GEOL0016 Structural Geology and Tectonics
Structural Geology and Tectonics
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GEOL0016 Structural Geology and Tectonics
Laboratory Practical 7 - Contractional deformation sandbox experiment
Introduction
Today we will conduct a contractional deformation experiment in the deformation sandbox. The
multilayer sequence to be deformed is a mix of salt and flour layers. Thin layers of red quartz sand
are used to highlight the layer boundaries and act as markers of fault offsets and folds.
We normally would record this experiment live in class, but we are now doing this remotely. I have
uploaded screenshots from the pre-recorded video for you to work with. Use these images to
document the nucleation and growth of folds and faults, and to note how these structures were
modified during progressive deformation – you will produce a report that follows the below
questions. You can annotate photos in your report as you see fit.
Questions
1. Calculate the bulk horizontal shortening strain during the experiment, as well as the maximum
and minimum bulk thickening strain.
2. Where does most of the shortening and thickening occur? Why do you think this is so?
3. How has strain been accommodated during the experiment? Illustrate your answer with
annotated sketches or images.
4. Describe and discuss any differences in the styles of deformation between the salt and flour
layers.
5. What is the dip of each major fault when it initiates? To assist descriptions, label the faults with
letters A, B, C etc on diagrams.
6. What are the fault cut-off angles with the layering when faults nucleate? Are they the same for the
salt and flour layers? Assuming 1 was horizontal, what does the fault dip in the salt and flour layers
indicate about the coefficient of internal friction in these cohesionless materials? Note that the
optimal activation angle opt is described by
2opt = 90 -
where tan is the coefficient of internal friction.
7. Do all faults remain active throughout the experiment? How does the fault dip change after fault
initiation? Why do fault dips change during progressive deformation? At approximately what dip
does each fault become inactive? Explain why faults eventually become inactive.
8. Produce a neat sketch or set of annotated images in which the chronological sequence of fault
development is indicated.
9. How does the development of folds relate to fault growth?
10. List any other key observations you have made during the experiment. Illustrate your points
using annotated images of the experiments or sketches.