31. It needs no assistance on the craton . 32. Most crustal rocks formed before 2.5 billion years ago are located in cratons . 33. Like all cratons , the latter is composed of the crystalline basement and sedimentary cover. 34. Cratons are subdivided geographically into geologic provinces.35. Metaigneous and metavolcanic rocks form the largest component of cratons and are high in silica. 36. Thick successions of carbonate rocks are often deposited on craton margins during sea level rise. 37. The greenstone belts of the various archean cratons are commonly altered to the greenschist facies. 38. Layered intrusions are found in typically ancient cratons and are rare but worldwide in distribution. 39. The Pilbara craton in western Australia is not well defined but formed around 3 Gya. 40. The Siberian craton , Australia and eastern Antarctica have all been suggested based paleomagnetic information.
