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Structure of the ocean–continent transition, location of the continent–ocean boundary and magmatic type of the northern Angolan margin from integrated quantitative analysis of deep seismic reflection and gravity anomaly data

By
L. Cowie
L. Cowie
1
Earth and Ocean Sciences, University of Liverpool, Liverpool L69 3BX, UK
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R. M. Angelo
R. M. Angelo
1
Earth and Ocean Sciences, University of Liverpool, Liverpool L69 3BX, UK
2
Present address: ConocoPhillips, Houston, TX 77079, USA
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N. Kusznir
N. Kusznir
1
Earth and Ocean Sciences, University of Liverpool, Liverpool L69 3BX, UK
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G. Manatschal
G. Manatschal
3
CNRS-EOST, Université de Strasbourg, 1 rue Blessing, F-67084 Strasbourg, France
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B. Horn
B. Horn
4
ION Geophysical/GX Technologies, Houston, TX, USA
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Published:
January 01, 2017

Abstract

The crustal structure and distribution of crustal types on the northern Angolan rifted continental margin have been the subject of much debate. Hyper-extended continental crust, oceanic crust and exhumed serpentinized mantle have all been proposed to underlie the Aptian salt and the underlying sag sequence. Quantitative analysis of deep seismic reflection and gravity anomaly data, together with reverse post-break-up subsidence modelling, have been used to investigate the ocean–continent transition structure, the location of the continent–ocean boundary, the crustal type and the palaeobathymetry of Aptian salt deposition. Gravity inversion methods (used to give the depth to the Moho and the crustal thickness), residual depth anomaly analysis (used to identify departures from oceanic bathymetry) and subsidence analysis have all shown that the distal Aptian salt is underlain by hyper-extended continental crust rather than exhumed mantle or oceanic crust. We propose that the Aptian salt was deposited c. 0.2 and 0.6 km below global sea-level and that the inner proximal salt subsided by post-rift (post-tectonic) thermal subsidence alone, whereas outer distal salt formation was synrift, prior to break-up, resulting in additional tectonic subsidence. Our analysis argues against Aptian salt deposition on the Angolan margin in a 2–3 km deep isolated ocean basin and supports salt deposition on hyper-extended continental crust formed by diachronous rifting migrating from east to west and culminating in the late Aptian.

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Geological Society, London, Special Publications

Petroleum Geoscience of the West Africa Margin

T. Sabato Ceraldi
T. Sabato Ceraldi
BP Exploration, UK
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R. A. Hodgkinson
R. A. Hodgkinson
Dana Petroleum, UK
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G. Backe
G. Backe
BP Exploration (Epsilon) Ltd, Oman
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Geological Society of London
Volume
438
ISBN electronic:
9781786203106
Publication date:
January 01, 2017

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