Ecors deep seismic data and balanced cross sections: Geometric constraints on the evolution of the Pyrenees

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Abstract
The ECORS deep seismic profile and additional geological and geophysical data are used to constrain the balancing of a structural section crossing the Pyrenees. To minimize the effects of the mid‐Cretaceous strike‐slip motion along the North Pyrenean fault, we have chosen to restore the geometry to the period after the Albian‐Cenomanian strike‐slip faulting and before the Late Cretaceous compressional tectonics. At least 100 km of shortening must be accounted for in the deep crust in order to balance the cross section. The estimated length of the top of the Iberian Paleozoic basement is 40 km shorter than the length of the layered Iberian lower crust as measured on the ECORS seismic line. A variety of restorations are thus discussed to accommodate this discrepancy. The first solution considers that the discrepancy is due to an initial absence of lower crust underneath part of the Iberian margin. This solution implies a simple shear model involving low‐angle detachment faulting during the opening stage of Albian basins. The favored solution considers that the missing Iberian deep crust is currently stacked within the axial zone; it implies that Albian basins formed as pull‐apart basins along the North Pyrenean fault system.