, fndonesn) orth dct'oss fhe Aleuftdn Islands of A/aska, andsouth along the codst of Norlh and sout'h Anertca> fn a 4O.aOA kn horseshoe thape, tt' is dssociated wifh a nearly canlinuous series ofoc.anic frenchet, volcanic arcs, and volcanic be/ts and/or plare movenenls

iii) Tronsform boundories. Known os conservolive plote maagin beco(se crusicl aocks ore being neilherdeoled ot deslroyed.. Occur when two ploles move parolle! or neorly porollel to eoch oiher.. Defined by inlense "sheoring" ond foulting forces.. Locoted an colifornio ( ie: Scn Andreos Fault) ond Souihe.n Turkey ( ie: Deod5eo Tronsform syslem)

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b) Distribuiion ond formotion of lqndforms ond phenomenq qt differentplofe boundories.. Lqndforns: Feolures thot moke up the eoalh s surfoceEg: Fold Mountoins, Volconoes. Mid Oceonic Ridges etc etc.. Phenomenor Potterns of oclavatyEg: Volconic octivity, Eorlhquokes. It is ot ihe Dlote boundories thot most of the world's mojor londforms qndvolconic ond eorthquoke aclivity is locoJed.. The type of londforms ond phenomeno found o1 plote boundories will depend on

> The noture of cruslo! moteriol ot the plofe boundcries ( ie: oceonrc orcontinentol)" The lype ol movement ( ie: divergent, conretgenl, l.dnsform). The notul.e of the c.uslal moterrol ond direcfion of movemeni will leod 1odifferent p.ocesses operoting ot drfferent boundories, thereby leoding lo disfinct

types of londforms ond phenomeno ot diffeteal plote bounddries.

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Types of Plote boundories

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(b) I. Londforms ond phenorneno ot Oceonic - O ceanic divergeht bouhdoriesProcesses qnd Londforms:

divetging convection curaents in ihe underlying monlle. This leods to o gqping crock o. rifl in ihe crust. A subnqrine rift vollgy isinitiolly formed ot the rift. Bosoltic mogmo rises up from the oslhenosphe.e ond energes from ihe fissureof fhe submq.ine rift volley.. New oceonic crust is being formed by occreljon (growth by oddition) fhrough rheuprising of bosoltic mogmd. As fhe basaltic lovo cools ond solidjfies, ii dttoches ifself to fhe plote on eitherside af lhe sprecding zone, which is c symmetricol process This leods to theexlension of the seo floor over fime, o process known o: seafloor spreadtrry. A long choin of mountoins ore formed on bolh sides of ihe spredding center/ ftThis is referred to os o mid,oceqnic ridqe.Eg 1: Mid A tlantic Rtdge ( Fonned by rhe separarion af the Euraslon plote ond NorthAnertcan Plole, and lhe Afncan Plate fron the South Anerlc.tn pldte n the soutllFg 2: East Pocrfic Pise ( Forned by sepafafion of Nozca and paciflc p/are). As bosallic mogmo rises up th.ough the fissures, volconoes_ore formed olongsidelhe mid-oceonic ridge5. Eecouse these initiolly formed volconoes dre underv/oter,they ore olso terned os submorihe volcohoes.. Ihese submorine volconoes eventuolly develop into volconic islonds whenemerged above the seo level .Eg 1: Ice/ond ond Azores ( Located on the id At/onti. Rtdge.)Eg Z: Arcension Islands ( Lacoted along ,4lid At/antic pidqe)Eg 3: aster klands ( Lacated in asr Pacific Rtse)

they

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As seofloor spreoding continues, the newly formed volcanoes will groduolly bebnoughf further ond furlher owoy from ihe spreoding cenlet la becofi\e exlinctvolcqnoes. These exlincl volconoes qre terned os seomounts-Over time. the top of the seomounts ol.e eroded ond quyofs ore formed.6uyotsore found furihest from the spreoding cenlre.

Occurrence of PhenotnnolVolconic oclivity: The frocfuring of the crust provides crocks cnd fissureslh.oqgh which mogmo con flow through to reoch the eorths surfac. Thiscontribules to volconic octivily ot ond neor the mid-oceonic ridgesEorthquake octivity: Tensionol forces genetoled couse rocks to rupture understress When the aocks rqpture, seismic woves ofe genetoled, leoding to theshdking of the ground ( ie: eorthquakes) Mosf of the eorthquokes hove shollowfocus( ie: less thon lO km dep) qnd smoll in mognitude (Fig 17)

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Chorocteristics of Londf orms :hlid-oceanic RidgesThe oceonic tidge is on exfensive submqrine mountoin ronge on the floor of cli mojorogeqn bo!,ihs (1f9 1!}

t -lllt+*s.""Figure t8. World Distr,button of Mid oceonac Ridgeshttp:,//rubs usqs q o! /p-rtqllto,i.rojs / I ex t / b(r se bo ll hfml

. fypified by rugged volconic mounioin ronges, consisting of porollel r-idges. Oceonic rtdges are the site of the most octive volconism on eorth. Mony shollow focus eorlhquoke epicenteas ore locoted on ihe nid-oceonic l.idges.. Along the cenlre of the tidge is oflen o centrol submorine rifi volley thoi is up fo48kn1 wide

