444 TH! BODY OF THE EARTH: INTIRNAI, IROCESSES

Iigure 19-3A tdple jLrnction- Plates 1, 2, and 3 meet atthe intefseclion of a sPreading zone, a subduction zone, and a transform fault. Thearrows de!ict relative motion beiween ad-

edge of an earlier plate margin, isochrons that areof the same ts€e but on opposiie sides of an oceanr dgp , dn he brought oge l- . r lo show l 'P postiorc of the plates and the configuration of theconiinents as they were in that earlier iime Bythis means we can reconstruct, for example, theopening of ihe Atlantic Ocean, as shown in Figure19-7.*

3. The point ai which three plates meet iscalled a triple junctior. Figure 19-8 shows an example oI a point at which a spreading zone, a sub-duciion zone. and a transform fault meet. If therelaiive motion beiween two pairs of plates isk n o w n . w c L d n , o t r e f o r . h . h r d b ) - ' ' n g d " i mple equation (see Box 1S-1).

'The Gr€at Pyramjd ol E8t'pt is ained slightly east ol tn€nof th .D id theanc ien tEe}? t ianashononersmakeamis lake inorienling Lhe pyranid 40 centr.i.s ago? Probablyrot. Ove.thispoiod of rin€ Aftica drilled enough ro rotate the pyrdnid ouiof alignnenl with true !ort!.

r :Ancient Seograph c po e

M;gneti. and deep sea drilljng data a.e used to cha{ ihe northNard drifl of the continenlsand the opening ol the Ailanlic Ocean over the past 200 million y€arc' The Central Atlanlir'.the Cadbbean, and the GuH of Mexico began to form about 200 million years a8o in Tri_d s s . , : m " , $ h F n A l r ' c a a n d s o r t h q n F c d d r i n " d . h r I o m \ o r h A m F r ' , . a . h e S o u l ha t ' " i c o p e n e d d b o , r I 5 0 n r ' l ' o n v c a s d J o d i l - h F c F p t r a l o r o l s o L ' l q m p r '

" r o mAfrjca. As the contin€nts drifted apart, they also miSrated in a north€rlv direction to thenpresent positions. Note that the equator passed through the soulhern parts ol the-UniiedSlates and Europe in Triassi. time. IFron J. D. Phillips and D Forsl,th, Bull Geol socAmerico, v. 83, p. 157S, 1972.1

i[,]iBox 19-1 SOLVINC IOR THE RELATIVE MOTIONS O[ PLATES

Velocity is a vector quantity, one thaL has both dteciion and nragnitude. A simpl€ exrnpLe of how vectoFare added is shown in ihe figure above. If a man walkssingle blocks north on Avenue A, east on Firsl Street,soulh on Alenue B. hc cnds up al d place he couldhavcrcached dire.ily by walking one blo.k east on Se.ondSireet. In vector addition this dhect route is equal tolhe sum of the segmenis ihat makc up the long roLtle.

In the figure ai lhe right (palt a), let the velocilies ofthe three platcs meeting at a lriple junction be Vr, Vr,V.. The velocit-! ol plate 2 relative to plate 1 is Vz VriV, V3 and V3 - Vr are Lhe oihcr possible relaiiveplate velocities. lL is clear that the sum of the relativevelocities ol lhe platcs, takeD in ofder around the hiplejunction, musi be zero, since

( v " -v , ) + (v3-v , ) + (v ' - vs l =o

' V , v ,

1\- Zr,-l '

(v, - v,) = (v3 v') + (v' - v.)

or, rearranging this.

(v: - vj)= (vj v, l +(v,-vJ.This cnables us to solve for Vj V1, thc direction andamount of relative motion aooss the subduotlon zonebecause the directions of the vcctom V, V3 andV3 - Vr are pa.allel to ihe transfom and perpendicul " r h F . p - p d J " g d \ , . p . D r ' \ - l J . r 1 , l t h " t r d o r -

ludes of the relativc motions can be obtained tuon themagnetio stdpes. Part b ol the figure below shows thesoluiion for Vj Vr in terns ol leclor addition.

The poinl where ihe Pacific, Cocos, and Nazcaplates meet (see inside back cover) is an actualtriple junction. Three spreading zones meet ai thisu n ' n n . a . r h o w n : n h p F n a r g F d v i p w i n F g , r e

19 9. The unknown motion, found by \.ector addition, was that between the Nazca and Pacificplates, the motions between th€ Pacific-Cocosand Cocos-Nazca plates having been worked outfrom transform faults and magn€tic-anomalysiripes. Thc arrows show the resdtant platemovements. Note also how th€ isochrons benci tobecome parallel to the spreading centers, wherethe-v originated, and how they are offsel by thetransform faults. The spacing of the isochrons re-flects the spreading rates, which are larsest for thePacific-Nazca plates and least for the CocosNazca plates.

Up to ihis point we have considered plates slid-ing on a plane. Although much can bc learnedabout plate moiions by making this simplication.platcs actually move on the Earth's spherical sul

CLOBAT PLATE TECTONIC$ THE UMFr1NC MODEI,

Triple junction forned by the interse.tion of the Pacific,Nazca, and Cocos plates, thfee spfeadine zones in the southeasi Paclfrc Ocean. The schemaiic isochrons parallel th€ ridge. , e q f r o n s h c h r b ' t m i g , d l F { t d s F a l o o r d g p q o n dspreads. The spacine beiween isochrons is a meas!.e of thespreadilg velocities. lAfter R. N. Hey, K. S. Defieyes, G. L.lohnson, and A. I-owrie, Thc Galapasos Triple lunction,"Noiure, \'. 237, p. 20, 1972.1

