TERTIARY DEFORMATION AND KINEMATICS OF THE SOUTHERN PART OF THE TAMBOAND SURETTA NAPPES (VAT-BREGAGLIA, EASTERN SWISS ALPS)

The southern part of the Tambo and Suretta nappes (Eastern Swiss Alps) records several structural phases during Tertiary orogenesis. Based o n micro- and mesostructural methods and kinematic indicator analysis, a tectonic model with four deformation phases is proposed: (i) A top t o the NNW shearing (D1) correlated to the nappe stacking event. (ii)Th e strongest deformation of the area forming the main schistosity (D2), with vertical shortening and E-W extension showing a top to the E she ar sense. This phase may be responsible for the bulk reduction of thic kness in the SE part of the nappe pile. (iii) Localized deformation cr eating open N-verging folds and N-thrusting steep shear zones during d ifferential uplift of the Penninic domain. This D3 deformation causes reorientation and steepening of nappe contacts and main S2 schistosity in the southern part of the Suretta and Tambo nappes. (iv) Normal fau lting (D4) to the NE corresponding to a late tectonic event under brit tle conditions.