Le gth/Width/Heaghtl. The lenglh con ronge frorn 64,000km. The Miidth con ronge from 480 To 4BOOkm. They con.ise {.rp lo 3500m obove the ocecn floor.. The highest points of th oceonic ridge above lhe seo level form volconic islcnds.. The height of the mid-oceonic ridge depends on ihe rote ot which mogmo is beingexfruded ond the rote of novement.. Fost spreoding ridges hove genile slopes ond lqck o rift volley (e.9. Pocific Ridge)while slow moving ridges (eg. Mid-Aflonfic Ridge) hgve s'teep slopes ond deep rift

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vottey IDepth: I. As the crusf spreods oway from the morgin it cools, becomes denser ond srnks down ]hence, the oceon becomes deeper os distonce from th morgin increose,]Aset I. The oge of the oceonic crust is progressively older owoy fronr the spreoding centre (lFig 19)

t!@ o 5, illtun !'ei.-@g 5 23 irillior; !1'a".Fs5te t3 :|s,-itri-,i'r..".-6tr::-e Ja 53,nittiort ra.nrrCsffil 5.r 6s rnillio,r -r-earJ65 r:J5 rrtllio !.srlF'gure 19 Age of Oceoni. Crusr in the Atloniac Oceon

Mognetic Reversol:. Alternote b,rnds of normoily ond reversely orTcnged mognelised .ocks, symmetricollyorrcnged cround the Mid Oceonic RidgeTronsform FoulfsiIf is olso nof o confinuous ronqe buf comprises o succession of segmenls which hovebeen shifted oul of line by tronsform foults ot,ented ot right ongles 10 fhe ridges. (Fie20 ,Fis zt\ 0(erq+ts ai all pla(e bour,do/ ties

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Conicol hills or mountoins build up by the eJection of mogmo through a vent ot the eorth'ssurfoceNoture of Volconoes:. Oceonic oceonic davergent boundories ore sites of oclive volconism.. Volcqnoes formed here ore bosolt;c in noture: This meqns thot they ore built up bybotollic mqgmo. Such volccnoes ore ossocioted wath faequent but gentle eruptions.. These volconoes con either be submo.ine volccnoes ( under- woter) or volconicislonds (obove the woler)

fo'rlt along the hid-oceonic.idge

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. When they ote extinct, fhey will become seomounts ond guyots.Seomoqdts ond 6uyots:. Seomounls qre under-woter geologic feotures thot rise steeply from the ocednlloor. They ore defined os hcving on elevotion of more thon 1000 rn.. A guyot is q flat-topped hill rising lrom the oceon floor. They are underwoterfeqtures, ond form when the fop of q seo mount is ploned ocross by mo.ine erosron.

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(b) 2 Londforns ond phenomeno ot Continentol-Contihehfolboundories L(nliMtttql d r i F+i ryPToce5ses cnd Londforms:

divergenJ

Process ontiiv nlql d ni{+illllI\,t/l tql ql t\ lr/ln.e;il yalky l1orsls qnd ) ftrAuslondformsunderlying drvrgrng.onvection (urrents

. As plotes move aport, the coniinentol crust is stretched ond thinned. Thebrittle crust froclures on eoch side of the stressed oreo, ollowing sections todrop down, forming o rifi volleyThis process by which the confinentol crust slowly frociures opo.f over time rsolso referred to os contineniol riftihg.The rift volley profile is mode up of block nountains. Block mountoins oreformed when downlhrown blocks ( ie_grobens) ore flonked by upliffed blocks(ie: horsts)Eatt African Bift l/alley Fornted where tlt. Arabion plate 6 spltttng owar frcn the9,

. Tensionol forces moy leod to the subsidence of crust in certoin secfions of therift valley When woter flows inlo ihese subsided oreos, lokes will forrnE.g: Loke Victorto. Lake toaganyika, Lake Turkdna, Lake Molaw; (East A frican Rifr Vo//ey). Mcgmc rises io ihe sLrrfoce ond emerges olong zones of weokness creoted bythe pr..rlling dp(rrt of the c.ust. This contriblles 10 ihe formotion of volcdnoes

olong the rift volleyEg l4t KrnanJoro, l|t Kenya, Ertd A/e. Nyiragongo ( Fast African Rift Valley)O ccur r ence a f Ph enomeno.

Volcdnic octivily: The frqcfuring of the crust provrdes crocks ond fi55uresthrouqh which mogmo con flow through to .eoch the eo.fh's sitrfoce- Thiscontrjbufes 10 volconic activity in fhe rifl volley.. Eorlhquoke octivity: Tensionol fotces genetaled couse Tocks io .l]pture undersfress. When the rocks rupture, seismic wove5 o(e genetoted, leoding to the

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shoking of the ground ie: eorlhquokes). Similor to eorthquokes ot oceonrcoceonic divergent boundory, most of the eorihquokes here hove shollow focus{ ie:less thon 10 km deep) ohd smail in rnogn,tude.

