The IPOD programme on passive continental margins

1980 ◽  
Vol 294 (1409) ◽  
pp. 17-33 ◽  
Keyword(s):  
Internal Structure ◽  
Ocean Basin ◽  
Continental Margins ◽  
Plate Edge ◽  
Passive Margins ◽  
The Past ◽  
Subsidence History ◽  
Lithospheric Plates ◽  
History Of ◽  
Active Continental Margins

During the past 200 Ma (1 Ma = 10 6 years) the arrangement of continents and ocean basins has been reorganized from a pattern of one supercontinent, with mainly plate edge, subduction, or active continental margins bordering one essentially contiguous ocean basin, to the present configuration of dispersed continents and several oceans. Most of the world’s present continental margins which were formed during that 200 Ma period are ‘passive’ margins lying within the interiors of lithospheric plates. Several models of rifting and evolution of these passive margins have been proposed. The objectives of IPOD include testing of these models by learning as much as we can about the history of rifting of passive continental margins, their internal structure, distribution of facies, subsidence history, and the nature of the transition and modification of the crust at the margin. These objectives cannot be attained by drilling alone, and geophysical surveying and analysis of samples from the drilling are essential parts of the overall programme.

scholarly journals Evolution and demise of passive margins through grain mixing and damage

2021 ◽  
Vol 118 (4) ◽  
pp. e2011247118
Author(s):  
David Bercovici ◽  
Elvira Mulyukova
Keyword(s):  
Plate Tectonics ◽  
Ocean Basin ◽  
Passive Margin ◽  
Continental Margins ◽  
Sea Floor ◽  
Passive Margins ◽  
Grain Damage ◽  
Lithospheric Plates ◽  
Compositional Gradients ◽  
Ocean Lithosphere

How subduction—the sinking of cold lithospheric plates into the mantle—is initiated is one of the key mysteries in understanding why Earth has plate tectonics. One of the favored locations for subduction triggering is at passive margins, where sea floor abuts continental margins. Such passive margin collapse is problematic because the strength of the old, cold ocean lithosphere should prohibit it from bending under its own weight and sinking into the mantle. Some means of mechanical weakening of the passive margin are therefore necessary. Spontaneous and accumulated grain damage can allow for considerable lithospheric weakening and facilitate passive margin collapse. Grain damage is enhanced where mixing between mineral phases in lithospheric rocks occurs. Such mixing is driven both by compositional gradients associated with petrological heterogeneity and by the state of stress in the lithosphere. With lateral compressive stress imposed by ridge push in an opening ocean basin, bands of mixing and weakening can develop, become vertically oriented, and occupy a large portion of lithosphere after about 100 million y. These bands lead to anisotropic viscosity in the lithosphere that is strong to lateral forcing but weak to bending and sinking, thereby greatly facilitating passive margin collapse.

Morphology of the continental margin

1978 ◽  
Vol 290 (1366) ◽  
pp. 75-85 ◽  
Keyword(s):  
Continental Margin ◽  
Turbidity Currents ◽  
Continental Margins ◽  
Island Arcs ◽  
Horizontal Shear ◽  
Passive Margins ◽  
Shelf Slope ◽  
Shear Motion ◽  
Continental Shelf Slope ◽  
Active Continental Margins

