Abstract

Multilayer analog models comprising a brittle upper layer (sand and clay), a strong ductile middle layer (high-viscosity silicone putty), and a weak ductile basal-layer (low-viscosity silicone putty) are used to demonstrate the importance of lithospheric strength maxima in the development of rift basins and low-angle detachments. Although a wide range of rift geometries formed, a general evolution can be derived from the experimental results. An initial period of distributed extension is followed by localized deformation into rift basins due to boudinage of the strong layer. Delamination at the interface between the strong putty and weak putty layers results in the formation of subhorizontal ductile shear zones below the strong ductile layer. This basal shear zone alters the symmetry of the boudins and sets up a stress regime mechanically suitable for the growth of low-angle normal faults in the neck lines of developing rift basins. Continued boudinage eventually tears the strong ductile layer. The brittle upper layer is subsequently dragged over the basal ductile layer along a series of listric detachment faults.

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