Thick-skinned deformation

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.

Deformation in geology refers to any alterations to the size or shape of a rock formation since the time of its creation. There are many different ways deformation can occur but it is always the result of some amount of stress within a formation. This stress leads to the formation of many structures that can either extend or shorten the length of the crust in the area. Some of the most common structures are faults and folds. Thick-skinned deformation is a specific type of deformation that can take the form of either faults or folds. The term thick-skinned specifically applies type of deformation which affects not only the sedimentary and metamorphic cover rocks near the surface but also affects the much deeper crystalline rock of the basement and may extend even deeper into the lower crust. Thin-skinned deformation is the counterpart to thick-skinned deformation and can frequently be found in similar areas. As the term implies, thin-skinned deformation is deformation that only affects the upper layers of the cover rocks and does not continue into the deeper basement. There is also one other term which may be used as an intermediary between these two extremes. The term basement-involved thin-skinned deformation can be applied to deformation that affects the cover rocks and may cut some into the basement then level off before going too deep.

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.

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