449

Box 1e-2 PLATE MOTIONS ON A SPHERICAI EARTH

2- spread nc zon€

- Translom lau I4 Subdu. ton

ceom€try allows us to describe th€ sepafaiion of iu,oplates on a sphere-for example, plate A and plate B inihe figue-as a rotation oI ts with respect to A aboutsome pole of rotation, called a pole ol spreading. Noteon ihe diagram of plaies (inside back cover) that alongmid-ocean ridges where plates separate, the axis oIspreading is not continuoN bui is offset by lransformfaulis, approxlmately at right anSles to th€ axis. Whythis occurs is not fully understood. but it appeam to beeasier for plates to break apa|t lhjs waywith ihe platestypically rliding by each other at the transform fault,rather thanpulling apdt or overlapping there. Becauseof this geometry, if one imagines latiiudes and longi-tudes drawn with respect io the pole of spreading, thetransform faults lie on lines of laiitude, md lines perpendicular to ih€m are longitud€s that convefge at ihepole of spreading. To understand why this must be so,consider the following analogy: If a tcnnis ball Neresliced in iwo paris and put back together, one couldrotate the iwo pa s along the cut (as on a iransfornfauLi). The cut would also desoibe a latitude centeredon a pole of rotation, which can be located by drawinslongitudes perpendiculdto the cut. The intersection oltwo or more such longitudes is the pole of roiaiion. Ona model ofihe Earth, ifgreat circles are drawn perpendicular to transform laults between a lair of plates.thet intersection locates the pole of spreadin8, whicho 8 p h F r w i l h h e s p f F r d . n b f d l p ' o m p l F l F l j o e s ' r i b F \nF fF.ar i re mu .o i o InF $o p.drFs. Thp spcedo.nC

.ate is zero ai the pole of spreading and inoeases to amaximum 90' away at the equator of spreading, as the

wesl oig(ude

After W. J. Morgan, "Rises, Tr€nches, Grcat Iauits.and Crustal Blocks," I. Geophysjcol nesedrch, v 73,pp. 1959-:1982, 1968.

figure indicaies. Tlis maximum equatorial value is tuequently cited as the spreading rate between plaies.

To see how a pole of spreadlng is located ln practice,refer again to the inside ofthe back cover, which showsthczone ofspreading and the iransform faults that sep-arate the Atuican and American plates. Great circlesperpcndicule to the transtorm faulls are drawn in thefigure below. They iniersect near ihe point 58'N. 36'Woff the southeast coast ol Greenland. This isthe pole ofsp 'pad 1g o lbpop l$L Er-d f ls lF. Don bo bFr BornBthere. for there is noihing io be seen. The pole ofspreadinghas Do physical si8niicance. lt seNes only asa construction point. a convenience for describi]18 therelative motion of plat€s merely by giving ihe laiitude

face. Box 1S-2 cxplains how plate movemenls on

a sph€re can be dcscr ibed With the appl icar ion otl h , , . g e u m - l f l p i n . : o l P r r w d - l r . b o i g d r ^ 'i ions and magnel ic anomalies to dcduce sprcading rates. ihe relalive motions of the lithosphericplales are being worked out ('orldwidc. Som€ re-sults have already been picturecl in Figures :18 2land 1g-4. Howcver, g€ophysicists ar-A searchingfor ways to measurc lhe absoiute motions of incLi-

vidual plates rathcr thaD their motions relative tocach olher. If the hot spols discussed in Chapter 15 lurn oul to be fixcd in the mantle belowplates, lhen thc si ng of exi inct volcanoes trai l ingfrom the hLr( spot would record the movement ofindivi.hral plates as th€y glidc over the mantle(Figufe 15 3s). This js current ly a subjcct of .ct ive

SEA-FLOOR SPREADINGAND CONTINENTAL DRIFT:

RETHINKING EARTH HISTORY

Ore of us (F. P.) once help€d wri te a paper deal ing$ith the permarence of oc€an basins l f he were

allow€d to expunge lrom the scientific record the

one contribution he regrcLs the mosi, this wouldbe i t . The noi ion of the stabi l i t ) ' of global geo-qraphic features was not only a main tcnel of th€old geology but scems to bc t i rmlv rooted in the

human psych€. Wc noiv kno that on the geologi

cal iime scale the sea floor is far lrom permancntThe presenl ocean basins are being cr€ated bvsprcading and recycl€d by subducl lon on a l im€scale oI about 200 mil l ion years, which is about 4percent {r f the agc of the Earih Th€ l ikel ihood of

finding extersive older remnants ol sea floor is

slight. Continents, on ihe oth€r hand. arc mobile

but permanent featur€s. They are too buoyant tobe subducied. The-1' mav be fragmented, moved,r - r s - e m h " d , o f u r - e o , " n ' l P , o o e d d r ' l " e i r s u r

faces. bui lheir bulk does not seem to be mrchdiminished. Old Lerrahs \t'ith ages of around 3.5to 3.7 bi l l ionyesr 's can st i l l be lound ContincnLsgrow with time by lh€ gradual accumulation ofmaterials atong their margins N€w continentalst f ips can thcrefore be added on in di f ierenlplaces at di f rcrentt imes, depending on the historyof f ragmentat ion, movement, and reassembly.

With the emergcnce of thes€ revolutionarvid€as, geologists are rethinking Earth historvMost of thc evidencc for platc Lectot cs comesfrom the sea floor. a r€laiil,el-v simpl€ place com-par€d Lo the enormottsly complicated contincnis

Just how plale i€ctonics cxplains cont inenlal ge

CLOBAL PLATE TECTONIC$ THE UMFYINC MODEI, 45I

ologv is now receiving much alLent ion. New . levelopments reported in nearly evert ' issu€ of thcgeological journals show that thc subject has d-"finit€l-v been r€vitdlized. Rock associations, i..]lcan-ism, meiamorphism, thc cvoluiion ol mountainchains-al l are b€ing rexamired in lhe t lamc-work olplate tectonics. Some of the n€wintcrpretat ions lhat we dcscr ib€ in this chapter mav Dotstand the test of l im€. ID this conneot ion, tuturcedit ions of this book ma! show some changes, nir l. u - u , h r r l h F L 9 i u l u F o r D l , l . l p c l o n . ' - d . -thc details of fitting rcgional g€olog]' inlo th€overatl framclvork Th€ student (as w€ll as theauthors of i l sbook) should be caut ioned againstcalling on plate tcctonics for easv explanations ofcv€rything geological . l t is nol c lear, for cxample,hoi or rvhether thc ofigin of such structures asthe ozarks. the Black Hi l ls, the Colorado Plaieau,or such intracont inental , s€diment f i l led dcpressions as the Michigan Basin arc relai€cl to plate

Rock Assemblages and Plare Tectonics

Th€ only record rve hav€ olpasl Seologic events is

the ircomplete one found in the locks thal have

sur\ ived erosion or subduci ion Since onlv s€a

floor younger than 200 millior ycars (the last 4perc€nt of Earth history) has sur l ived s bduct ion'\ re musl focLls on the continents to find the cvidenc€ for most oI Earth history Some of thcmcthocls of reading the rock record have be!-ndcscr ibed in €arl ier chapters. Here we cxplor€ thcnature ot the rock assemblages lhat charact€rizediffcreni plat€ lcctonlc rcgimes as a lirst step inuDraveling the history of past platc motions. Ourd - i s o r ' c . n s l r r c l L P p o P " s o [ o l n , 1 l r " g -mentat ion dnd ocean d€velopment. to locale thesi les ol vanished oceans. and to recognizc the su-lures that mark ancient platc col l is ions.

