Basement-cover relationships in the Tambo nappe (Central Alps, Switzerland): geometry, structure and kinematics

Abstract

In the Pennine zone of the Central Alps, the Tambo nappe forms a thin crystalline sliver embedded in the Mesozoic cover. Four Tertiary Alpine deformations are observed. The D 1 ductile deformation is linked to the progressive Eocene stacking of the nappes towards the northwest. During D 1, basement deformation is governed by imbricate tectonics whereas cover is thin-skinned and intensively folded. These different structures reflect the original strong rheological contrast between basement and cover. During the heterogeneous and ductile D 2 deformation, the behaviour of the basement and cover became similar. The strong vertical D 2 shortening, associated with a ‘top-to-the-east’ shear, led to the folding of the prior SE-dipping structures, developing SE-vergent folds with axes close to the E-W L 2 stretching lineation. D 2 corresponds to post-collisional crustal thinning following D 2 crustal thickening. The D 3 and D 4 deformations occurred under retrograde conditions and can be correlated with uplift and late dextral movement on the Insubric line, respectively.