Fig 22 Divergenl continentol-conlinentol crusrol Plote bounda.y

Whof occurs 4LTER cohtinentol .ifttng?Continentol rifting morks the beginning of the formotion of o new oceonbosrn os fhe seo invcdes the oreo thot hos been torn oparf (Figu.e lB)

Eg: Ihe At/antic Ocedn '!os forned as the continent of Laurora wds spltt into two. oprocess that nay be repeoting rtse/f h East Afn.a (Refer ta Fg on next poge on East

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Figure 23 Ihe birfh of o nw oceon boein f.om o rifr v9!9v I

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BBC News: Ihursday B December 2005Trtle of adicle Geoloqists witness 'ocean birth'. Screntists say they have witnessed the possible birth of a fuiure ocean basrngrowing in the north eastern Ethiopia.. I he team watched an Bm rift develop in the ground in JUst three weeks in the Afardesert region in September.. lt is one small step rn a long-term split that is tearing the east of Ethiopja from therest of Africa and should eventually create a huge sea. ll began wath a large eafthquake and continued wath moderate tremors.. A week later, there was volcanic eruption and cracks appeared in the ground,some of wh,ch were more than a meke wide. Using satellite technrques they could see ground deformation, and about a monthafter the sequence a 60km long lissuae had opened up, and it opened up aboutBm rn its centralpa.l


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Chol"octerisf ics of Londf orms:Riff Valleys:A volley ihot hos developed olong a rift, especiolly one bounded by normol foulls.. Riff volleys ore usuolly norrow ond

long ond hove o relotively flot floor.. The sides of the rift volleystypicolly consist of multiple foultsco.ps ( Fig 24). Oflen occornponied by thepresence of lokes ond volccnoes. Mounloin mosses colled blockmountoihs or olso produced, rnregions where normol foultingoccurs 0n o mossive scale. Tensioncl stresses result in sholloweorthquakes olong the rift v6lley

Cose Sfudy: Eost Africon Rift Volley-> Formed by sepcrofion of Africanplole from Arob,on plale ( Frq /5)> In Africa, fhe rifi volley xtendsfor 4oo0krn from Mozombique to theRed Seo,) I n ploces. rls -id,s ore over o00m inheight while its width vories between1O ond 50km.) Where the lond hos been pulledoporl sufficiently, it hos been invodedby fhe sec. This represents the firststoge in the spliffinq oport of thecontinent to form o neu/ oceon bosin.

Fig 24 : i\,tultiple Fdult scorps olong the EostAfricon Rift Volley

F,9 25: Eosr Africon Rift Volley

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Block tllountarnsA block nounfantf9!!l:9',fr.(Horsf and Graben)(horsf) is an up/ifted block befween two nornal faults, which has steep

Block mountoins cre formed whenblocks ore disploced relolive toeoch olher due io the presence offoulfs.A fqq[ in the brittle rocks of theeorlh5 crust occuTs when rock


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(b) 3- Londfo.ns ond phenoheno otProcesses qnd Londforms:

Oceonic-Oceo ic con\teageht boundories

suhdwliqL' 0u,rnic tr(.A6h'foico nic i5lqndP\"LAA Wn q ' l/cicqnic , Lqrthqrtalu. Two plotes consisting of oceonic caust of the edges rnove opaat due lounderlying converging convection curl ents.

,'ub fi q r;M t/ ol c(l t1,J e sqr(

. When these two plotes converge. subduclion occurs, where the older, denserocecnic crust will sank beneofh the olhet crust. The leading edge of thedescending plole (ie the oceanic plote) is cooler thon the surroundingoslhenosphere ond will sink further down

. A deep deptession morks the locqtion wheae the oceonic crust subducls benoththe other. This deep depression is known os o trench.Eg 1: l4ariana Trench G the wo ds deepest trench with a depth exceeding iiknl(Convergence af the Paaftc ond the Phthpynes Pldte The denser Podfi. Plote subducrsbeneoth the Phtlippines Pldte)Eg 2: Jdpan rrench (Pociftc plate subducts beneath Euroridn pldte)Eg 3: Aleuhans rtench ( Pa.ific plate subducts beneath North Anericdn P/ate)Eg4 Jav.t nench ( Indo-Austra/ian pldte subducts beneath Eurdsian pldte). Por"tiol nelting of the subducled oceonic c.ust occurs ct o depth of lOO km inthe oslhenosphere due 10 the high temperotures ot depth. Andesilic or

rhyolitic moqmo is produced.. Being lighter thon the surrounding monlle noleriol. the ondesific mdgmo rrsesverficolly ond emerges from the oceon floor to forn o choin of dndesificvolconoes on ihe overriding plote. These choin of volconoes will initiolly beunderwoler os subrnorine volconqes- This choin of volconoes will eventuolly riseobove the woler to form q choin of volconoes porollel to the laench , to form ovolconic islond orc.E9 1: fhe Philippind (Phi/ippnes plate subducts beneath Eurasian p/ate)Eg 2: Japan ( Pacific p/ate subducts beneotb Eurosion plate)Eg 3: Aleutian Itlandt ( Pocific plate subducts beneath North Anerican Plate)Eg 4. tndonesio ( Indo Austrahan p/afe subductr beneoth Eurasian plate)

