F~UTTERWORTH I-~'IE I N E M A N N Marine and Petroleum Geology, Vol. 12, No. 8, pp. 893-915, 1995 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0264-8172/95 $10.00 + 0.00 Eastern Pyrenees and related foreland basins: pre-, syn- and post-collisional crustal-scale cross-sections J. Verges*, H. Millan, E. Roca, J. A. Mufioz and M. Marzo Dept de Geo/ogia Din~mica, Geof/sica i Pa/eonto/ogia, Univ. de Barcelona, Mart/ i Franqu&s, s/n, 08071 Barcelona, Spain J. Cites Servei GeolOgic de Cata/unya, /CC, Parc de Montju/'c, 08038 Barcelona, Spain T. Den Bezemer, R. Zoetemeijer and S. Cloetingh Facu/ty of Earth Sciences, Vrije Univeriteit, Amsterdam, The Netherlands Received I October 1994; revised 15 February 1995; accepted 9 May 1995 A new crustal-scale cross-section through the Eastern Pyrenees shows a minimum of 125 km of total shortening across the belt. Convergence rates of 6 mm/yr (during early and middle Eocene time) between the northern domain of the Iberian plate and Europe can be evaluated from calculated shortening rates in both sides of the orogen. Two stages of orogenic growth can be determined in the Eastern Pyrenean transect. A first stage (from Early Cretaceous to middle Lutetian time) is characterized by a low topography, submarine emplacement of the thrust front, fast rates of south-directed shortening up to 5mm/yr and widespread marine foreland deposition. This stage is also characterized by equivalent amounts of mountain erosion and detrital foreland accumulation. A second 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 times the foreland basin accumulation, leading to a large by- pass of sediments towards the Atlantic before the final endorrheic stage of the basin. 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 early Miocene rock uplift rates in the Eastern Pyrenees, which account for 0.2-0.35 mm/yr, suggesting that erosion has been discontinuous through time. Inferred maximum river incision rates since the middle Miocene opening of the Ebro Basin towards the Mediterranean Sea account for less than 0.1 mm/yr. Keywords: eastern Pyrenees; balanced cross-sections; shortening rates The growth of an orogenic wedge and the formation of a related foreland basin is the result of geodynamic processes on a lithospheric scale that are strongly dependent on the forces acting on the plates and the rheology of the lithosphere (e.g. Cloetingh et al., 1989) as well as on the geological processes acting within the orogenic wedge (Davis et al., 1983; Dahlen and Suppe, 1988). Precise control of the major processes acting during the evolution of mountain ranges and their adjacent foreland basins is not always easy to decipher, particularly in ancient orogens. However, inactive orogens occasionally preserve a geological record of major tectonic events, allowing us to better understand * Correspondence to Dr J. Vergrs how mountain ranges and related flexural basins evolve through time. A new balanced and totally restored crustal-scale cross-section through the Eastern Pyrenees based on the available geophysical and geological data is presented in this paper. In addition, a restored section during middle Lutetian time is also presented. This restoration corresponds to the final stage of marine evaporitic conditions in the Ripoll Trough. The aim of this paper is to document and discuss the geological constraints on a crustal cross-section through the Eastern Pyrenees before, during and after contrac- tion. This study is part of an iterative process of cross- section construction and flexural modelling in which both techniques build on one another (Mill~in et al., this issue). Marine and Petroleum Geology 1995 Volume 12 Number 8 903