Strain partitioning at orogenic contacts during rotation, strike–slip and oblique convergence: Paleogene–Early Miocene evolution of the contact between the South Carpathians and Moesia

Abstract

Oblique convergence accompanied by large-scale strike–slip deformation taking place between orogenic units is an inherent feature of highly bended mountain chains. Strain partitioning during subduction and collision takes place between differently oriented orogenic segments and creates contrasting styles of deformation that may include coeval extension, strike–slip and shortening, in particular when large amounts of rotations are recorded. A typical area is the one connecting the Balkans with East Carpathians along the highly bended South Carpathians Mountains that were affected by large scale Paleogene–Miocene strain partitioning at the contact with their lower Moesia unit in what is commonly known as the Getic Depression. We analyse this contact by the means of a number of seismic transects calibrated by exploration wells. The kinematic restoration of these transects is correlated with connecting depth information and with previously published studies. This has allowed the definition of a novel kinematic evolution of the deformation observed in the Getic Depression. This evolution is compatible with the definition of a Paleogene–Early Miocene period of transtensional opening by using strike–slip faults that terminate along horsetail geometries. This transtensional deformation migrates in space and time across the basin and is kinematically connected with the oblique shortening taking place in the eastern part of the Getic Depression and SE/East Carpathians. In particular interesting is the mechanism of transtensional migration E-wards and contractional migration W-wards that took place coevally during the rotation and E-ward translation of the upper Carpathians units along the strike of the Getic Depression. This has been subsequently followed by shortening and transpression during Middle Miocene–Quaternary times that was recorded at the scale of the entire studied area.