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O ccurrence of ghenoll'g.noVolconic octivity: Portiol melting of subdr.tcted crust produces ondesitic orrhyolilic mqgrno thot reoches lhe earth's surfoce vio crocks ond fissures. Thiscontribules lo volconic octivity olong oceonic lrenches.Eorthquoke ocliviiy: Most of the eorfhquokes ote genetoted olong thesubduclion zone. The intense qmount of stress built up ond releosed in thrs zone

leods to eorthgudkes. This lineor zone of eorthquokes rs olso known os fheBenioff zone. Unlike divergent boundoraes. focus of eorlhquokes vories fromshqllow to dee\ eorthquake foci tends to 6e deepe. further owoy from thelrench-

28. Oceonic-oceonic convergent ptote boundory


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Oceanic Trench: (oceqnic Vs oceonic)Deep, norrow ond steep sided V-shoped depressions locoted ot the bose of the deepoceon floor{Fiq 29\

Chorocferistics of Londf ormsi

Figurc 29. Wotld Distributionhere areDist.ibution/Locof aoh :. Morks fhe position where the oceoniccrust subducts into the monfie. The be5T developed oceonic lrenchesore found in the western Pocific,where lhe Pacilic Plate meets theAuslralion ond Eurosion PlolesF,g : A/eutidn I'rench. Marnnos rrench.rongo rrench. Japdn hench. KurteKonchalka Trench. Outside the Pccific ()cean, they orefound in fndonesio (Javo Trench),Corribeon ond the South SondwichfslondsFeotures:. Asymmetricol in profile os theseowoad sid iends to be smootherond hcve o gently curved siope while

of oceonic Trenches ( Note thqt nof oll trenches feoru.edfoined by oceonac-oceonic conve.gence)

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'ffiwdlFrgu.e 30: Prof'le of the ,,lorronos lrench. ]Nor,ce rhe osyrnmerflcol prot'le of the itrenchhI Ip:/ l4!!1 !!r st!.s!!!!qlL s!9r!lFo,,hnni

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. Oceonic lrenches ore sedinent tropsond they moy be shoped to sonedegree 6y lhe deposltsDepth/Width:. They con l>e os deep os llkrn, over

3OOOkm long ond 5 km wide ot the. Found oboul 1OO to 200km ou/oy

faom the islond crcs os the disloncedepends on the ongle of subducfion

Volcanic Island Arcs; (oceonic-oceanic)Arcuate(ie: curved) choins of volconic islonds thol ore convex lowoads the open ocean.Form porollel to oceonic trenches-fnpottaht potht to nofe: AII island arcs are made up of volcanic islands bul hot ally9k44!94!9!4J?4-lL9t9 d above mid-oceanic ridoes) form isla4d arcs] , i ' .:;r:, :-.11," ', ll;.,,.1.. , .:, , ',,',. l,,i;i l- ' l;l :' ... ,r,'rl .ll) i. 1' r I . " ;'.,.':'..ji'": ''. '- - -';",''. -t t'*.-' 1,. ,^]. t,, t "::-, i,..'.,r;..,, ;l? ,,. , , rl. . ' 'ri," ,o,,,, '.._ '.l,i: ';,.. ", .;; ';i :. ' ,; -i"' ::r;j::r". *.1:: l:.tl; ir '";.*, ;+' "il-t'i: ::rtj '. l'''r:i,:: l] I ) ',t g -H'' rl. - i;,' " '*; ip;.-rI,;-"i '''rr.i," ".. ]lI,t *.- !::" l| "" ,,,' "rJl ,_ |] a. ,1 r: ,r o0 L c0, .. ,. ,: 90 . /. t^ !! n :. .a,,:\i "-*"^'".::::: :"-r: Lanqtude ]figrl.e 31. Wo.ld dislribution of Islcnd Arcs ond Oceonic Trenches4l


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Disf rib!tion/Locof ion :. Locoted porollel io oceonic irenches.. Most ore locoted on the westernmorgins of the Pocific Oceon olongthe Pccific Ring of FireE9: JaPan. rhe Phi/ppines, Aleutnn rsldnds,. The olher 2 oteas ore lhe West

fndies ond fhe Scofio Arc at theAtlontic Oceon (Fig 32)

Chorocterisfics:. Andesitic or rhyolitic in nature: Thismeons thoi they ore built !p byqndesitic or .hyolitic mogmo. Andesiticor.hyolitic rnogmo is formed by theporfiol melting of subdqcted crusf.

Because of thei. different mineralcomposilion, fhey are distinctlydif ferenl fron the mqny ocednicrslond groups ond seo mountoins oflhe fitd oceonic ridge.Regions of cleep loci ond shollow focieorthquokes The shollow f ocieorthquakes ore concentroted underlhe oceon c trench u/hile lhe deeperfoci ecclhquokes oae locotedp.og.essively further behind thevolconic islcnds. (Fi9 33)

Figure 32 Mop of Wsl Indies Notice fhoraslond arc is CURVED.

