No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
John Tuzo Wilson: a Canadian who revolutionized Earth Sciences
Canadian Journal of Earth Sciences
Abstract
John Tuzo Wilson (1908–1993) was one of the greatest Canadian scientists of the 20th century. His contributions to Earth Sciences, leading the formulation of the theory of plate tectonics, have revolutionized our understanding of how the planet Earth works and evolved over the past 4 billion years. This 50th anniversary special issue of the Canadian Journal of Earth Sciences is dedicated in honour of John Tuzo Wilson, who inspired tens of thousands of students all around the world to study the Earth. This special issue contains 12 papers dealing with various aspects of the “Wilson Cycle” in the geologic record, plate tectonics, mantle plumes, and how John Tuzo Wilson accepted “continental drift” and formulated the theory of plate tectonics. The contributions have mostly been made by geoscientists who directly or indirectly associated with John Tuzo Wilson and have contributed significantly to the plate tectonics paradigm.
... Paranaiba Basin in Brazil, and West Siberia Basin in Russia) (Middleton, 1989;Allen et al., 2015;Daly et al. 2018). A number of retrospective papers have been published in recent times, highlighting the work and notable contributions by Tuzo Wilson to plate tectonics (Garland, 1995;Polat, 2014;Dewey, 2016) and the Wilson Cycle concept more A C C E P T E D M A N U S C R I P T generally (Burke, 2011;Buiter & Torsvik, 2014). Between 1961 and1968, Tuzo Wilson made several seminal contributions to our understanding of Earth Sciences, identifying a number of key elements of global geodynamics that dominated the evolution of our planet, namely plate tectonics, mantle plumes of deep origin, and the "Wilson Cycle" of ocean opening and closing (Burke 2011). ...
It is now more than fifty years since Tuzo Wilson published his paper asking “Did the Atlantic close and then re-open?”. This led to the “Wilson cycle” concept in which the repeated opening and closing of ocean basins along old orogenic belts is a key process in the assembly and breakup of supercontinents. This implied that the processes of rifting and mountain building somehow pre-conditioned and weakened the lithosphere in these regions making them susceptible to strain localization during future deformation episodes. Here we provide a retrospective look at the development of the concept, how it was evolved over the past five decades, current thinking and future focus areas. The Wilson Cycle has proved enormously important to the theory and practice of geology and underlies much of what we know about the geological evolution of the Earth and its lithosphere. The concept will no doubt continue to be developed as we gain more understanding of the physical processes that control mantle convection, plate tectonics, and as more data become available from currently less accessible regions.
... Modern plate tectonic processes observable in the present plate mosaic serve as examples of the complexities that might be anticipated in assessment of the presence or absence of Wilson Cycles in ancient cratons. Consider, for instance, a simple Wilson Cycle, which describes the geologic consequences of plate separation and later convergence and collision (e.g., Polat, 2014). When a continent breaks up, the two initially contiguous pieces move apart, their rifted margins thermally subside, and any rift-related volcanic or sedimentary rocks are covered by sandstones, shales, and carbonates of a passive margin. ...
Archean cratons have map patterns and rock associations that are diagnostic of the Wilson Cycle. The North China Craton (NCC) consists of several distinctly different tectonic units, but the delineation and understanding of the significance of individual sutures and the rocks between them has been controversial. We present an actualistic tectonic division and evolution of the North China Craton based on Wilson Cycle and comparative tectonic analysis that uses a multi-disciplinary approach in order to define sutures, their ages, and the nature of the rocks between them, to determine their mode of formation and means of accretion or exhumation, and propose appropriate modern analogues. The eastern unit of the craton consists of several different small blocks assembled between 2.6 and 2.7 Ga ago, that resemble fragments of accreted arcs from an assembled archipelago similar to those in the extant SW Pacific. A thick Atlantic-type passive margin developed on the western side of the newly assembled Eastern Block by 2.6-2.5 Ga. A > 1,300 km- long arc and accretionary prism collided with the margin of the Eastern Block at 2.5 Ga, obducting ophiolites and ophiolitic mélanges onto the block, and depositing a thick clastic wedge in a foreland basin farther into the Eastern Block. This was followed by an arc-polarity reversal, which led to a short-lived injection of mantle wedge-derived melts to the base of the crust that led to the intrusion of mafic dikes and arc-type granitoid (TTG) plutons with associated metamorphism. By 2.43 Ga, the remaining open ocean west of the accreted arc closed with the collision of an oceanic plateau now preserved as the Western Block with the collision-modified margin of the Eastern Block, causing further deformation inthe Central Orogenic Belt. 2.4-2.35 Ga rifting of the newly amalgamated continental block formed a rift along its center, and new oceans within the other two rift arms, which removed a still-unknown continental fragment from its northern margin. By 2.3 Ga an arc collided with a new Atlantic-type margin developed over the rift sequence along the northern margin of the craton, and thus was converted to an Andean margin through arc-polarity reversal.
