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[1] Experimental models scaled for density and viscosity were performed to investigate the effects of indentation obliquity and rheological stratification on the deformation patterns caused by continental indentation. The shape and orientation of the indenter were inspired by the Dolomites indenter of the southern Europeans Alps. The results of our experimental models showed that small changes in the angle of convergence induce marked differences in the patterns of deformation. The only models whose fault patterns satisfyingly reproduced that of the Eastern Alps were characterized by NNE directed motion of the indenter. In these models, E-W extension formed in front of the leading edge of the indenter, as observed in the Eastern Alps along the Brenner extensional fault. Extensional deformation of the models maintained compatibility between the areas located on both sides of the indenter edge, which shortened at different rates and in different directions. Therefore extension was not caused by gravitational instabilities but by the kinematic and geometrical boundary conditions imposed by the indenter shape and the convergence direction. Lateral escape was always modest in our models, reaching a maximum of 20%. This value is much smaller than previous estimates of lateral escape in the Eastern Alps but very close to the amount inferred by our reassessment of Tertiary E-W extension in the Eastern Alps.

A lithospheric model scaled for density and viscosity was shortened obliquely in front of an indenter whose shape and orientation match those of the South Alpine indenter. Deformation was initially localized into subparallel sets of conjugate transpressive thrusts. These structures evolved into folds, which were strongly amplified and converged closer together during ongoing shortening, finally forming a series of tight antiforms. At the same time, this tightly folded structure locally accommodated significant orogen-parallel extension, attaining 100% in front of the leading edge of the indenter, but only 15% on the scale of the entire model. The internal architecture and fault pattern of the model in map view are very similar to those of the Tauern Window in the Eastern Alps, emphasizing the importance of localization of folding and shortening rather than orogen-parallel extension for its formation. Keywords: Tauern Window, Eastern Alps, indentation tectonics, synorogenic extension, orogen-parallel extension, metamorphic domes.

Tomographic images of the mantle below the Hercynian belt of Brittany display strong anomalies of P-wave traveltimes that likely represent variations in composition, and whose trends change above and below 130 km. A quantitative strain analysis of surface geological structures has shown that the crust in the area was affected by regional-scale distributed simple shear. The change of trends of tomographic anomalies below and above 130 km is largely removed by extending the simple shear model down to 130 km. From this, we infer lithospheric-scale wrenching, and therefore deep-seated horizontal decoupling, possibly at the lithosphere-asthenosphere boundary. Simple shear restoration further provides arguments for the occurrence of a steeply dipping slab. Geological data support its interpretation as a remnant of oceanic lithosphere subducted prior to the Hercynian collision. Beyond regional implications, the study underlines the interest of combining geology and tomography for the understanding of lithosphere deformation. Keywords: Hercynian lithosphere, mantle deformation, seismic tomography, shear belt, central Brittany.

The Higher Himalaya Crystalline in Ladakh, northwestern Himalaya was generated by regional extension around 25 Ma due to post-thickening, high-temperature conditions resulting in an asymmetric gneiss dome. This event was restricted to the Indian crust overlying the Main Central Thrust (MCT), upon which thrusting continued beyond the termination of the event. During the process of thermal softening, the MCT acted as a decoupling zone between the lower and upper Indian crust. Analysis suggests that synconvergent extension was favored by thermally anomalous layers.