Marine geology of the Rockall Plateau and Trough

The Rockall Plateau is an extensive shallow water area located south of Iceland and west of the British Isles: it is separated from the British Isles by the 3000 m deep Rockall Trough. Rockall Island, composed of 52 ± 9 Ma aegirine-granite is the sole subaerial expression. The Rockall Plateau is interpreted as a continental fragment or microcontinent isolated during the sea floor spreading evolution of the North Atlantic Ocean. A geological reconnaissance of the Rockall Plateau and Trough has been made by using a 650 cm 3 (40 in3) seismic reflexion profiling system, supplemented by sparker (8 kJ) profiles on Rockall Bank and arcer (60 kJ) profiles across the margin west of the British Isles. Stratigraphic interpretation of these profiles has been aided by deep sea drilling data, bottom sampling on Rockall Bank and by the relation between the various reflecting horizons and oceanic basement dated by oceanic magnetic anomaly identifications. Analysis of the microtopography of the area has given information on Post-Palaeogene sedimentation processes. Three major sedimentary basins are present in the area. The Hatton-Rockall Basin is developed in thinned continental crust on Rockall Plateau. The Rockall Trough is developed on continental crust and includes oceanic crust believed to have been generated in Late Jurassic-Early Cretaceous time. The Porcupine Seabight may be developed on thinned continental crust. All three basins have a faulted basement and exhibit a history of progressive and/or intermittent subsidence. The subsidence phases correlate closely with estimated changes in sea-floor spreading rate. This correlation and the regional pattern of uplift and subsidence is discussed with reference to the effects of thermal subsidence and differential loading of the lithosphere beneath continental margins. Post Upper Eocene sedimentation throughout the area was characterized initially by widespread chert deposition and subsequently by differential deposition of Early Miocene to Recent oozes. The onset of widespread differential deposition in the Early Miocene indicates the present near bottom-circulation was established at this time and may be related to subsidence of the Iceland-Faeroes Ridge. The relation between differential deposition, topography and circulation is discussed in terms of flow around obstacles.

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Comoros – New Evidence and Arguments for Continental Crust

10.2118/afrc-2572434-ms ◽

2016 ◽

Author(s):

John Milsom ◽

Phil Roach ◽

Chris Toland ◽

Don Riaroh ◽

Chris Budden ◽

...

Keyword(s):

Continental Crust ◽

Fracture Zone ◽

Seismic Data ◽

Gravity Anomalies ◽

Magnetic Anomalies ◽

Magnetic Data ◽

The West ◽

Sea Floor ◽

Inappropriate Use ◽

Sea Floor Spreading

ABSTRACT As part of an ongoing exploration effort, approximately 4000 line-km of seismic data have recently been acquired and interpreted within the Comoros Exclusive Economic Zone (EEZ). Magnetic and gravity values were recorded along the seismic lines and have been integrated with pre-existing regional data. The combined data sets provide new constraints on the nature of the crust beneath the West Somali Basin (WSB), which was created when Africa broke away from Gondwanaland and began to move north. Despite the absence of clear sea-floor spreading magnetic anomalies or gravity anomalies defining a fracture zone pattern, the crust beneath the WSB has been generally assumed to be oceanic, based largely on regional reconstructions. However, inappropriate use of regional magnetic data has led to conclusions being drawn that are not supported by evidence. The identification of the exact location of the continent-ocean boundary (COB) is less simple than would at first sight appear and, in particular, recent studies have cast doubt on a direct correlation between the COB and the Davie Fracture Zone (DFZ). The new high-quality reflection seismic data have imaged fault patterns east of the DFZ more consistent with extended continental crust, and the accompanying gravity and magnetic surveys have shown that the crust in this area is considerably thicker than normal oceanic and that linear magnetic anomalies typical of sea-floor spreading are absent. Rifting in the basin was probably initiated in Karoo times but the generation of new oceanic crust may have been delayed until about 154 Ma, when there was a switch in extension direction from NW-SE to N-S. From then until about 120 Ma relative movement between Africa and Madagascar was accommodated by extension in the West Somali and Mozambique basins and transform motion along the DFZ that linked them. A new understanding of the WSB can be achieved by taking note of newly-emerging concepts and new data from adjacent areas. The better-studied Mozambique Basin, where comprehensive recent surveys have revealed an unexpectedly complex spreading history, may provide important analogues for some stages in WSB evolution. At the same time the importance of wide continent-ocean transition zones marked by the presence of hyper-extended continental crust has become widely recognised. We make use of these new insights in explaining the anomalous results from the southern WSB and in assessing the prospectivity of the Comoros EEZ.