The history of geoscience is marked by the work of exemplary scientists, who through their endeavours, changed the way we think about the Earth, its history, processes and resources. Some made huge intuitive leaps, recognising, for example, the immensity of geological time or the mobility of the continents. Others described rocks, minerals and fossils in the field, or laboratory, and provided vital data that allowed theories to develop. Others still embraced new technologies, such as geophysics, that enabled what cannot be observed directly to be interpreted. Many led colourful lives or overcame adverse circumstances. These are people worth knowing more about, not least, for the inspiration they provide.
The free e-book "Great Geologists" can be found at the Free Neftex free online geoscience resource. To access, please sign up here: https://geoweb.neftex.com/home/explore. Existing subscribers will find the book within the magazine pages.
The Archean craton of West Greenland consists of many fault-bounded Eoarchean to Neoarchean tectonic terranes (crustal blocks). These tectonic terranes are composed mainly of tonalite-trondhjemite-granodiorite (TTG) gneisses, granitic gneisses, metavolcanic-dominated supracrustal belts, layered anorthositic complexes, and late- to post-tectonic granites. Rock assemblages and geochemical signatures in these terranes suggest that they represent fragments of dismembered oceanic island arcs, consisting mainly of TTG plutons, tholeiitic to calc-alkaline basalts, boninites, picrites, and cumulate layers of ultramafic rocks, gabbros, leucogabbros and anorthosites, with minor sedimentary rocks. The structural characteristics of the terrane boundaries are consistent with the assembly of these island arcs through modern style of horizontal tectonics, suggesting that the Archean craton of West Greenland grew at convergent plate margins. Several supracrustal belts that occur at or near the terrane boundaries are interpreted as relict accretionary prisms. The terranes display fold and thrust structures and contain numerous 10 cm to 20 m wide bifurcating, ductile shear zones that are characterized by a variety of structures including transposed and redistributed isoclinal folds. Geometrically these structures are similar to those occurring on regional scales, suggesting that the Archean craton of West Greenland can be interpreted as a continental scale accretionary complex, such as the Paleozoic Altaids. Melting of metavolcanic rocks during tectonic thickening in the arcs played an important role in the generation of TTGs. Non-uniformitarian models proposed for the origin of Archean terranes have no analogs in the geologic record and are inconsistent with structural, lithological, petrological and geochemical data collected from Archean terranes over the last four decades. The style of deformation and generation of felsic rocks on outcrop scales in the Archean craton of West Greenland and the Mesozoic Sulu orogenic belt of eastern China are similar, consistent with the formation of Archean continental crust by subduction zone processes.
In the Archean, like now, the granitoids that constitute the core of the continental crust formed in subduction zones. Hydrous basaltic magmas from the mantle wedge rose to the base of the crust where they fractionally crystallised or remelted underplated rocks to yield more evolved granitic magmas. Alternative models to explain Archean granitoids, which call on melting in intraplate settings such as the bases of oceanic plateaus, are implausible because such settings lack the water that is essential to form voluminous granitic melt. From the end of the Archean to the late Proterozoic, the continental crust grew in a series of major pulses, each triggered by accelerated mantle convection. The arrival of large mantle plumes displaced material from the upper mantle, accelerating the rate of subduction and causing a pulse of crustal growth. The Hadean crust was mafic and it underwent internal partial melting to produce the granitic melts that crystallised the Jack Hills zircons. This crust was disrupted by the Late Heavy Bombardment and from then on, since about 3.9 Ga, plate tectonics has operated.
