BASEMENT COVER RELATIONSHIPS IN THE TAMBO NAPPE (CENTRAL ALPS, SWITZERLAND) - GEOMETRY, STRUCTURE AND KINEMATICS

In the Pennine zone of the Central Alps, the Tambo nappe forms a thin crystalline sliver embedded in the Mesozoic cover. Four Tertiary Alpin e deformations are observed. The D1 ductile deformation is linked to t he progressive Eocene stacking of the nappes towards the northwest. Du ring D1, basement deformation is governed by imbricate tectonics where as cover is thin-skinned and intensively folded. These different struc tures reflect the original strong rheological contrast between basemen t and cover. During the heterogeneous and ductile D2 deformation, the behaviour of the basement and cover became similar. The strong vertica l D2 shortening, associated with a 'top-to-the-east' shear, led to the folding of the prior SE-dipping structures, developing SE-vergent fol ds with axes close to the E-W L2 stretching lineation. D2 corresponds to post-collisional crustal thinning following D1 crustal thickening. The D3 and D4 deformations occurred under retrograde conditions and ca n be correlated with uplift and late dextral movement on the Insubric line, respectively.