36Cl and 10Be production rate calibrations in the Pleistocene Ardèche lava flows (eastern edge of the Massif Central, France).
Dr Régis Braucher1, Dr Guillaume Duclaux2, Dr Vincent Godard1, Mr Karime Keddadouche1, Mr. Georges Aumaître1
1CEREGE, CNRS, Collège de France, IRD, INRAE, Aix Marseille Univ., Aix en Provence, France, 2Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, IRD, Géoazur, Valbonne, France
In situ produced cosmogenic nuclides have revolutionized geomorphology by allowing quantification of surface processes operating at the Earth’s surface. Numerous studies have been dedicated to the calibration of production rates in common target minerals (quartz for¹⁰Be, CaCO₃ mainly for ³⁶Cl) because these minerals contain the main target elements (O, Si for ¹⁰Be, Ca for ³⁶Cl). Most of these calibrations have been performed on geomorphological features (moraines, glacially polished rocks, boulders from landslides) where accurate independent ages are available (mostly from ¹⁴C), most of them being younger than 20 ka, minimizing the effects of denudation.
The aim of this project is to work on minerals from basaltic rocks collected in the Ardéche mountains (SE France) on sites already studied and dated by Ar/Ar by Sasco et al (2017). As these well preserved and well exposed lava flows cover a temporal range of 20 to 200 ka, they offer a unique opportunity to calibrate production rates over such a long period and to assess if these long term production rates are in agreement with the ones actually used.
We will present preliminary results obtained on two lava flow surfaces dated at ~30 ka by Sasco et al. (2017) for which ³⁶Cl concentrations have been measured in whole rock. Together with these methodological developments we will also discuss the significance of this region geomorphology, where deeply incised valleys formed within ~300 Ma old basement rocks and tectonic forces have uplifted a plateau above 1400m despite downwearing due to long term denudation processes.
Sasco, R., Guillou, H., Nomade, S., et al. 2017. 40Ar/39Ar and unspiked ⁴⁰K-⁴⁰Ar dating of pper Pleistocene volcanic activity in the Bas-Vivarais (Ardèche, France). Journal of Volcanology and Geothermal Research, 341, p. 301-314.
My research interests focus on applying cosmogenic nuclides to the quantification of the various processes (tectonics, climate, …) affecting and modelling the Earth’s surface over the last few millions years. To do so, I am working on improving our knowledge of the production mechanisms for commonly used cosmogenic nuclides such as 10Be, 26Al, 36Cl. I have also developed the depth profile approach allowing the direct determination of both exposure age and denudation rate affecting the studied surface.
Since June 2020 I am at the head of the LN2C / ASTER facility.