How the Earth's earliest crust was formed and when present-day plate tectonics (i.e., subduction) and life commenced remain fundamental questions in Earth sciences. Whereas the bulk composition of the crust is similar to that of rocks generated in subduction settings, it does not necessarily follow that melting and crust formation require subduction. Many workers suggest that subduction may have only commenced toward the end of the Archean or later. Here we observe that both the stratigraphy and geochemistry of rocks found in Quebec, Canada, that have been variously argued to be 4.4 or 3.8 Ga in age, closely match those from the modern-day Izu-Bonin-Mariana forearc. We suggest that this geochemical stratigraphy might provide a more robust test of ancient tectonic setting than individual chemical or isotopic signatures in rocks or detrital minerals. If correct, the match suggests that at least some form of subduction may have been operating as early as the Hadean or Eoarchean. This could have provided an ideal location for the development of first life.
Laterally extensive belts of mélange characterize Phanerozoic
convergent plate margins, but are rare in Archean terranes. We document
a late Archean mélange in the Zanhuang Massif of the North China
Craton (NCC). The Zanhuang mélange separates a passive margin to
foreland basin sequence developed on the western edge of the Eastern
Block of the NCC from an arc terrane consisting of trondhjemitic,
tonalitic and granodioritic (TTG) gneisses in the Central Orogenic Belt
(COB) of the NCC. The mélange belt contains a structurally
complex tectonic mixture of metapelites, metapsammites, marbles and
quartzites mixed with exotic tectonic blocks of ultramafic and
metagabbroic rocks, metabasalts that locally include relict pillow
structures, and TTG gneisses. All units in the mélange have been
intruded by mafic dikes that were subsequently deformed, and are now
preserved as garnet-amphibolite boudins. We interpret the
mélange to mark the suture zone between the Eastern Block and the
arc terrane in the COB. Field relationships and geochemistry suggest
that the exotic ultramafic-metagabbroic-metabasaltic blocks
are possible slivers of an intra-oceanic arc or fore-arc ophiolite
incorporated into the mélange during the arc-continent
collision process. A circa 2.5 Ga granitic pluton intrudes the
mélange and undeformed circa 2.5 Ga pegmatites cut the
mélange. Tectonic models for the evolution of the COB are varied,
but include models that favor collision at 2.5 Ga, 2.1 Ga, and 1.8 Ga.
This work shows clearly, from field structural relationships and
geochronology, that the first collision must have occurred prior to 2.5
Ga, consistent with late Archean suturing of the western margin of the
Eastern Block with an arc terrane (Fuping terrane) during an
arc-continent collision. The presence of an Archean mélange
with exotic blocks in a suture zone between an Archean arc and
continental margin is clear evidence for the operation of plate
tectonics at circa 2.5 Ga.
To investigate formation of the Earth's earliest continental crust, partial-melting experiments were conducted (at 900–1100 °C and 0.5–3.0 GPa) on two greenstones from the 4.3 Ga Nuvvuagittuq complex of Quebec, Canada. For comparison, experiments were also conducted on a compositionally similar but modern arc volcanic (a Tongan boninite). At 1.5–3.0 GPa and 950–1100 °C, the experimentally produced melts are compositionally similar to the tonalite-trondhjemite-granodiorite (TTG) granitoids that compose most of Earth's early continental crust, including a 3.66 Ga tonalite that encloses the Nuvvuagittuq Complex. Because the degree of melting needed to produce the TTG-like melts is comparatively high (>30%), the relative concentrations of most incompatible elements in the melts are similar to those in their greenstone parent rocks. These greenstones have compositional affinities with modern subduction zone magmas and do not resemble mid-oceanic ridge basalts. That arc-like mafic rocks could have been selectively involved in TTG formation (in spite of their volumetrically subordinate status in most greenstone terrains) must reflect tectonic circumstances that were specific to their generation. These must have enabled accumulations sufficiently deep to melt at the 1.5–3.0 GPa needed to generate TTG magmas from eclogitic sources. They are also likely to have been related to some form of crustal recycling whereby mafic crust and water were returned to the mantle and arc-like mafic magmas generated as a consequence. To what degree these circumstances replicated modern plate tectonics is difficult to say, but it seems likely that, as in the modern Earth, the Hadean crust was organized into different tectonic environments and that one of these gave rise to the first continental crust.