O l L e h f n i n C r o P d l p l ' o ' r d r e ' ' , r '

nighl expect distnct sLlites (assemblagcs) ofrocks io bc assocjaLed ' i th plate divergercc and

coovergence- At fransform faults no distinct or

character is l ic rock assemblages ar€ to bc ex-pected. Discontinuilics across th€ fault are 1(Juod,however, siDcc rock formations fonned an.l altered elsewhcfe hav€ sl ipped past one aDother,and once'cont inrous formal ions or structural foatures ar€ displac€d.

Think of all that happens at a zor€ of diver'gence. where ptat€ accrct ion and spreading occur,an.]-r 'ou can predi i r i the kinds of rock that wouldcharacter ize thc place dnd the process. Deca s€

THt BOD\ Or THt EA(TH: INIIRNAL IROCE9SES

figure 19-10ldealized section of an ophiolite suite. The combin-ation of deep'sea sedineDts, submarine lavas, andmafic igneous intrusiois indi.ates a dee! sea oriSin.\4-r i 3, olL8iqlq lod \Fl 'F!F ool iol i "s o bF lrdg-ments of oceaoic l i ihosphere emplaced on a coni i -nent as a rcsult of plate .ollisions.

thcre is extensive undersea \.olcanisn, one ('ouldcxpect 1.) find submarine basaltic lava, perhapspillow lavas, ihe volcanic rock formed when hotlava is quenched by cold sea water (Chapter 15).Suboceanic crust and mantle are created here:dredge hauls and geoph-\,sical data show theselayers to consist of mafic rocks, such as gabbroand peridotite, often showirg,j\.idenc€ of altera-tion in a ('at€r environment (hydfous metamor-phisrn). A caryet of deep-sca sedim€nts wouldcovcr al l of this. From Chapters 10 and 11rve re-member that these d€poslts are recognizcd bythin layers of shale, limestone, and the siliceousrock chert, often with thin, disconiinuous tubr-diies between them. Some or all of these layers-

" y L o , r r a . n [ o - . i r " - . ' . t o p e , - o , F " n r d r n ,organisms. A combinat ion of deep-sea scdiments,. u o m a r i n L , u - a l i , r v . . a r d m a f i i g n e o r "instrusions like that shown in idealized section inFigure 19-10, is called an ophiolite suite. Th€presence of nalrow ophiol i ie zones in conver-gcncc fcalures l ike Lh-" Alpine Himalayan belt

The development of a geosyncline on a fifted conti-nental margin off ihe Atlantic coast of the UniledStates. A rift delelops in Pangaea as lhe ancient con-tineni spliis. Volcanics and Triassic nonmarine sedi'ments are deposited in the faulted vallcys (a). Seafloor spreading begins, the lithosphcrc cools and contracts. and the receding .ontin€ntal margins subsidebelow sea level. Evaporites, deltaic deposiis, aodcarbonates (b) are deposiled and then covered byJurassi. aDd Creta.eous scdiments de.ived honcontlnental erosion (c and d).

and ihe Ural and Appalachian bells may indicatethat sl ices of oceanic crust and manLle or iginal lyproduced at accreting plate margins were thrLsionto land when an anci€ni ocean finally disappeared as two cont inenis converged. I l is generally bclieved that the Appalachians. for example,mark the site at whioh the ancestral AtlanticOcean (called Iopetus for one of the Gre-"k gods)closed when North America and Africa con-verged about 375 million years ago. The Ailanticreopened a few hundrcd kilometers east ()1 thiso ' d s ' . ' u r e . a D o r | 2 0 0 - i ' o r r " " r s a g o . i n aspreading episode that is sLill underway.

M e l n o -

Iigule 19-12Ceologic lcatums and activitics associatcd with platc collisions and subductionocean trcnchcs. mdlangc dcposits. magmatic beLts, mctamorphism, volcanism earthq!akes (dots) The d.awins is not 1o scule i thc th ickness a l l i lhos lhere is about70 km, det lh or rhe ocea. r ren.h 10 km, a.d the d is tan.e l ron l fench io ar . js300 ,100 km.

Contin€ntal-shelf deposfts are sedimcntaryrock assemblages that are l€id down in an orderly\ F q r p n c e ' . n J t s r l e c l o n i " l l y q , r i F , o r d ' i o n r i n dgeosyncline at a rcceding continental margin. FiS-ures 19 1:l and 10 29 show thc orderly scqucncco l d c p o . i s i l h e g e ^ s \ n l i n - l h a i s s l l l t . r m . n Poff the Allantic coasl of thc United Stat€s. Thecontinental margin there was form€d when iheAmerican plate separated from th€ Europeanplate abort 200 million years ago. Resling on theoffshore shell is a wedge shaped deposit of sedi-ments eroded from the continent and carried intoshal lo 'water. Because lhe trai l ing edge of thecontinent slowl-v subsides as ihe sprcadinS litho-sphere cools and contracts, the ge osyncline contin-u€s to receiv-. sedim€nts for a long tim€. The loadofthe gfowing mass of sedimcnt lurther depressesh , c r J s , i s o " " i c " l i . ' o l J ' F p q ' y ' l : n p . J

' p , a i \ p s i l l I u p m d r e . " l i o m l " n d . f o . " r " r rthree mct€rs of sedim€nts receiv€d. lhe crust s inkstwo meters. The resull o[ thcsc lwo cffocts is ihaithe geosynclinal d€posits can accumulate m anorderly fashion to thicknesses of 10 kilom€ters ormore. Al the same time, the supply of sedim€nis is,r f f iL ient ,^ mu nta n hc.hal lon $d u enriron-ment of the g€osyncl ine. or miogeosyncl ino, as wecal led i t in Chaplcr 11.

The dcposits show all of ihe characteristics ofshal low'watef condit ions (Chapler 11). At the boi-tom of the entirc scquence are rift l.allevs con-taining basahic lavas and nonmarine depositsformed during the early stages of continental fissdring. ln the early stages of sheu deposition.o o o I m d l . , r s , l d I J o f i . l l h e d F p r p . s r o n .

