Types of Deformation

There are two types of deformation in the lithosphere, according to the morphology of the Earth’s continents. They are orogeny and epeirogeny. The former has taken place recently, between 45 and 50 million years ago, and it is still going on, while the latter dates back to the Proterozoic era, having begun about 4 billion years ago.

Orogeny is the deformation of the Earth crust through the mountain-building process, which involves the violent collision of two tectonic plates and the ejection of molten rocks that are uplifted as they get solidified. This dynamic geological process comprises faulting, folding, strong seismicity, and a linear mountain chain of high-altitude sharp peaks. It is relatively new, from the Tertiary period of the Cenezoic era. An example of orogeny is the Andes mountain range in South America, which is the product of the South American plate and the Nazca plate collision as it is 47 million years old. The word orogeny derives from Greek, with oros meaning ‘mountain’, and –geny, ‘genesis’ (creation, development).

Epeirogeny is the broad and slow warping of the lithosphere. It does not involve local intense folding, faulting; nor is there seismicity. This type of deformation has given way to plains (due to erosion), to the emergence of plateaus, as well as large areas of depression. Sometimes these geographical features are surrounded by very old, low mountains. The cratons are examples of this process, such as the Guayana’s Highlands in Venezuela and Brazil. Granite and basalt rock outcrops and the absence of seismicity are two common features of epeirogeny. Thus, it only occurs in stable and solidified portions of the Earth’s crust. Also from Greek, with epeiros meaning ‘continent’, and -geny, ‘genesis’.