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This thesis investigates mechanisms and boundary conditions that steer the early localisation of deformation and strain in carbonate multilayers involved in thrust systems, under shallow and mid-crustal conditions. Much is already understood about deformation localisation, but some key points remain loosely constrained. They encompass i) the understanding of which structural domains can preserve evidence of early stages of tectonic shortening, ii) the recognition of which mechanisms assist deformation during these stages and iii) the identification of parameters that actually steer the beginning of localisation. To clarify these points, the thesis presents the results of an integrated, multiscale and multi-technique structural study that relied on field and laboratory data to analyse the structural, architectural, mineralogical and geochemical features that govern deformation during compressional tectonics. By focusing on two case studies, the Eastern Southern Alps (northern Italy), where deformation is mainly brittle, and the Oman Mountains (northeastern Oman), where ductile deformation dominates, the thesis shows that the deformation localisation is steered by several mechanisms that mutually interact at different stages during compression. At shallow crustal conditions, derived conceptual and numerical models show that both inherited (e.g., stratigraphic) and acquired (e.g., structural) features play a key role in steering deformation and differentiating the seismic behaviour of the multilayer succession. At the same time, at deeper crustal conditions, strain localises in narrow domains in which fluids, temperature, shear strain and pressure act together during the development of the internal fabric and the chemical composition of mylonitic shear zones, in which localisation took place under high-pressure (HP) and low-temperature (LT) conditions. In particular, results indicate that those shear zones acted as “sheltering structural capsules” in which peculiar processes can happen and where the results of these processes can be successively preserved even over hundreds of millions of years.

The Dolomites geologically belong to the south-verging eastern Southern Alps of Italy. They record the effects of multiple deformation episodes from the Permian onward and thus offer the possibility to study the role of earlier inherited structures upon the Cretaceous-Neogene Alpine deformation history. In the Passo Rolle area, Permian extension was followed by Late Triassic-Early Jurassic extensional tectonics during which the NNW-SSE striking Passo Rolle Fault (PRF) contributed to the development of horst and graben structures. The Alpine orogenesis in the Passo Rolle area was responsible for the build-up of the Pale di San Martino mountain range during ~ NNWSSE compression. During this stage, the NNW-verging Cimon della Pala backthrust formed concomitant with the activation of minor thrusts and strike-slip faults, and the reactivation of Late Triassic-Early Jurassic extensional faults. The genetic relationships between the broad suite of tectonic structures in the Passo Rolle area have never been investigated in detail. To this end we performed mesostructural analysis of key representative exposures to add geometric and kinematic constraints on the tectonic structures associated with the different tectonic phases registered in the Passo Rolle area. We focused on collecting fault-slip data that we used for paleostress analysis aiming at reconstructing the local paleostress evolution through time. We show that (i) the PRF accommodated significant Alpine transpression and (ii) the Permian-to-Jurassic tectono-stratigraphic framework promoted the localization of Alpine deformation to the east of the PRF, where a thick carbonate-siliciclastic multilayer deformed through first-order folds and thrusts. To the west of the PRF, where the Permian ignimbrite formed instead a relatively rigid and thus less deformable block, only minor thrusts and strike-slip faults formed, commonly exploiting suitably oriented inherited structures.

We present a 1:7500 scale geological map of part of the footwall of the south verging Belluno Thrust of the seismically active eastern Southern Alps of northern Italy. We report a previously unknown thrust zone, the “San Donato-Costa Thrust Zone”, that cuts across the local Meso-Cenozoic stratigraphic succession. 1:2500 and 1:5000 geological mapping, in combination with the revision and improvement of the local lithostratigraphy and detailed structural analysis, provided new insights into the thrust geometry and the setting of the greater area it deforms. We show that the recorded deformation style (e.g. folding vs. faulting) exhibits notable variations within the affected Meso-Cenozoic stratigraphic succession, with shortening accommodated by fold trains and several subparallel thrust splays with variable amounts of stratigraphic offset cumulated during repeated faulting. Our results contribute to a better definition of folding and faulting within the Mesozoic carbonate multilayer system of the eastern Southern Alps.