Analogue modelling

In the TecLab, we typically perform the following experiments:

  • lithosphere-scale models: simulation of deformation affecting the entire lithosphere
  • crustal scale models: simulation of deformation affecting the crust or parts of the crust

By means of these so-called physical analogue models, we can better understand deformation on a crust and lithosphere scale. They are physically realistic, scaled-down models of, for instance, the crust of the Earth or of a sedimentary basin. The crust and basins are typically composed of a stack of (quasi)horizontal layers, where each layer is a different type of rock, i.e. different composition, density, mechanical properties (Figure 1A). This stacked layering of different rocks in nature is simulated in an analogue model by constructing also a stack of layers, however here with each layer composed of different types of sand, viscous fluids or other types of materials (Figure 1B).

  • Figure 1A

    Example of a mountain, consisting of a stack of horizontal layers, with each layer a different type of rock.

  • Figure 1B

    Cross-section of an analogue model, which is also constructed as a stack of horizontal layers. The layers are composed of different types of analogue materials such as sand and silicon putty.

Lithosphere-scale models

These models consist of layers of sand and silicone putty representing different layers in the Earth's lithosphere that are built on top of a liquid layer that simulates the asthenosphere. These models can be used for example to model processes such as subduction. The result of such an experiment is shown in Figure 2. Analogue models are used in this study (Willingshofer et al. 2013) to investigate how the strength of different layers affects the style of deformation.  Figure 2 consists of a topographic image, made by a surface scanner and a cross-section of the model, which is made by cutting the model after the experiment has run.

 

Experimentele resultaten van een lithosfeermodel van subductie uit het onderzoek van Willingshofer et al. (2013).
Figure 2: Experimental results of a lithospheric model of subduction from Willingshofer et al. (2013).

Due to the relatively high density of oceanic lithosphere, it can sink into the hot upper mantle, a process we call subduction. Subduction progresses until all oceanic material has been consumed in the upper mantle, thereby forcing adjacent lighter continental lithosphere to subduct as well. When the subduction stalls, the dense oceanic material slowly separates from the lighter continental material by breaking.

The detached plate sinks slowly into the asthenosphere, towards the upper-lower mantle boundary (here the bottom of the tank). The time scale of such a process is minutes to hours in the laboratory, but millions of years in nature.

Video: An analogue model of “slab break-off”: a process where part of the lithosphere, in this case oceanic, detaches after it has undergone subduction. Copyright © Elsevier, 2019. Tectonophysics (journal): https://www.journals.elsevier.com/tectonophysics

The material simulating the lithosphere in the video shown above is a mix of organic plasticine, PDMS putty, silicon oil and iron powder (called “60OPL 40PDMS 24oil” in Broerse et al., 2019), which has a stress-dependent strength (non-Newtonian). The material that is used to simulate deformation behaviour of the asthenosphere is glucose with a Newtonian rheology. The tank in this experiment has dimensions (w x l x h) 34.5cm x 44.5cm x 20cm.  

From: Broerse, T., Norder, B., Govers, R., Sokoutis, D., Willingshofer, E., & Picken, S. J. (2019). New analogue materials for nonlinear lithosphere rheology, with an application to slab break-off. Tectonophysics, 75,73-96. 
https://doi.org/10.1016/j.tecto.2018.12.007. 
Preprint: https://eartharxiv.org/repository/view/1318/

Crustal scale models

These models are used to study deformation processes in the outermost layer of the Earth comprising oceanic or continental crust. Models of sand and silicone putty are built on top of flat tables allowing for setting up geometrically complicated models related to various tectonic settings. In either case deformation is applied by pulling or pushing the initially horizontal layers of the models.

In Figure 3 the experimental results of a crustal scale model from Gabrielsen et al. (2016) are shown. A series of experiments was designed to understand how faults link across weak (ductile) layers, during extension. The cross-section above shows these weak layers and the faults that have developed during extension of the model.

 

Experimentele resultaten van een korstmodel van Gabrielsen et al. (2016)
Figure 3: Experimental results of a crustal scale model from Gabrielsen et al. (2016).