Much was droppcd on thc continental slope, onl-vto be moved laier to the cont inental r ise by lufbidity curlents. In deep wat€r, very thick depositsd n L ^ L , l r r p n r h i . r , 1 . A . l - . " l - p ' m ; o g F o

syncl ine bui lds up, deposit ion may bccom€ dominated by shales and carbonale plal form deposits-indicators of a decrease in the supply ofdetritus hom ihe continent.

Think what might happen to these geosynclinesi f the orderly, s€quent ial ly 1ay€r€d, g-"nt ly dippinCsedimenis u'ere to become the leading edge of aplate in collision. In the following sections wedescribc some of the many possibi l i t ies.

Jusl as the events that take place in a convcfgencc zone are different from div€rgenc€-zon€phcnomena, so do th€ rock assemblages have dif-fercnt character ist ics. Thc main f-"atures olocean ocean or ocean-cont in€nt col l is ior aeshorvn in transvers€ sectior in Figure :19 12.Thick marine sedim€nts, mostly turbidiies.eroded from the contirent or the island drc. rapidly fill the long marginal d€pressions. In dc-- ' e n d ' n g . r h F , o l d u " a - i , r l d L " "

- . h e t " C i o nbelowthe inner wal l of the l rench with these sedi-mcnls and with deep sea materials brought withlhe incoming plate. Regions of this sort are enormously complex and highh variabl€, as they in-cludc turbidilies and ophiolitic shreds scraped offthe do\.ngoing slab by the edg€ of th€ overr idingplate al l highly folded, int f icalely sl iced andmetamorphosed. Thcy are difficr t to map in detai l but rccognizablc b-v their dist inct ivc mix 01matcrials and structural feat r€s. Such a chaoticncss has been cal led a mdlange. Thc mctamor

THE BODY OF THE EARTH: INTERNAL PROCESSES

phism is Lhe kind characteristic of high pressureand low temperatLrrc because the material may bccanied relatively rapidly lo depths as great as 30kilometers, \^'here r€.rystallization occurs in theenvironment of the cold slab. Som€how, perhapsby buo5'ancy and mountain building. lhe materialrises bdck to the s rface much lat€r. Find amdlange dnd you can' t be too far f rom the placc ofdovnturn of an ancient plate, long sjnce con-sumed, bui leaving this r-" l ic of i ts existence.

R€fer again to Figufe 19-12. Parallel to rhemdlangc is a magmatic belt that makes p the arcuat€ sysi€m of volcanoes, intrusions, and meta-morphic rocks formed on the edge of the ovelrid,ing plate. Here the conditions are dominated bythe rise of ma:tma from ihe descending plale. Atthe interface, where the desc€nding plate sl idespast the overr iding one, perhaps fr ic l ion is greaienough to melt the uppcr part of the downturnedslab, including the subducted wct sediments andocean crust. Thc liquids ris€ buoyantly ftomdepths of 100 lo 200 kilometers to erupl and buildthe volcanic chains on the leading edges ol plates.The character is l ic igneous rocks produced areandesilic lavas and $anitic intrusives. lslandarcs, buiit up from the sea floor, may containldrger amounts of basalii continental nargins typ,ically erupl rhyolitic ignimbrlte and are intrudedby granitic batholiths below (see Chapter 15). lncontrast to that in a m61ange, the metamorphismin the magmatic belts is typically the result of recrystallization rurder conditions of high temperatures and low pressures. This is because the hotfluids rise close to the surfac€, delivering muchheat to a low pressure environment.

Paired belts of m6lange and magmatism(Fig. 1s-12) are the sisnature of subduction. Theesscntial elements of these features ot collisionhave been fo nd in nany places in ihe geologicrecord. One can see mdlangc in th€ FranciscanFormation of ihc California Coast Ranges andmagmatism in ih€ parallel beli of ihe Siera Ne-vada to the east (Fig. 19-13). This pair€d beltmarks the Mcsozoic borndarv between the colliding Pacific and American plates. It even shows thepolar i ly of the conlefgenoe by the locat ion ofmdlangc on the wesL and magmatism on the eastithe Pacif ic plate was the subd cied onc. Orherpaircd belts-for cxample, in Japan-can b€found along the continental mdrgins framing thcPacific basin. Th-" ccntral AIps, a European example, were produced by the convergencc of a Meditel.I€nean plate ll'ith lhc European continent.

Seismic ref lecl ion prof i les (see Box u-1) arebesinning io p.o\.ide 'x ray" viervs of layers de€p

FiBlre 19-13This paleoSeokgic nap oI the wesLern Uniied Statessbo('s ihe Ceology of ihe region as it was at the be-ginning of Tertiary time. The paired nelange aDdmdgddl ic bel ls indi .ate a .ol l is ion of the Paci ic andq n - r i c " r p J l * i v F q o / o i . . n d r h e l ) , ' i f p l d "being the subduoted one. [Afier W Hanilton andw B M r " r . ( 6 r n l ^ i , T 4 , o r r ' . E L r ' . a s o l L " . -piysics, v. 4, p. 541, 1966.1

wiihin the crust. Figure 19 :14, a remarkabie ex,ample of this new technique, shows ihe Austra-' i d n

o l " r , b H n g . u b d u c r e d u ' l J - r . e t r r " s r d n

Orogeny and Plate Tectonics

Orogeny means mounlain makins, particularly byfolding and thrusting of rock layers. ln th-" ||ame-work of plate tectonics, orogeny occurs pri.I1arilval lhc boundaries of col l id ing plates. wherc mar-ginal sedimentary deposits are crumpled andmagmatism and volcanism a.c ini t iated.

