Dewey, John F.

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GEOSCIENCE CANADAMARKING 50 YEARS OF THE WILSONCYCLETuzo Wilson: An Appreciation on the 50thAnniversary of  His 1966 PaperJohn F. DeweyUniversity College OxfordHigh Street, Oxford OX1 4BH, United KingdomE-mail: jfdeweyrocks@gmail.comJohn Tuzo Wilson probably had a greater influence on thedevelopment of  the earth sciences than any geologist sinceWilliam Smith and Charles Lapworth. Prior to the early 1960’s,he was a staunch anti-drifter but, in 1965, he pulled togethermany threads to create a cohesive paradigm that embracedcontinental drift, sea-floor spreading, subduction, and verylarge motions on transcurrent faults that defined the bound-aries of  and sites of  relative motion between plates, the basisof  what would come to be known as plate tectonics. Implicitin his analysis was the torsional rigidity of  plates. Torsionalrigidity means that plates have sufficient strength to avoid dis-tortion in map view although they may be distorted along theiredges (plate boundaries) and are more easily distorted by flex-ure in cross-section. Apart from the well-known contributionsof  Wegener (1929), Holmes (1931), Griggs (1939), Creer et al.(1958), Hess (1962), Runcorn (1962), Heezen (1960), Dietz(1961), and Vine and Matthews (1963), two lesser known andappreciated observations were instrumental in the formulationof  plate tectonics. First, Harry Wellman (1955) already recog-nized that the Alpine Fault in New Zealand joined trencheswith opposite polarities and is elongating. Secondly, BertQuennell (1958) described the sinistral relative motion ofAfrica with respect to the Arabian Plate along the small circleof  the Dead Sea Fault around a rotation pole near Gibraltar,implying torsional rigidity of  the adjacent blocks. Simultane-ously with Tuzo’s 1965 paper, Bullard et al. (1965) assumedtorsional rigidity to make finite difference rotations aroundpoles of  rotation, to achieve fits and minimizing misfits,between the continents around the Atlantic. McKenzie andParker (1967) described the relative motion among the torsion-ally rigid Pacific, North American, and Gorda plates and thetheory of  plate tectonics was born. Tuzo’s fundamental rolecame between 1962 and 1965 in his papers on the Cabot Fault(1962), and interpretations of  oceanic islands (1963a) andHawaii (1963b) as hot-spot tracks, culminating in his definitive1965 paper that founded plate tectonics and his clever paper(1966) on the Caribbean and Scotia plates moving throughgaps between continents and invading ‘innocent’ oceans withrifted margins. Strangely, Tuzo did not use rotation poles todescribe relative motion among his global plate mosaic, in spiteof  the implicit rigidity of  plates, even though used, explicitly,by Wellman, Quennell, and Bullard et al. Within a few years,plate tectonics was developed as a quantitative, integrated the-ory by McKenzie and Parker (1967), Morgan (1968), LePichon (1968), and Isacks et al. (1968).Of  great importance in tectonics, during this period, wasTuzo’s 1966 paper, “Did the Atlantic close and then re-open?”(Tuzo enjoyed framing his papers as questions, which manyjournals no longer allow). In 1965, I was a young lecturer inCambridge deeply absorbed in developing new courses inVolume 43 2016 283Geoscience Canada, v. 43, http://www.dx.doi.org/10.12789/geocanj.2016.43.108     pages 283–285 © 2016 GAC/AGC®COMMENTARYFigure 1. There are many ‘official’ pictures of  Tuzo Wilson, but it seems moreappropriate to use this lovely photograph by renowned Canadian photographerHarry Palmer, and we reprint it with his kind permission. Harry took splendid andcandid photographs of  many ‘Companions of  the Order of  Canada,’ and Tuzo wasawarded this honour in 1969, three years after his famous paper.structural geology and working on the geology of  western Ire-land, Nova Scotia, and Newfoundland. Both Harry Hess andTuzo were on sabbatical leave in Madingley Rise, the thenDepartment of  Geophysics in Cambridge presided over