Distribution of buried hydrothermal alteration deduced from high‐resolution magnetic surveys in Yellowstone National Park

Abstract

Yellowstone National Park (YNP) displays numerous and extensive hydrothermal features.Although hydrothermal alteration in YNP has been extensively studied, the volume, geometry, and type of rock alteration at depth remain poorly constrained. In this study, we use high-resolution airborne and ground magnetic surveys and measurements of remanent and induced magnetization of field and drill core samples to provide constraints on the geometry of hydrothermal alteration within the subsurface of three thermal areas in YNP (Firehole River, Smoke Jumper Hot Springs, and Norris Geyser Basin). We observe that hydrothermal zones from both liquid-and vapor-dominated systems coincide with magnetic lows observed in aeromagnetic surveys and with a decrease of the amplitude of short-wavelength anomalies seen in ground magnetic surveys. This suggests a strong demagnetization of both the shallow and deep substratum within these areas associated with the removal of magnetic minerals by hydrothermal alteration processes. Such demagnetization is confirmed by measurements of rock samples from hydrothermal areas which display significantly decreased total magnetization. A pronounced negative anomaly is observed over the Lone Star Geyser and suggests a significant demagnetization of the substratum associated with areas displaying large-scale fluid flow. The ground and airborne magnetic surveys are used to evaluate the distribution of magnetization in the subsurface. This study shows that significant demagnetization occurs over a thickness of at least a few hundred meters in hydrothermal areas at YNP and that the maximum degree or maximum thickness of demagnetization correlates closely with the location of hydrothermal activity and mapped alteration.

Heat and Mass Transport in a Vapor‐Dominated Hydrothermal Area in Yellowstone National Park, USA: Inferences From Magnetic, Electrical, Electromagnetic, Subsurface Temperature, and Diffuse CO2 Flux Measurements

“…Our study builds upon previous geophysical studies that imaged subsurface structures, fluid flow pathways, and hydrothermal alteration in volcano‐hydrothermal systems (e.g., Aizawa et al, ; Bouligand et al, ; Byrdina et al, ; Finn et al, ; Finn & Morgan, ; Gresse et al, , ; Hase et al, ; Pasquet et al, ; Revil et al, ; Rosas‐Carbajal et al, ; Soengkono, ). In contrast to many of these studies that used a single geophysical method and often resulted in a nonunique interpretation, we combine several different geophysical methods and quantify the spatial relationships among the diverse data sets.…”

“…Topography used for processing the geophysical data was determined using a 1‐m resolution lidar‐derived digital elevation model (https://doi.org/10.5069/G99P2ZKK) combined with a 30‐m digital elevation model from the National Elevation Datasets. Below is a brief description of data acquisition and processing with further details provided in the supporting information (Texts S1–S5; Bhattacharyya, ; Bouligand et al, ; ; Byrdina et al, , ; Christiansen & Auken, ; Christiansen & Blank, ; Finn & Morgan, ; Guspi, ; Ishido, ; Jardani & Revil, ; Johnson et al, ; LaBrecque & Yang, ; Linde et al, ; Marquardt, ; Menke, ; Nordstrom et al, ; Revil et al, ; Revil & Jardani, ; Revil & Pezard, ; Tarantola & Valette, ; Ward et al, ; White et al, ).…”

Imaging the magmatic system of Mono Basin, California, with magnetotellurics in three dimensions

“…The deep gravity signatures in Figure k indicate a low‐density zone in the C1 and C3 region. Additionally, both C1 and C3 are at the eastern border of a magnetic low (Figure l), arguing for temperatures above the Curie point (existence of partial melt) and/or demagnetization of country rock due to alteration by hot, magmatic fluids [ Bouligand et al , ; Finn and Morgan , ].…”

Dynamics of the Yellowstone hydrothermal system

“…All of the major thermal areas including those within Yellowstone Lake and the geyser basins along the Firehole and Gibbon River drainage basins are associated with negative magnetic anomalies, reflecting hydrothermal alteration that has destroyed the magnetic susceptibility of minerals in the rhyolites [ Finn and Morgan , ; Bouligand et al ., ]. However, most of the magnetic lows extend beyond the active thermal areas, implying either that subsurface alteration is more widespread or that postglacial hydrothermal activity migrated with time.…”