Large-Volume and Shallow Magma Intrusions in the Blackfoot Reservoir Volcanic Field (Idaho, USA)
gravity, volcanic field, inversion, volcanotectonic, Basin and Range, silicic eruptions
Digital Object Identifier (DOI)
he Blackfoot Reservoir volcanic field (BRVF), Idaho, USA, is a bimodal volcanic field that has hosted silicic eruptions during at least two episodes, as recently as 58 ka. Using newly collected ground and boat-based gravity data, two large negative anomalies (-16 mGal) are modeled as shallow (< 1 km) intrusions beneath a NE-trending alignment of BRVF rhyolite domes and tuff rings. Given the trade-off between density contrast and model volume, best-fit gravity inversion models yield a total intrusion volume of 50-120 km3; a density contrast of -400 kg m-3 results in two intrusions, each ~9 km x 4.5 km and about 0.5 km thick, with cumulative volume of 100 km3. A network of 340°-360° trending faults lies directly above and on the margins of the mapped gravity anomalies. Most of these faults have 5-10 m throw; one has throw up to ~50 m. We suggest that the emplacement of shallow sill-like intrusions produced this fault zone and also created a ENE-trending fault set, indicating widespread ground deformation during intrusion emplacement. The intrusions and silicic domes are located 3-5 km E of a regional, 20 mGal step in gravity. We interpret this step in gravity as thickening of the Upper Precambrian to lowermost Cambrian quartzites in the Meade thrust sheet, part of the Idaho-Wyoming Thrust Belt. Silicic volcanism in the BRVF is a classic example of volcanotectonic interaction, influenced by regional structure and creating widespread deformation. We suggest volcanic hazard assessments should consider the possibility of large-volume silicic eruptions in the future.
This work is licensed under a Creative Commons Attribution 4.0 License.
Was this content written or created while at USF?
Citation / Publisher Attribution
Journal of Geophysical Research: Solid Earth, v. 126, issue 11, art. e2021JB022507
Scholar Commons Citation
Hastings, M. S.; Connor, C. B.; Wetmore, P.; Malservisi, R.; Connor, L. J.; Rodgers, M.; and Femina, P. C., "Large-Volume and Shallow Magma Intrusions in the Blackfoot Reservoir Volcanic Field (Idaho, USA)" (2021). School of Geosciences Faculty and Staff Publications. 2338.
Supporting Information S1
2021jb022507-sup-0002-movie si-s01.mp4 (1665 kB)
2021jb022507-sup-0003-movie si-s02.mp4 (1644 kB)