byTeddy Bullard. I owe these three earth scientists more than Ican say in transforming my approach to geology, in theiradvice to expand my horizons to include a global tectonicscale. Tuzo came into my room in the Sedgwick Museum manytimes for morning coffee and chats about regional and globalgeology, especially the relationship between structural geologyand tectonics. One morning, with that inscrutable gentle smilethat usually characterized his face, he announced “I have dis-covered a new class of  fault.” I confess that I was scepticaluntil he drew from his bag his now-classic paper model of  aridge-to-ridge transform and repeatedly opened and closed itunder my nose. I was transfixed by the spectacle of  a spreadingridge offset by a transcurrent fault that had the opposite senseof  motion to that intuitively thought of  as displacing the ridgeaxis along a classic transcurrent fault. Once seen, the pattern isobvious but was the most exciting thing in geology that I hadwitnessed in my short career thus far. It was even more fulfill-ing and instructive as Tuzo spent the next hour with me cut-ting up cards to illustrate the offsets along faults that connect-ed trenches with the same and opposite polarities, ridges totrenches with ridge-facing and ridge-opposed polarities andseveral kinds of  triple junction. Tuzo told me that he wasabout to publish all this as a coherent global model (his 1965paper) and that he would introduce the term ‘transform’ forlarge-offset lithosphere-cutting faults that terminate at a ridge,trench or triple junction. Thus, he established the global pat-tern of  continuous plate boundaries. I still have that model andthe pieces of  card (Bristol Board upon which I drew most ofthe illustrations for my papers until the digital revolution ofAdobe Illustrator) as one of  my most treasured possessions.As if  all this was not enough, the following month Tuzo strodeinto my room and (paraphrasing) announced “my globalmodel means that continents are carried around as passengersthat oceans open with trailing rifted margins and close withcollisions that make mountain belts. It seems to work for theAppalachian–Caledonian Orogenic Belt in relation to theAtlantic Ocean. The Orogen was probablydeveloped by the closing of  a LowerPalaeozoic ocean and split to form thepresent Central and North Atlantic leavingbits of  the margins of  the Lower Palaeo-zoic ocean (now termed Iapetus) on bothsides of  the present Atlantic.” In 1973,Burke and Dewey coined the term ‘WilsonCycle’ to describe the opening and closingof  oceans. Tuzo showed me a draft of  apaper that he had begun to write thatappeared in Nature in 1966. This, togetherwith my work with Art Boucot and StuartMcKerrow in Nova Scotia and MarshallKay in Newfoundland in 1964, Bob Jas-trow’s Goddard Conference in New Yorkin 1965 and further work in Newfound-land in 1966, developed my interest in try-ing to understand the NorthernAppalachians and the British and IrishCaledonian Orogen. By serendipity, ChuckDrake was on sabbatical leave in Cam-bridge in 1966 and, knowing of  myAppalachian interests, invited me to Lam-ont for a six month sabbatical leave in thesecond half  of  1967. While in Lamont, thewhole picture of  plate tectonics was solid-ifying as a ‘complete’ theory with the workof  Morgan, McKenzie and Parker, LePichon, Isacks et al., and Pitman. Duringthe sabbatical, I developed a tectonic mapof  the Appalachian and Caledonian Chain,on a massive roll of  tracing linen, uponwhich I plotted Lower Palaeozoic conti-nental shelves/platforms, ophiolites, islandarcs, subduction zones, collision zones andall the geological corollary hallmarks of284 John F. Deweyhttp://www.geosciencecanada.caFigure2. The changing views of  the North Atlantic borderlands. On the left is a redrawn coloured version of  the hand-drawn Figure 3 from Tuzo’s 1966 paper in Nature, showingthe concept of  his “Atlantic Ocean of  Lower Paleozoic time.” We see the inference that parts of  Scandinavia andthe British Isles were once part