Jean-Pierre Burg

Dome structures in collision orogens: Mechanical investigation of the gravity/compression interplay

Domes and basins are evidence for vertical movements in both compression and extension tectonic environments. They are thus evidence for interplay between gravity and tectonic forces in structuring the continental crust. We employ analytical and numerical techniques to investigate the respective roles of gravity and compression during the growth of crustal-scale buckle anticlines and diapirs submitted to instantaneous erosion. The analytical perturbation method, which explores the onset of both types of instability, yields a “phase-diagram” discriminating eight folding-diapirism modes, fi ve of which are geologically relevant. Numerical simulations show that the phase diagram is applicable to evolved, fi nite amplitude stages. Calculated strain fi elds in both diapirs and folds show normal sense of shear at the interface if the upper layer is thick compared to the lower layer. We conclude that the present-day structural techniques applied for distinguishing diapiric domes and folds are ambiguous if detachment folding and intense erosion take place during deformation, and that domes displaying extensional structures do not necessarily refl ect extension.