Apollo 14 mineral ages and the thermal history of the Fra Mauro formation.

The thermal inertia of the Fra Mauro formation limits its rate of cooling. The calculations of Jaeger (1961) for the cooling of an extrusive sheet are used to estimate the time required for a central temperature drop of 10%. This time is found to be about 45 years. For a 90% temperature drop, the time is about 200 years. Analytical methods used in the investigations are discussed together with the diffusion of Rb and Sr within lunar basalt. Isochron diagrams for various minerals are presented.