Structural analysis in the Montagne Noire, including a study of inclusion trail patterns in andalusite, garnet, and staurolite porphyroblasts, reveals a succession of five foliations in alternately steep and flat-lying orientations. This is inferred to reflect multiple gravitational collapse phases that intervened during continuous plate convergence. Initial crustal thickening by foliation development and folding (D1) was responsible for eclogite-facies metamorphism in the gneissic basement. Subsequent thrusting and recumbent folding (D2) generated a subhorizontal crenulation cleavage during Namuro-Westphalian times, while previous steep structures became rotated. Petrological and microstructural evidence indicate that thrust nappes were emplaced by a gravitational spreading mechanism, while undergoing internal thinning. An important amount of basement exhumation took place synchronously. These observations form the basis for a new orogenic model in which thermal reequilibration of a previously thickened orogen induces gravitational instability in the upper crust. Collapse of the upper crust causes it to spreadout horizontally over continuously converging relatively cool plates thereby creating low-angle thrust nappes. The upper crustal thinning facilitates simultaneous extrusion of lower crust in vertical root zones at the orogen center, which on reaching the higher part of the orogen can be incorporated in the nappes and displaced horizontally. Following such a mechanism of nappe tectonics, renewed horizontal shortening (D3) produced the Montagne Noire gneissic dome by upright folding of nappe-related foliations with orogen-parallel stretching. Previous crustal thinning had led to an increased heat flux between basement and cover so that during D3, cover sequences were still rising in temerature, while basement rocks had already commenced their retrograde path during D2. Peak-metamorphic conditions in the cover triggered a second gravitational collapse during Namurian times (D4) producing a 2 km wide subhorizontal shear zone in which orogen-parallel stretching continued. At the surface, deformation was accommodated by decollements, normal faulting, and basin formation. Gneissic rocks below the shear zone were not affected by the collapse because a stronger rheology and horizontal shortening was probably continuous here. Retrograde cooling of the cover restored gravitational equilibrium and caused its renewed upright folding during late-Variscan times (D5). Permian postorogenic extension (D6) oriented at a high angle to the previous orogen-parallel stretching completed exhumation of the gneiss dome. The dome structure of the Montagne Noire metamorphic core complex was acquired during compressional tectonics and later modified (flattened) by synorogenic and postorogenic extensional events. A similar polyphase origin appears not to be excluded for other metamorphic core complexes with poorly constrained preextension histories. ¿ 1998 American Geophysical Union