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Anomalous melt production after continental break-up in the southern Iberia Abyssal Plain

By
T. A. Minshull
T. A. Minshull
1
School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, European Way, Southampton SO14 3ZH, UK (e-mail: tmin@soc.soton.ac.uk)
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S. M. Dean
S. M. Dean
1
School of Ocean and Earth Science, University of Southampton, Southampton Oceanography Centre, European Way, Southampton SO14 3ZH, UK (e-mail: tmin@soc.soton.ac.uk)
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R. S. White
R. S. White
2
Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge CB3 OEZ, UK
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R. B. Whitmarsh
R. B. Whitmarsh
3
Challenger Division, Southampton Oceanography Centre, European Way, Southampton SO14 3ZH, UK
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Published:
January 01, 2001

Abstract

Recent geophysical work and Ocean Drilling Program drilling in the southern Iberia Abyssal Plain have indicated that, in a transition zone up to 170 km wide between thinned continental crust and oceanic crust, the basement consists of serpentinized peridotite mantle with sparse mafic intrusive or extrusive rocks. There is no evidence for the addition of significant magmatic material to the stretched continental crust landward of this zone during the last phase of rifting, whereas seaward of this zone, where the halfspreading rate is about 10 mm a-1, the crust rapidly reaches a thickness of c. 6 km, which is normal for Atlantic oceanic crust. Models of melt generation during pure shear, finite-duration continental rifting can successfully reproduce the observed absence of significant syn-rift magmatism on, within and beneath the thinned continental crust if the rifting episode is longer than 10–20 Ma. However, for normal mantle potential temperatures, such models predict significant melt generation in the transition zone seaward of the thinned continental crust even for rift durations longer than 20 Ma. Restricted melting beneath the transition zone might be explained partly by lateral heat loss to the adjacent continental lithosphere, by anomalously low mantle potential temperatures at break-up time, or by depth-dependent stretching such that the observedinfinite stretching factor for the crust is not representative of the lithosphere as a whole. An additional mechanism for restricted melt production involves a transitional state between the end of continental extension and the onset of steady-state sea-floor spreading, during which mantle upwelling is less focused than at normal oceanic spreading centres.

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Geological Society, London, Special Publications

Non-Volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea

R. C. L. Wilson
R. C. L. Wilson
The Open University, UK
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R. B. Whitmarsh
R. B. Whitmarsh
Southampton Oceanography Centre, UK
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B. Taylor
B. Taylor
University of Hawaii, Hawaii
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N. Froitzheim
N. Froitzheim
University of Bonn, Germany
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Geological Society of London
Volume
187
ISBN electronic:
9781862394353
Publication date:
January 01, 2001

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