Large‐Volume and Shallow Magma Intrusions in the Blackfoot Reservoir Volcanic Field (Idaho, USA)

The Blackfoot Reservoir volcanic field (BRVF), Idaho, USA, is a bimodal that has hosted silicic eruptions during at least two episodes, as recently 58 ka. Using newly collected ground and boat-based gravity data, large negative anomalies ( mGal) are modeled shallow km) intrusions beneath NE-trending alignment of BRVF rhyolite domes tuff rings. Given the trade-off between density contrast model volume, best-fit inversion models yield total intrusion volume ; kg results in intrusions, each km about 0.5 thick, with cumulative 100 . A network trending faults lies directly above on margins mapped anomalies. Most these have m throw; one throw up to m. We suggest emplacement sill-like produced this fault zone also created ENE-trending set, indicating widespread deformation emplacement. located E regional, 20 mGal step gravity. interpret thickening Upper Precambrian lowermost Cambrian quartzites Meade thrust sheet, part Idaho-Wyoming Thrust Belt. Silicic volcanism classic example volcanotectonic interaction, influenced by regional structure creating deformation. hazard assessments should consider possibility large-volume future.