Age and cooling rate of the geothermal system of Larderello

Mineralogical, chemical and geocronological analyses have been conducted on core samples of granite from deep (2 to 4.5 km depth) at Larderello, in order to gather data for a conceptual model of the duration of the thermal anomaly. Two models are possible: 1) a single large intrusion of at least 3.8 Ma, emplaced and monotonically cooled; 2) different intrusions emplaced at ~3.8, ~2.5 and ~1.0 Ma. Even assuming this re-heating process, the very long life of the thermal anomaly can be explained only with a continuous heat supply from the astenosphere.