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Icelandia

10.5194/egusphere-egu21-13797 ◽

2021 ◽

Author(s):

Gillian Foulger ◽

Laurent Gernigon ◽

Laurent Geoffroy

Keyword(s):

Continental Crust ◽

Structural Complexity ◽

Ne Atlantic ◽

Sea Floor ◽

Passive Margins ◽

The North ◽

The Pacific ◽

Ne Atlantic Ocean ◽

Sea Floor Spreading ◽

North And South

<p>The NE Atlantic formed by complex, piecemeal breakup of Pangea in an environment of structural complexity. North of the present-day latitude of Iceland the ocean opened by southward propagation of the Aegir ridge. South of the present-day latitude of Iceland breakup occurred along the proto-Reykjanes ridge which formed laterally offset by ~ 100 km from the Aegir ridge to the north. Neither of these new breakup axes were able to propagate across the east-westerly striking Caledonian frontal thrust region which formed a strong barrier ~ 400 km wide. As a result, while sea-floor spreading widened the NE Atlantic, the Caledonian front region could only keep pace by diffuse stretching of the continental crust, which formed the aseismic Greenland-Iceland-Faroe ridge. The magmatic rate there was similar to that of the ridges to the north and south and so the stretched continental crust is now blanketed by thick mafic flows and intrusions. The NE Atlantic also contains a magma-inflated microcontinent &#8211; the Jan Mayen Microplate Complex, and an unknown but probably large amount of stretched continental crust blanketed by seaward-dipping reflectors in the passive margins of Norway and Greenland. The NE Atlantic thus contains voluminous continental crust in diverse forms and settings. If even a small portion of the sunken continental material contiguous with the Greenland-Iceland-Faroe ridge is included the area exceeds a million square kilometers, an arbitrary threshold suggested to designate a sunken continent. We have called this region Icelandia. The conditions and processes that funneled large quantities of continental crust into the NE Atlantic ocean are common elsewhere. This includes much of the North and South Atlantic oceans including both the seaboards and the deep oceans. Nor are such processes and outcomes confined to oceans bordered by passive margins. They are also found around the Pacific rims where subduction is in progress. Indeed, these conditions and processes likely are generic to essentially all the world's oceans and are potentially also informed by observations from intracontinental extensional regions and land-locked seas.</p>

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Cretaceous

Geological Society London Memoirs ◽

10.1144/gsl.mem.1992.013.01.13 ◽

1992 ◽

Vol 13 (1) ◽

pp. 131-139 ◽

Cited By ~ 6

Author(s):

J. M. Hancock ◽

P. F. Rawson

Keyword(s):

Early Cretaceous ◽

Sedimentary Basins ◽

Major Change ◽

The Arctic ◽

Sea Floor ◽

The North ◽

Marine Sedimentation ◽

History Of ◽

Sea Floor Spreading ◽

Sea Area

AbstractEarly CretaceousThe Cretaceous Period lasted for about 70 million years. During this time there was a major change in the sedimentary history of the area as tectonism died down and deposition started of an extensive blanket of coccolith ooze: the Chalk. The change took place mainly over a brief interval across the Albian/Cenomanian (Lower/Upper Cretaceous) boundary, at about 95 Ma. Until that time crustal extension along the Arctic-North Atlantic megarifts continued to influence the tectonic evolution of northwest Europe (Ziegler 1982, 1988). This tensional régime caused rifting and block faulting, particularly across the Jurassic-Cretaceous boundary (Late Cimmerian movements) and in the mid Aptian (Austrian phase). During the latter phase, sea-floor spreading commenced in the Biscay and central Rockall Rifts. The northern part of the Rockall Rift began to widen too, possibly by crustal stretching rather than sea-floor spreading (Ziegler 1988, p. 75). During the Albian the regional pattern began to change and by the beginning of the Cenomanian rifting had effectively ceased away from the Rockall/Faeroe area.Most of the Jurassic sedimentary basins continued as depositional areas during the Early Cretaceous, but the more extensive preservation of Lower Cretaceous sediments provides firmer constraints on some of the geographical reconstructions. The marked sea-level fall across the Jurassic-Cretaceous boundary isolated the more southerly basins as areas of non-marine sedimentation, and it was not until the beginning of the Aptian that they became substantially marine.The extent of emergence of highs in the North Sea area is difficult to assess, especially where

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Geochemical discriminators and the palaeotectonic environment of the North Mountain basalts, Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e80-181 ◽

1980 ◽

Vol 17 (12) ◽

pp. 1740-1745 ◽

Cited By ~ 10

Author(s):

J. M. Wark ◽

D. B. Clarke

Keyword(s):

Nova Scotia ◽

Continental Crust ◽

Early Jurassic ◽

Late Triassic ◽

Chemical Characteristics ◽

Sea Floor ◽

The North ◽

Sea Floor Spreading

The late Triassic – early Jurassic North Mountain basalts of Nova Scotia have been analyzed for various elements believed to be useful in determining the palaeotectonic environment of eruption. The discriminant diagrams show these basalts to have within-plate affinities, with a possible indication of oceanic chemical characteristics. An oceanic environment, however, is at variance with the field relations, which show the within-plate environment to be continental; thus the oceanic chemical characteristics may suggest eruption through a continental crust that was thinning prior to the onset of active sea-floor spreading later in the Jurassic.

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