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.

scholarly journals OESbathy version 1.0: a method for reconstructing ocean bathymetry with generalized continental shelf-slope-rise structures

2015 ◽  
Vol 8 (9) ◽  
pp. 2735-2748 ◽  
Author(s):  
A. Goswami ◽  
P. L. Olson ◽  
L. A. Hinnov ◽  
A. Gnanadesikan
Keyword(s):  
South America ◽  
Continental Shelf ◽  
The Arctic ◽  
Global Ocean ◽  
Continental Margins ◽  
Sediment Layer ◽  
Passive Margins ◽  
Shelf Slope ◽  
Continental Shelf Slope ◽  
Cooling Model

Abstract. We present a method for reconstructing global ocean bathymetry that combines a standard plate cooling model for the oceanic lithosphere based on the age of the oceanic crust, global oceanic sediment thicknesses, plus generalized shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to develop a methodology for reconstructing ocean bathymetry in the geologic past that includes heterogeneous continental margins in addition to abyssal ocean floor. First, the plate cooling model is applied to maps of ocean crustal age to calculate depth to basement. To the depth to basement we add an isostatically adjusted, multicomponent sediment layer constrained by sediment thickness in the modern oceans and marginal seas. A three-parameter continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Parameters of the shelf-slope-rise structures at active and passive margins are determined from modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and central Atlantic, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth to basement, ocean bathymetry with an isostatically adjusted multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

Mid-Ordovician subduction, obduction, and eduction in western Newfoundland; an eclogite problem

2021 ◽  
Author(s):  
J.F. Dewey ◽  
J.F. Casey
Keyword(s):  
Subduction Zone ◽  
Shear Zone ◽  
Continental Margin ◽  
Amphibolite Facies ◽  
Island Arcs ◽  
Early Ordovician ◽  
The North ◽  
Shelf Slope ◽  
Major Strike ◽  
Laurentian Margin

Abstract. The narrow, short-lived Taconic-Grampian Orogen occurs along the north-western margin of the Appalachian-Caledonian Belt from, at least, Alabama to Scotland, a result of the collision of a series of early Ordovician oceanic island arcs with the rifted margin of Laurentia. The present distribution of Taconian-Grampian ophiolites is unlikely to represent a single fore-arc from Alabama to Scotland colliding at the same time with the continental margin along its whole length; more likely is that there were several Ordovician arcs with separate ophiolites. The collision suture is at the thrust base of obducted fore-arc ophiolite complexes, and obduction distance was about two hundred kilometres. Footwalls to the ophiolites are, sequentially towards the continent, continental margin rift sediments and volcanics and overlying rise sediments, continental shelf slope carbonates, and sediments of foreland flexural basins. The regionally-flat obduction thrust complex between the ophiolite and the rifted Laurentian margin is the collision suture between arc and continent. A particular problem in drawing tectonic profiles across the Taconic-Grampian Zone is several orogen-parallel major strike-slip faults, both sinistral and dextral, of unknown displacements, which may juxtapose portions of different segments. In western Newfoundland, most of the Grenville basement beneath the Fleur-de-Lys metamorphic complex (Neoproterozoic to early Ordovician meta-sediments) was eclogitised during the Taconic Orogeny and separated by a massive shear zone from the overlying Fleur-de-Lys, which was metamorphosed at the same time but in the amphibolite facies. The shear zone continued either to a distal intracontinental “subduction zone” or to the main, sub-fore-arc, subduction zone beneath which the basement slipped down to depths of up to seventy kilometres at the same time as the ophiolite sheet and its previously-subcreted metamorphic sole were being obducted above. Subsequently, the eclogitised basement was returned to contact with the amphibolite-facies cover by extensional detachment eduction, possibly enhanced by subduction channel flow, which may have been caused by slab break-off and extension during subduction polarity flip. Although the basal ophiolite obduction thrust complex and the Fleur-de-Lys-basement subduction-eduction surfaces must have been initially gently-dipping to sub-horizontal, they were folded and broken by thrusts during late Taconian, late Ordovician Salinic-Mayoian, and Acadian shortening.