of  the North American continent, and that parts of  eastern North America moreproperly belong with Europe or Africa. On the right is a later reconstruction of  the Appalachian–Caledonian Oro-gen by Hank Williams, from the Decade of  North American Geology volume (Williams 1995), showing thespreading axis of  the modern North Atlantic. It incorporates more detail on the components of  what we now call‘Iapetus,’ but its heritage remains clear. This analysis remains a cornerstone of  regional geology and tectonics inour 21st century, and it is a direct descendant of  Tuzo’s prescient thinking in 1966. Wilson’s (1966) paper, “Did theAtlantic close and then re-open?” surely deserves recognition as one of  the most influential contributions to geo-logical science.plate tectonics, which led to a string of  papers, e.g. Dewey andKay (1968), at the same time as those of  many others, such asAtwater (1970), Hamilton (1969), and Smith (1971). In all this, Tuzo was my main influence, inspirer, and prin-cipal encourager for which he has my eternal gratitude andrespect. Like Bullard and Hess, Tuzo was a kind and generousman with his time, ideas, and encouragement of  the young. Hismind was quick, fertile, and imaginative with an astonishingcapacity for organizing, analyzing, and synthesizing hugeamounts of  data. Above all, he was prepared to admit that hewas wrong and changed his mind in a flash. He was brilliant atasking the right question and following it up with a prodigiousamount of  reading and plotting, seeing through and castingaside irrelevance, and linking apparently disparate notions anddata coherently. He was always well-dressed in suit and tie witha polite but confident demeanor, seemingly happy and con-tented. He is remembered as a brilliant and original synthesizerwho formulated global plate tectonics. He remarked to me andto Kevin Burke that, if  he had known Euler’s Theorem (amethod of  finding the simplest paths between once contigu-ous points), he would have ‘nailed’ plate tectonics cold. It issignificant that Harold (Hank) Williams gained his PhD at theUniversity of  Toronto in 1961 under the supervision of  TuzoWilson. Williams unleashed a productive period in our under-standing of  the geology of  Newfoundland (e.g. Williams 1979)and the opening and closing of  Iapetus. One might fairly saythat Tuzo’s 1965 paper changed the course of  global tectonicsand that his 1966 paper led to a complete new understandingof  the implications of  his 1965 paper for the origin of  moun-tain belts resulting from super-continent cycles, the mostimportant paradigm change in the history of  geology.REFERENCESAtwater, T., 1970, Implications of  plate tectonics for the Cenozoic tectonic evolu-tion of  western North America: Geological Society of  America Bulletin, v. 81,p. 3513–3536, http://dx.doi.org/10.1130/0016-7606(1970)81[3513:IOPTFT]2.0.CO;2.Bullard, E., Everett, J.E., and Smith, A.G., 1965, The fit of  the continents aroundthe Atlantic: Philosophical Transactions of  the Royal Society London, v. A 258,p. 41–51, http://dx.doi.org/10.1098/rsta.1965.0020.Burke, K., and Dewey, J.F., 1973, Plume-generated triple junctions (Abstract): EOSTransactions American Geophysical Union, v. 54, p. 239.Creer, K.M., Irving, E., Nairn, A.E.M., and Runcorn, S.K., 1958, Palaeomagneticresults from different continents and their relation to the problem of  continen-tal drift: Annales de Geophysique, v. 14, p. 492–501.Dewey, J.F., and Kay, M., 1968, Appalachian and Caledonian evidence for drift in thenorth Atlantic, in Phinney, R.A., ed., The history of  the Earth’s crust: PrincetonUniversity Press, p. 161–167.Dietz, R.S., 1961, Continent and ocean basin evolution by spreading of  the sea floor:Nature, v. 190, p. 854–857, http://dx.doi.org/10.1038/190854a0.Griggs, D., 1939, A theory of  mountain-building: American Journal of  Science, v.237, p. 611–650, http://dx.doi.org/10.2475/ajs.237.9.611.Hamilton, W., 1969, Mesozoic California and the underflow of  Pacific mantle: Geo-logical Society