Life cycle of the East Carpathian orogen: Erosion history of a doubly vergent critical wedge assessed by fission track thermochronology

Abstract

Apatite fission track (FT) thermochronology applied to the East Carpathian fold‐and‐thrust belt in Romania constrains the interaction between the erosion history and the tectonic evolution of the orogen. The long‐lived constant asymmetric topography of the orogen and the erosion pattern as inferred from apatite FT data are in agreement with the style of evolution predicted by doubly vergent critical Coulomb wedge models. During the Miocene, up to 4 km of erosion took place over the actively deforming orogen, and the erosion patterns forms a mirrored image of the subsurface deforming wedge. The erosion products are deposited in flanking molasse basins which subsided contemporaneously due to the growing topographic weight of the wedge. Deformation of the wedge was presumably active from the early to late Miocene, but apatite FT ages between 14 and 9 Ma and track length modeling predict an acceleration of erosion rates (0.5–0.3 mm/yr) initially in the middle to late Miocene (≈13±2 Ma). The onset of erosion coincides with the last phase of convergence and a climax in the deformation history. These features are interpreted to have been caused by underrating of the European continental margin. Convergence ceased before the Pliocene according to the activity of thrust faults. During the Pliocene and Quaternary, up to 2 km of overburden was removed by erosion, leading to isostatic rock uplift of the entire region. The use of apatite fission track “minimum ages” supports the general idea that the orogen has a diachronous evolution from north to south. The orogen in the southern Bend Zone has a more juvenile tectonic character, and the main erosion phase took place during the Pliocene and Quaternary (≈5–0 Ma). The integrated approach of large scale morphology and fission track analysis confirms the applicability of the theoretical Coulomb wedge mechanics to a natural compressive fold‐and‐thrust belt. The study complements the geometric features of the orogenic wedge with quantified erosion histories and illustrates the effects of orogen evolution on vertical movements in the entire convergent setting.