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.

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.

4. Subduction of oceanic lithosphere

2015 ◽  
pp. 53-76
Author(s):  
Peter Molnar
Keyword(s):  
Oceanic Lithosphere ◽  
Great Depth ◽  
Continental Margins ◽  
Island Arcs ◽  
The Andes ◽  
Mid Ocean Ridge ◽  
Subducting Plate ◽  
Ocean Ridge ◽  
Large Earthquakes ◽  
Adjacent Rock

‘Subduction of oceanic lithosphere’ begins with the notion that for the Earth not to expand, the sum total of new lithosphere made at a spreading centre (or mid-ocean ridge) must be matched by the removal, by subduction, of an equal amount of lithosphere elsewhere. The subduction process is asymmetric: one plate will slide beneath the other at island arcs and continental margins like the Andes of South America. Before it plunges beneath the island arc, the subducting plate of lithosphere bends down gently to cause a deep-sea trench. The subducting plate slides beneath the region between the trench and volcanoes, commonly in large earthquakes, and plunges to great depth, pulled down by gravity acting on the dense slab of subducted lithosphere. Water carried to depth by the subducting plate lowers the melting temperature of the adjacent rock and enables volcanoes to form.

Plate Tectonics

2021 ◽  
pp. 114-136
Author(s):  
Elisabeth Ervin-Blankenheim
Keyword(s):  
Plate Tectonics ◽  
Plastic Material ◽  
Convergent Margins ◽  
Island Arcs ◽  
Mountain Ranges ◽  
Ocean Ridges ◽  
Rock Types ◽  
The Pacific ◽  
The Pacific Ocean ◽  
The Many

Plate tectonics, the grand unifying theory of geology, and its relation to the Earth is explained in this chapter. The planet transforms through time by means of the movement of rigid plates carrying the continents riding on the plastic material in the Earth’s upper mantle. Three major plate boundaries are divergent margins, where new ocean floor is being created along mid-ocean ridges and plates separate from one another; convergent margins, where the material is subducted and consumed as different types of plates collide, creating trenches, island arcs or mountain ranges, and transform boundaries; and where plates slide past one another. Besides the three predominant boundaries, hot spots caused by mantle plumes and diffuse boundaries make up additional dynamic forces in tectonics. Beyond these categories, geologists still are learning about tectonics; some boundaries are unknown or speculative. Plate tectonics explains why many of the Earth’s hazards are found where there are. Earthquakes trace many plate margins, as do volcanoes. The area around the Pacific Ocean is called the “Ring of Fire” because of the many volcanoes related to subducting plates. Tectonics accounts for why certain rocks are located where they are; for example, all rock types are found at convergent margins. The theory also predicts where valuable mineral and economic deposits are located.

Links of planetary energetics to moon size, orbit, and planet spin: A new mechanism for plate tectonics

2022 ◽  
Author(s):  
Anne M. Hofmeister ◽  
Robert E. Criss ◽  
Everett M. Criss
Keyword(s):  
Plate Tectonics ◽  
Large Scale ◽  
Low Velocity ◽  
Radiogenic Heat ◽  
Plate Motions ◽  
Low Velocity Zone ◽  
Ocean Ridges ◽  
Inertial Response ◽  
Rocky Planets ◽  
Velocity Zone

