scholarly journals A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) ‘The fit of the continents around the Atlantic’

2015 ◽  
Vol 373 (2039) ◽  
pp. 20140227 ◽  
Author(s):  
John F. Dewey
Keyword(s):  
Plate Tectonics ◽  
Torsional Rigidity ◽  
Continental Drift ◽  
Shear Zones ◽  
Continental Margins ◽  
Real Motion ◽  
Euler’S Theorem ◽  
The 1960S ◽  
Conjugate Margins ◽  
350Th Anniversary

In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160 Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900 m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society .

Plate Tectonics Now and in the Past

2004 ◽  
Author(s):  
John J. W. Rogers ◽  
M. Santosh
Keyword(s):  
Plate Tectonics ◽  
Oceanic Lithosphere ◽  
Continental Margins ◽  
Island Arcs ◽  
Low Velocity ◽  
S Waves ◽  
Ocean Ridges ◽  
1960S And 1970S ◽  
Tectonic Contact ◽  
The 1960S

The concepts known as plate tectonics that began to develop in the 1960s built on a foundation of information that included: • The earth’s mantle is rigid enough to transmit seismic P and S waves, but it is mobile to long-term stresses. • The earth’s temperature gradient is so high that convective overturn must occur in the mantle. • The top of the mobile part of the mantle is a zone of relatively low velocity at depths of about 100 to 200 km. This zone separates an underlying asthenosphere from a rigid lithosphere, which includes rigid upper mantle and crust. • Seismic activity, commonly accompanied by volcanism, occurs along narrow, relatively linear, zones in oceans and along some continental margins. • The zones of instability surround large areas of comparative stability. • Ocean lithosphere is continually generated along mid-ocean ridges and destroyed where it descends under the margins of continents and island arcs. This causes oceans to become larger, but shrinkage of oceans can occur where lithosphere is destroyed around ocean margins faster than it is formed within the basin. • Some of the belts of instability are faults with lateral offsets of hundreds of kilometers. • Some continental margins are unstable (Pacific type), but others are attached to oceanic lithosphere without any apparent tectonic contact (Atlantic type). • Different areas containing continents and attached oceanic lithosphere move around the earth independently of each other. Most of this chapter consists of a summary of plate tectonics in the present earth, including processes along plate margins and the types of rocks formed there (readers who want more detailed information are referred to Rogers, 1993a; Kearey, 1996; and Condie, 1999). We also briefly discuss plumes and then finish with a word of caution about interpreting the history of the ancient and hotter earth with the principles of modern plate tectonics. Starting from the body of continually expanding information summarized above, numerous earth scientists in the 1960s and 1970s began to establish a conceptual framework that would organize scientific thinking about the earth’s tectonic processes. This required a new terminology, and it arrived rapidly (Oreskes, 2002). Geologists decided to call the stable areas “plates” and the unstable zones around them “plate margins.” Thus, the concept became known as “plate tectonics.” Plates are essentially broad regions of lithosphere, although the failure to detect low-velocity zones under many continents leaves unresolved questions.

1. The basic idea

2015 ◽  
pp. 1-16
Author(s):  
Peter Molnar
Keyword(s):  
Rapid Growth ◽  
Plate Tectonics ◽  
Continental Drift ◽  
The Earth ◽  
Chemical Stratification ◽  
The Face ◽  
The 1950S ◽  
The 1960S

‘The basic idea’ presents the principles of plate tectonics and describes how this revolutionary theory took hold. It begins with Alfred Wegener in 1912, who proposed the concept of continental drift and a former huge continent, Gondwanaland. In the face of strong opposition, this theory was supported by the development of palaeomagnetism in the 1950s and, in the 1960s, became subsumed within the broader framework of plate tectonics. Three major events precipitated this change: a switch in emphasis from continents to ocean basins and their exploration; rapid growth in seismology; and a shift in perspective from the chemical stratification of the Earth, in terms of crust and mantle, to another that emphasized strength—a strong lithosphere, some 100–200 km thick, overlying a weak asthenosphere.

On crustal plates

1975 ◽  
Vol 65 (5) ◽  
pp. 1495-1500
Author(s):  
Don Tocher
Keyword(s):  
Plate Tectonics ◽  
Seismic Waves ◽  
Continental Drift ◽  
Active Regions ◽  
Continental Margins ◽  
Island Arcs ◽  
Low Velocity ◽  
Transform Faults ◽  
Sea Floor Spreading ◽  
Velocity Layer

Abstract During the decade just past, developments in Seismology have played an active and central role in the development of the concept of Plate Tectonics. Observational Seismology has provided support for and verification of a number of the dynamic aspects of the hypotheses of continental drift, sea-floor spreading, transform faults and the underthrusting of the lithosphere at island arcs and some continental margins. Those types of seismological evidence which bear on the question of the thickness of the lithosphere are either indirect or circumstantial, or both. As early as 1926, Gutenberg postulated the existence of a layer at a depth of 80 to 150 or 200 km, probably worldwide in extent, in which the velocities of seismic waves are slightly lower than in the immediately overlying layers. Some plate tectonics workers equate this low-velocity layer to the relatively-weak asthenosphere required by Plate Tectonics to underlie the stronger, more brittle lithosphere. In this review, several lines of evidence are marshalled in support of a plate model of the continental crust in seismically active regions in which a layer of decoupling of an upper, lithospheric layer from the weaker substrate may lie in the crust itself at a depth of perhaps 10 to 15 km.

