EASTERN PYRENEES AND RELATED FORELAND BASINS - PRECOLLISIONAL, SYNCOLLISIONAL AND POSTCOLLISIONAL CRUSTAL-SCALE CROSS-SECTIONS

A new crustal-scale cross-section through the Eastern Pyrenees shows a minimum of 125 km of total shortening across the belt. Convergence ra tes of 6 mm/yr (during early and middle Eocene time) between the north ern domain of the Iberian plate and Europe can be evaluated from calcu lated shortening rates in both sides of the orogen. Two stages of orog enic growth can be determined in the Eastern Pyrenean transect. A firs t stage (from Early Cretaceous to middle Lutetian time) is characteriz ed by a low topography, submarine emplacement of the thrust front, fas t rates of south-directed shortening up to 5 mm/yr and widespread mari ne foreland deposition. This stage is also characterized by equivalent amounts of mountain erosion and detrital foreland accumulation. A sec ond stage (middle Lutetian to late Oligocene) is marked by an increase in structural relief, subaerial emplacement, a decrease in shortening rates and widespread continental sedimentation. This leads towards a non-equilibrium condition in which mountain erosion is almost three ti mes the foreland basin accumulation, leading to a large bypass of sedi ments towards the Atlantic before the final endorrheic stage of the ba sin. Erosion rates based on area conservation between middle Lutetian and present day sections in a two-dimensional calculation indicate an average of 0.15 mm/yr. This rise is lower than middle Lutetian to earl y Miocene rock uplift rates in the Eastern Pyrenees, which account for 0.2-0.35 mm/yr, suggesting that erosion has been discontinuous throug h time. inferred maximum river incision rates since the middle Miocene opening of the Ebro Basin towards the Mediterranean Sea account for l ess than 0.1 mm/yr.