Transfer of deformation in back-arc basins with a laterally variable rheology: Constraints from analogue modelling of the Balkanides-Western Black sea inversion

Abstract

The balance between extension and contraction in back-arc basins is very sensitive to a number of parameters related to on-going subduction and collision processes. This leads to complex back-arc geometries, where a lateral transition between crustal blocks with contrasting rheologies is often recorded. One good example is the back-arc region of the Balkanides–Pontides orogens, where lateral variations in rheologies are observed between the Balkanides–Moesian block and the Pontides–Western Black Sea Basin. The latter opened during Cretaceous–Eocene, and has been inverted together with the former starting during late Middle Eocene. The inversion generated contrasting geometries along the orogenic strike, with a narrow zone of high deformation in the Balkanides–Moesia region, wide areas of thrusting with low offsets in the Pontides– Western Black Sea Basin and a transitional zone characterized by highly curved geometries. This overall type of inversion is investigated here by the means of analogue modelling testing the role of inherited crustal geometries during inversion. Our modelling suggests that the contrasting architecture of inverted structures observed in the Balkanides–Pontides domain are the result of pre-existing crustal stretching geometries of various blocks inherited from the Cretaceous–Eocene extension. The stretched and weak back-arc basins can transfer contraction deformation at large distances, explaining structures derived by observational studies. The collisional deformation recorded in the Pontides was transmitted at large distances that are in the range of the contraction structures observed in the centre and northern part of the Western Black Sea. In the light of analogue modelling results we argue that the Western Black Sea was a rheologically weaker domain when compared with the adjacent western onshore at the beginning of the inversion, in contrast with previous results derived from numerical modelling studies that argued for a strong West Black Sea domain at the beginning of inversion.