Effectiveness of Combined K-Ar and 40Ar/39Ar Dating Methods in the 14C age Range
Abstract
Several studies achieved during the last decade evidence the strong endeavor to push toward younger and younger ages the 40Ar/39Ar chronology. In parallel, all these progress have extended the scope of application of the 40Ar/39Ar chronology especially in paleoclimatic studies to provide Astronomical independent ages for oxygen isotope stages. Most of these promising results are based on K-rich feldspars, from tephra layers, which allow a direct comparison between oceanic and continental records. However, K-rich feldspars-bearing tephra are scarce and improvements to date effusive volcanic rocks, covering much wider area, have to be done to enlarge the field of chronological studies in Quaternary times. To participate to this challenge a new 40Ar/39Ar laboratory has been set up at the LSCE to complete the already existing K-Ar facility. The unspiked K-Ar and the 40Ar-39Ar methods have each their own drawbacks and advantages and the combination of these two methods is very efficient to obtain accurate and reliable age determinations as demonstrated by the recent dating of the Laschamp excursion (Guillou et al., 2004, EPSL). To extend this approach toward younger ages, we studied two lava flows which emplaced around 30 ka, based on preliminary datings within the Teide - Pico Viejo volcanic complex in the Canary Islands. The first sample, which has a conventional radiocarbon age of 32,360 +/- 800 yrs B.P. is K-Ar dated at 33 +/- 2 ka and 40Ar/39Ar dated at 33 +/-2 ka. The second sample is K-Ar dated at 32 +/- 2 ka and 39Ar-40Ar dated at 35 +/-3ka. These similar ages and therefore successful comparison between the two methods validate the performances of the new LSCE 39Ar-40Ar facility and is a very promising approach to calibrate the Quaternary timescale.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.V13A2098G
- Keywords:
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- 1100 GEOCHRONOLOGY;
- 1105 Quaternary geochronology;
- 1115 Radioisotope geochronology;
- 1794 Instruments and techniques