A new structural and petrological study, associated with a detailed geological mapping, allowed to better understand the tectonic relationships between the Dora Maira Massif and the Piedmont Zone in the middle Susa Valley. In the study area, a thick sequence of calcschists, previously attributed to the stratigraphic cover of the Dora Maira, is interpreted as belonging to the Piedmont Zone. Four deformation phases were identified: D 1 represents the eclogite facies stage, D 2 developed under greenschist facies conditions, transposed the early foliation and was responsible for the development of the regional schistosity S 2 . D 3 is characterized by close to open folds with N dipping axial surfaces and finally, D 4 developed macro-scale folds with E-dipping axial planes. Structural analyses allow to infer a relative timing for the tectonic contact between the two nappes which were coupled after the eclogite facies metamorphism but before the development of the S 2 foliation under greenschist facies conditions. Petrographic investigation into metapelite samples permitted to identify two main metamorphic assemblages within the Dora Maira polymetamorphic basement: M 1 (Phe ? Pg ? Cld ? Grt ? ChlI ? Qtz ? Rt) assemblage defines the S 1 relict foliation, while M 2 (Ms ? Pg ? Ab ? ChlII ? Qtz ? Ilm ± Bt) assemblage is related to the regional foliation S 2 . PERPLE_X pseudosection modelling allowed to reconstruct a P-T path for a garnet-chloritoidbearing micaschist from the northern part of the Dora Maira Massif, which reached eclogite facies conditions at 18-20 kbar and 515-525°C (M 1 /S 1 event) and then was exhumed during increasing T (10-11 kbar and 555-565°C). The M 2 assemblage defining the S 2 regional foliation developed at P \ 7 kbar and T \ 575°C. According to the structural evolution, the tectonic coupling between Dora Maira and Piedmont Zone took place during exhumation along the subduction channel.

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