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At that depth, craton roots extend into the asthenosphere, [15] and the low-velocity zone seen elsewhere at these depths is weak or absent beneath stable cratons. [16] Craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy and a low intrinsic density.
Laurentia basement rocks. Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America.Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although originally it also included the cratonic areas of Greenland and the Hebridean Terrane in northwest Scotland.
Earth cutaway from core to exosphere Geothermal drill machine in Wisconsin, USA. Temperature within Earth increases with depth. Highly viscous or partially molten rock at temperatures between 650 and 1,200 °C (1,200 and 2,200 °F) are found at the margins of tectonic plates, increasing the geothermal gradient in the vicinity, but only the outer core is postulated to exist in a molten or fluid ...
East European Craton, the core of Baltica. Volgo-Uralian Craton, Russia (3.0–2.7 Ga) Baltic Shield, part of the East European Craton; Fennoscandian Shield, the exposed Northwestern part of the Baltic Shield in Norway, Sweden and Finland (3.1 Ga) Karelian Craton, part of the Fennoscandian Shield in Southeast Finland and Karelia Russia, (3.4 Ga)
The craton appears to have formed when three Archean cratons fused: Leo-Man-Ghana, Taoudeni and Reguibat. The first two docked around 2.1 Ga (billion years ago), and the Reguibat Craton docked with the craton around 2 Ga. The roots of the combined craton extend to a depth of over 300 km (190 mi) in the sub-continental lithospheric mantle. [4]
[1] [3] [4] The North China Craton is an ancient craton, which experienced a long period of stability and fitted the definition of a craton well. [1] However, the North China Craton later experienced destruction of some of its deeper parts (decratonization), which means that this piece of continent is no longer as stable. [3] [4]
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A craton is an ancient stable continental block. [13] Also, a craton has survived from plate tectonics that pull apart, collide or tear continents. [13] On average, the felsic volcanic rocks only contribute to ≈15-20% in volcanic rocks of greenstone belts. [6] See Figure 2 and Table 1 for Examples of Archean felsic volcanic rocks occurrence.