A PALEOMAGNETIC STUDY OF PERMIAN AND TRIASSIC ROCKS FROM THE TOULON-CUERS BASIN, SE FRANCE

It has been known for some time that the use of paleomagnetic poles from the Permian of Laurasia and Gondwana results in significant continental overlap between both continents when used to reconstruct Pangea in a classical Wegnerian fit (Pangea A). If this inconsistency in the paleomagnetic data set is caused by problems unrelated to the Geocentric Axial Dipole hypothesis and/or does not reflect significant inclination shallowing, the problem can be solved by positioning Gondwana roughly 3000 km to the east with respect to Laurasia while maintaining the original latitudes. This operation results in a so called Pangea B configuration. However, since the Atlantic Ocean undebatedly opened from a Pangea A assemblage, Gondwana has to move into this configuration prior to the Jurassic requiring 3000 km of westward translation along a major dextral strike-slip diffuse plate boundary running through the present Mediterranean. This concept, however, is still under heavy scrutiny and the traces of the mega shear are difficult to identify. One way towards the identification of this shear zone is determination of tectonic blocks, the amount and sense of rotation within the shear zone.

Here, we present new paleomagnetic data from mainly red sandstones from Permian and Triassic sedimentary basins and Permian volcanics from the Toulon basin in SE France. All samples show rather simple paleomagnetic behaviour. Thermal demagnetization up to 675°C is successful in resolving the directional spectrum. After removal of a low temperature component by heating to ~200°C, a second high temperature component, which generally points towards the south and up, can be identified in almost all Permian samples. Lower and Middle Triassic samples display similar behaviour, however, two polarities of magnetization are present. The primary character of magnetization is supported by a positive conglomerate test performed on a polygenic conglomerate within the Les Salettes formation. The latitudes of the resulting paleopoles agree well with the Permian segment of the European Apparent Polar wander path, while the associated longitudes are dispersed and define a small circle segment spanning ~ 60°. This is taken as significant evidence for block rotations within the Toulon basin and suggests that the basin formed within a zone of dextral megashear.