Earthquake FocusFi9 33: Benioff Zone. Notice thotloci is deeper awoy from fhe

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. The distonce between ihe islond orcand lhe oceonic trnch depends onthe a gle of subduction ot theBenioff Zone. If the o gle as steep.the islond orc wil! be locoted closerto the oceonic trench ond vice verso(Fis 3a)

. Morine sediments in the oceonicIrenches ate also deformed ondmetomorphosed by the compressionolforces of lhe two converging plotes.This leod 10 the formotion of youngfold mountorns on ihe volconrcislondsEs: Japanese Ahs

Fig 34: Distance beflven oconic trench ondislond orc. Notice thot disfonce of orc fromtrench is furlher when ongie of subduction isqentler.fttl hlq,td wrislqltds lsrn 5 o,t- Actfu vp s( volLqnic hlqftd| h,af no-f t [l r/hlcqa^---.---slanrl qrts - 0( vs 0( zonveryenpfr

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(b) 4, Lcndforns ond phenonenc oi Oceonic-Continentol cohvergehi boundqriesProcesses ond Londforms:

lonaforms t0noctqn)c F f e0olr, , (rll 'ft)ou,tlqios. Vo{cqnic 4leplaAJnxlq'V0l*41" ac1,.til.1 t L-, rhq,tq,..e acivitv. When two plotes waih continentol ciusl ond oceonrc crust ot iheir edges collide,the leodi^g edge of lhe denser oceonic crusf subducts beneath lhe lighferconiinentol plote ond dives into the montle. The leoding edge ol the descendingplole (i.e. the oceonic plote) is cooler thqn the sur.ounding osihenosphere ondwill sink fu.the. down

. A deep depression morks the locolion where the oceonic crusl subducfs beneoththe continentol caLtst This deep dep.esslon is known os o trench.Eg: Peru-Chile Trench rs located offshore fron the weslern coast of Sout'hAnerica. ft /5 forned fron lhe convergence of the Nazca Plate dnd the SouthAmeflcan Plate. The denser Nazca Plate subducls beneath lhe fhinker and buovanfSouth American Plafe

. As the descending plote sinks benedth the over-riding plote, low denrity moainesediments ore scroped oft the surfoce of the descending/subdlcted plote byihe overriding plote

. These seditnents qccumulote ot the contanentol slope ond shelf o^d they oresubsequenlly deformed by folding ond fouliang to form ygg4q jq!9l49gq1q!45 ino process known os orogenesisEq. Andes lUounlans. It t5 locoled pat-allel ta the Peru chile trench and was fo ned when

Nazca plate subducted beneolh the South Aneflcon p/ale. Portiol melting of the subdlcted oceonic crust occurs ot c depth of 1OO km inthe osfhenosphere 1o form ondesilic or rhyolilic mogma.. Being lighter thon the su.roundang montle moienol, some of lhe andesitic orrhyolific mogmo forces i1s woy upword through crocks ond fissures to thesur'foce. The lovo cools cnd solidifies to forn ondesific or rhyoliiic volconoes on

the continenf5-

14


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These chain of volccnoes on ihe continentol crust is known os o volconic orcEg 1: Paficultn, Nevado de/ Butz. Pbpocatepetl forhed dlong the Andes ,iLlountonsEg 2: Cascode Bange ( cansislng of volconoes such as i,tf 5t Helens, Three sisters, t,1tHood, Mt Adans et. erc etc .) forned uhen Juan De Fuco plafe subducted beneath |,tor.rhOccurrence of Dhenomenoi. Volcqnic octivity: Po.tioi rnelting of subducled crust produces ondesiiic orrhyolitic mogmo lhot.ecches the eorths surfqce vic crocks ond fissores Thisconiributes fo volc(rnic octivity olong oceqnic lrenches.. Eorthquoke octivify: Most of the eorthquokes cre generqted olong theslbduciion zone The infense omouni of stress buiit up ond releosed in this zoneleods to eorthquokes This lineor zone of eqrthquokes is olso known os theBenioff zone Unlike divergent boondories, focus of eorthqr:okes vories fromshollow fo deep: eorthquoke foci fends to be dzeper further owoy from thetrench

Cru*li 6en!cLiihqsFh'ere

Ocaafi,lc.coft lir!erilsl corl.v6rgie!iceFigure 35 Oceanic continenlol convergent plcte boundary

USGS

li


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(!c!)c-- u)OJOO

I L:.d;*** * *

alO.gc(go0o

,.' ^y,.7," ^S'.'l :1.^\a\.-._,/,.1.