ABSTRACT Lateral accelerations require lateral forces. We propose that force imbalances in the unique Earth-Moon-Sun system cause large-scale, cooperative tectonic motions. The solar gravitational pull on the Moon, being 2.2× terrestrial pull, causes lunar drift, orbital elongation, and an ~1000 km radial monthly excursion of the Earth-Moon barycenter inside Earth’s mantle. Earth’s spin superimposes an approximately longitudinal 24 h circuit of the barycenter. Because the oscillating barycenter lies 3500–5500 km from the geocenter, Earth’s tangential orbital acceleration and solar pull are imbalanced. Near-surface motions are enabled by a weak low-velocity zone underlying the cold, brittle lithosphere: The thermal states of both layers result from leakage of Earth’s internal radiogenic heat to space. Concomitantly, stress induced by spin cracks the lithosphere in a classic X-pattern, creating mid-ocean ridges and plate segments. The inertial response of our high-spin planet with its low-velocity zone is ~10 cm yr–1 westward drift of the entire lithosphere, which largely dictates plate motions. The thermal profile causes sinking plates to thin and disappear by depths of ~200–660 km, depending on angle and speed. Cyclical stresses are effective agents of failure, thereby adding asymmetry to plate motions. A comparison of rocky planets shows that the presence and longevity of volcanism and tectonism depend on the particular combination of moon size, moon orbital orientation, proximity to the Sun, and rates of body spin and cooling. Earth is the only rocky planet with all the factors needed for plate tectonics.

scholarly journals Lithospheric thinning due to hydration and melting at oceanic transform plate boundaries

2021 ◽  
Author(s):  
Zhikai Wang ◽  
Satish Singh ◽  
Cecile Prigent ◽  
Emma Gregory ◽  
Milena Marjanovic
Keyword(s):  
Plate Tectonics ◽  
Melting Zone ◽  
Oceanic Lithosphere ◽  
Small Scale ◽  
Deep Penetration ◽  
Plate Boundaries ◽  
Transform Fault ◽  
Equatorial Atlantic ◽  
Low Velocity ◽  
Velocity Anomaly

Abstract Transform plate boundaries, one of the key elements of plate tectonics, accommodate lateral motions and produce large earthquakes, but their nature at depth remains enigmatic. Using ultra-long offset seismic data, here we report the presence of a low-velocity anomaly extending down to ~60 km depth beneath the Romanche transform fault in the equatorial Atlantic Ocean. Our result indicates the presence of deep penetration of water leading to extensive serpentinization down to 16 km, followed by a shear mylonite zone down to 32 km over a low-temperature water induced-melting zone, elevating the lithosphere-asthenosphere boundary and hence thinning the lithosphere significantly beneath the transform fault. The presence of a thinned lithosphere and the melt underneath could lead to volcanism, migration and mixing of the water-induced melt with the high-temperature melt beneath the ridge axis, and small-scale convections beneath transform boundaries. Hence, a thinned lithosphere will have a major impact on the dynamics of ridge-transform system, and will influence the evolution of fracture zones and oceanic lithosphere.

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 .

Ken Russell's Wartime Imagery

2015 ◽  
Vol 12 (4) ◽  
pp. 539-555 ◽  
Author(s):  
Kevin M. Flanagan
Keyword(s):  
Second World War ◽  
World War ◽  
War Films ◽  
Personal Style ◽  
American Cinema ◽  
1960S And 1970S ◽  
The 1960S ◽  
Second World ◽  
Wartime Experience ◽  
National Experience

This article traces Ken Russell's explorations of war and wartime experience over the course of his career. In particular, it argues that Russell's scattered attempts at coming to terms with war, the rise of fascism and memorialisation are best understood in terms of a combination of Russell's own tastes and personal style, wider stylistic and thematic trends in Euro-American cinema during the 1960s and 1970s, and discourses of collective national experience. In addition to identifying Russell's recurrent techniques, this article focuses on how the residual impacts of the First and Second World Wars appear in his favoured genres: literary adaptations and composer biopics. Although the article looks for patterns and similarities in Russell's war output, it differentiates between his First and Second World War films by indicating how he engages with, and temporarily inhabits, the stylistic regime of the enemy within the latter group.

