New 40Ar/39Ar eruption ages reveal an important temporal relationship between mafic and silicic volcanism in the Yellowstone Plateau volcanic field

The chronology of mafic eruptions and their temporal relation to rhyolitic volcanism in the Yellowstone Plateau volcanic field are poorly known, thereby limiting our understanding of the way(s) in which mafic magmatism drives rhyolitic activity. To address this, we measured ⁴⁰Ar/³⁹Ar eruption ages on 13 mafic samples collected from Henrys Fork Caldera (eastern Idaho, western United States), which represents a region of known volcanic activity immediately west of Yellowstone caldera for which the relationship to Yellowstone volcano’s most recent caldera-forming cycle remains unclear. Our new ages indicate that mafic activity was occurring throughout the Henrys Fork Caldera both leading up to and following the emplacement of the Lava Creek Tuff. Furthermore, these ages reveal that mafic volcanism in the Henrys Fork Caldera region occurred concurrently with second- and third-cycle rhyolite volcanism in and around Yellowstone caldera. Our new ages therefore provide unique and definitive evidence that the mafic magmatism of Henrys Fork Caldera played a critical role in the development of shallow-crustal rhyolitic magma chambers that ultimately fueled the large caldera-forming eruptions within the Yellowstone volcanic system.