Evolution of a continental collision belt: ECORS-Pyrenees crustal balanced cross-section

Abstract

Construction of a crustal balanced cross-section across the Pyrenean chain shows a minimum shortening of 147 km, 112 km of which are related to stacking of basement thrust sheets in the southern Pyrenees. Metamorphic conditions of the basement rocks, as well as thrust geometry, indicate the maximum depth for the detachment level to be at 15 km. In the restored cross-section, the upper crust is 110 km longer than the lower layered crust. The lower crust was subducted together with the lithospheric mantle into the asthenospheric mantle and has not been imaged by geophysical data probably because an increase of density through eclogitic meta-morphism. The upper crust constitutes an orogenic lid mainly deformed by thrust structures. The balanced cross-section has been constrained by the ECORS deep reflection seismic profile as well as detailed surface data and available commercial seismic and oil well data. The restored cross-section provides a better picture of the middle Cretaceous combined strike-slip and extensional fault system as well as of the Hercynian crust. Hercynian geological features have been used as an additional tool for the restoration of the basement thrust sheets.