Insights on the thermal history of the Valles caldera, New Mexico: evidence from zircon fission-track analysis

The zircon fission-track dating method was applied to the VC-2B core obtained from the active hydrothermal system at Sulphur Springs, Valles caldera, New Mexico. Four samples were analyzed to obtain both zircon ages and track length data from Permian strata to Precambrian quartz monzonite, the present temperatures of which are from 222 to 294 °C. Zircon ages obtained from the deeper three samples indicate partially annealed ages of about 450–600 Ma. Thus, zircons from Permian strata probably originated from Precambrian rocks. Contrary to the normal relationship between FT ages and temperatures of the sampling points, non-correlation between them is probably due to hot fluid flow and/or hot vein emplacement associated with recent volcanic activity. Zircon ages of the shallowest sample were much younger than the Permian, the reason for which is unknown. The closure temperature of the zircon fission-track dating method seems to be higher than that previously determined from geological data.