N0)0)-ao_aoC0)ca

(!c',ooE{JEc)o

ootnoodoz:foc0uJFJo*Fzu(,tlrl>lzlol(Jl

c)GIoCo)Eoo-&

&

46


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Chorqcterisiics of Londf orms:Oceonic Trenches (oceonic-continentql)Deep. narrow and iteep sided V-shaped depressions located at fhe base of thedeep ocean floor.

fotured here ore th resslt of oceonic continental convergence)

Distribution/Locotion :. At oceonic-continentol convergent plote boundories, they develope


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Curved belf of nounfain system whrch consists of dctive volcanoes of andestlic orrhyolilic conpoiition

found of the edge of the continents along convergent plo.efrenches thot mork the line of descent of the oceonic

rhe to/-oaoe< ot the aoscadc Bangc and the Ande, dtA shifting regaon\on ranp flet. .n ! t \','n{|,6\l'Fn+[h6|lolt'k6'

Making the ground shake:.?jl5."i::];ill"^*"-idl!tonllsr(.lA@'(a.(gl!n].IaleTsoialeleslqol'|,'.dgll.:'

".,"..Pryil_",,",,,"or,i,i'o,,

18


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I irrku( re pl.ur nra.9 n:_: lduo afldtoulh Ahe..an

jrrf!lar.\ ra,t ll!.i.J) ,rfrna rr Anfus^.d.r s.orrii.rl brlti?'in.rrr!. .r r.ll rrrno lHi{r.rne3.r

lo..ahndr irdnr.nra4

Figure 38 rhe coAvergence of Nqzco ond South American PloteSource: Dovid Wou{lh, 20OOPlo1e subsequently produces volconoes such os Pqrictltin, Nevodo del Ruiz, ]Popocdfepetl dlong the Andes. ( Fiq 38)

IFeorures. vtry vieroqs({h}cL ). Aades,ltc or rhyolrtrr rn notur'e I hrs meo4s lho' rhey ore burlr up or fed byondesitic or rhyolitic mogno. Andesiiic or rhyolitic mogmo is formed by the]portidl meliing of subducied c.ust- I( q,4t d hy itp jas. I. Regron' o{ oeep focr ond shollow io.i eorlhquokps lhe shollow lorr eorrhquolas Iore concentaoted under the oceanic lrench while the deeper foci eorlhglokeso.e locdted p.ogressively furfher behind the volcahic rlrc

. The dislonce between the volconic orc ond the oceonic lrench depends on the iongle of subduction ot the Beniolf Zone If the ongle is sleep, the islond orc Iwill be locofed closer fo the oceonic trench ond vice-verscl

The Andes : In South Amer,co, the subduclion ond portial neltinq of ihe Nozco


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young Fold llouhfait s: (oceohic-confinentol)High rugged mountains (alpine chains) which fom long conftnuous chatnt fhaf canextend thousands of kilonete6 in length..Locotion./Distribulioh :. Along the edges of continents.Eg: And*( l4/estern edge of Soufh Aherica)Feotures: 0t0*1,M5ls. Foldrng! foulting ond volconic octivity contrib!te fo the mountoin-bilildingprocess ot such boundoaies_*Refer to the notes on chat"acterisfks of youhg fold mountains undercontinental-continehfal convergent plote boundaries

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(b) 5- Lcndforrns cnd phenonenaboundcriesProcesses ond Londforms:

ot Continentol Cohtinentol convergenl

B"':* Iqe]Londforms l,Fal ;


33/45

,.- -:+ ";\+.' *b.cS$F

conr,nenrar crusr ( llrh.fbua't,t(\1( 4lt,1t

s

C o li t I n r! 11 i 6 I' c () r1 t i n e fi ts I c $ n v G r g d nc 6 LI S GSFi9 39: Continentol Conlinentsl convergent boundory

CONVERGENT PLAIE BOUNDARY ( CC vs Cc)

)l


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Chorocleristics of Londf ormslFold /Uounfdias:A range of nounlains resulting from the bending and folding of crusfalndferial. Height vories depending on the o9e_. Geologicolly younger ( ie: formed less thon 50 millioh yeors ogo). fold mountoins

hove higher elevolion ( ie: which exceeds 3OOOn in height obo ve sea level).. This i5 because tl\ete is o shorter lime for the forces of eroston ond lveoihering

underlying rock on foult surfoces of low inclinolion These are overlhl.ust fo{rlts. The entire defor'med rock rnoss produced by srch conpressiondl mountdin mokingis colled on orogen, ond the evenf ihot event thot produced it is known 05 orogeny.

to work os compored to the older fold mountoins.

. Hrghly rrregulor telief due lo vprircol rncrsron ond prosion by rrvers ond movrng rLe{ re. slo"rorron) 1lcr.o tle4: tngt|fllff 61 i4 1lg*l:. Composed of thick loyers of sedimentory rock3.. Geologically ocfive qs uplifting confinues 10 occur ond shollow foci ecrthquokesore evidence of rhe geotogic acrivify Qeoloqjc"lly qclilO, -_c0npU SSiOttFolding ond Foulting:. Fold mountoins fypicolly consist of intensely deformed strotq ihqt o.e tightlycompressed into wovelike structures, colled folds (Fi1 aO Fiq 41,Fig 4?.). Along,"./ith the foldrng is o form of foulfing in which slices of rocks move under the

Nuppe l5llus o{ (a.kslndiuicluql roLL 5licB q(e c,tlkd +hvtl rlrulE

)i


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t, - .,1.: -,:!:,1 ::- : n.t-,: TUecumb"'ntI ,FecLrfibenl/ ron

{)verthrustjne

Thaustshel

Figure 40: Typs of folds Fioure 41: Cross-section of d fold

Figure 42 Typs of Folds

t


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Cqse Himoloyds (Collision of Eurosion with Indo-Austrolion plotes)

