Crustal structure and orogenic material budget in the west central Pyrenees


  • Antonio Teixell


Surface and subsurface data are combined to construct a crustal-scale cross section of the western central Pyrenees (France and Spain) at the boundary between the European and Iberian plates. The position of Moho reflections in the ECORS-Arzacq reflection profile suggests a tectonic wedge of European crust and upper mantle had indented the Iberian plate at lower crustal levels. The European wedge is overlain by an upper, Iberian wedge thus constituting a double (stacked) wedge geometry. The upper wedge was delaminated and deformed giving rise to the Pyrenean orogenic prism, manifested as a bivergent fan in upper crustal levels. The underthrust lower Iberian plate has been imaged to depths of 55–60 km, but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km. Total orogenic contraction calculated from surface structures is about 75–80 km, which was accomplished between the latest Cretaceous and the early Miocene at an averaged rate of 1.2 mm/yr. Consistent with these moderate values, exhumation of the orogen is much less than in the more shortened eastern parts of the range. Paleozoic basement and preorogenic Mesozoic rocks are little eroded, and much of the exhumation involved cannibalization of early foreland basins, which once covered the entire, poorly emergent orogen at this transect. This resulted in a continuous process of sediment recycling and, coupled with a considerable lateral arrival of material, a bulk negative erosion-sedimentation budget.