of  America Bulletin, v. 80, p. 2409–2430, http://dx.doi.org/10.1130/0016-7606(1969)80[2409:MCATUO]2.0.CO;2.Heezen, B.C., 1960, The rift in the ocean floor: Scientific American, v. 203, p. 98–110, http://dx.doi.org/10.1038/scientificamerican1060-98.Hess, H.H., 1962, History of  Ocean Basins, in Engel, A.E.J., James, H.I., andLeonard, B.F., eds., Petrologic studies: A volume to honor A.F. Buddington:Geological Society of  America, Boulder, CO, p. 599–620, http://dx.doi.org/10.1130/petrologic.1962.599.Holmes, A., 1931, Radioactivity and Earth movements: Transactions of  the Geolog-ical Society of  Glasgow, v. 18, p. 559–606, http://dx.doi.org/10.1144/trans-glas.18.3.559.Isacks, B., Oliver, J., and Sykes, L.R., 1968, Seismology and the new global tectonics:Journal of  Geophysical Research, v. 73, p. 5855–5899, http://dx.doi.org/10.1029/JB073i018p05855.Le Pichon, X., 1968, Sea-floor spreading and continental drift: Journal of  Geophys-ical Research, v. 73, p. 3661–3697, http://dx.doi.org/10.1029/JB073i012p03661.McKenzie, D.P., and Parker, R.L., 1967, The North Pacific: an example of  tectonicson a sphere: Nature, v. 216, p. 1276–1280, http://dx.doi.org/10.1038/2161276a0.Morgan, W.J., 1968, Rises, trenches, great faults, and crustal blocks: Journal of  Geo-physical Research, v. 73, p. 1959–1982, http://dx.doi.org/10.1029/JB073i006p01959.Quennell, A.M., 1958, The structural and geomorphic evolution of  the Dead Searift: Quarterly Journal of  the Geological Society, v. 114, p. 1–24,http://dx.doi.org/10.1144/gsjgs.114.1.0001.Runcorn, S.K., 1962, Palaeomagnetic evidence for continental drift and its geophys-ical cause: International Geophysics, v. 3, p. 1–40, http://dx.doi.org/10.1016/B978-1-4832-2982-9.50006-1.Smith, A.G., 1971, Alpine deformation and the oceanic areas of  the Tethys, Mediter-ranean, and Atlantic: Geological Society of  America Bulletin, v. 82, p. 2039–2070, http://dx.doi.org/10.1130/0016-7606(1971)82[2039:ADATOA]2.0.CO;2.Vine, F.J., and Matthews, D.H., 1963, Magnetic anomalies over oceanic ridges:Nature, v. 199, p. 947–949, http://dx.doi.org/10.1038/199947a0.Wegener, A., 1929, Die Entstehung der Kontinente und Ozeane, 4th ed.: Braun-schweig, Friedrich Vieweg and Sohn Akt. Ges., 231 p.Wellman, H.W., 1955, New Zealand quaternary tectonics: Geologische Rundschau,v. 43, p. 248–257, http://dx.doi.org/10.1007/BF01764108.Williams, H., 1995, Temporal and spatial divisions, in Williams, H., ed., Geology ofthe Appalachian–Caledonian Orogen in Canada and Greenland: GeologicalSurvey of  Canada, Geology of  Canada, 6, p. 21–44.Williams, H., 1979, Appalachian Orogen in Canada: Canadian Journal of  Earth Sci-ences, v. 16, p. 792–807, http://dx.doi.org/10.1139/e79-070.Wilson, J.Tuzo, 1962, Cabot Fault, an Appalachian equivalent of  the San Andreasand Great Glen faults and some implications for continental displacement:Nature, v. 195, p. 135–138, http://dx.doi.org/10.1038/195135a0.Wilson, J.Tuzo, 1963a, Evidence from islands on the spreading of  ocean floors:Nature, v. 197, p. 536–538, http://dx.doi.org/10.1038/197536a0.Wilson, J.Tuzo, 1963b, A possible origin of  the Hawaiian Islands: Canadian Journalof  Physics, v. 41, p. 863–870, http://dx.doi.org/10.1139/p63-094.Wilson, J.Tuzo, 1965, A new class of  faults and their bearing on continental drift:Nature, v. 207, p. 343–347, http://dx.doi.org/10.1038/207343a0.Wilson, J.Tuzo, 1966, Did the Atlantic close and then re-open?: Nature, v. 211, p.676–681, http://dx.doi.org/10.1038/211676a0.Wilson, J.Tuzo, 1966, Are the structures of  the Caribbean and Scotia arc regionsanalogous to ice rafting?: Earth and Planetary Science Letters, v. 1, p. 335–338,http://dx.doi.org/10.1016/0012-821X(66)90019-7.GEOSCIENCE CANADA Volume 43 2016 285http://www.dx.doi.org/10.12789/geocanj.2016.43.108

Tuzo Wilson: An Appreciation on the 50th Anniversary of his 1966 Paper

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Tuzo Wilson: An Appreciation on the 50th Anniversary of his 1966 Paper

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