A ndmow oceon bosrn,Trhys Seq, initiollysepdrdted Indro from Asid

.r0 50 ur Eventudlly. lhis oceonbasrn wds closed bysubdu.faon: fhenofihetn edge of theInd,on plote (oceonicc.!st) wos subductedLrnl,l ihe Indion s(rbontinent(contrneniolc.urt) lodged dgdinsi

Lri], (,,1,fir, ,rr

The Himoloyos ore still rising todoy,northwordS 0i q

l\' *; "fi r'-. roo ,h'.! o.d roo'f m ,oa r dpn.,iy ro bp

' $,$F


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Cdse Study: Alps ond Atlos. The Africon plote collided with the Eurosion plofe fo form the Alps qnd the Atlqs/\lountdins. In the Europeon Alps, ihdividqol rock slices colled thrust sheets ( noppes: iqblecloth in French) ore corried nony tens of kilometers over the underlying rock.They moy be thrusl over the oihr fo form o greot pile.. The Alps ore still octively being uplifted by compressionol forces. .

56


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(c) 6.Londforms ond Phehonehq oi Tronsforn (Consrvotive) boundoriesProcess

f\o di5lirrct lq(dforml[Vl VolucrltlicAQrHoilfl[e5ldLo11 aclitlity

Known 05 conservotive plotedestroyedOccur when two plotes moveThe sheoring motion ocrossfoult.

norgin becouse crustdl rocks ore being neither creoted or

porollel or neorly porollel to eoch oiher.foult produces ridqes ond trouqhs thot ruh porollel to the

. Shollow eorthquokes do toke ploce i.e. son Froncisco Eorthquoke of 1906 but noincidence of vulconiciiy becduse lhere is no subductioh of ploles or upwelling of rnogrno.Eg #1: The san Andreas Faulf is a lransfo n plote baundary seporoting lhe Pacific Plale to thewdt of if fron the North Anerican Plate tn the eastEg #2: l4iddle Easf, where the Arabian Plate is sliding posl northwards the African Plate along ahuge troneform fau/t This has crealed sone 9!llL9!l!!-!dgtdles! such as the Dead 5ea, 6ulf ofAqabo, Sea of 6a/ilee and Lake Baikol

Fi9; Conservotive Plole Boundoryhltpi//www.stvincent.oc.uk/Resources / e ort h S ci / 7 ect ani cs / images/ conserr.eif

Conserualive pleie margin aa,thquate rui @ ucra..nr .onr,nu.rut prnr.'


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Fg: san Andreos Foulf. sepordtingthe Pdcific Plofe from th NorthAmericdn PlofeSource:hlI pt / / www.scec.or o / walloceq eek/ onlinelsof.httnl

Fig: Tronsforn plotethe Middle East boundory in

pln!?bqr hdFwrsrqn h!t.Thi5 hxoplild upr r! b.,ol


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Eu.asian Plate \ -- ) '\t./''Rjng of Fite '

(c) Distribution ond forrnotion of Londforms ond phenomeno BEYOND plcteboundariesActive Volcanoes, Plale Tectonics, and the "Ring of Fire'

Fig 4r D,\lflbur'on of vor. dnoes Wo.ldhrde. Not all londforms ond phenorneno occur olong plole bolindories.. 5pecificolly, not oll volconic ocfivity con be explcined by plote hovement.. In foct, 57" o{ lhe worlds volcdnrc ociiviiies do nof occur neor ploteboundories. In steod, they occur.in the rniddle of plotes. This con be qttrrbufed to the occurrence of hof spofsFormotaon of "hot spof" volconic dctivity

Spreading Ptum-Hot Spot

Fig 44: Hol spots ond mdntle plumes Fig 45: Move'r.e l of plote ovr d hot spotal


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. Hot spof tef ets to a locotion on the earth's surfoce lhoi is subJecled tovolconic octivify.

. The ideo of hol spots wqs first estoblished in 1963 by J Tuzo Wilson, theConodiqn geophysicisi !!ho discovered tronsform faults, from ob5ervolions ofIhe geology of these islonds.

. This volconic octivity is the resqlf of nontle pl']nes. (Fig 44)

. l^ontle plunes ore isoloted. lonq. slender columns of mcgmo ihoi r,se slowlytowords the eo.th's surface.

. As these nontle plumes reoch the eorlh's surfqce. the heal coused by ihemagno will "burn" a hole through ihe continentol crust , thereby providing onopporiqnity for mognq to reoch the ecrth's surfoce.> Daometers of montle plumesr lOO 240 knr Rising rote of montle plumes : the magna rises at rofes of 2 m peryedr,> Depths; Originafe at depths of mote than 7OO kn tn the nantle oreven at fhe core-nantle boundaty

