Dynamics of the earth magnetic field in the 10-75 kyr period comprising the Laschamp and Mono Lake excursions: New results from the French Chaîne des Puys in a global perspective

•New lava flows recording the intensity low of the Mono Lake.•New flows recording the Laschamp excursion with a mean age of 41.3±0.6ka (2σ).•∼1500yr (intensity), 640 yr (directions) duration for Laschamp excursion.•Full intensity recover between the well distinct Laschamp and Mono Lake excursions.•Rate of decrease for the Laschamp excursion similar to that observed since 1840.

We report here on a new paleomagnetic (directions and intensities) and coupled K/Ar and 40Ar/39Ar analysis of 35 different flows, emplaced in the Chaîne des Puys during the 75 to 10 kyr interval, which contains the Mono Lake and Laschamp excursions. There is a remarkable agreement between the new set of absolute volcanic intensities and published sedimentary (GLOPIS-75) and cosmogenic (10Be and 36Cl) records. The Laschamp and Mono Lake excursions are clearly revealed by a very significant intensity drop at 41.2±1.6ka and 34.2±1.2ka respectively. The duration of the Laschamp excursion is ∼1500yr and about 640 yr when the drop of paleointensity or the directional change are considered respectively. The intensity drop at the Mono Lake is twice as short. In the ∼7ka interval separating the two excursions, the field intensity recovers to almost non-transitional values. The rate of decrease of the field intensity during these excursions attains 18 nT/yr for the Laschamp and even greater value (33 nT/yr) for the Mono Lake. This figure is, for the Laschamp excursion, similar to the present field intensity decrease in the last two centuries so that one may wonder whether such a high rate of change may be characteristic of an impending geomagnetic event (reversal or excursion). We suggest that the name Auckland excursion should be used for the present-day called Mono Lake.

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