A supervolcano and its sidekicks; a 100 ka eruptive chronology of the Fish Canyon Tuff and associated units of the La Garita magmatic system, Colorado, USA

Establishing temporal constraints on major volcanic eruptions is limited by the precision of existing geochronometers. Prior work on the La Garita caldera (Colorado, USA), created by the eruption of the Fish Canyon Tuff, failed to resolve temporal differences between pre-, syn-, and post-collapse er...

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Bibliographic Details
Published in:Geology (Boulder) 2019-05, Vol.47 (5), p.453-456
Main Authors: Morgan, Leah E, Johnstone, Samuel A, Gilmer, Amy K, Cosca, Michael A, Thompson, Ren A
Format: Article
Language:English
Subjects:
absolute age
alkali feldspar
Ar/Ar
Bayesian analysis
Cenozoic
Chronology
Chronostratigraphy
Coastal inlets
Collapse
Colorado
eruptions
feldspar group
Fish
Fish Canyon Tuff
Fluence
framework silicates
Geochronology
Geologic depressions
Geological time
Geology
igneous and metamorphic rocks
igneous rocks
Irradiation
La Garita Caldera
Magma
nesosilicates
Oligocene
orthosilicates
Paleogene
Petrology
Probability theory
pyroclastics
San Juan volcanic field
sanidine
silicates
southwestern Colorado
statistical analysis
Statistical methods
Tertiary
Tuff
U/Pb
United States
Volcanic eruptions
volcanic rocks
volcanism
volcanoes
zircon
zircon group
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Summary:Establishing temporal constraints on major volcanic eruptions is limited by the precision of existing geochronometers. Prior work on the La Garita caldera (Colorado, USA), 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 ∼100 ka eruptive history of the La Garita caldera, and resolving the timing of the pre-caldera Pagosa Peak Dacite, syn-caldera Fish Canyon Tuff, and post-caldera 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 ∼60 ka pre-caldera eruptive history and a hiatus of 0-20 ka prior to the eruption of post-caldera 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.
ISSN:0091-7613
1943-2682
DOI:10.1130/G45898.1