Strain partitioning along a curved strike-slip fault system during indentation: inferences from analogue modelling

Large-scale continental strike-slip faults are associated with significant strain partitioning in releasing/restraining bends and often display map-view curvatures ending in horse-tail structures. Commonly, these strike-slip faults are associated with indentation, where shortening in front of rigid blocks is transferred laterally to transpression, strike-slip and the formation of transtensional and extensional basins. We investigate how these structurally distinct domains are kinematically linked by performing a series of crustalscale analogue modelling experiments where a deformable crust is moved against a stable and rigid indenter. The modelling demonstrates that the geometry of the indenter margins is the major controlling parameter driving strain partitioning and deformation transfer from thrusting and transpression to strike-slip and transtension, whereas the rotation of the mobile plate controls the opening of triangular shaped transtensional basins. Flow of the ductile crust distributes the deformation over a wider area, facilitating strike-slip splaying into transtension/extension behind the indenter. These results (Figure 1) show a very good correlation with the Moesian indentation in the Carpatho-Balkanides orogenic system of South-Eastern Europe, where the >100 km of Cerna-Timok dextral offset is partitioned to thrusting in the frontal, Balkanides, part of the Moesian indenter and to transtension and extension in the neighboring South Carpathians, behind the Moesia. The modelling also infers that the gradual transfer of strike-slip deformation from the Cerna-Timok system to thrusting/transpression and extension/transpression explains their observed variability in offset along strike