Craton

A craton ( /ˈkreɪtɒn/ KRAYT-on, /ˈkrætɒn/ KRAT-on, or /ˈkreɪtən/ KRAY-tən;[1][2][3] from Ancient Greek: κράτος kratos "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle.

They have a thick crust and deep lithospheric roots extending several hundred kilometres into Earth's mantle.

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

This low-density offsets density increases from geothermal contraction and prevents the craton from sinking into the deep mantle.

[17] Rock fragments (xenoliths) carried up from the mantle by magmas containing peridotite have been delivered to the surface as inclusions in subvolcanic pipes called kimberlites.

These inclusions have densities consistent with craton composition and are composed of mantle material residual from high degrees of partial melt.

The extraction of so much magma left behind a solid peridotite residue that was enriched in lightweight magnesium and thus lower in chemical density than the undepleted mantle.

[23] Jordan suggests that depletion occurred primarily in subduction zones and secondarily as flood basalts.

[27] The properties of mantle xenoliths confirm that the geothermal gradient is much lower beneath continents than oceans.

Jordan notes in his paper that this mechanism could be effective for constructing craton roots only down to a depth of 200 kilometers (120 mi).

[29] A second model suggests that the surface crust was thickened by a rising plume of molten material from the deep mantle.

A third model suggests that successive slabs of subducting oceanic lithosphere became lodged beneath a proto-craton, underplating the craton with chemically depleted rock.

[29][18][22] A fourth theory presented in a 2015 publication suggests that the origin of the cratons is similar to crustal plateaus observed on Venus, which may have been created by large asteroid impacts.

[20] In this model, large impacts on the Earth's early lithosphere penetrated deep into the mantle and created enormous lava ponds.

For example, the Yilgarn Craton of Western Australia was flattish already by Middle Proterozoic times[36] and the Baltic Shield had been eroded into a subdued terrain already during the Late Mesoproterozoic when the rapakivi granites intruded.