Factors controlling the Alpine evolution of the central Pyrenees inferred from a comparison of observations and geodynamical models

Abstract

Abstract. Geodynamical numerical modeling has been combined with crustal structural restoration of the central Pyrenees in order to gain insight into fundamental processes that control the evolution of collisional orogens. Models are based on deformation of the crust by stresses transmitted upward from kinematic basal boundary conditions corresponding to the subduction of part of the lithosphere. The influence of inherited crustal heterogeneities, denudation, subcrustal loads, and crustal mechanical properties, consistent with wellconstrained crustal partial restored cross sections of the central Pyrenees, is investigated by progressively incorporating them into model experiments. The primary result inferred from the modeling is that the asymmetry of the central Pyrenees double-wedge, seen as strain partitioning and in the morphological evolution, is a consequence of the asymmetric distribution of inherited crustal heterogeneity. The tectonic style of the central Pyrenees is the result of the inversion of the Early Cretaceous extensional fault system, during the early stages of the collision, and the reactivation of Hercynian heterogeneities during the late stages. Most of the upper crustal mass that entered the orogen during the calculated 165 km of convergence was accommodated by an increase of upper crustal cross sectional area or lost by denudation. To explain the upper crustal mass partitioning, as well as the geometry of the foreland basins and the preservation of synorogenic deposits in piggyback basins, a subduction load has to be applied to the models. Lower crust and mantle lithosphere were consumed by the mantle.

Plate kinematics in the Cantabrian domain of the Pyrenean orogen

“…Srivastava et al, 2000;Rosenbaum et al, 2002;Sibuet et al, 2004) predicts about 600 km of Mesozoic extension and a similar value of shortening in the eastern portion of the Pyrenean orogen. These values are incompatible with the amount of shortening in that area, which ranges from 80 km (Teixell, 1998) to 120 km (Vergés et al, 1995), up to a maximum of about 160 km in the central portion of the Pyrenees (Muñoz, 1992;Beaumont et al, 2000). Differences in the cumulative amount of shortening reduce when considering only the postSantonian seafloor magnetic anomalies (e.g.…”

“…This rules out any influence of the eastern Pyrenean domain, where subduction started in the Late Cretaceous (e.g. Beaumont et al, 2000), in determining subduction nucleation in the Cantabrian domain. Conversely, the westward propagation of the eastern, north-directed, Pyrenean lithospheric architecture influenced the subsequent step of deformation, when the symmetric mantle syncline was forced toward a north-verging framework.…”

Orogeny and orography: The effects of erosion on the structure of mountain belts

“…Other studies have continued to use the Southern Alps as the type example and have used simpler erosion models, but more sophisticated tectonic models in order to investigate the importance of erosion to patterns of exhumation, topography, and cooling rates [Beaumont et al, 1996b;Batt and Braun, 1997]. Other orogenic belts that have been the subject of similar investigations include the European Alps [Beaumont et al, 1996a; Schlunnegger and , the Pyrenees [Beaumont et al, 1999b], the Andes, [Masek et al, 1994] and the Himalayas [Jamieson et al, 1996].…”

Geology of the Cotiella thrust sheet, southern Pyrenees (Spain)

“…It's structural style and evolution was strongly controlled by the inversion of previous Upper Jurassic-Lower Cretaceous syn-rift extensional basins and by Upper Cretaceous post-rift basins that developed as a result of the opening of the central Atlantic and Bay of Biscay (Beaumont, Muñoz, Hamilton, & Fullsack, 2000;Derégnaucourt & Boillot, 1982;Malod & Mauffret, 1990;Roest & Srivastava, 1991). One of these basins is the middle Coniacian -lower Santonian Cotiella Basin.…”