Interpreting Faults and Fractures in Hydrothermal Basins With High-Resolution Aeromagnetic Data in Yellowstone National Park

Hydrothermal systems in Yellowstone National Park originate at deep structures and manifest on the surface along faults and fractures. Precisely locating the controlling structures is essential to understanding fluid flow, geochemistry, and natural hazards of the hydrothermal systems. Structural interpretation in Yellowstone's hydrothermal basins is problematic, however, due to intense alteration of the country rock, widespread glacial deposits and myriad directions of apparent linear trends. To address this problem, high-resolution aeromagnetic data are examined to identify abrupt changes in magnetization attributed to juxtaposition of hydrothermally altered rocks, in which magnetic minerals have been destroyed, with their unaltered equivalents. These data show that near-surface hydrothermal manifestations within Yellowstone Caldera correlate with structures inferred from aeromagnetic-derived maximum horizontal gradient and minimum point of curvature analyses. The maximum horizontal gradients reflect changes in magnetic susceptibility along shallow (depths <100m) fractures. Minimum point of curvature analysis reveals deeper (depths <500 m) structures interpreted as buried faults and fractures. In turn, the interpreted geologic structures and forward modeling of the magnetic and thermal features data are used to constrain simple fluid flow models