The Paving Stone Theory of World Tectonics

2018 ◽  
Author(s):  
Roy Livermore
Keyword(s):  
Indian Ocean ◽  
Plate Tectonics ◽  
Earth Science ◽  
Transform Faults ◽  
Plate Motions ◽  
Euler’S Theorem ◽  
History Of ◽  
New Ideas ◽  
Entire History ◽  
The Indian Ocean

Tuzo Wilson introduces the concept of transform faults, which has the effect of transforming Earth Science forever. Resistance to the new ideas is finally overcome in the late 1960s, as the theory of moving plates is established. Two scientists play a major role in quantifying the embryonic theory that is eventually dubbed ‘plate tectonics’. Dan McKenzie applies Euler’s theorem, used previously by Teddy Bullard to reconstruct the continents around the Atlantic, to the problem of plate rotations on a sphere and uses it to unravel the entire history of the Indian Ocean. Jason Morgan also wraps plate tectonics around a sphere. Tuzo Wilson introduces the idea of a fixed hotspot beneath Hawaii, an idea taken up by Jason Morgan to create an absolute reference frame for plate motions.

Definition of tectono-sedimentary elements for rifted continental margins of the Norwegian and Greenland seas

2021 ◽  
pp. M57-2021-31
Author(s):  
Harald Brekke ◽  
Halvor S. S. Bunkholt ◽  
Jan I. Faleide ◽  
Michael B. W. Fyhn
Keyword(s):  
Lower Jurassic ◽  
Passive Margin ◽  
Continental Margins ◽  
Axial Line ◽  
Continental Breakup ◽  
The North ◽  
Tectonic Development ◽  
Definition Of ◽  
Conjugate Margins ◽  
Greenland Margin

AbstractThe geology of the conjugate continental margins of the Norwegian and Greenland Seas reflects 400 Ma of post-Caledonian continental rifting, continental breakup between early Eocene and Miocene times, and subsequent passive margin conditions accompanying seafloor spreading. During Devonian-Carboniferous time, rifting and continental deposition prevailed, but from the mid-Carboniferous, rifting decreased and marine deposition commenced in the north culminating in a Late Permian open seaway as rifting resumed. The seaway became partly filled by Triassic and Lower Jurassic sediments causing mixed marine/non-marine deposition. A permanent, open seaway established by the end of the Early Jurassic and was followed by the development of an axial line of deep marine Cretaceous basins. The final, strong rift pulse of continental breakup occurred along a line oblique to the axis of these basins. The Jan Mayen Micro-Continent formed by resumed rifting in a part of the East Greenland margin in Eocene to Miocene times. This complex tectonic development is reflected in the sedimentary record in the two conjugate margins, which clearly shows their common pre-breakup geological development. The strong correlation between the two present margins is the basis for defining seven tectono-sedimentary elements (TSE) and establishing eight composite tectono-sedimentary elements (CTSE) in the region.

Tectonic modelling state of the art and future challenges 

2021 ◽  
Author(s):  
Laetitia Le Pourhiet
Keyword(s):  
Numerical Modelling ◽  
Continuum Mechanics ◽  
Plate Tectonics ◽  
Shear Bands ◽  
Plate Boundary ◽  
Shear Zones ◽  
Thermal Dependence ◽  
Brittle Behavior ◽  
Viscous Shear ◽  
Analogue Models

<p>Tectonic modelling is a very wide area of application over a large range of time scale and length scale. What mainly characterize this modelling field is the coexistence of brittle fractures which relates to the field of fracture mechanics and plastic to viscous shear zones which belongs to the two main branch of continuum mechanics (solid and fluid respectively).</p><p>This type of problems arises sometimes in engineering but material do not change their behavior with loading rate or with time or with temperature, and rarely are engineers interested in modelling large displacement in post failure stage.  As a result, tectonicists cannot use commercial packages to simulate their problems and need to develop methodologies specific to their field.</p><p>Historically, the first tectonics models made use of simple analogue materials and corresponded more to modelism than actual analogue models. While the imaging of the models, and the characterization of the analogue materials have made a lot of progress in the last 15 years, up to recently, most analogue models still relied on sand and silicone putty to represent the brittle and viscous counter part of tectonic plates.</p><p>Since the late 80’s, but mostly during the years 2000, numerical modelling has exploded on the market, as contrarily to analogue modelling, it was easier to capture the thermal dependence of frictional-viscous transition, I use frictional here because most models in tectonics use continuum mechanics approach and in fine do not include brittle material s.s. but rather frictional shear bands. Some groups run these types of simulation routinely in 3D today but this performance has been made at the cost of a major simplification in the rheology: the disappearance of elasticity and compressibility which was present in late 90’s early 2000 simulations and is still very costly because the treatment of “brittle” rheology seriously amped code performances.</p><p>Until recently, in both analogue and numerical modelling, I have some kind of feeling that we have been running the same routine experiments over and over again with better performance, or better acquisition.  </p><p>We are now entering a new exciting era in tectonic modelling both from experimental and numerical side: a ) emergence of complex analogue material or rheological laws that efforts in upscaling from micro-mechanical process observed on the field to plate boundary scale, or from earthquake cycle to plate tectonics, b) emergence of new interesting set up’s in terms of boundary conditions in 3D, c) development of robust numerical technics for brittle behavior d) development of new applications to make our field more predictive that will enlarge the community of end-users of the modelling results</p><p>I will review these novelties with some of the work develop with colleagues and students but also with examples from the literature and try to quickly draw a picture of where we are at and where we go.</p>

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