TY - JOUR
T1 - Large-Volume and Shallow Magma Intrusions in the Blackfoot Reservoir Volcanic Field (Idaho, USA)
AU - Hastings, M. S.
AU - Connor, C. B.
AU - Wetmore, P.
AU - Malservisi, R.
AU - Connor, L. J.
AU - Rodgers, M.
AU - La Femina, P. C.
N1 - Funding Information:
Comments from two reviewers and the Associate Editor greatly improved this manuscript. We thank them for their interest and efforts! Troy Berkey, Brad Mack, and Tonian Robinson participated in the collection of gravity data in this project. Nigel Brady (Dynamic Gravity Systems) assisted in the collection and processing of boat‐based gravity data. Mathieu Vallee assisted with the logistics of the boat‐based gravity survey. We are grateful to the Torgansen family for providing access to their land, as well as other landowners in the region for enabling our survey. This project was supported by a grant from NASA (NNH 16‐ESI16‐0030).
Publisher Copyright:
© 2021. The Authors.
PY - 2021/11
Y1 - 2021/11
N2 - The 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 ((Formula presented.) mGal) are modeled as shallow ((Formula presented.) 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 (Formula presented.) (Formula presented.); a density contrast of (Formula presented.) kg (Formula presented.) results in two intrusions, each (Formula presented.) km (Formula presented.) km and about 0.5 km thick, with cumulative volume of 100 (Formula presented.). A network of (Formula presented.) trending faults lies directly above and on the margins of the mapped gravity anomalies. Most of these faults have (Formula presented.) m throw; one has throw up to (Formula presented.) 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 (Formula presented.) 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.
AB - The 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 ((Formula presented.) mGal) are modeled as shallow ((Formula presented.) 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 (Formula presented.) (Formula presented.); a density contrast of (Formula presented.) kg (Formula presented.) results in two intrusions, each (Formula presented.) km (Formula presented.) km and about 0.5 km thick, with cumulative volume of 100 (Formula presented.). A network of (Formula presented.) trending faults lies directly above and on the margins of the mapped gravity anomalies. Most of these faults have (Formula presented.) m throw; one has throw up to (Formula presented.) 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 (Formula presented.) 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.
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U2 - 10.1029/2021JB022507
DO - 10.1029/2021JB022507
M3 - Article
AN - SCOPUS:85119823246
VL - 126
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - 11
M1 - e2021JB022507
ER -