Geological structures: Structural geology and plate boundaries 3.3.2
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|(a)||how earthquakes occur when elastic strain energy stored in rocks is released
(elastic rebound theory)
|(b)||how plate movement at transform boundaries causes shear dominated tectonic
environments, which can lead to rock deformation as a result of tectonic induced stresses
|To include stress transfer.
||how plate movement at convergent boundaries causes compressive and shear dominated tectonic
environments, which can lead to rock deformation as a result of tectonic or gravity induced stresses
|To include: fold mountains, overfolds, isoclinal folds, nappes, thrusts.
|(d)||how plate movement at divergent boundaries causes tensional dominated tectonic environments, which can lead to rock deformation as a result of tectonic or gravity induced stresses.
||To include: graben (rift), horst, relationship between spreading rate and topography, and ocean core complexes.|
This topic brings together the tectonic environments and the types of stress applied at each, learners can link this to the geological features found, often displayed as cross sections of a setting. There is opportunity to use lots of sources of data and examples here including geological maps and large scale geological features. Studying the occurrence of earthquakes could introduce how rocks store strain energy, learners could consider the time elapsed between large earthquakes for this to build up. Learners can apply this to transform boundaries where the shear stress dominates and also consider how boundaries will evolve in the future. The compressive stress regime of a convergent plate margin allows learners to look at some impressive large scale features which are often clearly seen on the natural cross section of a mountain side. In comparison, the features associated with the tensional stresses of a divergent boundary are more difficult to view, these features can be seen in seismic sections of oil and gas basins.
Common misconceptions or difficulties students may have:
From studying each of these tectonic environments learners may believe that each is associated with just one type of stress, all compressive at a convergent, all shear at a transform and all tensional at a divergent boundary, idealised diagrams may support this. When locations and examples are studied in detail there will be evidence for more than one type of stress in a tectonic setting and the features found will highlight that. To support this, compare specific examples to general diagrams and consider weaknesses of any model.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course:
This topic has links with 5.4.1 metamorphic petrology where learners consider the metamorphic fabrics as a result of stress during a mountain building event and how the fabrics give evidence for the direction and type of stress the rocks were subjected to. The unit also considers how the original rock type and the conditions control how a rock will be deformed. In 7.2.2 learners use their knowledge of rifting and faulting in the North Sea to account for where oil and gas traps may form.
An introduction to learners on types of fault and how rocks can store energy like a spring and what happens when this energy is suddenly released. The context of the site is the San Francisco Earthquakes.
The link to ‘live eye’, provides up to date seismic data.
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