A possible Lower Permian age for the onset of ocean floor spreading in the northern North Atlantic

Russell, Michael J.

doi:10.1144/sjg12040315

Cited by 39 publications

(11 citation statements)

References 32 publications

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“…Most hypotheses consider southern Rockall Trough to be oceanic (Joppen et a/. in preparation), with the spreading beginning possibly as early as the Permian (Russell 1976), or in the Late Cretaceous (Vogt & Avery 1974;Roberts 1975). Spreading ceased in Rockall Trough around the time of magnetic anomaly 33-34, as the spreading axis moved westwards to the Labrador Sea (Srivastava 1978).…”

Section: Formation Of the Rockall P L A T E A Umentioning

confidence: 99%

The Hatton Bank continental margin-I. Shallow structure from two-ship expanding spread seismic profiles

Spence

White

Westbrook

et al. 1989

Geophysical Journal International

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The Hatton Bank passive continental margin exhibits thick seaward dipping reflector sequences which consist of basalts extruded during rifting between Greenland and Rockall Plateau. Multichannel seismic reflection profiling across the margin reveals three reflector wedges with a maximum thickness near 7 km, extending from beneath the upper continental slope to the deep ocean basin. We present results of the velocity structure within the dipping reflector sequences at eight locations across the margin, interpreted by synthetic seismogram modelling a set of multichannel expanding spread profiles parallel to the margin. At the top of some reflector sequences, we observe a series of 100 m thick high-and low-velocity zones, which are interpreted as basalt flows alternating with sediments or weathered and rubble layers. At the profile locations, the base of the dipping reflectors correlates with P-wave velocities near 6.5 km s-'. However, elsewhere the reflectors appear to extend significantly deeper than the inferred 6.5 km s-' velocity contour, indicating that the velocity structure may not be controlled solely by lithological boundaries but also by metamorphic effects. Shear-waves were observed on two lines, permitting the calculation of Poisson's ratio. The decrease in Poisson's ratio from 0.28 to near 0.25 in the upper 5 km of crust may also indicate the effect of metamorphism on seismic properties, or alternatively may be explained by crack closure under load.

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Section: Formation Of the Rockall P L A T E A Umentioning

confidence: 99%

The Hatton Bank continental margin-I. Shallow structure from two-ship expanding spread seismic profiles

Spence

White

Westbrook

et al. 1989

Geophysical Journal International

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“…If the former is the case, then dykes may not be crust-penetrating features. Gravity or magnetic modelling of a dyke provides little or no constraint on the depth to base of the body, other than that the base is at least an order of magnitude greater than the dyke width, which can Russell (1976) first recognized the regional importance of this onshore dyke swarm as an indicator of late Palaeozoic rifting, and pointed out the extension of the Dunbar dyke magnetic anomaly offshore to the east. Francis (1978), in contrast, placed the dyke swarm in the context of the contemporanous late Hercynian collision to the south.…”

Section: Mafic Dyke Swarms and Plate Tectonicsmentioning

confidence: 99%

Geophysical evidence for ultrawide dykes of the late Carboniferous quartz-dolerite swarm of northern Britain

Smythe

1994

Geophysical Journal International

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A compilation of the late Carboniferous quartz-dolerite dyke swarm of northern Britain has been made using existing geological maps, augmented by new ground and airborne magnetic surveys. Aeromagnetic data in the North Sea show that dyke anomalies can be traced eastwards on an arcuate trend for up to 200 km from the UK coast, as far as the western margin of the Central Graben. Individual dykes, which are generally up to 30m wide onshore, attain widths of well over 1 km offshore. These are at least as wide as any known dykes. The swarm is probably as extensive and voluminous as the well-known and better-exposed Palaeocene tholeiitic swarm of NW Britain.

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“…Although this body of evidence is very compelling for a late Triassic to Early Jurassic sedimentation date for all evaporite rocks in the region, we note that the rocks on which it is based are those accessible on the flanks of the central Atlantic rift zone and in en echelon peripheral graben (Burke, 1976). Yet along the northward extension of the main rift direction, in and near the British Isles where the geology is better exposed, rift structures and their sedimentary fillings are found to be nearly continuous through the Permian and Triassic (e.g., Russell, 1976;Francis, 1978;Pegrum and Mounteney, 1978;Russell and Smythe, 1978;Ziegler, 1980). A Permian radiometric age in a rift on the eastern edge of the West African craton "may relate to a widescale episode of rifting in Pangea whose manifestations elsewhere include ... Corsica, the North Sea and southern Norway."…”

Section: Depositional Agementioning

confidence: 99%

Geochemistry and Petrology of Evaporites Cored from a Deep-Sea Diapir at Site 546 offshore Morocco

Holser¹,

Saltzman²,

Brookins³

1984

Initial Reports of the Deep Sea Drilling Project

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At Site 546, below the Mazagan Escarpment at a water depth of 4 km, 36 m of salt rock was cored from the top of one of a field of salt domes. The core was studied by thin section and a variety of geochemical procedures. The salt rock contains 0.1 to 3% carnallite and lesser amounts of sylvite and polyhalite, which with the corresponding high level of bromide place it within the potash evaporite facies. The bromide profile is of a dominantly marine evaporite deposited in moderately shallow brine which, however, was not repeatedly desiccated. A mineralogical argument suggests that the brine surface was not below sea level.An average of about 5"7o elastics, with dispersed anhydrite, darken the salt rock to deep shades of red, brown, and gray green. Most of the included materials are in highly deformed boudins or dispersions in the salt rock that has also undergone cataclasis in a subsequent, probably tectonic, deformation. The salt rock is slightly deficient in anhydrite, and the usual separate beds and laminae of anhydrite are virtually absent.Stable isotope ratios of sulfur and oxygen in the sulfate are clearly derived from sea water of Permian to Scythian age, in contrast to the late Triassic or Early Jurassic age of evaporites onshore in Morocco and Portugal and the corresponding evaporites offshore Maritime Canada. In contrast to those evaporites off the axis of Atlantic rifting, the salt at Site 546 may have been deposited in a very early central rift fed by marine waters from Tethys through the Gibraltar or South Atlas fracture zones.

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A possible Lower Permian age for the onset of ocean floor spreading in the northern North Atlantic

Cited by 39 publications

References 32 publications

The Hatton Bank continental margin-I. Shallow structure from two-ship expanding spread seismic profiles

The Hatton Bank continental margin-I. Shallow structure from two-ship expanding spread seismic profiles

Geophysical evidence for ultrawide dykes of the late Carboniferous quartz-dolerite swarm of northern Britain

Geochemistry and Petrology of Evaporites Cored from a Deep-Sea Diapir at Site 546 offshore Morocco

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