Imaging magmatic rocks on the Faroes Margin

Roberts, Alan; White, R. S.; Lunnon, Z.; Christie, P. A. F.; Spitzer, R.; Team, iSIMM

doi:10.1144/0060755

Cited by 13 publications

(8 citation statements)

References 36 publications

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“…This is also in accord with consistent imaging of strong wide‐angle Moho reflections beneath volcanic continental margins where the melt rising from the mantle ponds as sills in the lower crust (e.g. White et al 2002; Roberts et al 2005). Indeed, the structure under the TVZ is very similar to that found on stretched volcanic continental margins, where typically 15 km of heavily intruded lower crust underlies the stretched continental crust and extrusive volcanics on the margin.…”

Section: Interpretation Of Velocity Modelsupporting

confidence: 84%

“…Indeed, the structure under the TVZ is very similar to that found on stretched volcanic continental margins, where typically 15 km of heavily intruded lower crust underlies the stretched continental crust and extrusive volcanics on the margin. There are usually only weak reflections off the top of the intruded lower crust, but strong, continuous wide‐angle Moho reflections off the base of the crust (Fowler et al 1989; Barton & White 1997; Roberts et al 2005).…”

Section: Interpretation Of Velocity Modelmentioning

confidence: 99%

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Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Harrison

White

2006

Geophysical Journal International

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S U M M A R YSeismic data from both explosive and earthquake sources have been used to model the crustal and upper-mantle velocity structure beneath the Taupo Volcanic Zone (TVZ), an active backarc basin in central North Island, New Zealand. Volcanic sediments with P-wave velocities of 2.0-3.5 km s −1 reach a maximum thickness of 3 km beneath the central TVZ. Underlying these sediments to 16 km depth is material with velocities of 5.0-6.5 km s −1 , interpreted as quartzo-feldspathic crust. East and west of the TVZ, crust with similar velocities is found to depths of 30 and 25 km, respectively. Beneath the TVZ, material with P-wave velocities of 6.9-7.3 km s −1 is found from 16 to 30 km depth and is interpreted as heavily intruded or underplated lower crust. The base of the crust at 30 km depth under the TVZ is marked by a strong seismic reflector, interpreted as the Moho. Modelling of arrivals from deep (>40 km) earthquakes near the top of the underlying subducting Pacific Plate reveals a region with low mantle velocities of 7.4-7.8 km s −1 beneath the crust of the TVZ. This region of low mantle velocities is best explained by the presence of partially hydrated upper mantle, resulting from dehydration of hydrous minerals (e.g. serpentinite) carried down by the underlying subducting plate. Within the lower crust beneath the TVZ, a region of high (0.34) Poisson's ratio is observed, indicating the presence of at least 1 per cent partial melt. This melt probably fractionates and assimilates crustal material before some of it migrates into the upper crust, where it provides a source for the voluminous rhyolitic magmas of the TVZ.

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Section: Interpretation Of Velocity Modelsupporting

confidence: 84%

Section: Interpretation Of Velocity Modelmentioning

confidence: 99%

Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Harrison

White

2006

Geophysical Journal International

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“…Various consortia have focused on this imaging problem over recent years with many techniques tested including very long cables and very large sources (Roberts et al 2005). Despite progress, the authors consider that there is more to do to Figure 2 Farfield signature amplitude spectra (normalized with respect to maximum amplitude at 0 dB).…”

Section: T H E P R O B L E Mmentioning

confidence: 99%

Seeing below the basalt – offshore Faroes

Gallagher¹,

Dromgoole²

2007

Geophysical Prospecting

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Exploration in the basalt covered areas of the Faroes offshore has always suffered from poor seismic imaging below the basalt. Long offset 2D and 3D seismic data were acquired and a significant improvement in the seismic image below top basalt has been achieved. Deep towing of the source and receiver cables helped by extending the seismic bandwidth towards lower frequencies. Bubble‐tuned rather than conventional peak‐tuned source arrays gave little, if any, incremental benefit. The improvement in the imaging comes primarily from the approach to processing the data. High frequencies (dominantly noise) are filtered out of the data early in the processing to concentrate on the low frequency data. Careful multiple removal is important with several passes of demultiple being applied to the data using both Surface‐Related Multiple Elimination (SRME) and Radon techniques. Velocity analysis is performed as an iterative process taking into account the geological model. Reprocessing legacy 2D surveys, acquired with wide‐ranging parameters, using these processing techniques improved these datasets significantly, indicating that sub‐basalt imaging seems to be more sensitive to processing than to the choice of acquisition parameters.