Consider t i rst some scenarios of plate conver-genc€. ln Figur€ 19 15a. a plaie rvith a continent at

Seisnic reflection profile across the Java Trench subduction zone south of Bali, along longitude 112'E.Subductcd ocean floor {bctween larse arrows) dips aboul 6' under overthrust wedge of hishly deformedsediments. The occan floor can be folloived from lhe beginning of srbduction al ihe north wall of thetrench to a deplh of 12 km below sea level. lcoufresy ol R. H. Beok and p. Lehner, Shell Internationale

Figure 19-15Possjble stages in platc collisions. (a) Convergence beiween plates {ith contjnental andoceanjc liihospherc at lcading edges. Magmaiic belt, folded mountains, and ndlange depo$tsare feahues of thc ovcrriding continenial boundary. (b) Colljsion of continents, producinga mountain range! magmaiic belt, and thickened continental cNst. Since the continent istoo buoyant to be carried down into ihe mantle, plate motions may be brought to a halt.(c) Alternaiively, the pLate may break ofi and a new subduction zone be started elsewhereAn extinct subduction zone mav shov as a s.ar i. the form of a mountain belt within aconiineni. Exam!les are the U.al Mountains and the Himalayas. lAfter "Plate Tectonics"by J. F. Dewey. Copyright O 1972 by Scientifrc Amefican, Inc. All rights reseNed.l

456 rHE BoDy oF rHE EARrH: TNTERNAL pRocEssEs

the leading edg€ collides r\'ith another plai€ carrying a continent. ln lhe €arly stage, during whichthe convergence is betwcen contin€nt and subducted oceanic lithosphere, a magmatic belt,folded mountains. and mdlange deposits may befeatures of the o\.erriding contincntal boundary.An example exists today along the Pacific codst oISouth America, where the American and NazcaplaLcs dre colliding. Look at the illNtration insiilethe b6ck cover to see lhe setting of the plates. TheAndes, from which the name oI the volcanic rockandesite is derived, lie in the magmatic belti sub,duction is taking place under the Peru-Chilelr€nch.

In a later siage, continent may m€et contincnt,as shown in Figure 19-15b. Since continentalcrust is too light for much of ii to be carried down,the plaie motions could be sloi{ed or halteo. ,.\n-o h p r p o s s h l i r \ . r h , o 1 p d p p ' c t F d ' r t h F f i g u r e . i Jthat the plaie motions continue, with subcluctionceasing at thc continenfcontinent sutute butstarting up anew €lsewhere. CoId and dense as thedescending slab is, chunks of it may break off, fallh " p l t . n , o r h p m d n p

" - d h F r " \ o u p d . A s f , g u "19 15c sholvs, the suture is mdrked by a mouniainrange madc up of eiiher folded or thrusi rocks. orboth, colncidcnt lvith or adjacent to th€ magmaticbelt, and by a much-thickened continental crust.A prime example of continent continent collisionis the Himalayas, which began forming some 25million years ago when a plate carrying India raninto the Asiatic plate (the collision and uplift aresiill going on). This may be how the rooi undeflying the Himalayas originated (sec Chapter 18).Th€ plale tectonic cycl€ of the closing of an oceanbasin, a continent-coniinent collision, and the for-mation of an lntracontinental mountain belt hasbeen called the Wilson cycle, aft€r ihe Canadiangcologist I. Tuzo Wilson. who first suggested theidea ihal an ancicnt ocean closed io form thcAppalachian mouniain b€lt and then reop€ned ioform th€ present day Atlantic Ocean.

Displaced Terrains

Geologists have come across blocks within conti-nents whose rock sequences, fossils, and paleo-m o g n a l ! - n J r - d l i , n l o l h p r . u f l o u ' d n g \ T h prock assemblages and the fossils indicate differentenv onmenls and ages than the surroundingterrain, and the paleomagnetic poles imply thatthe block o.iginated in a different latitude. Thesear-a now belicved to be fragments of other conti-nents or of ocean oust that were swept up andplastcred onto a contin€nt ir th€ process of plate

collisions and separations. Coastal NeI'\' Englandand Newfoundland may be slices of Europei partsof Alaska, Bri t ish Columbia, and Nevada mayhave been soaped off Asia; and central Flor iddmay b€ a ffagment of Africa. Displaced te ainshave also been found in Japan. Southeast Asia,China, and Siberia, buL Lheir or iginal iocat ionshave yet to be worked out.

Th€ Grand Reconstruction

At the clos€ of the Paleozoic. some 250 mitlionyears ago. there lvas a single supercontinentP d n g d e r . s F " h n s f i o m o o l e o p o l F r F i s . . - l a ) .The fragmentation of Pangaea as a result of plaietectonics and continental drift over Mesozoic andCenozoic time to form Lhe modern continents andoceans js documented in the well pr€served record of magn€lic reversal stripes on the oceanfloor. Eut whai of the pre-Pangaean distributionof continents? Whai were their shapes and wherewfie they located? There is growing €vrdenceihat Pangaea was form€d by lhe collision of con,tinental blocks-not ihe same continetrrs weknow today but continents that exist€d earlierin the Paleozoic. The ocean-floor record for thisperiod has been destroyed by subduct ion, sowe mrlst rely on the older evidence preservedon continents io identify and chart the move-ments of thcse paleocontinents. Old mountainb€lts like the Appalachians and Lhe Urals markthe col l is ion boundaries of the paleocont inents.Rock assemblagcs th€re reveal anci€nt episod€sof rifiing and subduction. Rock types and fossilsalso indicate the distributlon of shallow seas,glaciers, lowlands. nountains. and climaticcondit ions. Paleomagnel ic data can be used tofind the latitude and ihe north-south orienrationof the paleocontinents. Latitudes can also be' h F ' L e i l h t o a l p o , t i n a t , o d " . A t h o , g n i \not possible to assign longi iudinal posi t ion toth€ paleocont inents, the relai ive sequence of con-tinenis around the globe can be piec€d togetherilom the fossil record. Ore of the first efforts todepict thc prc-Pan€aean configuraiion of con-tinents using th€se methods is shown in Figure19 16. Ihe abi l i ty of modern science to recovcrthe geography of this strange world of hun-r l e d s o f r i l i o r " o l ! c d , s d d u i " , r u l r i - p r p . s i \ pGeologists may be able to continue to sort outmore details of this complex jigsaw puzzle,whose individual pieces change shape over geologic time.

Figure 1S-:l7 reconsi.ucts the most recentbreakup of Pangaea as we now understand it. Fig-

- - , , i " . l o le 'n ' tL r \ r ' ' hdr

"v P 'd ' o !

