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A supervolcano and its sidekicks: A 100 ka eruptive chronology of the Fish Canyon Tuff and associated units of the La Garita magmatic system

March 21, 2019

Establishing temporal constrains on major volcanic eruptions is limited by the precision of existing geochronometers. Prior work on the La Garita caldera, created by the eruption of the Fish Canyon Tuff, failed to resolve temporal differences between pre-, syn-, and post-collapse eruptive units. Here, we report 40Ar/39Ar geochronologic data supporting a ca. 100 ka eruptive history of the La Garita caldera, and resolving the timing of the precaldera Pagosa Peak Dacite , syncaldera Fish Canyon Tuff, and postcaldera Dacite of Nutras Creek. Minimizing uncertainty in neutron fluence by rotating samples during irradiation and employing Bayesian statistical interpretation of analytical data enables resolution of the ca. 60 ka precaldera eruptive history and a hiatus of 0 - 20 ka prior to the eruption of postcaldera lavas. The improved precision demonstrated using these methods provides previously unresolvable temporal constraints on physical processes in the La Garita magmatic system and underscores the potential of unraveling other closely-spaced events in geologic time.