▪ Abstract Turkic-type orogeny is a class of collisional mountain building, in which the precollision history of one, or both, of the colliding continents involves the growth of very large, subcontinent-size subduction-accretion complexes, into which magmatic arc axes commonly migrate and thus enlarge the continent to which they are attached. A review of the evolution of two Phanerozoic (Altaids, Nipponides), one Neoproterozoic (East African), and one Archean (Yilgarn) Turkic-type orogens shows that this type of orogeny may have been the principal builder of the continental crust through recorded Earth history. The total juvenile material added to Turkic-type orogens at any one time in the Phanerozoic seems close to 1 km3/year, which about equals the amount of material annually fed into the mantle at subduction zones. As some 0.02 to 0.03% of that material is generally agreed to return to the crust by arc magmatism, these figures provide a minimum net growth rate for the continental crust during the Phane...
The earliest compounds forming Earth's first continental crust were magmatic rocks with tonalitic-trondhjemitic-granodioritic composition (TTGs). TTGs are widely seen as originating from melting of hydrated oceanic crust in subduction zones. Alternative models argue that they may have formed by melting within thickened mafic oceanic protocrust. To simulate formation of Eoarchean TTGs in different tectonic regimes, we combine for the first time the thermodynamic calculation of residual assemblages with subsequent modeling of trace element contents in TTGs. We compare water-absent partial melting of two hydrated starting compositions, a modern mid-oceanic-ridge basalt (MORB) and a typical Eoarchean arc tholeiite from the Isua Supracrustal Belt that represents the country rock of Earth's oldest TTGs in southern West Greenland. At 10 kbar, partial melting of MORB-like residues results in modeled TTG compositions that are very different from natural ones. Melting at higher pressures (14 and 18 kbar) leads to a better match, but several key trace element parameters in TTGs are still amiss. A perfect fit for trace element compositions is achieved by melting of Eoarchean arc tholeiites at 10 and 14 kbar. These protoliths contain less Al and Na and more Fe and Mg as compared to present-day MORB and form amphibole-rich and plagioclase-free residues even at low pressures. Formation of Earth's oldest continental crust is therefore best explained by melting within tectonically thickened mafic island-arc crust.
The amphibolite facies Eoarchaean Isua supracrustal belt (northern part of the Nuuk region, southern West Greenland) is dominated by strongly deformed metabasalts, with chert, banded iron formation, felsic volcanic and volcano-sedimentary rocks and minor gabbro and sedimentary carbonates. It comprises a suture zone between a northern terrane formed at ca. 3700 Ma and a southern one formed at ca. 3800 Ma. At the junction between these two terranes is a strongly tectonised, thin unit of metachert, BIF and carbonate-bearing rocks with minor detrital components, named the dividing sedimentary unit. Away from the belt, the northern terrane is dominated by ca. 3700 Ma tonalites and the southern one by ca. 3800 Ma tonalites.
A sheeted-dike complex within the approximately 3.8-billion-year-old Isua supracrustal belt (ISB) in southwest Greenland provides the oldest evidence of oceanic crustal accretion by spreading. The geochemistry of the dikes and associated pillow lavas demonstrates an intraoceanic island arc and mid-ocean ridge-like setting, and their oxygen isotopes suggest a hydrothermal ocean-floor-type metamorphism. The pillows and dikes are associated with gabbroic and ultramafic rocks that together make up an ophiolitic association: the Paleoarchean Isua ophiolite complex. These sheeted dikes offer evidence for remnants of oceanic crust formed by sea-floor spreading of the earliest intact rocks on Earth.
This persuasive, elegantly written book argues that understanding evolution has never mattered more in human history. The author uses evidence from archaeology, geography, anatomy, biochemistry, radiometric dating, cell biology, chromosomes, and DNA to establish the inescapable conclusion that we evolved and are still evolving. He also explains in detail how health, food production, and human impact on the environment are dependent on our knowledge of evolution. This is essential reading for gaining a fuller appreciation of who we are, our place in the great expanse of life, and the importance of our actions.
It is noted that different physicists and geologists have in recent years espoused not less than four groups of theories of the physical behavior of the Earth's interior. Recent observations of submarine geology, heat, and rock magnetism have tended to support some form of continental drift rather than the older concept of a rigid earth.The Hawaiian Islands are one of seven, parallel, linear chains of islands and seamounts in the Pacific Ocean of Tertiary to Recent age. Their nature had previously been explained in terms of a series of volcanoes along parallel faults. Horizontal shear motion along these faults was supposed to be extending them southeasterly.The inadequacies of this explanation are pointed out. If there are convection currents in the Pacific region and if the upper parts of these cells move faster than the central parts, sources of lava within the slower moving cores could give rise to linear chains of progressively older volcanic piles such as the Hawaiian Islands. This view is shown to be compatible with seismic observations and age determinations.