"- . l , i ' : " ' - ' - : ' ' ' ' ' In rhe p'o 'r cs o' prdrP br;"-k"p "iTa;s";";"-itd

noltxnuersrd

wffi ^^",.,.",ffi

WE tnn,,*. C lI e*p.t"-**" M

""n.( i i d ca l r o ho l . d i y ( i d ca t i ns wa rm.ond i r o . s ) hum d .ond i l ons )

(a) Paleocontinenis in the Middle Ordovjcian, about 475-4s0 dillion years ago. At that iimethe continents consisied of Gondwana (ftade u! of South Anerica, Southern Errope, Af'rica, th€ Near East, India, AusLralia. New Zealand and Anta.ctica), Laurentia (Norlh Amer-ica and Cre€nland). Baltica (nost of Northern Europe and Eufopean Russia), Kazakhstanii(Central Asia) China (China, Malaysia), and Siberi€. (b) Paleocontinents in Eafl,\t Carbonilerous, about 340-360 million years ago. Gondwana has noved a.ross ihe South Pole enier-ing the opposite hemispherei Baltica has collided s'ith Laurentia to form a larger contincntLaurussia. The continents are assembling for ihe collisions that formed the supercontinentPangca ai the end of the Paleozoic. lAlter R. K. Bambach, C. R. Scolese, and A. M. Ziegle..Americon Scicntist. ianua\' 1980.1

ure 19-17a shows the world as it looked in Permian times, a little more than 200 million yearsago. pangaea was an irregularly shaped land masssurrounded by a universal ocean call€d Panthalassa, ih€ anc€stral pacific. The T€ihys Sea, be-tween Africa and Eurasia, I,vas the anceslor of

part of th€ Mediterranean. The fit of North andq o u h q m F i , r w i ' h F r r o p e a n d A f r i , a r s r e ngood in deiail when taken at the outer edge of thecontinental shelves, instead of at the presentshorelines, lvhich arc some distance from th€original rift. It is ihe fit for which we have the

The br€akup of Pan8aea. {a) Thc ancient landmass Pansaea, meonins "all lands," nay have lookedlikc this some 2oo milllon years r8o at the closc of the Paleozojc and begioning of thc Mcsozoi..PaDthalassd ( 'a l l seas ' ) errohred inLo the prcscnt Paci ic OceaD and the p.esent Medi ler .aD€an Scais a remnant of the ]'ethys. Pcrnian glacial deposjts dre tound in widely scparated areas, srch asSouth Amcrica, Afrjca India, and Australia. This dist.ibuiion is simply exllaincd bir postulating as inglc cont lnenl i l g lac ier f loNing ovcr the south polar regions of Gondwanaldnd in Pernian t ime,before the brcaku! of the .onlinents. -fhe probable extent of the glacier is shown by shading.(b) One view of world gcogralhy at the end ol the Triassic Period, 180 million lEars ago, after some20 millioD )ears ol drift. New ocean floor is shoivn in color. Sp.eading zones are re!resented bydark brown lines. transform faults by bla.k lines, and subduction zones by hatched lines. Afroi{sde!ict moilons of.onlinents since drift began. (c) World geography at ih€ end of the Jurassic Period,135 millioD ycam ago, aller some tjs million ycars of diifi. Occan floor created jn the preceding 45nillion ycars is shorvn in color. (d) World gcography at the end of the Creia.eous Period, 65 millionyeaB aga. Color indicatc floor crealed afte. some 135 nillion "lcars of drift. (e) WorldSeogralhv loday. Color sholrs s.a floor produced dufing the !ast 65 million -!cars, in the CenozoicPeriod. lAlier

'The B.eakup of Pangaea ' by R. S. Dietz a.d J. C. Holden. Coly.Aht O 1970 by Sci-ent i f ic Amer ican. I . . . A l l . iehts icseN€d. l

460 THE 3ODY OF THE EARTHI INTERNAL ?ROCESsEs

firmest €\,idence. The positions of Central America, India, Australia, and Antarctica are lesscertain.

The breakup of Pangaea was signaled by the

opening of ritts'hom which basalt poured Relics

of this great event can be found todav in the Triassic basait flows atl over N€w Eneland. Radioac

tiv€ dating of these flows provides the estimare of

about 200 million -vears for lhe beginning of driJt

The geography of rhe world afier 20 million

l,ears of drift-at the end ot the Triassic some 180

million years ago-is sketched in Figue 19-17b'fhe Atlantic has opencd, th€ Tethvs has contracted, and the no hen coniinents (Laulasia)

have all but split awa-v ftom the southern continents (Gondwana). New ocean floor has also sepa-rated Aniarctica-Australia ftom Africa-SouthAmerica. India is off on a trip to the north

Ey the end o{ the Jurassic period. 135 million

vears aso, drift had been underlvav for 65 million

;ears. fhe bis event ai thls time is the splitting oflorth America from Africa, which signals the

birth of the South Atlantic (Fig 19-17c). The

North Ailantic and lndian oceans are enlarged,but the Tethys Sea continues to close lndia con-tinues iis northward journey

The close of the Cretaceous period 65 millionyears ago sees awidened Souih Atlantic, lhe split_

S;enatic sections showins modem p1ate, ocean, continent,

fAlter I. F. Dewey and I M Bird, 'Mountain Belts and Nelv

i. ceoihysiccl R;sear.fi, v. 75, pp 2625-2647' 7s7o)

and island arc felationshiPs.

tins of Madasascar ftom Africa, and ihe close of

thJTethys to form an inland sea, the Mediterra

nean (Fig.19-17d). After 135 million vears of drift,

the modern configuration of continenis becomes

discernible.The modern world, produced over ihe past 65

million years, is shown in Figure 1S-17e Ifdia has

collided with Asia, bringing its trip to an endAustralia has separated hom Antarctica. Nearlyhalf of ihe presenrday ocean floor was created in

this period. Figure 19-18 shows sev€ral schematicsections that summarize modem plate' ocean.continent. and island arc relaiionships for theAmerican. African, Eurasian, and Indian plates

