8In subduction settings, the tectonic regime of the overriding plate is closely related to the 9 geometry of the subducting plate. Flat-slab segments are supposed to increase coupling at the 10 plate interface in the Andes, resulting in an increase and eastward migration of the shortening 11 in the overriding plate. Above the Peruvian flat-slab, a 200 km-long normal fault trend 12 parallel to the range and delimits the western flank of the Cordillera Blanca. In a context of 13 flat subduction, expected to produce shortening, the presence of the Cordillera Blanca normal 14 fault (CBNF) is surprising. We performed a systematic inversion of striated fault planes in the 15 Cordillera Blanca region to better characterize the stress field above the Peruvian flat-slab. It 16 evidences the succession of different tectonic regimes. NE-SW extension is predominant in 17 most of the sites indicating a regional extension. We suggest that the Peruvian flat-slab trigger 18 extension in the Western Cordillera while the shortening migrated eastward. Finally, we 19propose that flat-slab segments do not increase the coupling at the trench neither the 20 shortening in the overriding plate but only favor shortening migration backward. However, 21 the stress field of the overriding plate arises from the evolution of plate interface properties 22 through time due to bathymetric anomaly migration. 23 24
Key-works 25Inversion of striated fault planes; crustal stress field; mountain building; Peruvian flat-slab; 26 Cordillera Blanca 27 28