Resolution of the sixty year debate over continental drift, culminating in the triumph of plate tectonics, changed the very fabric of Earth Science. This four-volume treatise on the continental drift controversy is the first complete history of the origin, debate and gradual acceptance of this revolutionary theory. Based on extensive interviews, archival papers and original works, Frankel weaves together the lives and work of the scientists involved, producing an accessible narrative for scientists and non-scientists alike. This third volume describes the golden age of marine geology and geophysics. Fuelled by the Cold War, US and British workers led the way in making discoveries and forming new hypotheses, especially about the origin of oceanic ridges. Discovery of transform faults in the ocean crust and symmetric patterns of geomagnetic reversals either side of mid-oceanic ridges in the mid 1960s led to the rapid acceptance of seafloor spreading and the birth of plate tectonics.
Fifty years after a paper linked sea-floor magnetic stripes with continental drift, Naomi Oreskes explains its legacy as a lesson in achieving scientific consensus.
It is noted that different physicists and geologists have in recent years espoused not less than four groups of theories of the physical behavior of the Earth’s interior. Recent observations of submarine geology, heat, and rock magnetism have tended to support some form of continental drift rather than the older concept of a rigid earth.The Hawaiian Islands are one of seven, parallel, linear chains of islands and seamounts in the Pacific Ocean of Tertiary to Recent age. Their nature had previously been explained in terms of a series of volcanoes along parallel faults. Horizontal shear motion along these faults was supposed to be extending them southeasterly.The inadequacies of this explanation are pointed out. If there are convection currents in the Pacific region and if the upper parts of these cells move faster than the central parts, sources of lava within the slower moving cores could give rise to linear chains of progressively older volcanic piles such as the Hawaiian Islands. This view is shown to be compatible with seismic observations and age determinations.
Science as a Way of Knowing is a project being developed by the American Society of Zoologists' education committee. The project, co-sponsored by several professional organizations, seeks to increase the effectiveness of college-level biology. A report on the project's goals, symposia, publications, reprints, and sponsorship needs is presented. (DH)
Orogeny, the process by which the earth's prominent mountain ranges are
constructed, has been a central topic of interest in the earth sciences
since at least the end of the 18th century. The recognition that strains
and displacements of very considerable magnitude occur along all of the
three dimensions within an orogenic belt during its evolution has grown
gradually during the last two centuries. Emphasis on primary vertical
movements dominated the ideas on the nature of orogeny during the first
half of the 19th century, whereas compression and consequent uplift
across mountain belts were believed to be the main cause for their
origin during the subsequent one hundred years or so that were spent
under the dominance of the fixist contraction theory. Mobilist
tectonicians realised that continental drift in places also required
motion along the trend of orogenic belts, but this view did not gain
general acceptance. Recognition of significant strike-slip motion
parallel or subparallel with mountain ranges evolved independently and
mostly within the fixist camp. By the 1960's presence of important
motions both along and across mountain belts had become common
knowledge, but no theoretical basis existed to account for them all.
By 1968, J. Tuzo Wilson had identified three basic elements of geodynamics: plate tectonics, mantle plumes of deep origin, and the Wilson Cycle of ocean opening and closing, which provides evidence of plate tectonic behavior in times before quantifiable plate rotations. My pre-1968 experience disposed me to try to play a part in testing these ideas. Most recently, with colleagues, I have been able to show that deep-seated plumes of the past ∼5.5 × 108 years have risen only from narrow plume generation zones (PGZs) at the core-mantle boundary (CMB) mostly on the edges of two Large Low Shear wave Velocity Provinces (LLSVPs) that have been stable, antipodal, and equatorial in their present positions for hundreds of millions of years and perhaps much longer. A need now is to develop an understanding of Earth that embodies plate tectonics, deeply subducted slabs, and stable LLSVPs with plumes that rise from PGZs on the CMB.
A Brief History of Science - As seen through the development of scientific instruments
- T Crump
What Evolution Is. Basic Books
- E Mayr
The Scientists - An Epic of Discovery
- A Robinson
Science – In 100 Key Breakthroughs
- P Parsons