Mind Bending, Mental Seduction and Menticide: Brainwashing in British Spy Dramas of the 1960s

2013 ◽  
Vol 10 (1) ◽  
pp. 27-48 ◽  
Author(s):  
Alan Burton
Keyword(s):  
Cold War ◽  
Thought Control ◽  
Cultural Contexts ◽  
Scientific Background ◽  
Mind Control ◽  
1960S And 1970S ◽  
The 1960S ◽  
The Cold War ◽  
The Mind ◽  
Cultural Fantasy

Brainwashing assumed the proportions of a cultural fantasy during the Cold War period. The article examines the various political, scientific and cultural contexts of brainwashing, and proceeds to a consideration of the place of mind control in British spy dramas made for cinema and television in the 1960s and 1970s. Particular attention is given to the films The Mind Benders (1963) and The Ipcress File (1965), and to the television dramas Man in a Suitcase (1967–8), The Prisoner (1967–8) and Callan (1967–81), which gave expression to the anxieties surrounding thought-control. Attention is given to the scientific background to the representations of brainwashing, and the significance of spy scandals, treasons and treacheries as a distinct context to the appearance of brainwashing on British screens.

The ‘Modernisation’ of Scotland and its Impact on Glasgow, 1955–1979: ‘Unwanted Side Effects’ and Vulnerabilities

2016 ◽  
Vol 25 (3) ◽  
pp. 294-316 ◽  
Author(s):  
Chik Collins ◽  
Ian Levitt
Keyword(s):  
Side Effects ◽  
Government Policy ◽  
Regional Policy ◽  
Excess Mortality ◽  
Policy Agenda ◽  
Policy Makers ◽  
Uk Government ◽  
1960S And 1970S ◽  
The 1960S ◽  
The Impact

This article reports findings of research into the far-reaching plan to ‘modernise’ the Scottish economy, which emerged from the mid-late 1950s and was formally adopted by government in the early 1960s. It shows the growing awareness amongst policy-makers from the mid-1960s as to the profoundly deleterious effects the implementation of the plan was having on Glasgow. By 1971 these effects were understood to be substantial with likely severe consequences for the future. Nonetheless, there was no proportionate adjustment to the regional policy which was creating these understood ‘unwanted’ outcomes, even when such was proposed by the Secretary of State for Scotland. After presenting these findings, the paper offers some consideration as to their relevance to the task of accounting for Glasgow's ‘excess mortality’. It is suggested that regional policy can be seen to have contributed to the accumulation of ‘vulnerabilities’, particularly in Glasgow but also more widely in Scotland, during the 1960s and 1970s, and that the impact of the post-1979 UK government policy agenda on these vulnerabilities is likely to have been salient in the increase in ‘excess mortality’ evident in subsequent years.

The Fragmentation of the Palestinian Political Field

2018 ◽  
Vol 11 (1-2) ◽  
pp. 189-216
Author(s):  
Jamil Hilal
Keyword(s):  
Women Workers ◽  
Political Leadership ◽  
The Political ◽  
Political Field ◽  
Cultural Field ◽  
National Representation ◽  
1960S And 1970S ◽  
The 1960S ◽  
Palestinian National Movement ◽  
The Relationship

The mid-1960s saw the beginnings of the construction of a Palestinian political field after it collapsed in 1948, when, with the British government’s support of the Zionist movement, which succeeded in establishing the state of Israel, the Palestinian national movement was crushed. This article focuses mainly on the Palestinian political field as it developed in the 1960s and 1970s, the beginnings of its fragmentation in the 1990s, and its almost complete collapse in the first decade of this century. It was developed on a structure characterized by the dominance of a center where the political leadership functioned. The center, however, was established outside historic Palestine. This paper examines the components and dynamics of the relationship between the center and the peripheries, and the causes of the decline of this center and its eventual disappearance, leaving the constituents of the Palestinian people under local political leadership following the collapse of the national representation institutions, that is, the political, organizational, military, cultural institutions and sectorial organizations (women, workers, students, etc.) that made up the PLO and its frameworks. The paper suggests that the decline of the political field as a national field does not mean the disintegration of the cultural field. There are, in fact, indications that the cultural field has a new vitality that deserves much more attention than it is currently assigned.

Sign in / Sign up

Export Citation Format

Share Document