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The Morocco-Canaries Atlantic margin – a classic rifted margin or a more complex failed-breakup basin?

Author(s): Alan Roberts Badley Geoscience, North Beck House, Hundleby, Lincs, PE23 5NB, UK
Andy Alvey Badley Geoscience, North Beck House, Hundleby, Lincs, PE23 5NB
John Fisher Genel Energy, 1 Grafton St, London, W1S 4FE
Dave Burnett Genel Energy, 1 Grafton St, London, W1S 4FE
Nick Kusznir Badley Geoscience, North Beck House, Hundleby, Lincs, PE23 5NB/3Dept of Earth & Ocean Sciences, University of Liverpool, L69 3BX

The continent-ocean-boundary offshore southern Morocco is traditionally thought to lie between the Moroccan coast and the Canary Islands. OCTek gravity inversion, however, shows a ribbon of thick crust extending NE from the Canaries, one interpretation of which is that the Canaries are located on a rifted continental block or “micro-continent”, rather than on oceanic crust. We have tested this hypothesis via: - Further analysis of the gravity inversion results - Geodynamic analysis of four regional seismic transects between the Moroccan coast and the Canaries, focussed on backstripping, with supportive structural forward-modelling - A new plate-reconstruction model for the N.Africa-N.America Atlantic margins

Best-case crustal-thickness and thinning-factor maps for the central and southern Atlantic have been produced from the gravity inversion. These incorporate corrections for regional dynamic topography and volcanic addition during rifting and breakup. From these maps profiles of integrated extension across the conjugate N.Africa-N.America margins have been calculated in order to constrain the magnitude of the pre-breakup rifting phase within the new plate-reconstructions.

Backstripping analysis of basement-subsidence suggests that, in the area between Morocco and the Canaries, oceanic crust is only likely to be present in the far north. Thinning-factors decrease southwards within this area, suggesting that Morocco and the Canaries are primarily separated by highly-thinned continental crust rather than oceanic crust. This result is compatible with the “V-shaped” basin and thinning-factor distribution identified by gravity inversion.

Further backstripping analysis of the Jurassic-Tertiary stratigraphy along the Moroccan coast suggests that the whole area is currently supported by ~500m of dynamic uplift, possibly initiating during the Late Cretaceous. This result is compatible with the assumptions used in the gravity inversion. A likely origin for the dynamic uplift is the proximity of the Canaries magmatic province. Incorporating dynamic uplift into the backstripping model allows us to make predictions of palaeobathymetry and depositional environments back from the Tertiary into the Jurassic.

Finally, all of the preceding work has been incorporated into a new plate-reconstruction model, which highlights: (i) the “plate overlap” resulting from pre-breakup rifting along the conjugate margins (ii) initial propagation of Atlantic seafloor-spreading southwards into the Morocco-Canaries “V-shaped” basin (iii) abandonment of this initial plate-boundary as a “failed-breakup basin”, leading to (iv) final separation of Africa from America to the west of the Canaries.

The hypothesis that Morocco and the Canaries are separated by thinned continental crust, rather than oceanic crust, has implications for petroleum-systems analysis in the area. As a consequence we have modelled the temperature/heat-flow history at a number of key-locations constrained by continental stretching-factors from the gravity inversion and backstripping analyses, together with temperature constraints from nearby wells.

Failed-breakup basins with a “V-shaped” geometry are not uncommon at rifted continental margins, other examples on the eastern Atlantic margin are the Faeroes-Shetland Basin and the Galicia Interior Basin. We believe they are diagnostic of the segmented manner in which offset zones of continental stretching ultimately link together into an ocean margin as continental rifting proceeds to continental separation.


Title:
The Morocco-Canaries Atlantic margin – a classic rifted margin or a more complex failed-breakup basin?
Type:
Oral
Origin:
Industry
Day:
2
Session:
2
Daily sequence no.:
18
Lead author last name:
Roberts
Lead author first name:
Alan
Affiliation(s):
Badley Geoscience, North Beck House, Hundleby, Lincs, PE23 5NB
Country:
UK
Abstract status:
Author details missing
UID:
63