cooling age

In geochronology, "cooling age" refers to the age of a rock as determined by the time it cooled below a specific temperature, which "resets" the isotopic clock within certain minerals. This is distinct from the rock's primary age, which is the age of its initial formation.1

Different minerals have varying "blocking temperatures" at which they become closed systems for radioactive decay. By analyzing minerals with different blocking temperatures, scientists can reconstruct a rock's cooling history. For example, minerals like zircon, datable by the uranium-lead method, have high blocking temperatures and can record the primary age even after prolonged exposure to high heat. In contrast, minerals like biotite, dated by potassium-argon or rubidium-strontium methods, have lower blocking temperatures and are more easily reset by heat, thus recording younger cooling ages. This method is crucial for understanding the thermal events a rock has experienced since its formation.1