Several different techniques have been used to construct analogue models of large-scale tectonic processes, such as subduction, rifting, gravity spreading, indenter tectonics, escape tectonics and convection. A first division can be made between models, which are designed as such to be used in the normal field of gravity and models constructed for the usage in an artificially high field of gravity.
The latter of these two groups are performed in a centrifuge, where the centrifugal force plays the same role in the models as the force of gravity does in geological processes. The advantage of this technique is that the analogue materials used for centrifuge experiments have a relatively high strength and are therefore relatively easy to work with during construction and analysis of the model. The obvious disadvantage is that an entire (expensive) centrifuge is needed to conduct an experiment. Furthermore, every time an intermittent stage in the structural evolution of an experiment needs to be examined, the machine has to be turned of. Centrifuge modelling was first introduced to analogue modelling of geological processes by Bucky . The centrifuge modelling technique took a great step forward in the early 1960’s due to the work of Hans Ramberg, who build an entire analogue lab around a centrifuge at the University of Uppsala in Sweden. His work led to a better understanding of the role of gravity in deformation of the Earth’s crust and lithosphere [Ramberg, 1967, 1981]. From this time onwards, centrifuge modelling has been widely used to investigate geological processes [Ramberg, 1970; Dixon, 1974, 1975; Talbot, 1977; Dixon and Summers, 1985; Koyi, 1988; Liu and Dixon, 1991; Koyi and Skelton, 2001]. The centrifuge technique has dominated analogue modelling for some three decades, but has now largely been replaced by analogue models deformed in the normal field of gravity, in which much weaker materials are used [Koyi, 1997].
Experiments performed in the normal field of gravity should be made of extremely weak materials, in order to be properly scaled for gravity. The advantage of this approach is that it does not require an (expensive) centrifuge in order to run an experiment and that the evolution of an experiment can be recorded continuously. Furthermore, most materials used in these type of experiments (such as granular material and syrups) are relatively cheap and easy to obtain (except for silicone putties). A disadvantage of this approach is that the construction of models is more difficult, especially for experiments with inverted density profiles (e.g. a dense oceanic lithosphere overlying a less dense asthenosphere). Several different modelling approaches exist, which are mainly related to the rheological approximation of the lithosphere and sub-lithospheric mantle.
(1) The first approach has been developed by the analogue modelling group in Rennes (France). In this approach, analogue models are constructed of materials with different rheologies (brittle and viscous), to incorporate the different behaviour of rocks at different depths in the crust and mantle. Brittle behaviour in rocks is modelled by granular material (such as sand), which deforms conform a Mohr-Coulomb type behaviour [Mandl, 1977; Krantz, 1991; Schellart, 2000]. The viscous behaviour of rocks is simulated with viscous material such as silicone putty, honey and glucose syrup. These models have been used to investigate a wide variety of geological phenomena, including extrusion tectonics, subduction, rollback, back-arc extension, gravity spreading and continental collision [Faugere and Brun, 1984; Davy and Cobbold, 1988, 1991; Ratschbacher et al., 1991; Brun et al., 1994; Faccenna et al., 1996, 1999; Hatzfeld et al., 1997; Brun, 1999; Diraison et al., 2000; Keep, 2000; Martinod et al., 2000; Schellart et al., 2002a,b; Burg et al., 2002].
(2) In a second approach, plastic materials are used to model the deformation of rocks. This approach has been used to model the India-Eurasia collision [Tapponnier et al., 1982]. This approach has also been applied by Alexander Chemenda, with models primarily constructed of plastic and viscoplastic hydrocarbon waxes to simulate the lithosphere and water to simulate the asthenosphere. These models have been build to investigate processes such as subduction, extension, slab rollback and back-arc deformation [Shemenda, 1992, 1993, 1994; Shemenda and Grocholsky, 1992, 1994; Chemenda et al., 1995, 1996, 1997, 2000, 2001].
(3) In a third approach, the lithosphere and sub-lithospheric mantle are modelled with viscous rheologies only. Each layer is represented by a material with a homogeneous viscous rheology. Thus, these experimental designs are effectively the same as those used in numerical models using the thin viscous sheet approximation to simulate the lithosphere [e.g. Bird and Piper, 1980; England and McKenzie, 1982, 1983; Vilotte et al., 1982; Houseman and England, 1986]. With such an analogue set-up, modellers have investigated slab kinematics and dynamics during subduction [Olson and Kincaid, 1991; Griffiths et al., 1995; Guillou-Frottier et al., 1995; Funiciello et al., 2000, 2002; Faccenna et al., 2001b].
(4) In a fourth approach, the lithosphere and sub-lithospheric mantle are modelled with temperature dependent viscous or plastic rheologies. An appropriate vertical temperature gradient is applied to the experiment, simulating the geothermal gradient in the Earth's lithosphere and sub-lithospheric mantle, thus influencing the rheological behaviour of the analogue materials during deformation. These models have been build to investigate various geological processes such as rifting [Brune and Ellis, 1997], subduction, [Kincaid and Olson, 1987] and the thermomechanical development of orogenic wedges [Rossetti et al., 2000].