. This contributes to isolofed volconic ocfivitv -one or c feu/ volconoes rnJheoverlyinq lilhospherewo,t+ ,h4rge porit. Dn. The lo.oions of monfle plumes oae stofionory ond ore independent of plote

motion-. As o lithospheric plofe moves over the (oppo.ently) stqtionory montle plume. thevolcqnoes die. ond the plumes forms o new centre of volconic ociivity.. Thus, monlle plumes leove troils of volconoes in fhe overlyinq plo1e. (Fig 45). By cqlculoting the oge of Ihese volconoes, we con tell both speed ond directionof plofe movemenl with respect to the montle plumes.. Anolysis showed thot the bosqlt erupted from hoi spots rs drfferent from thebosolt thot forms from the upper nontle ot spreoding centres-. This as believed lo 6e dne to the lovos being derived from well below theosthenosphere. Mqy be temporory feaiures - typicol life spons: 1OO million yeors

;8


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Distribltioh of Hot spots:

EXPLAS.IATIONOivd.qenr platc !avndorlci-Wli.e dew c.ust ir e6fte.itdit t114 gtat{i pqll sw.y tromCoovrgnt plst ho{nda.is.-Where c.ui i3.nnri,flrrd;n rh.t.rtrr'r inrcri4. x$ ona pldle

.'--. T.aftllorm pl.!s tlounda.is-Wt! 6.c rrq{ b .cithe. t}rodqc.daor d6stroy.d ft Fl6166 6lidehorl!.dt6lly prJt o.n otheti:.\ijlj Pr",. b"u"dd.v zones Broad"**' hcltr in whilh d.lo.mrlion i.ditf!s6 d.! bouodr.ier rr norwnll dollded

e Slec ted proftlie(r lrotsAo!tDistribution of Hot spots.

d;vdt !ndE. a.o!h6r.Figlre 46:

. While hot spots con occur in fhe middle of plotes, they con olso occur nedr orot plole boundqries.

. Most of the world's oclive hot spots ore locoted in the middle ( ond oi theedges) of Ihe Pc.cific ond Afric(Jn plale.

. Exqmples of volconic dcfivities ossocioled with hot spots include Howoiionrslonds ond yellowstone Nqlronol Pork

59


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Cqse Study: The Howoiion IslqndsHdone pknp rlporl r151Jr rourUrF, or mlgna noT r1a, oi flr pr lh oLtl tlo .,Lr d.he r.n*" O'n,, O, " ,., 'n".icaisv.l6iir "t.rilr" rr(h & lia llapaiian htlidr

F,9 47: Formoiion of Howoaadn Islqnds

locoTed qf o fixed spotConveclive pllines rise from the lower mantle ond lhe magmo is exl.uded ontothe oceanic plote.As the Pocific pldte move ocross fhis hoi spol, mogmo extTusion i5 continued dtone site while the previously extruded volconoes ore coTried awoy on the movrngplate (Fig 47)Howoii is the youngest islond in the group. If is slill octive dnd lies ot thesouthwestern end of the ch(rinThe islonds become progressively older to the norfh wesl ond oll ore voiconicbuf extinciThe oldest volconic rocks on Kouoi, the norihwesfern most inhobited Howorronislond, ore oboqt 5-5 rnillaon yeors old ond are deeply eroded. By comporison, onthe "Big Islond" of Hdv/oii - southeosternmost in fhe choin ond presamobly strll

t10[ir,l c41tfi (0i!

61)


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positioned over the hotspot the oldesf exposed rocks ore less thon O 7 millionyeors old ond new volcanic rock is continuolly beinq formed (Fig 48)

I

l tig 4a: Age of Hoqraiion islonds

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"A" Level Quesfion: Plofe boundories ond their ossocictedlondforms and phenomena ITo whot extenf con the plale tecfonics theory exploin thedistribufion ond formction of lorge scale londforms?

RephroseHow con we use the Plote tectonics theory to exploin the fornotion ond location ollorge scole londforms2 Con Plote tectonics theory be used to exploin the formclionond locstion of all large scole landforms?

**'*T*DIA6RAM5 ARE NECES5ARY TO TLLUSTRATE YOUR POINTS

Question hos two porfs which condidoles mu5t oddress:

1) How can we use p/ate tecfonics theory to explain fhe fomafion and dBtrtbutionof landiarms.>) Condidotes need fo provrde o detiniiion of pl.rte rectonics theo.y and o bref overwevt ofifskeyfedtu.es As expldined byPioie tecronic theory. cdn.l,dotes n]uji stdte thot most ofihe molor landforms orc lor:ote,l olong pidte bounddrrcj Feotu.es of rhe pldte recronrcarheory ( section 10)t Condidotes nust select ol least 3londforms ond describe ih disrribuiion of these{ondforms olong the plote boundo.res: Disrribufion of ptste boqndoraes (Section Zo)> candtdotes will ned to expld,n rh fornrarron of rhese fyper of landforms or ihedilterenl plote boundcfles: Distriburjon ond formotion of landfo.ms ond phenomno ordiffereht plote bosndories (seclion 2b)2) What is lhe limifaflon of plate tecfontcs theory in explainng the fornation anddtst.ibu trcn of landforns2) Candidotes must exploin thot plofe tectqnics rhory connor expld,n ihe forlnorjon of olllandforms: Distribution ond fo.motion of Landforms ond phenoheno BEyONO ptdteboqndories ( Section 2c)

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applying plate tectonics

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