Thermochronometry and cooling rates deduced from single sample records of successive magnetic polarities during uplift of metamorphic rocks in the Alps (France)

Abstract

SUMMARY Pyrrhotite-bearing metamorphic calcschists from the Western Alps very probably carry a TRM acquired during slow cooling of the unit during the late Tertiary. Sequences of successive polarities have been recorded and can be unravelled by very detailed thermal demagnetization. Polarity versus temperature profiles on single samples are compared to the polarity time-scale, allowing on a statistical basis the estimation of a cooling rate of SOOCMyr-' at the time of TRM acquisition (20-25 Ma). Low apparent palaeointensities (=I0 pT) are estimated by comparison with artificial TRM.