YBCs sanidine: A new standard for 40Ar/39Ar dating

Abstract

The 40Ar/39Ar dating technique is based on neutron fluence monitors (standards). Recent investigation demonstrates that currently used standards are not as homogenous as believed and new standards are needed (Philips and Matchan, 2013). In this study, we report a new sanidine standard, YBCs, collected from a phonolite at Yabachi in Tibet, China, for single-grain 40Ar/39Ar dating. Aliquots were distributed to four international laboratories for analysis and intercalibration. The results show that YBCs crystals are homogenous in K content, 40Ar*/39ArK (F-value) and age at the single grain level. The standard deviations of the F-value and age have small ranges from 0.29% to 0.53% and from 0.42% to 0.52%, respectively. These show that YBCs is a suitable standard for 40Ar/39Ar geochronology. The calibrated age of YBCs is 29.286 ± 0.206 Ma, or neglecting the error in the decay constant, 29.286 ± 0.045 Ma. Finally, the intercalibration factors (which allow direct comparison between standards) between YBCs and FCs, GA1550, ACs and HB3gr are calculated as: R YBCs/FCs = 1.044296 ± 0.003968, R YBCs/GA1550 = 0.291261 ± 0.001148 R YBCs/ACs = 24.443066 ± 0.068432 and R YBCs/HB3gr = 0.020312 ± 0.000885. These values can be used to compare YBCs with other standards directly.