No abstract

Lithospheric-scale centrifuge models are used to investigate the process of continental rifting at the margins of cratonic areas. Models reproduce extension between a resistant cratonic lithosphere and an adjacent, weaker mobile belt and investigate the infl uence of the strength contrast between craton and belt and the presence or absence of an intervening weak zone (such as a suture) on the extensional deformation. Model results suggest that regardless of craton and belt strength contrast, the presence of the weak zone strongly localizes deformation, leading to the development of narrow, deep rift valleys corresponding at depth to marked lithospheric thinning. Depending on the pre-rift rheology (in particular depending on the presence of a signifi cant decrease of the brittle-ductile transition depth in the belt domain), the resulting basin can be largely asymmetric, with a major border fault system on the craton side. When the weak zone is absent, deformation is typically more distributed and lithospheric thinning more homogeneous. In these conditions the strength contrast between craton and belt strongly controls deformation: when the contrast is minimal, no major faults form at the craton-belt boundary, and a roughly symmetric deformation affects a wide region inside the strong mobile belt after the initial stages of extension. Conversely, for high strength contrasts, more asymmetric deformation is localized on a major fault system at the craton margin at the beginning of extension; with progressive extension, minor faulting propagates inside the weak belt, widening the deformed zone. Comparison with different natural examples suggests that these results may be important and have relevance for the development of continental rifts at the margins of cratonic areas.