Abstract
Understanding the architecture and structural evolution of highly curved orogens is essential for understanding the variability of geodynamic processes related to plate convergence. Arcuate orogens, or oroclines, often form by an interplay between subduction and indentation processes. The PhD thesis aims to increase our understanding of the mechanisms controlling strain
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partitioning during oroclinal bending around indenters. The thesis combines field structural observations in the southern Carpatho-Balkanides orocline of South-Eastern Europe and crustal-scale analogue modelling to build process-oriented hypotheses and validate them against other worldwide examples.
The introduction (Chapter 1) defines the context of highly curved orogens affected by a complex poly-phase tectonic evolution and significant strain partitioning. Chapter 2 studies field kinematic data to understand the kinematics of nappe stacking and the mechanics of oroclinal bending in the Serbian Carpathians segment of the Carpatho-Balkanides. Results demonstrate a poly-phase evolution, where the Early Cretaceous nappe stacking was followed by Oligocene–middle Miocene ~40° clockwise rotations around the Moesian indenter and by a late Miocene E-ward thrusting of the Upper Getic sub-unit. These results show that the oroclinal bending is associated with strain partitioning between strike-slip faulting and bi-modal extension, driven by different but overlapping geodynamic processes.
Chapter 3 investigates lateral transfer of shortening in front of indenters to transpression, strike-slip and the formation of transtensional/extensional basins by using the crustal-scale analogue models. Results show that the geometry of the indenter is the major parameter controlling strain partitioning and deformation transfer from thrusting to transtension, whereas the rotation controls the opening of triangular-shaped transtensional basins. The ductile crust flow distributes deformation over a wider area, facilitating strike-slip splaying into transtension/extension behind the indenter.
Chapter 4 focuses on field kinematics to derive the mechanics of indentation and strain partitioning in the backarc-convex Carpatho-Balkanides orocline. The results demonstrate that deformation was accommodated by the Circum-Moesian Fault System surrounding the Moesian indenter, where the strain was partitioned to coeval strike-slip, thrusting and normal faulting. It is one of the largest European intra-continental strike-slip deformation zones, with an accumulated 140 km dextral offset. The strike-slip offset is transferred eastwards to thrusting in the Balkanides and westwards to orogen-parallel extension. The deformation was driven by subduction of the Carpathians embayment, resulting in laterally variable amounts of translation and rotation around the Moesian indenter.
Continental indentation is often affected by slab roll-back-driven back-arc extension. Chapter 5 uses crustal-scale analogue models to investigate the effects of different extension directions on the strain partitioning during indentation. The results show that extension parallel to the strike-slip margin of the indenter creates subsidence behind the indenter, while the extension perpendicular to the strike-slip margin distributes transtensional deformation away from the indenter. The results are in good correlation with the evolution of the Carpatho-Balkanides orocline, where oroclinal bending is coeval with extension along the strike-slip margin and behind the indenter.
The thesis conclusion discusses the results of the field kinematics and analogue modelling studies in the context of indentation and oroclinal bending, setting the stage of future studies in similar orogenic areas.
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