Sedimentary facies on the rises and slopes of passive continental margins

1980 ◽  
Vol 294 (1409) ◽  
pp. 169-176 ◽  
Keyword(s):  
Sediment Transport ◽  
Debris Flows ◽  
Thermohaline Circulation ◽  
Dominant Role ◽  
Sedimentary Facies ◽  
Turbidity Currents ◽  
Continental Margins ◽  
Passive Margins ◽  
New Evidence

JOIDES drilling results provide new evidence concerning facies patterns on evolving passive margins that strengthens and extends hypotheses constructed from studies of morphology, seismic reflexion data and shallow samples on modern margins, and from field geologic studies of uplifted ancient margins. On the slopes and rise, gravity-controlled mechanisms - turbidity currents, debris flows, slides and the like - play the dominant role in sediment transport over the long term, but when clastic supplies are reduced, as for example during rapid transgressions, then oceanic sedimentation and the effects of thermohaline circulation become important. Sedimentary facies models used as the basis of unravelling tectonic complexities of some deformed margins, for example in the Mesozoic Tethys, may be too simplistic in the light of available data from modern continental margins.

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 OESbathy version 1.0: a method for reconstructing ocean bathymetry with realistic continental shelf-slope-rise structures

2015 ◽  
Vol 8 (4) ◽  
pp. 3079-3115
Author(s):  
A. Goswami ◽  
P. L. Olson ◽  
L. A. Hinnov ◽  
A. Gnanadesikan
Keyword(s):  
South America ◽  
Continental Shelf ◽  
The Arctic ◽  
Global Ocean ◽  
North Coast ◽  
Sediment Layer ◽  
Passive Margins ◽  
Shelf Slope ◽  
Continental Shelf Slope ◽  
Cooling Model

Abstract. We present a method for reconstructing global ocean bathymetry that uses a plate cooling model for the oceanic lithosphere, the age distribution of the oceanic crust, global oceanic sediment thicknesses, plus shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to reconstruct realistic ocean bathymetry based on parameterized relationships of present-day variables that can be applied to global oceans in the geologic past, and to isolate locations where anomalous processes such as mantle convection may affect bathymetry. Parameters of the plate cooling model are combined with ocean crustal age to calculate depth-to-basement. To the depth-to-basement we add an isostatically adjusted, multicomponent sediment layer, constrained by sediment thickness in the modern oceans and marginal seas. A continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Shelf-slope-rise structures at active and passive margins are parameterized using modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and Central Atlantic Ocean, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth-to-basement, ocean bathymetry with an isostatically adjusted, multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

The Mesozoic successions of western Sierra de Zacatecas, Central Mexico: provenance and tectonic implications

2015 ◽  
Vol 153 (4) ◽  
pp. 696-717 ◽  
Author(s):  
BERLAINE ORTEGA-FLORES ◽  
LUIGI A. SOLARI ◽  
FELIPE DE JESÚS ESCALONA-ALCÁZAR
Keyword(s):  
Continental Margin ◽  
Active Tectonics ◽  
Upper Jurassic ◽  
Central Mexico ◽  
Petrographic Analysis ◽  
Continental Margins ◽  
South American ◽  
Detrital Zircon Geochronology ◽  
Sierra Madre ◽  
Active Continental Margins

AbstractCentral Mexico was subject to active tectonics related to subduction processes while it occupied a position in western equatorial Pangea during early Mesozoic time. The subduction of the palaeo-Pacific plate along the western North American and South American active continental margins produced volcanic arc successions which were subsequently rifted and re-incorporated to the continental margin. In this context, the fringing arcs are important in unravelling the continental accretionary record. Using petrographic analysis, detrital zircon geochronology and structural geology, this paper demonstrates that the Guerrero Arc (Guerrero Terrane) formed on top of a felsic volcaniclastic unit (Middle Jurassic La Pimienta Formation) and siliciclastic strata (Upper Triassic Zacatecas Formation and Arteaga Complex) of continental Mexican provenance, deposited across the continental margin and oceanic substrate. This assemblage was rifted away from continental Mexico to form an intervening oceanic assemblage (Upper Jurassic – Lower Cretaceous Las Pilas Volcanosedimentary Complex of the Arperos Basin), then accreted back more or less at the same place, all above the same east-dipping subduction zone. The accretion of the Guerrero Arc to the Mexican continental mainland (Sierra Madre Terrane) caused the deposition of a siliciclastic unit (La Escondida Phyllite), which recycled detritus from the volcaniclastic and siliciclastic underlying strata.

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