Modelling of non-cylindrical boudins

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Noncylindrical boudins are common deformation structures in naturally deformed rocks which can develop by different processes. These processes have been hardly investigated experimentally. In the present study we will carry out scaled single-phase and polyphase experiments using natural rocks (anhydrite layer in halite matrix) and rock analogues (plasticine) to produce non-cylindrical torn and drawn boudins, which result from brittle fracture and viscous necking, respectively. Incremental runs in combination with computer-tomographic analyses will demonstrate the growth of non-cylindrical boudins through space and time. The aim of the experiments is to constrain geometrical parameters which are inherent in distinct types of non-cylindrical boudins and can be used to identify such structures in nature. As the geometry of boudins is controlled by the rheological behavior of matrix and layer, the geometrical parameters can be used as a paleoviscometer. The new results will be of interest to structural geologists worldwide, the more so as boudinage in rocks could be important for the formation of ore deposits, the migration of oil and gas, and the deposition of nuclear waste in salt domes.