The continental margin is the surface morphological expression of the deeper fundamental transition between the thick low density continental igneous crust and the thin high density and chemically different oceanic igneous crust. Covering the transition are thick sediment accumulations comprising over half the total sediments of the ocean, so that the precise morphological boundaries often differ in position from those of the deeper geology. Continental margins are classified as active or passive depending on the level of seismicity. Active continental margins are divided into two categories, based on the depth distribution of earthquakes and the tectonic regime. Active transform margins, characterized by shear and shallow focus earthquakes, result from horizontal shear motion between plates. Active compressional margins are characterized by shallow, intermediate and deep earthquakes along a dipping zone, by oceanic trenches and by volcanic island arcs or mountain ranges depending on whether the margin is oceanocean or ocean-continent. Passive margins, found in the Atlantic and Indian Oceans, are formed initially by the rifting of continental crust and mark the ocean-continent boundary within the spreading plate. They are characterized by continental shelf, slope and rise physiographic provinces. Once clear of the rifting axis, they cool and subside. Sedimentation can prograde the shelf and load the edge leading to further down warping; changes of sea level lead to erosion by wave action and by ice; ocean currents and turbidity currents redistribute sediments; slumps occur in unstable areas. The passive and sediment-starved margin west of Europe is described where the following factors have been significant: (a) faulting related to initial rifting; (b) infilling and progradation by sediments; (c) slumping; (d) contour current erosion and deposition; (e)canyon erosion.

The age and geological history of the Wollaston, Peter Lake, and Rottenstone domains in northern Saskatchewan

1980 ◽  
Vol 17 (3) ◽  
pp. 333-347 ◽  
Author(s):  
G. E. Ray ◽  
R. K. Wanless
Keyword(s):  
Ocean Basin ◽  
Continental Margins ◽  
Zircon Age ◽  
Plate Movement ◽  
Tectonic Model ◽  
Northern Saskatchewan ◽  
History Of ◽  
Successive Generations ◽  
The Relationship ◽  
Age Determinations

Three U–Pb zircon and four K–Ar mineral age determinations from national topographic system (NTS) area Geikie River (SE) in northern Saskatchewan are presented and the geology of the region is described. The area lies within the Churchill Province of the Canadian Precambrian Shield and includes parts of the Wollaston, Peter Lake, and Rottenstone domains; the relationship between the geological histories of these domains and the age determinations is discussed. Zircon age measurements suggest a period of late Archean magmatism ca. 2500 Ma was responsible for both the Wollaston domain granitic basement and a suite of basic plutons in the adjoining Peter Lake domain.The overall lithological differences of the presumed lower Proterozoic supracrustal rocks in the region are examined in the context of a plate tectonic model. This invokes late Archean continental rifting accompanied by limited volcanism close to the present Needle Falls Shear Zone, followed by continental separation and the generation of an Aphebian ocean basin. Deposition of shelf and deeper water sediments along the trailing edge of the Wollaston domain continental margin was followed by reversal of plate movement, oceanic subduction, and the formation of an island-arc complex. This marked the start of the Hudsonian Orogeny and was accompanied by the development of successive generations of granitic material, including the Wathaman batholith. The regional emplacement of this batholith ca. 1865 Ma ago is compared to other volcano-plutonic belts described elsewhere along Cordilleran-type continental margins.

On The Possibility of an Autonomous History of Modern Southeast Asia

1961 ◽  
Vol 2 (2) ◽  
pp. 73-105 ◽  
Author(s):  
John R. W. Small
Keyword(s):  
Southeast Asia ◽  
Contemporary History ◽  
The Past ◽  
History Of

It is generally accepted that history is an element of culture and the historian a member of society, thus, in Croce's aphorism, that the only true history is contemporary history. It follows from this that when there occur great changes in the contemporary scene, there must also be great changes in historiography, that the vision not merely of the present but also of the past must change.

Stellar Evolution

1962 ◽  
Vol 11 (02) ◽  
pp. 137-143
Author(s):  
M. Schwarzschild
Keyword(s):  
Solar System ◽  
Stellar Evolution ◽  
Space Craft ◽  
New Techniques ◽  
Substantial Body ◽  
Individual Stars ◽  
The Past ◽  
Evolution Of Galaxies ◽  
History Of ◽  
Fast Flow

It is perhaps one of the most important characteristics of the past decade in astronomy that the evolution of some major classes of astronomical objects has become accessible to detailed research. The theory of the evolution of individual stars has developed into a substantial body of quantitative investigations. The evolution of galaxies, particularly of our own, has clearly become a subject for serious research. Even the history of the solar system, this close-by intriguing puzzle, may soon make the transition from being a subject of speculation to being a subject of detailed study in view of the fast flow of new data obtained with new techniques, including space-craft.

