Deep seismic studies of conjugate profiles from the Nova Scotia – Moroccan and the Liguro-Provencal margin pairs

Thursday, 18 December 2014
Frauke Klingelhoefer1, Youssef Biari1, Mohamed Sahabi2, Daniel Aslanian1, Philippe Schnurle1, Michael Schnabel3, Maryline Moulin1, Keith E Louden4, Thomas Funck5 and Christian J Reichert3, (1)IFREMER, Plouzané, France, (2)University of Chouaïb Doukkali, Department of Geology, El Jadida, Morocco, (3)BGR Federal Institute for Geosciences and Natural Resources, Hannover, Germany, (4)Dalhousie University, Halifax, NS, Canada, (5)Geological Survey of Denmark and Greenland, Copenhagen, Denmark
The structure of conjugate passive margins provides information about rifting styles, opening of an ocean and formation of it's associated sedimentary basins. In order to distinguish between tectonic inheritance and structures directly related to rifting of passive margins conjugate profiles have to be acquired on margins on diverse locations and different ages. In this study we use new and existing reflection and wide-angle seismic data from two margin pairs, the 200 Ma year old Nova-ScotiaMorocco margin pair and the only 20 Ma Gulf of LionsSardinia margin pair. On both margin pairs wide-angle seismic data combined with reflection seismic data were acquired on conjugate profiles on sea and extended on land. Forward modelling of the deep crustal structure along the four transects indicates that a high velocity zone (HVZ) (> 7.2 km/s) is present at the base of the lower crust on all four margins along the ocean-continental transition zone (OCT). This may represent either exhumed upper mantle material or injection of upper mantle material into proto-oceanic crust at the onset of sea-floor spreading. However the width of the HVZ might strongly differ between conjugates, which may be the result of tectonic inheritance, for example the presence of ancient subduction zones or orogens. Both margin pairs show a similar unthinned continental crustal thickness. Crustal thinning and upper-to-lower crustal thickness vary between margin pairs, but remain nearly symmetric on conjugate profiles and might therefore depend on the structure and mechanical properties of the original continental crust. For the Mediterranean margin pair, the oceanic crust is similar on both sides, with a thickness of only 4-5 km. For the Atlantic margin pair, oceanic crustal thickness is higher on the Moroccan Margin, a fact that can be explained by either asymmetric spreading or by the volcanic underplating, possibly originating from the Canary Hot Spot.