HR: 1340h
AN: V23B-1435    [Abstracts]
TI: The new 39Ar/40Ar dating facility of the LSCE, background and performances.
AU: Scaillet, S
EM: stephane.scaillet@lsce.cnrs-gif.fr
AF: LSCE, CEA-IPSL-UVSQ, CEA Saclay, Orme des Merisiers, Gif sur yvette, 91191, France
AU: * Nomade, S
EM: sebastien.nomade@lsce.ipsl.fr
AF: LSCE, CEA-IPSL-UVSQ, CEA Saclay, Orme des Merisiers, Gif sur yvette, 91191, France
AU: Guillou, H
EM: herve.guillou@lsce.cnrs-gif.fr
AF: LSCE, CEA-IPSL-UVSQ, CEA Saclay, Orme des Merisiers, Gif sur yvette, 91191, France
AU: Scaillet-Vita, G
EM: Gracia.scaillet@lsce.cnrs-gif.fr
AF: LSCE, CEA-IPSL-UVSQ, CEA Saclay, Orme des Merisiers, Gif sur yvette, 91191, France
AB: Precise and accurate timescales are increasingly needed in most disciplines of the Earth sciences. To contribute to this challenging task, a new 39Ar/40Ar laboratory, specifically devoted to the dating of very recent (down to 1 ka) volcanic products, has been developed at the LSCE (CEA-IPSL-UVSQ, France). In this contribution, we present the first data obtained from this new facility. The laboratory comprises a VG 5400 mass spectrometer coupled with a high sensitivity and high dynamic range ion counting system. Gas extraction is achieved with a 25 watts C02 laser or a double vacuum furnace depending of the analyzed samples. The full metal vacuum and purification line feature a GP50 and a compact Ti flash getters which permit extremely low blank for all Argon isotopes (e.g. ~ 3.0 10e-19 Moles for 36Ar). Both analytical protocols and hardware were specifically developed and optimized to date extremely young samples. Analytical performances including protocols, flux monitoring as well mass spectrometer discrimination correction method will be presented in the light of data obtained over the last 10 months. All samples were irradiated, under cadmium, in the Β-1 position (~1.0 10e+13 fast n cm-2 s-1) of the 70MWh-1 OSIRIS reactor (Pierre Süe laboratory, CEA-Saclay, France). Irradiation package is composed of home-design Aluminium disks constituting a 4 cm stack (10 to 30 unknowns/irradiation). Analyzed neutrons flux standards indicate less than 1% variation along the 4cm stack and validate the use of this reactor for high-precision 39Ar/40Ar dating. The precision and accuracy of the facility has been checked from cross-comparison of international single grain standards including FCs (28.02Ma), ACR-2 (1.194Ma) and TCR (28.32Ma) using the most recent recommended values for these monitors. A total of 80 grains in two irradiations (10 and 120 minutes) will be presented in details. Results from single-grain analyses agree within errors with those proposed by Renne et al., 1998. These preliminary results show that the new 39Ar/40Ar facility housed at the LSCE meets with state-of-the-art performances required in high-precision 39Ar/40Ar dating of very young sample, as well as for the interlaboratory calibration of irradiation monitors across the whole range of the K/Ar chronometer.
DE: 1094 Instruments and techniques
DE: 1105 Quaternary geochronology
DE: 1115 Radioisotope geochronology
DE: 1145 Tephrochronology (8455)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting