History of the youngest members of the Valles Rhyolite, Valles Caldera, New Mexico using ESR dating method

摘要

The cooling history of the Valles caldera was studied by the electron spin resonance (ESR) dating method using Al and Ti centers in quartz grains which were separated from the youngest units of the Valles Rhyolite. The ESR apparent ages are much younger than fission track ages and (sup 39)Ar- (sup 40)Ar ages. Three possibilities are suggested, the first is that the ESR ages are real, the second is that ESR method did not work for these samples, and the third is that about 10--40 ka, the signal intensity was partially reduced by a thermal event such as proposed by Harrison et al. (1986). Research on the first and second possibilities is continuing. The third possibility might explain the difference between ESR ages and those by other methods (fission track and (sup 39)Ar- (sup 40)Ar). ESR dating has produced new insights regarding the history of the Valles caldera.