M o . o t l h p m u J . - r P d ' i l i , O ' c d n b a s n c o nsists of the Pacific plate side of the East Pacificrise spreading zone, as can be seen inside the backcover and in Figure 19-18b This implies that anarea equal to most of the Pacific Ocean has disap-peared by subduction under the Americas in thepasi 130 million years As much as 7000 kilome

ters (a300 miles) of Pacific s€a floor mav havebeen thrust under North Americal

Not one branch of geology. except perhaps

crystalio$aphy, remains uniouched by this grand

reconsiruction of the continents Economic geolo

eists are using the fit of the continents to frn'l min-

eral and oi1 deposits by correlating the formations

Hlma ' /ds Indra / Deveoprng r ren .h

in which they occur on onc contincnt wiih theirpredrift continudtions on anoth€r corrinent. paieontologists ar€ rethinking some-aspects of evolu-tion in the light of contin€ntat drift. t'or cxamptc,during most ol the age oI reptiles, the connnentswe know today were grouped together in twosupercont inents, Lauasia and condwanaland.Thcse continents were fragmentcd durjng most oIh P , E P u f m d - m , r \ \ r h t a , n r \ o e \ e o p i n s o

ihe daLrghter continents isolat€d lrom one an-oiher. Is lhis rvhy nammals diversificd into soman-\/ more ordcrs ihan the rept i les did, and in amuch shorter pcriod of time? S tru ctural gcoroS $ rsand petrologisis are extcnding their sights fromrcgional mapping to the world piciure. for fheconcept of plate tectonics provides the means otirt€rpreting such gcological processes as sedi-mentatron and orog€ny in gl.rbal rerns. For exam-ple, th€ Caledonian mountain bett thar runs alongthe northwest margin of Europ€ is the prerlrificontinuation ol the Appalachian belt. and rhelfend of th€ Andes may be fol lo lved into arLarc-t ica and Austral ia, as Figure 19 1S shor.s

Oceanographers are reconstructing currents asthey mighthave existed in the anccstrat oceans. rounderstand better thc modern circutat ion and to

CLOB\T PLATE TECTONIC+ THE ONII\INC MODET

account for thc var iat ions in deep sca sedrmenrs.Palcoclimalologists ar€ "f orccasting', backward intime to describe temperarure, winds, the exLent ofcontinental glaciers, and rhe level of rhe sca asthey were in pr€drift times. Wh€t berte. testrmony to thc tr iumph of this oncc-olr trageous hy,pothesis lhan s abi l i tv to revi tal ize and shedlignt on so many diverse topics!

THE DRIVING MECHANISMOF PLATE TECTONICS

Up io this point everything we have discussedmight be catcgorized as descripri\,-" plate recronics. The geomctry and rat-"s of ptate motions, iheconsequences of plate sepafar ion and col l js ionhav€ been desc bed. But what dr ives i t at l? We\t i l l not lu l ly understand plate rectonics unrl w€can answer lhis question. The tnte.narional ceodynamics Project enlisted Lhe efforts of thousarusof scient ists in se€king the und€rtying cause oI

It is gencraliv accepred that most ot the mantteis a hot solid, capable of flowin€ like a tiquid at aspeed ot alrout a .cntimcter pcr v€ar, aboLjt the

n

figure 19-19

r y ! - h " " ' , , | . o r : r p , o . p " r p " F . . . a , o 1 ! , r r i , F d , I n , | . a a o o l i d r v u L n a n so L I o p F n d l . F A p t d ' a , f d l v o r i . r ! t o r m J i o , t r l r , r s b " " t F . , o r o h i . c" F i n l o , m d d r o o l d ' " ' o . , r o - , h " F n t " o r a - t . o n 8 d , o i , o l t i n , r . . ' . \ a , o n r -uity ol rhe mountain belts thal exrends hom ihe An;icas acros" a"t""citc" l.JwesLe.n Australia suppo.ts rhe reconsirucrion. The Urals an.l olher ot.1 nountains' o I a i r u t b i o t " z o r p ! . r i r ( n J I r - - . q u t , r , " d , r \ F " i F - o d r . l - e o o , p d n j. n l l . . D l J l . T p ' l u r

: h \ ' . D F $ d J ( o I ' , r i S t O t o . 2 o J . , F n t . a l r a r , . a , ,lnL . A l l , , ch ts rcser \ed I

lF

oo :s " u , , \ n : I c , - a , i . t r \ o r p l . F ' . ! \ '

" ' ' . o r " ' " ' p $ n " J b \ ' \ ' w S r r o r F 8 e "

d l F r r ' ! o i . p " r g o r

' ' ' u l l r l b J ! ' o P a r y

4 . " " * - r ' " " " , L o h o r ' l \ ' o ' i " a r d g € J

lv coiveciion cuuent in manrlc k, The platc is rhc

c o , " d . . r , b o , , o a I F 8 r o f o r \ F u ' ": . , , , i . " . r . p a , " ' . p p ;

m r ' , . " . , r r ' r r o -

r I o l r m F r ' . " q r o n 8 r ' i l d F l \ ' ' ( r ! c s ' o s ' s

, l m - o F 1 r i . s a . " J ' P _ " d s d i ' \ d d g 8 r l g

rfr" pr.t".. l-t.it-a -tuin flow occurs throughout

the rcst of the maDlle

1. Accordinq to the theory of plate tectonics the lithosphcre is broken into abont a clozcn-

. i " ia. -" ' i ' "" or"* rhree ir pes of plate boundaries are def in€d bv the relat jve motion

f. i t , """o ploi"" , bouDdariF\ ot d1\crgence boundarics of convergence' and transtorm

faults.

2.In addit ion to €arthquake b€Its, nany large+cale qeologrcal lFdtufcs are associaled

with Dtat€ boundaries, such as narrolv mountain belts And uhain's or \ orr anoos bouno

;;;;i;;;;;';;;"; "'"."".g.r,"a r,,v a""p-sea tr€nch€s, incrined earthquake beris'

rai€ vour finsernails grou' Thc lilhosph€re is bro-

ken into rieij plates, someholv responsive in th€ir

motlons to rhc 1low in the underlldng mantle'

As is generat ly the case 'hen lherc is an ahun

clanc€ of data in scarch of a theorv, many hvpoth-

eses have been advanced Some lvould have

o r . * - u r r J p J , i l - ' s ' r g n n r r l - ' ' d g e ' I l h p

" " r . " t . p p o n 1 9 , | | ' J b n ' h " \ ! d u s r

eoins slab at s lrbduct ion zon€s Others hold that

+ " ; " , " . " , '

o t s s e d I u n s L ' ' F r r ' i ' r - P

. ' , d , ' 1 n g " s l - . n , ' o h ' F f e ' e ' e - : 0 c h o $ '

s o m . o h " - , d " " . - . ' n ' P s i l t i l r r ' ' r s s r o n n

i n ' n " r r . r h r h u " " s l - o \ P s l \ "

1 , . u " s . n o r ' n p r ' e r r o ' r b " d r l r r g l | o m p l ' \

i'onvcctrr,c flow, involving rising, hot, partiallv

molten mat€r ials and sinking cool sol id maier i-

als, unal€r a \ ,ar iety of condit ions ranghg lrom

m l i n q n - J L n c a ' o r a ' l T F r n g q ' ' g r '

