As cratons (Greek κράτος kratos - power ) refers to the geologically very old ( Precambrian ) core areas of the continents, which consist of highly metamorphic rocks.
In contrast, the edges of the continents are often composed of younger crust parts, which were affiliated to the cratons throughout the earth through mountain building.
The cratons of today's continents are divided into two sections:
Cratons are considered particularly tectonically stable, which is partly due to the very large cardinality of its relatively cool lithosphere, the lithospheric mantle keel can reach maximum depths of 250-300 km, which has a very high melting point due to its chemical composition, the crust is, however, only 35-40 km thick. Cratons caused by the relatively high temperatures in the mantle, especially in the Archean. The asthenosphere is relatively weak or non-existent in the rule.
The up to 200 km into the mantle -reaching - originally magmatic, in the course of time but mostly metamorphic overprinted - cratons of relatively ( to the rest of the earth's crust ) light can rock their age roughly corresponding fall into the following provinces:
- Tectons: consist of rocks as a result of tectonic events in the meso-and Neoproterozoic, ie in the period before 1.6 billion to 600 million years ago, formed or last overprinted metamorphic were (so-called tektonothermales age).
- Protons: are Kratonprovinzen with a tektonthermalen age from 1.6 to 2.5 billion years ago.
- Archone: are surrounded by younger Kratonprovinzen archaic " rock islands" (you in this case also speaks of archaic cores ) with a tektonothermalem age of more than 2.5 billion years ago, some of which contain even hadaisches material (older than 4 billion years).
Phanerozoic evolution of cratons
Cratons have experienced, etc. more often after the Proterozoic or even longer no tectonic deformation such as folding, bulging, and are therefore remained unchanged over eons by and large. They are the cores of the continents and were most intense verfaltet already in the Precambrian tectonic processes, transformed metamorphosed at great depths or intruded and severely eroded in the rule.
Cratons are divided geologically into shields and plaques. In the shields largely comes to light, the crystalline basement, since there the continental crust has a low density and high thickness and therefore constantly isostatic uplift is. In the table or platform regions, the shields are covered with undeformed sediments ( overburden ). These sediments are the bedrock generally unconformably, as Erstgenanntes had undergone a mountain formation and thus a period of erosion before deposition of the sediments panel. Accordingly, there is a time gap between the youngest rocks of the shield and the oldest ( bottom -most ) rocks of the sedimentary cover. As the crust of the basement of the panels has a smaller thickness or a higher density than that of the shields, it has less lift and could therefore be repeatedly covered over the past 500 million years from a Epikontinentalmeer, ultimately the cause of the deposition of the panel sediments had.
Cratons have old fault zones that can be reactivated in tectonic stress. So show some cratons, active or stalled grave breaches, in which case these trenches thick sediment layers were deposited or will be, and in some cases very large amounts of volcanic material was unearthed.
Because minerals and rocks as well as the precious metals contained therein, as well as various gemstones in general, and diamonds in particular, in the course of time tend to be separated into the crust and spread or even back to be melted in the mantle, are the oldest cratons - because they were not subjected to plate tectonic changes for eons - for prospectors and mining companies of most interest. Today is - particularly in Canada and Australia - worked with measurement of paleomagnetism and gamma radiometric, stratigraphic and geochronological sonarreflektorischen and other methods of discovery and exploration of this ancient continental parts of the earth. Even the inaccessible areas of the Siberian craton and the political unrest, mining technically interesting regions of Africa are the focus of the world economy. The overt lying craton of the Baltic Shield - the Kola Peninsula - is an important supplier of raw materials in Russia. Only the treasures of Antarctica are protected by the Antarctic Treaty from economic use.
List of cratons
This is a list of known shields and cratons and some involved the fact sheets, panels, basins and grave breaches.
- Antarctic Plate Mawson craton
- Grunehogna craton
- Australia - see also Australian Plate Altjawarra craton
- Curnamona Craton, South Australia
- Gawler Craton, Central South Australia
- Pilbara Craton, Western Australia
- Yilgarn Craton, Western Australia
- Canadian Shield, also, Laurentian Shield, Precambrian Shield or (not quite right, because of several cratons assembled) and North America craton Slave craton, Northwest Territories with the Acasta - gneiss ( 4030 mya )
- Superior craton in the south and east of the Hudson Bay to the Nuvvuagittuq greenstone belt ( possibly up to 4300 mya )
- Nain craton, part of the North Atlantic Craton in eastern Canada and Greenland ( Isua gneiss)
- Wyoming craton in the U.S.
- Residues greatly impressed cratons such as the Rae craton in northern Canada
- Africa - see also African Plate and Large African grave breach - East African rift Arab Kraton see also Arab plate, the north Anatolian plate, the Jordan Rift Valley
- Congo craton and basin, central southern Africa, and his Terran Bangweulu block, Zambia
- Eurasia - see also Eurasian Plate East European craton with the Baltic Shield and the
- Russian platform and the
- Sarmatian craton ( 3700-2800 mya )
South Africa: Kaapvaal craton
Australia: Gawler Craton
Antarctica: Mawson and Crohn Craton
China: Yangtze ( Yangzi ) Kraton
Sino - Korea