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Archaean continental geotherm |
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Many of the physical properties of the rock forming the lithosphere are temperature dependent. The continental crust was in the Archaean 2 to 6 times richer in radiogenic elements (diagram on the left). Upon desintegration those elements (mainly Uranium, Thorium, Potassium) release heat and increase the temperature in the crust. We can therefore expect the continental geotherm to be warmer in the Archaean. Since we know the average amount of radiogenic elements in modern continental crust, the half-live period of the radiogenic elements, and the amount of heat produced during their desintegration, one can calculate the total lithospheric radiogenic heat production in the Archaean (about 0.078 Watt per square meter).
The graph on the right shows a possible phanaerozoic and archaean geotherms based on the radiogenic heat distribution shown on the left. The temperature at the Moho for modern (phanaerozoic lithosphere) is about 540ºC whereas that of Archaean lithosphere is about 720ºC. The warmer geotherm as some interesting and fundamental consequences... |
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