. . r r r r ' . t . t h . - , r r r l r n r . b " n i o l " d l o r s r b s

. " " ;"* ' pts , ar ' o d' l t i . "sor '"

-{rn \ '

meters before bcing compl.1el-v resorbed Figure

1s 20c, shol\'s on€ ol the first computcr mod€ls oJ

the Droccss-one lhai n€81ects some of the effects

i r ' l m " n 1 4 n ' 1 , o . r l h d l n . \ e r F l

m " r r o l , s " n a r o ' . A r , ' n q n l m , o l h ' r m d ' "

r ial . ieatecl f rom bclon' , reach€s the surfAce al a

' ' ' e r o s p . " L l n g l n o ' ' o s d l r J _ l h t ' F r -

. I ' r r l P d n d l ' ' " e I l ' o u n d

arv b€com€s solirt. strong lithosphere Finallv

. , c o m 1 e n . i \ ' . r " l r ' F r ' ' o o " n r ' l i h u -

- p h e . ' . i . r ' s i r l " m a n r ' F n ' r b

, l rrct ion zone, 'hcre i t is reassimi latcd to be

h€atcd and to rise again in the future Anothcr

thcor"v (Fig. 19-20d) proposes that hol narrow' lctl ikc Dlum€s r is€ from the bot lom of thc nant le '

fcc. l the growing plate, and dt ive i t la ieral ly awa)'

f rom sDreading ccnters where lhe plumes mosl ly

occur. These same plumes are { , \ ' idenced at lhe

surlace by hot spots Among the problems lcf t to

the nextgeneral ion olEarlh scicnt ists is rhc ]ncor

' , . ' . , ; 6 o . r l h r m p o l , n L l F l - r r ' r s L F ' h F o " '

o n . r l p - , h " h i " l o r \ " l I ' i n \ e " r r " d r ' l h

formation and:{oll-th of conlinents into an expla

nation of th€ distribution of convectivc 'r'rrcnts

in l ime ard space.

SUMMARY

GLOBAL PLATT TECTOMCS: THE UNIFYING MODEL

mountains and volcanoes, and paired belts of mdlange and magmatism. The AndesMountains and the trenches of t}te west coast of South America are modern examples.Divergeni boundaries (for exampte, the mid-AtLantic rjdgel typically show as seismrc,volcanic, mid ocean ridges. A characteristic deposit of this environment is the ophio-lii€ suite. Transform faulis, along which plates slide past one another, can be recog-nized by their topogaphy, seismicity, and offsets in magnetic anomaly bands. Ancientconvergences may show as old mDuntain belts, such as the Appalachians.

3. The age of the sea flDor can be measured by means of magnetic-anomalv bands and ihestratigraphy of magnetic reversals worked out on land. The procedure has been veri-fled and extended by deep-sea drilling. Isochrons can now be drawn fof most of theAtlantic and for large seciions of the Pacific, enabling geologists ro reconstruct thehistory of opening and closing of these oceans. Based on ihis m€thod and on geologicatand paleomagn€iic data, the lragmentation of Pangaea over the last 200 mlltion yearscan be skeiched.

4. Although plate motions can now b€ described in some detail. the drivins mechanism isstill a puzzle. An attractive hypothesis proposes that the upper manile rs m a state ofconvection with hot material rising under divergence zones and cool maierial sinkingin subduction zones. The piates, according to this model. would be th€ cooled, upperboundarv resion of the convection cell.

EXERCISES

1. Summarize ihe principal geologic featufes of subduction zones and diverg€nce zones.

2. Explain the following in the contexi of plate tectonics: (a) lceland. (b) San Andreas fault of cahfornia.(c) Ural Mountains. (d) Aleulian ireDch..(e) Eafth,quakes in ItEly and Turke)'. {0 Andes Mountains.

3. How do we know that spreading along lhe East Pa-cific rise is lasi€r than alone the nid Atlaniic rjdge?

5 .

What ivould an astronaut look for on Mars to findout if plate iectonics is an aciive process on rh€!1anet?How would one recognize the boundaries beiweenancient plates no longer jn existence?

Can youthink of a way not mentioned in the text. bywhich to neasure absolute moiions of individualplates rathcr than relative motions between plates?

BIBI,IOCRAPHY

Bambach. R. K., C. R. Scotese, and A. M. Ziegler, Be-fore Pangea: The Geographies of the PaleozolcWorld," Anericon Scientist, v. 68. pp. 26-38, 1980.

Beloussou, V. V, Why Do I Not Accepi Plate Te.ton-ics?" EOS, v. 60, pp. 207-210, 1979. (See also comments on this paper bi' A. M. S. Sengijr andK. Burke on same pases.)

Cox, A., ed., Plot€ Tectonics ond ceonognelic Reversols. San Francjsco: W. H. Freeman and Company,1973.

DpwFv. - . c . . P d a Te,1oni , . . \L ien ' j f i qmFf i .nn

May 1972. (Offprint 900.JHallam, A., A Revolulion in the Eo.th Sciencesi From

Continentol Drjlt to Plate Tectonics. Oxfordr Clar-endon Press, 1973.

Le Pichon, S., I. Fran.hereau, and l. Bonnin, Ploie Te.-lonics. New York: Elsevier Publishing Company,1973,

Marvin, U. B., Continentoi Drift. Washinglon, D.C.:Smithsonian Instilution Press, 1973.

Meyerhoft. A. A., and H. A. Meyerhoff. "The New clo-bal Tectonicsr Major In.onsistencies." AmcrrconAssocidt ionoiPetro leum Ceologists Bul le t in ,v . 56,pp. 269 336. 1972.

Sniih, A. G., and j. C. Bride\ Mesozojc ond CenozoicPoJeoconijnenldl Mops. Cambridge: CambridgeUniversity Press, 1977.

Tarling, D., and M. Tarling, Continentdl D.jil. GardenCity, N.Y.: Doubleday, 1971.

Vine, F. j., "The Continental DriJt Debare,', Noiu.e,!. 266, pp. 19-22, 7972.

Wilson, J. T, ed., Con rjr ents Adriflr Reodjnss ton ScLp n " 1 6 A n " , ; , o n \ d - F r J r c i " , o : W h . f - p p n a rand Company, 1s70.

Wylie, P 1., Tne Woy the Ed.ifi Woiks. New Yorkr lohnWjleir & Sons, 1976.