New evidence for the age of the youngest eruptions in the Valles caldera, New Mexico

Abstract

New geochronologic data provide evidence for an age of about 50 to 60 ka for the youngest volcanic eruptions within the Valles caldera, New Mexico - an age that is significantly younger than most previous age determinations. Thermoluminescence age estimates for buried soils beneath the El Cajete pumice, a key stratigraphic marker in the region, range from 48 to 61 ka and {sup 14}C analyses of burnt logs within volcanic surge beds near the El Cajete vent yield similar ages of 50 to >58 ka. These data conflict with fissontrack, {sup 40}Ar/{sup 39}Ar, and K-Ar ages of 130 to >200 ka, but are supported by recent analyses by electron spin resonance. The results of this study reinforce the need to apply a variety of dating methods when evaluating the age of young volcanic events and support the hypothesis that the El Cajete eruptions were part of a new cycle of volcanic activity in the Valles caldera after an exceptionally long period of quiescence of nearly 460 ka. The new age constraints also suggest a previously unrecognized link between cycles of volcanism and pulses of hydrothermal activity in the caldera, such that hydrothermal outflow appears to decrease significantly following completion ofmore » eruptive cycles. 24 refs., 3 figs., 2 tabs.« less