Search

At present, it is widely accepted, that geometric, kinematic and dynamic features of the near-surface regions around subduction zones are controlled by slab-mantle interactions. Slabs are sinking and laterally moving in the mantle, inducing a mantle flow pattern with poloidal and toroidal components. The poloidal flow exerts vertical pressure, while the toroidal component exerts a shear stress on the base of the base of the lithosphere. Slabs can interact also with each other, via the dynamic pressure and the flow in the mantle, or by stress propagation in the more rigid lithosphere. The study of slab-slab interactions has come to the front of geodynamics researches to better explain geological and geophysical observations from tectonically complex areas. A key area to test models with multiple slabs is the Central Mediterranean, where minimum three subduction zone affected the region's tectonic evolution. One of the key features in the Central Mediterranean is the Adria plate, subducting on its two opposite sides. Additionally, the slab below the Central-South Apennines has been progressively breaking off during the last 2-3 Myr. The role of an outward dipping double-sided subduction system combined with an opening slab window is addressed by analog models at the scale of the upper mantle, realized using glucose syrup and silicone putty, to model the interaction between the Earth's mantle and the lithosphere. Our results show that the double subduction system has a regional effect through the induced mantle flow. Furthermore, the presence of a slab window modifies the pattern of mantle circulation, as well as the trench geometry and kinematics. In particular, the opening of the slab window induces the formation of two arcs flanking the window, while the mantle flows through it and turns towards the arcs, creating a small-scale toroidal flow. The effect of a slab window is more pronounced on double subduction systems, as the outflow through the window is amplified, while internal deformation is induced in the plate by the opposite slab pull force. These experimental results suggest that the origin of the Apenninic and the Calabrian arcs is the result of the formation of a slab window, providing a new interpretation of the surface deformation and the SKS shear wave splitting pattern of the Adria microplate. [ABSTRACT FROM AUTHOR]

The High Atlas of Morocco is a double-vergent mountain belt developed during the Cenozoic compression by inversion of a Triassic-Jurassic rift. The reconstruction of its Cenozoic kinematic and structural evolution is a fundamental key to unravel the processes that controlled its topographic growth and shape through time. However, this reconstruction is complicated by the scarce Cenozoic geologic markers and by the long residence of the High Atlas rocks at shallow crustal levels where they recorded deformation at least since the Paleozoic. To constraint its Cenozoic large-scale evolution, we combine detailed structural analysis with six geological cross sections distributed from west to east along the Moroccan High Atlas. We find that the large-scale physiographic differences between the Western and Central-Eastern regions of the Moroccan High Atlas reflects partly differences in their structural evolution. The western sector is a narrow mountain belt with basement rocks at its core, where shortening is largely accommodated along inherited structures acting as steep, reactivated, dextral transpressive faults, and with Mesozoic sediments along its borders, where deformation occurs by shallow folding and thrusting. The Central-Eastern High Atlas is, instead, a wide mountain belt that exposes a thick Mesozoic sedimentary cover deformed mainly by thrusts and folds. The complex distribution of deformation and its kinematic variations are related to the obliquity between the compression that caused the rift inversion and the inherited structures and to strain partitioning. Large heterogeneities in the occurrence of Mesozoic décollement layers and in the thickness of the Mesozoic sedimentary covers also play a major role by emphasizing the effects of strain partitioning. Moreover, in the western sector, the intensity of the deformation decreases northwards involving progressively younger strata that are as young as 6 Ma at the front and the main deformation event occurred during the Middle Miocene-to-Pliocene, at the same time with the activity of the Siroua volcanic field. The emplacement of this volcanic field, which lies between the High Atlas and the Anti-Atlas, is controlled by faults suggesting a possible bearing with the two orogenic systems during the Late Cenozoic shortening. [ABSTRACT FROM AUTHOR]