physics

Thick-skinned deformation

Thick-skinned deformation is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Thick-skinned deformation rather than just read about it. In short: Thick-skinned deformation is a geological term which refers to crustal shortening that involves basement rocks and deep-seated faults as opposed to only the upper units of cover rocks above the basement which is known as thin-skinned deformation. While thin-skinned deformation is common in many different localities, thick-skinned deformation requires much more strain to occur and is a rarer type of deformation.

Key takeaways

Thick-skinned deformation belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Thick-skinned deformation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Thick-skinned deformation from memory before moving on to harder problems.

Reference excerpt

Thick-skinned deformation is a geological term which refers to crustal shortening that involves basement rocks and deep-seated faults as opposed to only the upper units of cover rocks above the basement which is known as thin-skinned deformation. While thin-skinned deformation is common in many different localities, thick-skinned deformation requires much more strain to occur and is a rarer type of deformation.

Definition

Different processes can deform rocks, the deformation is almost always the result of stress. This stress leads to the formation of fault and fold structures, both can either extend or shorten of the Earth's crust. Thick-skinned deformation specifically affects deep crystalline rock of the basement and may extend deeper into the lower crust. Thin-skinned deformation affects the upper crustal layers and does not deform the deeper basement.

Causes Thick-skinned deformation is most commonly a result of crustal shortening and occurs when the region is undergoing horizontal compression. This frequently occurs in at the sites of continental collisions where orogenesis, or mountain building, is taking place and during which the crust is shortened horizontally and thickened vertically. The massive compressional forces involved in such a collision cause the basement rock and all of the units above it to deform. Deformation occurs in the form of both folds and thrust faults and may form a fold and thrust belt along the collisional zone or as crustal flow.

At convergent plate boundaries two plates move towards each other as one is subducted downwards beneath the other but when the crust of two continents meet at a convergent zone neither one of them will be subducted due to their low density. As the two continents are pushed together by tectonic processes a large amount of stress is put on the rock. Eventually deformation will occur in one or multiple ways in order to relieve the stress.

Folds Folding usually occurs in areas with a very slow strain rate or when the rock being deformed is relatively weak and ductile. As folding occurs the units of rock bend forming anticlines, ridges, and synclines, valleys. While the true thickness of the underlying crust may not be equal to the elevation changes of the resulting mountains and hills, the average crustal thickness is greater than before the deformation occurred. One way in which folding can occur in such a formation is by a small amount of subduction of one plate. One continent may be partially overridden by the other but since the plate is far too light to sink it will uplift the overriding plate creating very large folds that deform the entire crust.

Faults

Thrust faults are another common form of deformation to occur in these areas. Faulting is generally the result of greater strain rates and stronger or more brittle rocks. These faults have a high angle and cause thickening by uplifting the rock onto itself. These types of faults are identified by the vertically repeating stratigraphy that they produce. During a collision when the strain reaches the breaking point of the rock a fracture will form in the rock. This fracture cuts across layers of rock to form a ramp which will allow movement to dissipate the accumulated strain. Under compression the upper hanging wall rises and overrides the lower foot wall.

Crustal flow The final type of deformation is crustal flow. This type of deformation is only able to occur when the crustal material is heated to a very high temperature, approximately 2/3 of its melting temperature. When this occurs in a collisional zone then the rock can be deformed by creep and will behave similarly to a fluid over the long periods of geologic time.

Examples

Himalayan Mountains - The Himalayas of Tibet are at the location of a continental collision between the Indian and Asian continents and contains many examples of thick-skinned deformation. Andes Mountains - The Andes of South America are at the location of an subduction zone and are formed by thick-skinned deformation.

References

Sarkarinejad, K., and Goftari F., 2019. Thick-skinned and thin-skinned tectonics of the Zagros orogen, Iran: Constraints from structural, microstructural and kinematics analyses. Journal of Asian Earth Sciences 170, 249-273.

External links Thick-Skinned and Thin-Skinned Tectonics: A Global Perspective by O. Adrian Pfiffner (2017)

Illustrations

Thick-skinned deformation: Continent-continent collision — Continent-continent collision

Worked examples

Example 1 — a first encounter with Thick-skinned deformation

Start with the simplest possible case. Write down what Thick-skinned deformation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Thick-skinned deformation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Thick-skinned deformation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Thick-skinned deformation

In research: Thick-skinned deformation appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Thick-skinned deformation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Thick-skinned deformation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Deformation (mechanics), Plate tectonics, so understanding it makes those chapters shorter.
In everyday life: Look for Thick-skinned deformation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Thick-skinned deformation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Thick-skinned deformation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Thick-skinned deformation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Thick-skinned deformation in simple terms?

Why does Thick-skinned deformation matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Thick-skinned deformation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Thick-skinned deformation.