We report here new age determinations from four samples of the Middle-Paleozoic Viluy Traps in Siberia, east of the more famous Permo-Triassic Siberian Traps. These samples, which were collected from three drill cores, have been analyzed in parallel and independently in the Orsay (France) and Berkeley Geochronology Center (BGC; USA) geochronology laboratories, using respectively the Cassignol-Gillot K-Ar and the 40Ar/39Ar techniques. Dating these samples as a concerted effort in two independent laboratories working jointly on their interpretation is a rather rare yet very valuable exercise. With the K-Ar technique, ages ranging from 338 to 367 Ma with uncertainties on the order of 5 Ma were obtained. With the 40Ar/39Ar technique, integrated ages range from 344 to 367 Ma, with uncertainties on the order of 1 Ma, and two samples yielded plateaus, i.e. the best determined ages, at 360.3±0.9 and 370.0±0.7 Ma. Three out of four ages yielded by the two separate methods are in agreement within uncertainties. One sample yields incompatible ages and could be from a later, altered dyke event. The 40Ar/39Ar plateau age of 370.0 ± 0.7 Ma (conventional calibration) or 373.4±0.7 Ma (recalculated per Renne et al., 2010), the most reliable age obtained in this study, is compatible with recent determinations of the Late Devonian extinction events at the end-Frasnian (~376±3 Ma). These results underscore a need for further work, in progress...
Détails:
- Courtillot, V., Kravchinsky V.A., Quidelleur, X. Renne, P. and D.P. Gladkochub, 2010. Attempting to date the Viluy magmatic samples: on eruption of the Viluy Traps at the Frasnian-Fammenian boundary? Earth Planet. Sci. Lett., 300, 239-245.
