40AR/39AR GEOCHRONOLOGY AND VOLUMETRIC ESTIMATIONS OF POST-VALLES-CALDERA ERUPTIONS REVEALS POLYGENETIC DOME EMPLACEMENT WITH IMPLICATIONS FOR FUTURE SILICIC VOLCANISM IN THE SOUTHWESTERN US

New high-precision ⁴⁰Ar/³⁹Ar dating and volume estimations provide new insight into the timescales and fluxes of the post-caldera volcanism and resurgence at Valles caldera in northern New Mexico. The new data indicates that many domes were emplaced during polygenetic activity and that eruptive fluxes during dome emplacement are increasing. Following the caldera-forming eruption of the Tshirege Member at 1231.6 ± 1.0 ka, four polygenetic post-caldera dome complexes were emplaced between 1231.9 ± 4.8 ka and 997.0 ± 1.6 ka. Lifespans of these domes range from 11.4 ± 6.0 ka to 25.2 ± 5.6 ka. In contrast, the six domes emplaced between 932.3 ± 1.1 ka and 68.7 ± 1.0 ka have shorter lifespans of less than 6 ka, including at least 2 dome complexes that are likely monogenetic. This new dating indicates 15 post-caldera eruptive episodes—an increase from the 13 episodes based on prior dating. Volumetric estimations show a total range in post-caldera eruptive volumes from 0.8 km³ to 14.1 km³. The combination of new ages with volume estimations indicate an average post-caldera eruptive flux of 0.03 km³/ka, which is relatively low compared to other Quaternary calderas. However, eruptive fluxes during individual episodes have systematically increased from 0.9 km³/ka to 2.56 km³/ka, which also correlates to increasing inter-dome repose periods during post-caldera evolution. Should the current trend continue, a future eruption may yield a large eruptive volume and high flux that is similar to the most recent eruptions of the East Fork Member. Lastly, the high-precision ages of pre-, syn-, and the oldest post-resurgent eruptions constrain the average resurgent duration to between 74.4 ± 3.3 ka and 41.8 ± 6.7 ka, which is comparable to other resurgent calderas. These durations are both longer and higher precision than the previously published resurgence duration of 27 ± 27 ka. The new ages and volumes address long-standing unanswered questions at Valles caldera, and an approach similar to this study will prove beneficial at other Quaternary calderas.