Architecture and orogenic evolution of the northeastern Outer Carpathians from cross-section balancing and forward modeling

Abstract

New balanced and restored cross-sections and a 2D kinematic model illustrate the present geometry of the northeastern Outer Carpathians and quantify their orogenic evolution between the late Eocene and the late Miocene (~35.3 to ~11.0Ma). The balanced cross-section is built on extensive surface and subsurface data and depicts an imbricate fan internally stacked along high-displacement out-of-sequence thrusts. Section restoration yielded 507km of minimum orogenic shortening — at least ~230km more than proposed in previous studies. Our shortening estimate relies on accurate thicknesses of lithostratigraphic units, in most cases thinner than applied before. The average convergence rate between ~35.3 and ~11.0Ma is estimated at 20.8km/My. The forward model, constrained by lower and upper ages of syn-orogenic deposits, traces the advance of the Outer Carpathian accretionary wedge and proves kinematic admissibility of the balanced and restored cross-sections. Progradation rates of the foreland basin depositional sequences, evolving from 9–11km/My between ~41.5 and ~21.1Ma to 22–39km/My between ~21.1 and ~11.0Ma, suggest a two-phase dynamics of the orogenic system. The acceleration of foreland migration at ~21.1Ma likely reflects the onset of northward subduction retreat, linked to the rollback of the European lower plate that gave rise to coeval back-arc extension in the Pannonian Basin.