Tectonic processes during collisional orogenesis from comparison of the Southern Uralides with the Central Variscides

Abstract

A great deal of available multidisciplinary data that focused around URSEIS and DEKORP 2N-2S deep seismic profiles contribute to an advanced understanding of the respective Southern Uralide and Central Variscide transects. Both transects cross a continental margin and several terranes that accreted to it by subduction/collision processes during the Paleozoic. However, there are important differences in the present crustal architecture between the two orogens, mainly with respect to the geometry of the terrane boundaries, and in the structure at lower crustal and Moho depths. Major differences during the Devonian to Permian tectonic evolution recorded in each orogen are; the nature of the material accreted, the order of accretion, the orientation of the subduction zones, and the location/ distribution of active deformation through time. The comparison of the respective orogenic evolutions highlights the different tectonic processes that are dominant during continental assemblage in each orogenic system. In the Uralides, significant crustal growth occurred by accretion of newly formed volcanic arc crust to the continental margin and subsequent accretion of outboard subduction related accretionary material during the imbrication of the continental margin. In the Variscides, existing crustal material progressively accreted towards the continental margin by the forward advance of a growing orogenic wedge. The soft or rigid behaviour of the major crustal boundaries seems to have played an important role in the different nature and geometry of the deformation between the Uralides and Variscides. The collisional architecture in the central Variscides has been overprinted by post-orogenic processes and subsequent tectonic events, while that of the southern Uralides has been preserved from any major subsequent tectonic process.