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

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 ~ 11.0 Ma). 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 507 km of minimum orogenic shortening — at least ~ 230 km 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 ~ 11.0 Ma is estimated at 20.8 km/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 9–11 km/My between ~ 41.5 and ~ 21.1 Ma to 22–39 km/My between ~ 21.1 and ~ 11.0 Ma, suggest a two-phase dynamics of the orogenic system. The acceleration of foreland migration at ~ 21.1 Ma 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.

► The Outer Carpathians form an imbricate fan internally deformed by out-of-sequence thrusts.
► A forward model depicts the evolution of the Outer Carpathian accretionary wedge.
► The minimum orogenic shortening equals 507 km.
► Migration rate of the foreland basin increased at ~ 21.1 Ma from ~ 9 km/My to 22–39 km/My.
► The acceleration of foreland migration coincides with opening of the Pannonian Basin.