Syn-Rift Evolution, Salt Tectonics and Crustal Structure Offshore Morocco and Nova Scotia

Gabor C. Tari¹, Jabour Haddou², David Einarsson³, Keith Louden⁴, Wu Yue⁵, and David E. Brown^6
1OMV, Vienna, Austria
²ONHYM, Rabat, Morocco
³Geophysical Services Incorporated, Houston, TX
⁴Department of Oceanography, Dalhousie University, Halifax, NS, Canada
⁵Department of Earth Sciences, Dalhousie University, Halifax, NS, Canada
⁶Canada-Nova Scotia Offshore Petroleum Board, Halifax, NS, Canada

As the result of deepwater exploration, extensive 2D/3D reflection seismic and potential field data sets were acquired offshore Morocco during the last decade. Whereas the mature Jurassic salt basin masks most of the upper crustal structures over this Central Atlantic margin, just outboard from the salt basin, a large area with inverted syn-rift structures was found. The areal extent of the inverted structures coincides with the deepwater area which was inferred to have oceanic crust based on regional-scale potential field data. Several industry seismic data sets, however, show very well developed syn-rift half-grabens with locally up to 2 km section in them, suggesting highly extended continental crust. The seismic signature of these prominent syn-rift troughs, detaching within the upper crust, is identical to those which were recently described on the conjugate Nova Scotia margin.

The deepwater Moroccan margin also has a large anomalous basement high, the Tafelney Plateau, trending obliquely both to the coastline/shelf-edge and the expected orientation of Atlantic transform faults. The basement high beneath the Tafelney Plateau is interpreted as a syn-rift accommodation zone analogous to many well-studied examples in the present-day East African rift system. It developed between two normal fault systems with opposing polarities, i.e. SE-dipping syn-rift faults to the north of it and NW-dipping syn-rift faults to the south of it, defining lower/upper plate margins. The actual Early to Middle Jurassic breakup between Africa and North America occurred obliquely across the accommodation zone leaving most of it on the Moroccan margin. The significant along-strike variations in crustal structure, syn-rift salt distribution, salt tectonic styles and magmatism are all attributed to changes in the style of rifting along the margin.

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