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“…They suggested that the original thermal anomaly consisted of a quadrapole-junction of vertical connected sheets of asthenospheric mantle each extending about 1200 km from the centre of the anomaly (see fig. 1 of Roberts et al 2005, for a diagram of the extent of these suggested anomalies). Such a quadrapole-junction pattern, as well as triple-junctions of connected sheets have been modelled by Houseman (1990) as characteristic of the initial stages of rising mantle plumes created by boundary layer instabilities in the mantle.…”

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confidence: 99%

Influence of the Iceland mantle plume on oceanic crust generation in the North Atlantic

Parkin¹,

White²

2008

Geophysical Journal International

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SUMMARY When a mantle plume with elevated temperature underlies an oceanic spreading centre it affects the generation of oceanic crust by creating thicker crust. We map the variation in crustal thickness and seismic velocity along three long‐offset seismic profiles acquired over oceanic crust generated shortly after continental breakup in the North Atlantic: a 212‐km‐long flowline from the Faroes rifted continental margin across crust of 51–42 Ma age, where oceanic spreading developed close to the inferred centre of the Iceland mantle plume; a 256 km flowline extending from the Hatton rifted continental margin across crust of 52–40 Ma age, about 800 km south of the presumed centre of the mantle plume; and a 99 km strike line over oceanic crust formed at 43 Ma in the Iceland Basin off the Hatton continental margin. The crustal velocity structure along each profile is constrained by multichannel seismic reflection data, which is used primarily to map the sediments, and by densely spaced ocean‐bottom seismometers, which recorded wide‐angle reflections and refractions to offsets of more than 100 km. Over 56 000 crustal diving wave and Moho wide‐angle reflection arrivals were used in joint crustal refraction and reflection tomographic inversions. Quantitative error analysis shows that the seismic velocity of the crust is mostly constrained to within 0.1 km s−1 and the depth of the Moho to within ±250 m. We interpret the crustal thickness and velocity changes along the profiles as caused primarily by changes in the mantle temperature at the time of crustal formation. If all the oceanic crustal thickness variations are ascribed to mantle temperature changes, we infer that as mature seafloor spreading developed following continental breakup, the mantle cooled by ca. 75 °C over a 10 Myr period, although it still remained hotter than the global average of normal oceanic crust. The crust formed close to Iceland is at all times thicker than that formed further away, which we interpret as reflecting higher temperatures close to the centre of the thermal anomaly created by the mantle plume. Currently at the Reykjanes Ridge, south of Iceland, we interpret thicker than normal oceanic crust as being caused by the presence of hotter mantle, modulated by thickness variations of 1.5–2.0 km which are attributed to temporal variations in the mantle plume temperature of about 25 °C on a 3–6 Myr timescale. A 1.5 km increase in thickness of oceanic crust generated between 48 and 45 Ma on the Faroes line is similar in magnitude and duration to those occurring on the present day Reykjanes Ridge, which we suggest is due to a temperature pulse of ∼25 °C. Gravity lineations in the northern North Atlantic suggest that the oceanic crust has exhibited small thickness fluctuations of similar size throughout its history, interpreted as due to small fluctuations in the temperature of the Iceland mantle plume.

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Imaging magmatic rocks on the Faroes Margin

Cited by 13 publications

References 36 publications

Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Lithospheric structure of an active backarc basin: the Taupo Volcanic Zone, New Zealand

Seeing below the basalt – offshore Faroes

Influence of the Iceland mantle plume on oceanic crust generation in the North Atlantic

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