Experimental evaluation of thermal recording of successive polarities during uplift of metasediments

The discovery of a post-tectonic natural remanent magnetization (NRM) carri ed by pyrrhotite in the Dauphinoise Zone of the Western Alps allows us to t est the ability of these rocks to record a sequence of magnetic polarity ve rsus temperature acquired during their slow cooling. Several laboratory exp eriments [composite partial thermal remanent magnetizations (pTRMs), Thelli er-Thellier experiments, TRM thermal demagnetization] as well as NRM demagn etization were performed. This shows that the pyrrhotite grains are single- domain-sized and that they are able to record successive independent pTRMs The NRM thermal demagnetization analysis demonstrates the occurrence of sev eral antiparallel components. A comparison between NRM and TRM thermal dema gnetizations is attempted in order to highlight small pTRMs naturally recor ded in a temperature interval of only a few degrees. We attempt to retrieve the temperature at which each reversal occurs during the post-metamorphic cooling. This method. called thermopalaeomagnetism, is discussed and develo ped in order to delineate the sequence of polarity chrons recorded versus t emperature.