The eastern margin of the world's largest and highest orogenic plateau, the Tibetan Plateau, shows contrasted edges, with a steep topographic gradient along the Longmen Shan (LMS) north of the Xianshuihe strike-slip fault (XF), and gentler slopes across the Yalong margin to the south (Figure 1a). The driving mechanism(s) leading to such contrasts between margins are still poorly understood and have given rise to end-member models of plateau growth with different crustal structures: either a weak lower crust localizing crustal thickening ("channel flow model," e.g., Clark & Royden, 2000), or a more rigid crust, with thickening that includes the upper crust, in a brittle manner ("stepwise model," Tapponnier et al., 2001). Those two end-member models can be tested by investigating the role of thrusting mechanisms in SE Tibet. At present, upper crustal deformation of the LMS is dominated by reverse faulting with a small component of right-lateral motion, as shown by recent earthquake focal mechanisms such as that of the 2008 Mw7.9 Wenchuan earthquake (e.g., de Michele et al., 2010; Fielding et al., 2013). This event ruptured two subparallel reverse structures, the Guanxian and Beichuan thrusts (Figure 1b), with steep shallow ramps (up to 70°) which root between 15 and 25 km-depth on a sub-horizontal décollement zone (e.g.,