A 200-Year History of the Study of Childhood Language Disorders of Unknown Origin: Changes in Terminology

2020 ◽  
Vol 5 (1) ◽  
pp. 6-11 ◽  
Author(s):  
Laurence B. Leonard
Keyword(s):  
Language Impairment ◽  
Specific Language Impairment ◽  
Scientific Literature ◽  
Language Disorder ◽  
Language Disorders ◽  
Unknown Origin ◽  
Developmental Language Disorder ◽  
The Past ◽  
History Of ◽  
The Many

Purpose The current “specific language impairment” and “developmental language disorder” discussion might lead to important changes in how we refer to children with language disorders of unknown origin. The field has seen other changes in terminology. This article reviews many of these changes. Method A literature review of previous clinical labels was conducted, and possible reasons for the changes in labels were identified. Results References to children with significant yet unexplained deficits in language ability have been part of the scientific literature since, at least, the early 1800s. Terms have changed from those with a neurological emphasis to those that do not imply a cause for the language disorder. Diagnostic criteria have become more explicit but have become, at certain points, too narrow to represent the wider range of children with language disorders of unknown origin. Conclusions The field was not well served by the many changes in terminology that have transpired in the past. A new label at this point must be accompanied by strong efforts to recruit its adoption by clinical speech-language pathologists and the general public.

Suicidal Ideation Among Medical Students in Dammam, Saudi Arabia

Crisis ◽  
2020 ◽  
pp. 1-6
Author(s):  
Mohammed Madadin ◽  
Ritesh G. Menezes ◽  
Maha A. Alassaf ◽  
Abdulaziz M. Almulhim ◽  
Mahdi S. Abumadini ◽  
...  
Keyword(s):  
Saudi Arabia ◽  
Medical Students ◽  
Suicidal Ideation ◽  
General Health Questionnaire ◽  
Cross Sectional Study ◽  
Eastern Province ◽  
Cross Sectional ◽  
The Past ◽  
Depression Subscale ◽  
History Of

Abstract. Background: Medical students are at high risk of suicidal ideation. Aim: We aimed to obtain information on suicidal ideation among medical students in Dammam located in the Eastern Province of Saudi Arabia. Method: This cross-sectional study was conducted at the College of Medicine affiliated with Imam Abdulrahman Bin Faisal University in the Eastern Province of Saudi Arabia. Suicidal ideation in the past 12 months was assessed based on responses to four questions in the depression subscale of the General Health Questionnaire 28 (GHQ-28). In addition, data were collected to examine the association of suicidal ideation with various factors. Results: We found that 1 in 3 medical students in the study had suicidal ideation in the past 12 months, while around 40% had lifetime suicidal ideation. Suicidal ideation was associated with feelings of parental neglect, history of physical abuse, and dissatisfaction with academic performance. Limitations: The cross-sectional nature of this study limits its ability to determine causality regarding suicidal ideation. Conclusion: These rates are considerably high when compared with rates from studies in other countries around the world. This study provides a reference in the field of suicidology for this region of Saudi Arabia.

Post-Soviet economy development: From the past to the future

2017 ◽  
pp. 5-21 ◽  
Author(s):  
E. Yasin
Keyword(s):  
Present Situation ◽  
Soviet Economy ◽  
Market Reforms ◽  
Democratic Development ◽  
The Past ◽  
Current Period ◽  
The Future ◽  
History Of ◽  
Working Out ◽  
A Current

The article is devoted to major events in the history of the post-Soviet economy, their influence on forming and development of modern Russia. The author considers stages of restructuring, market reforms, transformational crisis, and recovery growth (1999-2011), as well as a current period which started in2011 and is experiencing serious problems. The present situation is analyzed, four possible scenarios are put forward for Russia: “inertia”, “mobilization”, “decisive leap”, “gradual democratic development”. More than 30 experts were questioned in the process of working out the scenarios.

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