Closure Temperature, Cooling Age and High Temperature Thermochronology

Abstract

The concept and analytical formulations of mean closure temperature(Tc ) and closure temperature profile in cooling geochronologicalsystems have been reviewed along with a discussion of their limitations.The conventional approach of retrieving the average cooling rateof a rock from Tc vs cooling age data of multiple geochronologicalsystems, which are applied to the same sample, suffers from the problemof circular logic in that the Tc of a given decay system itself dependson the cooling rate, especially when it falls below 10°C/Myr formany systems. It is, however possible to retrieve cooling rate ofa sample, without any knowledge of Tc , directly from (a) the extentof resetting of average mineral age during cooling and (b) the differencebetween the average ages of a central segment of a mineral grainand the bulk grain itself, as determined by a specific decay system.On the other hand Tc for a specific system, grain size and geometrycan be retrieved from the inferred cooling rate. These recent developmentsbetween the cooling age and cooling rate relations are reviewed inthis paper.