Experimental evaluation of thermal recording of polarity reversals during metasediments uplift.

Christian Crouzet (1) , Pierre Rochette (2) , Gilles Ménard (1)

1 LGCA - Laboratoire de Géodynamique des Chaines Alpines
2 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

The discovery of a post-tectonic natural remanent magnetization (NRM) carried by pyrrhotite in the Dauphinoise Zone of the Western Alps allows us to test the ability of these rocks to record a sequence of magnetic polarity versus temperature acquired during their slow cooling. Several laboratory experiments [composite partial thermal remanent magnetizations (pTRMs), Thellier-Thellier experiments, TRM thermal demagnetization] as well as NRM demagnetization 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 several antiparallel components. A comparison betweenNRM and TRM thermal demagnetizations is attempted in order to highlight small pTRMs naturally recorded 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 developed in order to delineate the sequence of polarity chrons recorded versus temperature.

Mots clés: magnetic polarities; metamorphism; partial thermoremanent magnetization (pTRM); pyrrhotite; slow cooling; Western Alps

Domaines: Sciences de la Terre

Christian Crouzet, Pierre Rochette, Gilles Ménard. Experimental evaluation of thermal recording of polarity reversals during metasediments uplift.. Geophysical Journal International, 2001, 145, pp.771-785. ⟨10.1046/j.0956-540x.2001.01423.x⟩. ⟨hal-00736898⟩