S. Toyoda et al., ESR DATING OF QUARTZ PHENOCRYSTS IN THE EL-CAJETE AND BATTLESHIP-ROCKMEMBERS OF VALLES RHYOLITE, VALLES CALDERA, NEW-MEXICO, Journal of volcanology and geothermal research, 67(1-3), 1995, pp. 29-40
The electron spin resonance (ESR) dating method was employed on quartz
phenocrysts separated from pumice of the El Cajete and Battleship Roc
k Members of the Valles Rhyolite in the Valles caldera, New Mexico. Th
e results of heating experiments indicate that Ti impurity centers hav
e two components; a thermally stable one and a less stable, temperatur
e sensitive one. ESR dates using the stable Ti center yield eruption a
ges of 59 +/- 6 ka for the Battleship Rock Member and 53 +/- 6 ka for
the El Cajete Member while recent C-14 dates (S. Reneau and J. Gardner
, unpub. data) from carbonized logs in the El Cajete pumice indicate t
hat its age is older than 50 ka. Our results indicate that volcanism i
n the Valles caldera is much younger than previously thought (greater
than or equal to 130 ka) and that recent revisions to the post-0.5 Ma
stratigraphy of Valles caldera are probably in error. The results sugg
est that ESR dating of quartz may be a useful method for obtaining age
s of units in other Quaternary volcanic areas.