The continent–ocean boundary south of Flemish Cap: constraints from seismic refraction and gravity

Todd, B J; Reid, I.

doi:10.1139/e89-119

Cited by 31 publications

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“…Unfortunately, this structure is not well-constrained due to the absence of receivers on the eastern end of the reflection profile. Similar velocities in the northern Newfoundland basin, adjacent to the southern boundary of Flemish Cap (figure 16), have been reported by Todd & Reid (1989). …”

Section: (C) Galicia Bank/iberia Abyssal Plain-newfoundland Basinsupporting

confidence: 85%

“…Basement types (B1, B2) and reflections (R1-R9) are discussed in text. Bathymetry of the southern Grand Banks and Newfoundland basin (shaded for depths less than 2000 m) (ETOP05) with locations of the 85-2 and 85-4 deep reflection profiles (thin lines with shot numbers)(Keen & de Voogd 1988) and refraction profiles (thick lines)(Todd & Reid 1989;Reid 1994). Thick dashed lines show location of anomaly M1(Tucholke et al .…”

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confidence: 99%

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The deep structure of non–volcanic rifted continental margins

Louden

Chian

1999

Philosophical Transactions of the Royal Society of London. Seri

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Delineating the nature of crustal variations across passive continental margins is fundamental to our understanding of how the uppermost lithosphere deforms under extension. This information is best obtained across margins where the extensional fabric within the crust has not been significantly modified by large-scale syn-rift volcanism. Previous studies of such margins have shown a range of extensional styles, which have been interpreted by various combinations of pure and simple shearing of continental crust and lithosphere. This paper reanalyses several key transects in the North Atlantic, including the conjugate margin pairs of Newfoundland-Iberia, Flemish Cap-Goban Spur and Labrador-W. Greenland. Analysis of both deep multichannel seismic reflection and wide-angle reflection/refraction profiles allows us to produce new joint constructions of velocity and reflectivity depth sections. These sections indicate major asymmetries in the width and faulting style of continental rifting between margin conjugates. They also show a general occurrence of a complex transition zone between extended continental and oceanic crust that is dominated by exposed and serpentinized upper mantle. Because serpentinite has a much lower strength than is typical of continental or oceanic crustal rocks, its existence within the transition zone may have a profound influence on how these margins develop. The possible effects that such time and spatially variable rheologies have on the development of these margins needs to be considered in future geodynamical models.

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Section: (C) Galicia Bank/iberia Abyssal Plain-newfoundland Basinsupporting

confidence: 85%

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confidence: 99%

The deep structure of non–volcanic rifted continental margins

Louden

Chian

1999

Philosophical Transactions of the Royal Society of London. Seri

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“…An approximately 25 km wide zone at the outer edge of the TZ has basement velocities of 6.3-7.7 km s 21 and was interpreted as exhumed, serpentinized mantle. Within the narrow TZ farther north, Todd & Reid (1989) observed a thin (2-3 km) 4.0-5.0 km s 21 layer overlying probably serpentinized mantle (7.3 km s 21 ) in one profile and overlying 8.0 km s 21 mantle in a second profile. There is little, if any, TZ present still farther north at the position of the SCREECH1 and W96 conjugate profiles (Figs 2 & 3).…”

Section: Transitional Crustmentioning

confidence: 87%

Breakup of the Newfoundland–Iberia rift

2007

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The Newfoundland-Iberia rift is considered to be a type example of a non-volcanic rift. Key features of the conjugate margins are transition zones (TZs) that lie between clearly continental crust and presumed normal (Penrose-type) oceanic crust that appears up to 150-180 km farther seaward. Basement ridges drilled in the Iberia TZ consist of exhumed, serpentinized peridotite of continental affinity, consistent with seismic refraction studies. Although the boundaries between continental crust and the TZs can be defined with relative confidence, there are major questions about the position and nature of the change from rifting to normal sea-floor spreading at the seaward edges of the TZs. Notably, drilling of presumed oceanic crust in the young M-series anomalies (,M5) has recovered serpentinized peridotite, and this basement experienced major extension up to approximately 15 million years after it was emplaced. In addition, existing interpretations place the 'breakup unconformity' (normally associated with the separation of continental crust and simultaneous formation of oceanic crust) near the Aptian-Albian boundary, which is also some 15 million years younger than the oldest proposed oceanic crust (anomaly M5-M3) in the rift.To investigate and potentially resolve these conflicts, we analysed the tectonic history and deep (pre-Cenomanian) stratigraphy of the rift using seismic reflection profiles and drilling results. Rifting occurred in two main phases (Late Triassic-earliest Jurassic and Late Jurassic-Early Cretaceous). The first phase formed continental rift basins without significant thinning of continental crust. The second phase led to continental breakup, with extension concentrated in three episodes that culminated near the end of Berriasian, Hauterivian and Aptian time. The first two episodes appear to correlate with separation of continental crust in the southern and northern parts of the rift, respectively, suggesting that the rift opened from south to north in a two-step process. The third episode persisted through Barremian and Aptian time. We suggest that during this period there was continued exhumation of subcontinental mantle lithosphere at the plate boundary, and that elevated in-plane tensile stress throughout the rift caused intraplate extension, primarily within the exhumed mantle. This rifting may have been interrupted for a time during the Barremian when melt was introduced from the southern edge of the rift by plume magmatism that formed the Southeast Newfoundland Ridge and J Anomaly Ridge, and the conjugate Madeira-Tore Rise. We propose that the rising asthenosphere breached the subcontinental mantle lithosphere in latest Aptian-earliest Albian time, initiating sea-floor spreading. This resulted in relaxation of in-plane tensile stress (i.e. a pulse of relative compression) that caused internal plate deformation and enhanced mass wasting. This 'Aptian event' produced a strong, rift-wide reflection that is unconformably onlapped by post-rift sediments that were deposited as a stable sea-fl...

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“…Flemish Cap (Todd & Reid 1989), the Senja (Jackson, Faleide & Eldholm 1991) and Hornsund (Eldholm, Faleide & Myhre 1987) margins; and deep reflection profiling (Faleide ef al. 1991;Keen, Kay & Roest 1990) provide better information on sheared margins.…”

Section: Discussionmentioning

confidence: 99%

Admittance signatures of rifted and transform margins: examples from eastern Canada

Verhoef¹,

Jackson²

1991

Geophysical Journal International

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Examination of the gravity and bathymetry data across the rifted Scotian margin and the sheared Grand Banks margin, off the Canadian east coast, using a spectral analysis or admittance approach. yielded different results. The admittance for the Scotian margin best fitted a regional compensation model; in contrast, a local compensation mechanism reproduced the transfer function for the Grand Banks margin. The results for the longer wavelengths were verified using satellite altimetry data. The effect of a hidden or subsurface load was investigated for both margins and this was also found to differ. The differences in the compensation mechanism between rifted and sheared margins was attributed to their formation mechanisms.Rifted margins are formed by upper crustal faulting and lower crustal flow parallel to the spreading centre. These characteristics are compatible with thin plate flexure compensation. In contrast, transform margins are formed perpendicular to the spreading ridge and the isotherms are only slightly raised as the spreading centre migrates along the margin producing a weak suture which accommodates local compensation.

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The continent–ocean boundary south of Flemish Cap: constraints from seismic refraction and gravity

Cited by 31 publications

References 0 publications

The deep structure of non–volcanic rifted continental margins

The deep structure of non–volcanic rifted continental margins

Breakup of the Newfoundland–Iberia rift

Admittance signatures of rifted and transform margins: examples from eastern Canada

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