Cooldown age

The cooling age (also cooling age ) is a term from geochemistry and marks the period from which a magmatic or metamorphic mineral has fallen below its closing temperature.

Below the closing temperature , the isotope system is closed, that is, there is no material balance through diffusion between the different phases (solid phases and / or fluids ) and thus no more exchange of radioactive isotopes takes place. The decay products of the isotope system can no longer escape either. This point in time can therefore be determined by radiometric counting of the recorded decay products and used for geochronology .

In contrast to the crystallization age , at which the closing temperature of the mineral is above its crystallization temperature, the cooling age does not necessarily mark the formation of the corresponding rock . For example, the closing temperatures of zirconium and garnet are between 800 and 1000 ° C for the U - Pb method , but between 400 and 500 ° C for rutile .

literature

• Hans Murawski, Wilhelm Meyer: Geological dictionary . 12th edition. Spektrum Akademischer Verlag, Heidelberg 2010, ISBN 978-3-8274-1810-4 , pp. 1 .
• Gregor Markl: Minerals and Rocks . 2nd Edition. Spektrum Akademischer Verlag, Heidelberg 2008, ISBN 978-3-8274-1804-3 , p. 536-537 .
• Martin Okrusch, Siegfried Matthes: Mineralogy. An introduction to special mineralogy, petrology and geology . 7th fully revised and updated edition. Springer Verlag, Berlin et al. 2005, ISBN 3-540-23812-3 , pp. 468 .