Recent developments in centrifuge modelling of tectonic processes: equipment,model construction techniques and rheology of model materials

The Experimental Tectonics Laboratory at Queen's University is equipped with a large-capacity centrifuge that is capable of subjecting tectonic models measuring 127 × 76 mm in plan and up to 51 mm in depth to accelerations as high as 20,000 g. This high capacity greatly extends the range of potential model materials and permits the use of relatively stiff and/or brittle substances.A number of new techniques of model construction have been devised, that permit internal and surface strain patterns and kinematic evolution to be monitored in detail. One particularly useful technique, which will find application in non-centrifuged experiments as well, allows the preparation of highly uniform anisotropic multilayers composed of alternating layers of Plasticine and silicone putty, with individual layer thicknesses as low as 20 μm and with controllable ratio between thicknesses of the relatively competent and incompetent units. Examples of models constructed using these new techniques are illustrated.One particular type of the commonly used model material, silicone putty, has been subjected to a series of rheological test. The results indicate that at strain rates in the range 10^?6-10^?3s^?1 (applicable to the centrifuge experiments) the silicone putty exhibits power-law rheology with n = 7 ± 2. At higher strain rates the material appears to tend towards linear behaviour.Available rheological data and dimensional analysis using standard scaling laws and appropriate model ratios suggest that the microlaminated Plasticine-silicone putty multilayer is a suitable analogue, in centrifuged experiments, for interbedded sequences of indurate limestone and incompetent shale. The excellent degree of dynamic similitude attained is demonstrated by the realistic form of fold and fault structures developed in models constructed of this material.