Craton

A craton ( /ˈkreɪtɒn/ KRAYT-on, /ˈkrætɒn/ KRAT-on, or /ˈkreɪtən/ KRAY-tən; from Ancient Greek: κράτος kratos "strength") is an old and stable part of continental lithosphere (the Earth's two topmost layers, the crust and the lithospheric mantle). Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates; the exceptions occur where geologically recent rifting events have separated cratons and created passive margins along their edges. Cratons are composed of ancient crystalline basement rocks covered by younger sedimentary rocks. They have a thick crust and deep lithospheric roots extending several hundred kilometres into Earth's mantle.

Cratons contain the oldest continental crust rocks on Earth. They were formed in the Archaean (4 to 2.5 billion years ago) and the Proterozoic (2.5 billion- 538.8 million year ago) geologic eons. Most were formed in the Archaean.

The term craton is used to distinguish the stable portion of the continental crust from regions that are more geologically active and unstable.

Bleeker and Davis (2004) define a craton as "a large, coherent domain of Earth's continental crust that has attained and maintained long-term stability, having undergone little internal deformation, except perhaps near its margins due to interaction with neighbouring terranes."

Scott King (2005) define the Archaean cratons as "relatively flat, stable regions of the crust that have remained undeformed since the Precambrian, forming the ancient cores of the continents."

Cratons are composed of two layers: the cratonic basement of metamorphosed crystalline and metamorphic rocks and the platform, which is a younger, weakly deformed sedimentary cover which overlies this basement. Continental shields are exposed (they crop out at the surface) cratonic basement rocks and are thus dominated by crystalline and metamorphic rocks. Shields and platforms are physiographic terms rather than tectonic entities.

The word craton was first proposed by the Austrian geologist Leopold Kober in 1921 as Kratogen, referring to stable continental platforms, and orogen as a term for mountain or orogenic belts. Later Hans Stille shortened the former term to Kraton, from which craton derives.

Examples of cratons are the Dharwar Craton in India, North China Craton, the East European Craton, the Amazonian Craton in South America, the Kaapvaal craton in South Africa, the North American Craton (also called the Laurentia Craton), and the Gawler craton in South Australia.